• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.636-636
• /
• 2013

Since first discovery of strong Raman spectrum of molecules adsorbed on rough noble metal, surface enhanced Raman scattering (SERS) has been widely used for detection of molecules with low concentration. Surface plasmons at noble metal can enhance Raman spectrum and using Au nanostructures as substrates of SERS has advantages due to it has chemical stability and biocompatibility. However, the photoluminescence (PL) background from Au remains a problem because of obtaining molecular vibration information. Recently, graphene, two-dimensional atomic layer of carbon atoms, is also well known as PL quenchers for electronic and vibrational excitation. In this study, we observed SERS of single layer graphene on or under monolayer of Au nanoparticles (NPs). Single layer graphene is grown by chemical vapor deposition and transferred onto or under the monolayer of Au NPs by using PMMA transfer method. Monolayer of Au NPs prepared using Langmuir-Blodgett method on or under graphene surface provides closed and well-packed monolayer of Au NPs. Scanning electron microscopy (SEM) and Raman spectroscopy (WItec, 532 nm) were performed in order to confirm effects of Au NPs on enhanced Raman spectrum. Highly enhanced Raman signal of graphene by Au NPs were observed due to many hot-spots at gap of closed well-packed Au NPs. The results showed that single layer graphene provides larger SERS effects compared to multilayer graphene and the enhancement of the G band was larger than that of 2D band. Moreover, we confirm the appearance of D band in this study that is not clear in normal Raman spectrum. In our study, D band appearance is ascribed to the SERS effect resulted from defects induced graphene on Au NPs. Monolayer film of Au NPs under the graphene provided more highly enhanced graphene Raman signal compared to that on the graphene. The Au NPs-graphene SERS substrate can be possibly applied to biochemical sensing applications requiring highly sensitive and selective assays.

• Progress in Superconductivity
• /
• v.6 no.2
• /
• pp.95-98
• /
• 2005

We present results of Raman spectroscopic studies of superconducting $YBa_2Cu_3O_7$ (YBCO) coated conductors. Raman scattering is used to characterize optical phonon modes, oxygen content, c-axis misalignment, and second phases of the YBCO coated conductors at a micro scale. A two-dimensional mapping of Raman spectra with transport properties has been performed to elucidate the effect of local propertied on current path and superconducting phase. The information taken from the local measurement will be useful for optimizing the process condition.

• Progress in Superconductivity and Cryogenics
• /
• v.18 no.2
• /
• pp.1-4
• /
• 2016

To observe the superconducting current and structural properties of high critical temperature ($T_c$) superconductors (HTS), we suggest the following imaging methods: Room temperature imaging (RTI) through thermal heating, low-temperature bolometric microscopy (LTBM) and Raman scattering imaging. RTI and LTBM images visualize thermal-electric voltages as different thermal gradients at room temperature (RT) and superconducting current dissipation at near-$T_c$, respectively. Using RTI, we can obtain structural information about the surface uniformity and positions of impurities. LTBM images show the flux flow in two dimensions as a function of the local critical currents. Raman imaging is transformed from Raman survey spectra in particular areas, and the Raman vibration modes can be combined. Raman imaging can quantify the vibration modes of the areas. Therefore, we demonstrate the spatial transport properties of superconducting materials by combining the results. In addition, this enables visualization of the effect of current flow on the distribution of impurities in a uniform superconducting crystalline material. These imaging methods facilitate direct examination of the local properties of superconducting materials and wires.

• Bulletin of the Korean Chemical Society
• /
• v.31 no.4
• /
• pp.999-1003
• /
• 2010

Raman spectra of a single layer graphene sheet placed in different gold substrates were obtained and are discussed in the context of surface enhanced Raman scattering (SERS). The gold substrates were composed of a combination of a thermally deposited gold film and a close-packed gold nanosphere layer. The SERS effects were negligible when the excitation wavelength was 514 nm, while the Raman signals were enhanced 3-to 50-fold when the excitation wavelength was 633 nm. The large SERS enhancement accompanied a spectral distortion with appearance of several unidentifiable peaks, as well as enhancement of a broadened D peak. These phenomena are interpreted as the local field enhancement in the nanostructure of the gold substrates. The difference in the enhancement factors among the various gold substrates is explained with a model in which the spatial distribution and polarization of the local field and the orientation of the inserted graphene sheet are considered important.

• Analytical Science and Technology
• /
• v.5 no.1
• /
• pp.115-120
• /
• 1992

The upper limit of solid solution of $Al_2O_3$ in $LiTaO_3$ was investigated using X-ray diffraction and Raman spectroscopy. By substituting cations in $LiTaO_3$ with $Al^{3+}$, the melting temperature was lowed and the ferroelectric properties can be improved. It is easier at lower temperature to fabricate the single crystal used for SAW filters and IR sensors. From the measured lattice constants and Raman band broadening, the solubility limit was X=0.25mol in $Li_{1-X}Al_{2X}Ta{1-X}O_3$, above which $Al_2O_3$ was obsered as a second phase. The Raman band of sintered $LiTaO_3$ was compared with that of the single crystal to see the effect of grain size on the band broadening.

