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Graphene can be used as a starting material for the synthesis of useful nano-complexes for flexible, transparent electrodes, therapeutic, bio-diagnostics and bio-sensing. In order to apply graphene in the medical field, chemical vapor deposition (CVD) method has been mainly utilized considering its large and near-homogenious carbon constituents. Especially, the less degree of perturbation of graphene monolayer (GM), which is followed by the underneath catalytic Cu surface morphology, is very crucial in terms of providing the suspended GM and relatively fluent lateral carrier mobility with lower sheet resistance value. In this work, we can suggest a surface-Enhanced Raman Spectroscopic (SERS) indicator in a quantitative way on the status of z-directional morphological corrugation of a CVD–grown GM (CVD-GM) by applying a Nanoparticle-on-Mirror (NPoM) system composed of Au nanoparticle (NP) / CVD-GM / Au thin film (TF) plasmonic junction structure. A new (or enhanced) Radial Breathing Like Mode (RBLM) SERS signal around ~150 cm-1 from CVD-GM spaced in NPoM is clearly observed by employing a local z-polarized incident field formed at the Au NP–Au TF plasmonic gap junctions. With this observation, the value of I[out-of-plane, RBLM] / I[in-plane, [2D] at certain domains, it can be suggested as a new optical nano-metrology value to relatively determine between lower z-directional morphological corrugation (or protrusion) status of a CVD-GM spaced in our NPoM system (lower I[RBLM] / I[2D] value) and higher degree of lateral carrier mobility of the CVD-GM associated with lower sheet resistance values as a result of higher blue-shifted Raman in-plane (G, 2D) peak maximum position. Furthermore, we will also expect the bio-sensing performances by utilizing the high specific surface area and ultrahigh flexibility of the CVD-GM in one of the future prospective works such as pressure-strain, strain-to-electricity and chemical-coupled sensor via I[RBLM] / I[2D] values.

Utilizing cellulose nanofibers (CNF) attracts tremendous attention in terms of developing a non-breakable film with high toughness and optically transparent properties. Here, the author introduces a new characterization method in order to compare the relative degree of the crystalline and amorphous characters of CNF by correlating Graphene-Quenching Raman Scattering (GQRS) with Electrostatic Force Microscope (EFM) results. This nano-metrology may pave the new way in quantitatively unraveling the degree of lignin and hemicellulose.

We have visualized surface-enhanced Raman scattering (SERS) nano-gap domains with electrostatic force microscopy (EFM). We constructed the SERS substrate using reactive-ion etching of a polyethylene terephthalate (PET) film, with subsequent sputtering of Au onto the etched PET. Because the nano-gap is more strongly charged than the native Au-nanoparticle (NP) surface, we can identify the SERS nano-gap due to the longer dwell time of the tapping EFM tip and the related phase shift of the signal. This produces a differentiating image contrast between the SERS nano-gap and the Au NP surface, with a spatial resolution of ~14 nm. More specifically, differences in the mode-independent Raman-signal enhancement and the peak shift of an adsorbed malachite green isothiocyanate (MGITC) molecule are only observed in the smaller SERS nano-gap (found in the surface with Ar+-sputtered Au nano-pillars). We interpret this in terms of the differing morphologies of the underlying Au substrates and the related mechanical compressive strains, which result in charge transfer (CT)-based single-molecule Raman-reporter detection sensitivity.

We present an out-of-plane directional charge transfer (CT)-assisted chemical enhancement (CM) in the surface-enhanced Raman scattering (SERS) of a graphene monolayer (GM) sandwiched at an individual Au prism-Au thin film (TF) plasmonic junction. By comparing previous reports, in which the enhancement of out-of-plane phonon modes of a GM was mostly governed by z-directional local field formed at a Au nanoparticle (NP)–Au TF junction, we can reveal that a CT-assisted CM along the z-direction has a pivotal role by enhancing radial breathing-like mode (RBLM) intensity at face-to-face junction types. The anticorrelation between 2D and RBLM intensity from ridge to flat domains of an Au prism indicates that a plasmonic EM effect is not a critical element at flat domain, whereas the RBLM intensity is strongly enhanced at face-to-face junction. Furthermore, the closest GM from a z-axis has a significant role based on vector-based investigation in enhancing CT-assisted CM effect between Au prism and TF. These phen...

We report a new way to enhance the electrical performances of large area CVD-grown graphene through controlling the ripple density and heights after transfer onto SiO2/Si substrates by employing different cooling rates during fabrication. We find that graphene films prepared with a high cooling rate have reduced ripple density and heights and improved electrical characteristics such as higher electron/hole mobilities as well as reduced sheet resistance. The corresponding Raman analysis also shows a significant decrease of the defects when a higher cooling rate is employed. We suggest a model that explains the improved morphology of the graphene film obtained with higher cooling rates. From these points of view, we can suggest a new pathway toward a relatively lower density and heights of ripples in order to reduce the flexural phonon-electron scattering effect, leading to higher lateral carrier mobilities.

We report that Raman enhancements of a graphene monolayer sandwiched at the Au nanoparticle-Au thin film junction are different and can be attributed to the influence of a z-polarized incident field. Closer to the center of the junction, radial breathing like-mode (RBLM) shows dramatic Raman enhancement in terms of the coincidence between the z-polarized incident field formed at the junction and the RBLM phonon axis. The appearance of an additional D* peak can be identified and is attributed to the additional out-of-plane sp(3) type defect signal. Correlating I(D*)/I(D) with RBLM intensity variation further substantiates that the observed D* peak is ascribed to another out-of-plane structural defect signal.

Simultaneous utilization of both in-plane and out-of-plane phonon vibration of graphene sandwiched between a Au nanoparticle (NP) and Au TF junction can have a significant role in quantifying the z-polarized electromagnetic (EM) field contribution. The layer breathing mode (LBM), which involves the relative displacement of the individual graphene layers in the graphene sheet in the normal directions, can be exclusively observed at Au NP–Au TF junctions. By employing the ILBM/I2D value at each junction, the author can show that a nearly 50–70-times stronger z-polarized EM contribution is present at Au NP–Au TF junctions. Additionally, the author can also determine that a Au NP with a truncated shape shows a relatively ∼1.3-times higher z-polarized EM contribution than a Au NP with a spherical shape because of the higher density of the pointed part from the truncated Au NP. Furthermore, the author reveals the evolution of the asymmetric shape of the LBM peak with increasing z-polarized EM strength. The incr...

We report a method to characterize z-directional surface roughness of chemical vapor deposition-grown graphene monolayers with the aid of surface-enhanced Raman scattering spectral signatures of “out-of-plane” phonon modes observed at Au nanoparticle (NP)–graphene–Au thin film junctions. This method reveals that intensities of the out-of-plane mode (Radial Breathing Like Mode) are strongly correlated with the Full Width at Half Maximum (FWHM) of the de-convoluted 2D peak. On the basis of our findings, in-plane 2D peak shape can be used as a straightforward, quantitative indicator in estimating surface roughness of graphene without loading Au NPs by calculating the FWHM [2D−]/FWHM [2D+] value. Furthermore, we examine the different ripple (RP) shapes on graphene by employing atomic force microscopy-correlated Raman microscopy to identify “threading” and “surrounded” RP types for further investigation on the relationship between spectral features and structural aspects. Electrostatic force microscopy (EFM)-based investigation further substantiates that threading-type RPs in graphene show higher EFM amplitude, indicating that the threading domains tend to be more neutral with a few more sp3 type defects than the surroundings.

Due to the large differences in the lattice constants and the thermal expansion coefficients between GaN and Si, GaN growth on a Si substrate usually leads initially to high defect densities and cracks. If high-quality GaN films on Si substrate are to be obtained, it is essential to understand the different growth characteristics of GaN layers grown on Si and on sapphire. In this study, the GaN specimens were grown on sapphire and Si (111) substrates with AlGaN and AlN buffer layers, respectively, by metalorganic chemical vapor deposition (MOCVD). Using transmission electron microscopy (TEM) and micro-Raman spectroscope, we carried out a comparative investigation of GaN growth by characterizing lattice coherency, defect density, and residual strain. These analyses revealed that the GaN layers grown on Si have much residual tensile strain and that strain has an effect on the formation of InGaN/GaN multiple quantum wells (MQWs) above the GaN layers.