• Journal of Korean Society for Atmospheric Environment
• /
• v.25 no.5
• /
• pp.450-458
• /
• 2009

The range-dependent overlap factor of a lidar system can be determined experimentally if a Raman backscatter signal by molecule is measured in addition to the usually observed elastic backscatter signal, which consists of a molecular component and a particle component. The direct determination of the overlap profile is presented and applied to a lidar measurement according to variation of telescope field-of-view and distance between telescope and transmitting laser. The retrieval of extinction coefficient by Raman method can generate high errors for heights below planetary boundary layer if the overlap effect is ignored. The overlap correction method presented here has been successfully applied to experimental data obtained in Gwangju, Korea.

• Bulletin of the Korean Chemical Society
• /
• v.24 no.8
• /
• pp.1102-1106
• /
• 2003

In our previous work we developed the Finite Field method in order to calculate the fifth-order Raman response. The method was applied to calculate various polarization components of the two-dimensional response of liquid $CS_2$. So far, all calculations relied on the dipole-induced dipole. Accurate time-dependent density functional theory calculations have shown that this model has big discrepancies, when molecules are close together as in the liquid. We now report results of investigations on the importance of multipole and electron overlap effects on the polarizability and the fifth-order Raman response. It is shown that these collision effects, especially the induced multipoles, are crucial in the description of the fifth-order response. The impact is found to be especially pronounced for the χ_{mmzzzz}^{(5)}$response that is solely due to interaction induced effects. The calculated response will be compared with various experimental results.

• Analytical Science and Technology
• /
• v.5 no.4
• /
• pp.359-366
• /
• 1992

Using micro-Raman spectrometer, we investigated the evaluation of microstress on silicon surface after the local thermal oxidation. The induced stress of silicon surface after local thermal oxidation shows maximum value at the interface of silicon oxide and active area. The smaller the size of active area, the larger stress. From the evaluation of three other device isolation processes, A, B and moB, whose active size has $0.45{\mu}m$ in length, moB process is turned out to have the lowest stress value and the smallest bird's beak effect.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.02a
• /
• pp.15-15
• /
• 2011

Atom-thick graphene membrane and nano-sized graphene objects (NGOs) hold substantial potential for applications in future molecular-scale integrated electronics, transparent conducting membranes, nanocomposites, etc. To realize this potential, chemical properties of graphene need to be understood and diagnostic methods for various NGOs are also required. To meet these needs, chemical properties of graphene and optical diagnostics of graphene nanoribbons (GNRs) have been explored by Raman spectroscopy, AFM and STM scanning probes. The first part of the talk will illustrate the role of underlying silicon dioxide substrates and ambient gases in the ubiquitous hole doping of graphene. An STM study reveals that thermal annealing generates out-of-plane deformation of nanometer-scale wavelength and distortion in $sp^2$ bonding on an atomic scale. Graphene deformed by annealing is found to be chemically active enough to bind molecular oxygen, which leads to a strong hole-doping. The talk will also introduce Raman spectroscopy studies of GNRs which are known to have nonzero electronic bandgap due to confinement effect. GNRs of width ranging from 15 nm to 100 nm have been prepared by e-beam lithographic patterning of mechanically exfoliated graphene followed by oxygen plasma etching. Raman spectra of narrow GNRs can be characterized by upshifted G band and strong disorder-related D band originating from scattering at ribbon edges. Detailed analysis of the G, D, and 2D bands of GNRs proves that Raman spectroscopy is still a reliable tool in characterizing GNRs despite their nanometer width.

• Bulletin of the Korean Chemical Society
• /
• v.28 no.2
• /
• pp.193-199
• /
• 2007

Raman and fluorescence spectroscopies were employed to study the coil effects on the intermolecular structure of a rod-coil liquid crystalline (LC) oligomer, the esterification products of ethyl 4-[4'-oxy-4-biphenylcarbonyloxy]- 4'-biphenylcarboxylate with poly(propylene)oxides (PPO) (DP=12) and poly(ethylene oxide)s (PEO) (DP=12). Three different vibrational modes (carbonyl, aromatic C-H, and aromatic C=C) obtained from the Raman experiment at variable temperature indicate that PPO and PEO coils induce the hydrogen bonding in a different manner. Further information about the micro-environment around the mesogenic unit obtained by fluorescence excitation spectra of P12-4 (LC with PPO coil) and 12-4 (LC with PEO coil) suggests that the mesogenic unit of P12-4 is quite different from that of 12-4 in intermolecular structure. This study supports the results obtained only from Raman spectroscopy, providing more accurate information about the intermolecular structural changes of liquid crystalline polymers at a molecular level during the phase transitions.