The authors present the blue-shift of Raman 2D and G peak of a single layer graphene film, which is fabricated via chemical vapor deposition, on the relatively even Cu foil domain with nearly uniform thickness. This can be interpreted that rather mechanically compressive strain is exerted between graphene and the even Cu domain compared to the uneven. We observe that relaxing compressive strain to minimize the perturbation from Cu surface to the graphene film by virtue of the uneven Cu domain has a critical role in forming a suspended graphene. Furthermore, mechanical strain influence derived from the underlying substrate morphology can be suggested as one of the crucial elements in evaluating high quality graphene film considering suspended shape.

We carried out the tip-enhanced Raman scattering (TERS) with a tip that is functionalized with a Aunanoparticle (AuNP, with a diameter of 250 nm). The AuNP tip is fabricated by a direct mechanical pickup of a AuNP from a flat substrate, and the TERS signal from the AuNP tip - organic monolayer - Au thin film (thickness of 10 nm) is recorded. We find that such a AuNP-tip interacting with a thin film routinely yields signal enhancement larger than ~10 4 , which is sufficient not only for local (with detection area of ~200 nm 2 ) Raman spectroscopy, but also the nanometric imaging of organic monolayers within a reasonable acquisition time (~20 minutes/image).

We measured the surface-enhanced Raman scattering (SERS) of individual gold nanoparticle-4-aminobenzenethiol (ABT)-gold film junctions to investigate the charge-transfer (CT) enhancement of the SERS signals. Despite the mild electromagnetic field enhancement (∼10(5)) and high surface density of the ABT-molecules (∼240 molecules/hotspot) at the junctions, we observed the clear spectral and temporal signatures of CT-enhanced single-molecule SERS (SM-SERS). The result reveals that only a small fraction of the molecules at the junction has a significant CT-enhancement of 10(1)∼10(3), whereas the rest of the molecules are nearly CT-inactive. Furthermore, the result also proves that overall (charge-transfer and electromagnetic) enhancement of 10(6)∼10(8) is sufficient to observe the SM-SERS of an electronically off-resonant molecule, which disproves the widespread belief that a minimum enhancement of ∼10(14) is required for SM-SERS.

Since the first observation of single-molecule level surface-enhanced Raman scattering (SERS) from randomly aggregated noble metal nanoparticles, much effort has been made to understand the electromagnetic and chemical mechanisms behind the observed enhancement, and to fabricate structures that exhibit strong and reproducible SERS activities. It is widely accepted that the locally enhanced electromagnetic (EM) field formed between the noble metal nanoparticles is mostly responsible for the strong SERS signals observed. However, the SERS-active junctions (hotspots) in self-assembled nanoparticle aggregates occur at unpredictable positions, and the SERS intensities vary by 5–6 orders magnitude from one hotspot to another within the same sample, which renders the quantitative prediction of the SERS activities challenging. The extremely irregular characters of the SERS signals appear to originate from the irregular geometries of the randomly formed junctions. Therefore, many “designed” SERS structures such as hexagonally close-packed gold nanospheres, rafts of silver nanowires, lithographically designed junctions, film-on-nanospheres structures (FON), and nanoparticle-plane assemblies, have recently been tested for consistent and reproducible SERS activities. However, the junction structures that exhibit site-reproducible (junctionto-junction invariant) SERS activities at the individual junction levels have yet to be reported. Herein we report that self-assembled nanoparticle–molecular monolayer–plane junctions show such reproducibility at the single junction level. Theoretical models predict that the nanosphere–plane junction would produce a strong local field and SERS signal via the coupling between the localized surface plasmon (LSP) of the nanosphere and the surface plasmon polariton (SPP) formed on the conducting surface. A few experimental reports have demonstrated that such junctions produce ensemble-averaged Raman enhancement of 10–10. However, the SERS activities and their microscopic mechanisms of the individual nanoparticle–plane junctions have not been experimentally examined in detail. Through the confocal SERS microscopy measurements on individual nanoparticle–plane junctions, we find that almost every nanoparticle–plane junction generates remarkably reproducible SERS signals. In addition, we observe that such junctions show strong preference towards the excitation and the SERS polarization directions parallel to the nanoparticle–plane junction axis, which strongly supports the LSP–SPP coupling model of the SERS from the nanoparticle–plane junction. The experiment was carried out with an epi-confocal Raman microscope combined with a tapping-mode atomic force microscope (AFM, Figure 1a, see also the Experimental Section), which enables the simultaneous measurements of the spatially

We demonstrate that high-resolution (~60 nm) near-field fluorescence images of fluorescent nanospheres can be obtained by utilizing the tip-induced fluorescence quenching process. A time-stamped photon counting (TSPC) technique employed enables us to efficiently measure the degree of fluorescence quenching caused by the dielectric or metallic atomic force microscopy tip. We find that the degree of quenching is not only determined by the tip-material but also by the local morphology of the tip. The fringe patterns around individual nanospheres observed are explained in terms of the interference between the excitation field that is directly induced by the laser source, and the scattered excitation field from the tip.

The lipid-rafts hypothesis proposes that naturally occurring lipid aggregates exist in the plane of membrane that are involved in signal transduction, protein sorting, and membrane transport. To understand their roles in cell biology, a direct visualization of such domains in living cells is essential. For this purpose, 6-dodecanoyl-2-(dimethylamino)naphthalene (laurdan), a membrane probe that is sensitive to the polarity of the membrane, has often been used. We have synthesized and characterized 6-dodecanoyl-2-[N-methyl-N-(carboxymethyl)amino]naphthalene (C-laurdan), which has the advantages of greater sensitivity to the membrane polarity, a brighter two-photon fluorescence image, and reflecting the cell environment more accurately than laurdan. Lipid rafts can be visualized by two-photon microscopy by using C-laurdan as a probe. Our results show that the lipid rafts cover 38 % of the cell surface.

The unimolecular dissociation dynamics of vinyl chloride on the ground electronic potential energy surface have been investigated. The vibrationally excited vinyl chloride in its ground electronic state is prepared using the isomerization process of α-chloroethylidene radical to vinyl chloride via the hydrogen atom migration, where the chloroethylidene radical is produced by the ultraviolet photolysis of 3-methyl-3-chlorodiazirine. The vinyl chloride molecule formed in this excitation scheme is highly vibrationally excited in its ground electronic state due to the bond formation between two carbon atoms, and undergoes unimolecular reactions of HCl elimination or C−Cl bond fission. The rotational and vibrational state distributions of the HCl fragments and the spin−orbit state branching ratio of the Cl atoms have been measured with a resonantly enhanced multiphoton ionization (REMPI)/time-of-flight mass spectrometry. The overall state distributions of the HCl and Cl fragments are much colder than those in ...

The local field distribution around gold nanosphere-gold plane junction has been studied using the finite-difference time-domain (FDTD) electrodynamics calculation procedure. We find that both the in-plane and out-of-plane polarized excitation produce enhanced field strong enough to explain the observed SERS activities of the junctions. Comparison with a simple dipole-image dipole model shows that the enhanced field primarily originates from the multipole-image multipole interaction, which indicates that the detailed fine-structures of the nanoparticles also play a significant role in the SERS activities as well.

The author investigates an intra-layer coupling effect through transverse acoustic (TA) phonon modes along the z-direction at Au nanoparticle (NP)–graphene monolayer (GM)–Au thin film (TF) plasmonic junctions in regard with sp3 type defect effect. The oxidation and resulting disorder of GM with breaking of six-fold symmetry have been explored. Because a Raman-forbidden D peak can be activated due to unwanted single-phonon inter-valley and intra-valley scattering processes, the quantitative estimation of the sp3 type defect is being performed by the intensity ratio between G and D peaks. By exploring the difference of the maximum peak position (TA3-TA1) and the intensity ratio, (TA1/TA3) the author can reveal that a lower z-protruded GM accompanied with weak intra-coupling and a weaker RBLM intensity show relatively high D/G. It means that larger surface area of a GM to be functionalized by oxidization can secure more easily than the higher z-protruded. This investigation presents the importance of controlling the degree of z-protrusion of GM surface in terms of not only the presence of high D/G but also its related and detailed nano-structural surface shape, leading to the enhancement of electrical properties such as a carrier mobility and sheet resistance value. The out-of-plane phonon modes will be considered as a key factor in further exploring nano-physical deformation of 2D materials in sync with its electrical performance.

We report an observation of a scrolled graphene nanoribbon (sGNR) produced via a chemical vapor deposition. The sandwiched sGNR between Au nanoparticle and Au thin film system can be identified by the remarkable enhancement of G peak accompanied with a subsequent splitting (G+ and G−) with strong Radial Breading Like Mode enhancement. Because the weak adhesion force between graphene monolayer and target Au substrate during transfer maybe result in a sparse distribution of sGNR with a z-directional curvature-induced G peak splitting. Reproducibility and mass production with a nanometer scale circuit devices may be anticipated from this work.

We examine the origin of the surface-enhanced Raman scattering (SERS) background mediating with a graphene monolayer at Au nanoparticle-Au thin film junctions. We find the degree of the asymmetric shape of the radial breathing like mode (RBLM) peak at 150 cm−1 is strongly correlated with the accompanied SERS background intensities. The SERS investigation with the out-of-plane modes (300~700 cm−1) of graphene gives significant clues that the SERS background, the degree of the tilted formation from the analysis of the transverse acoustic peaks, and the spectral shape of the RBLM peak are strongly correlated with each other, indicating that electron–phonon coupling plays a crucial role in increasing the SERS background.

A series of donor-pi-donor derivatives containing phenyl, naphthyl, and anthryl groups as the pi-center and heterocyclic rings as the conjugation bridge have been synthesized and their one- and two-photon spectroscopic properties and photostability were determined. These compounds show bathochromic shifts in the absorption and emission spectra, larger two-photon cross-section, and enhanced photostability in comparison to their open-chain analogues. In addition, a convenient method for the qualitative photostability measurement is proposed.

The author reports that the spatial luminescent distribution from Cu substrate is in special sync with the Cu substrate morphology in terms of suspended formation of the deposited graphene fabricated via chemical vapor deposition. Moreover, the Raman 2D and G peak position of the graphene relatively shift to high frequency on the even Cu foil domain, showing more compressive strain than the uneven region. The author can reveal that the reducing compressive strain by virtue of the uneven Cu domains in order to minimize the interaction between graphene and Cu substrate has one of the important roles in forming suspended graphene. Current mapping in small dimension additionally shows that the current flow is mostly detected at the nano-terrace regions than the even, further substantiating the significance of the detailed underlying Cu substrate morphology. The author can also shows the correlation between the graphene strain revealed via 2D peak shift on Cu surface and the sheet resistance value of graphene on PET substrate, suggesting the degree of suspended formation of the graphene on Cu may be one of the important factors in increasing electrical performance on PET substrate.

We report a spectroscopic indicator showing the bending of a chemical vapor deposition (CVD) graphene monolayer on Cu foil or an arbitrary substrate after transfer. Using a Au nanoparticle (NP)-graphene monolayer-Au thin film (TF) junction system, the Radial Breathing-Like Mode (RBLM) Raman signal from the sandwiched graphene monolayer is evidently observed by employing a local z-polarized incident field formed at the Au NP-Au TF junction. We also utilized the RBLM intensity as a quantitative tool with a wide dynamic range (∼300%) compared to the 2D peak width (∼35%) for determining the relative degree of bending on the Au TF substrate. The RBLM signal from the CVD graphene monolayer is anticipated to be used as a valuable marker in exploring out-of-plane directional properties.

Despite some setbacks – notably an indigenous launch failure – progress is being made in South Korea's space program and its public image has been boosted by the first flight of a Korean astronaut to the ISS. This report provides an update on recent and forthcoming space activities in the country and on its current cooperative arrangements.

We employ electrostatic force microscope (EFM) techniques to explore local electrical properties of suspended graphene on Cu foil, SiO2/Si and PET substrate. By using electrical modulation of amplitude in a tapping mode atomic force microscope tip, we can obtain distinguished electrostatic force amplitude mapping of graphene on various substrates. In particular, at nano-valley domains on Cu and a SiO2/Si surface, relatively weaker electrostatic attractive interaction is observed than at nano-peak domains. In SiO2/Si, we find that electrostatic force distribution of graphene still follows the substrate surface morphology. Furthermore, employing EFM to graphene on a PET system can be suggested as a facile tool to investigate electrical performance of graphene.

We can experimentally identify the layer-layer breathing mode and the other out-of-plane transverse acoustic phonon modes of a few layered graphene via employing z-polarized incident field formed at Au nanoparticle-Au film junctions. The observed out-of-plane mode phonon at ∼150 cm−1 and other transverse acoustic phonon type defect modes from 300 cm−1 to 700 cm−1 can be readily explored. Not only for the normally used optical method using focused plane wave but also direct applying the z-directional electromagnetic field on graphene will be expected for more detailed out-of-plane phonon characterization of graphene.

We present that the Raman 2D and G peak of graphene film fabricated via chemical vapour deposition (CVD) blue-shifts on the relatively even Cu foil domain, showing a rather compressive strain effect compared to the uneven domain. We experimentally figure out that the relaxing compressive strain, to minimize the adhesive interaction between the graphene and the Cu surface, has one of the critical roles in forming suspended few-layered graphene. The nanoscopic conductance investigation also reveals that the current flow is dominantly measured at the uneven nano-terrace domains rather than at the even, further signifying the importance of a detailed underlying Cu surface morphology.

We examine local electrostatic force distribution of polyethylene terephthalate (PET) film surface before and after transferring graphene in order to compare the influence of local electrostatic interaction between graphene and PET film in terms of the sheet resistance value of deposited graphene. By using the electrical modulation of amplitude in a tapping mode AFM tip, we can obtain the distinguished electrostatic force amplitude mapping of graphene. We determine that different electrostatic attractive interactions between Au-coated tip and bare PET are present and the observed difference can affect the graphene formation and electrical performance, which correlates with the sheet resistance difference.

We report the axially graded heteroepitaxy of Si1−xGex nanowires, by the kinetic controls of the Au-catalytic decomposition of precursors during chemical vapor syntheses. Transmission electron microscope studies demonstrate that the relative composition of Si and Ge is continuously graded along the uniformly thick nanowires, sharing the same crystal structures with the continuously varying lattices. We also employed a confocal Raman scattering imaging technique, and showed that the local variations in Raman phonon bands, specific to Si and Ge alloying (νSi–Si, νSi–Ge, and νGe–Ge), can be spatially and spectrally resolved along the individual nanowires, within the spatial resolution of ∼500nm.

The authors present the demonstration of nanowire field-effect transistors incorporating group IV alloy nanowires, Si1−xGex. Single-crystalline Si1−xGex alloy nanowires were grown by a Au catalyst-assisted chemical vapor synthesis using SiH4 and GeH4 precursors, and the alloy composition was reproducibly controlled in the whole composition range by controlling the kinetics of catalytic decomposition of precursors. Complementary in situ doping of Si1−xGex nanowires was achieved by PH3 and B2H6 incorporation during the synthesis for n- and p-type field-effect transistors. The availability of both n- and p-type Si1−xGex nanowire circuit components suggests implications for group IV semiconductor nanowire electronics and optoelectronics.