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(a) Enhancement of G-band and 2D-band Raman intensity taken in situ during PAS. The arrow indicated when synthesized AuNPs were deposited on graphene. (b) Ex situ Raman spectra taken on pristine graphene and graphene with 100 nm AuNP in ambience.
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This paper presents a convenient and reliable method to prepare gold nanoparticles (AuNPs) on graphene. Photo-assisted synthesis (PAS) was employed to grow AuNPs in AuCl4⁻ electrolyte on graphene. The size of AuNPs could be as large as 130 nm. This optical method had a steady growth rate of AuNPs. The distribution of AuNPs was well controlled by fo...
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... In addition the D-peak appears after Au deposition which might be due to lattice disorder produced in graphene during the deposition of gold film. Even under deposition of Au nanoparticles by photo-assisted synthesis with AuCl 4 − solution as electrolyte, lattice distortion of graphene is observed [33], which is attributed to local intensive plasmonic electro-magnetic field of Au. We observed significant blue shift in G and 2D peaks upon gold deposition. ...
Rutherford backscattering spectrometry (RBS) has been used to examine the inter-diffusion behaviour in Au thin films (∼30nm) deposited on CVD grown monolayer Graphene on copper (Au/Gr/Cu) with reference to gold film deposited on copper (Au/Cu), under thermal annealing and ion beam irradiation processes. Graphene is acting as a diffusion barrier in Au/Gr/Cu upto 220°C for the inter-diffusion of Au in Cu in thermal annealing process, while interdiffusion occurs below 200°C in Au/Cu. In high temperature regime, bulk diffusion mechanism is dominant in Au/Cu system whereas grain boundary diffusion is dominant in Au/Gr/Cu system. The dominant grain boundary diffusion in Au/Gr/Cu indicates that grain boundary defects in graphene play a greater role in interdiffusion process. Upon 9 MeV Si⁶⁺ ion irradiation, there is no ion beam mixing upto 5 × 10¹⁵ ions/cm² and at the ion fluence of 3 × 10¹⁶ ions/cm², ion beam mixing is observed in both Au/Cu and Au/Gr/Cu samples, with lower ion beam mixing rate and mixing efficiency for Au/Gr/Cu sample. This implies that graphene interlayer can prevent ion beam mixing to a certain extent due to its impermeable nature. The blue shift of Raman spectroscopy peaks G and 2D and the splitting of G-peak from graphene barrier layer signifies the compressive strain in Au deposited and thermally annealed Gr/Cu samples. Even though interlayer graphene can reduce the interdiffusion in Au/Cu system modestly, it becomes disordered with the formation of sp³ carbon bonds with increase in annealing temperatures and ion fluences, thereby loosing its impermeable nature.
... The vital dependence of the properties of 2D materials on the underlying substrate and the modulation of these properties by substrate engineering have been reviewed recently 16 . Integration of graphene with plasmonic metallic nanostructures has been shown to enhance the Raman signal of graphene by 2-3 orders of magnitude [17][18][19][20][21][22][23][24][25][26][27][28] . To this end, various kinds and geometries of metallic nanostructures have been employed, including nanodisks 23 , nanodots 24 , nanopyramids 22 , polygons, dendrites, dense clusters 27 , and irregular islands 18,27 , which resulted in measured enhancement factors of the Raman signal of graphene as high as 1000. ...
... For this substrate, the highest measured enhancement factor is F = 880 for the G peak and F = 420 for the 2D peak, both under 633 nm excitation wavelength. These values are similar to the highest measured enhancement factors reported in literature (~1000) for SERS of graphene on plasmonic substrates [17][18][19][20][21][22][23][24][25][26][27][28] . A higher enhancement is achieved when graphene is placed on top of plasmonic structures, as in this work, than when it is placed below them. ...
Integrating graphene with plasmonic nanostructures results in multifunctional hybrid systems with enhanced performance for numerous applications. In this work, we take advantage of the remarkable mechanical properties of graphene to combine it with scalable 3D plasmonic nanostructured silicon substrates, which enhance the interaction of graphene with electromagnetic radiation. Large areas of femtosecond laser-structured arrays of silicon nanopillars, decorated with gold nanoparticles, are integrated with graphene, which conforms to the substrate nanotopography. We obtain Raman spectra at 488, 514, 633, and 785 nm excitation wavelengths, spanning the entire visible range. For all excitation wavelengths, the Raman signal of graphene is enhanced by 2–3 orders of magnitude, similarly to the highest enhancements measured to date, concerning surface-enhanced Raman specrtoscopy (SERS) of graphene on plasmonic substrates. Moreover, in contrast to traditional deposition and lithographic methods, the fabrication method employed here relies on single-step, maskless, cost-effective, rapid laser processing of silicon in water, amenable to large-scale fabrication. Finite-difference time-domain simulations elucidate the advantages of the 3D topography of the substrate. Conformation of graphene to the Au-decorated silicon nanopillars enables graphene to sample near fields from an increased number of nanoparticles. Due to synergistic effects with the nanopillars, different nanoparticles become more active for different wavelengths and locations on the pillars, providing broadband enhancement. Nanostructured plasmonic silicon is a promising platform for integration with graphene and other 2D materials, for next-generation applications of large-area hybrid nanomaterials in the fields of sensing, photonics, optoelectronics, and medical diagnostics.
... In addition, the G and 2D peaks of as-prepared G@Cu samples had different degrees of enhancement compared with the transferred graphene (44 and 56 a.u. for G and 2D band respectively) which was caused by the EM of Cu particles and the plasmonic coupling caused by the interaction between Cu particles and graphene shell, where hot electrons can be injected into graphene layer [7,18,37]. To estimate the SERS activity of the as-prepared G@Cu substrates, 10 −5 M aqueous solution of R6G was chosen as the probe molecules. ...
We presented a graphene-wrapped Cu particle hybrid system (G@Cu) to be used as a high performance surface-enhanced Raman scattering (SERS) substrate. The Cu particles wrapped by a few-layer graphene shell were directly synthesized on SiO2/Si by chemical vapor deposition assisted with thermal annealing in a mixture of methane and hydrogen. The detailed explanation on the different morphology of Cu particles induced by different thermal annealing condition was carried out with both qualitative and quantitative analysis and a series of G@Cu 3D models of Cu particles with different shape anisotropy and inter-particle gap were also built for further study of Raman enhancement mechanism. The G@Cu showed fine SERS activities, including the fluorescence quenching effect, the stability of Raman signals, chemical and optical stability, with an enhancement factor (EF) of ~1.5 × 10⁶.
... In the case of G-Au, even after the deposition of AuNPs, the 2D peak appeared in the same position which ensured the few layer structure. The G-Au nanocomposite exhibited a marginal enhancement in the intensity of D band, corresponding to the lattice deformations caused by the local intensive plasmonic effects of AuNPs (Cheng et al. 2013). ...
In this study, a sonochemical approach was utilised for the development of graphene-gold (G-Au) nanocomposite. Through the sonochemical method, simultaneous exfoliation of graphite and the reduction of gold chloride occurs to produce highly crystalline G-Au nanocomposite. The in situ growth of gold nanoparticles (AuNPs) took place on the surface of exfoliated few-layer graphene sheets. The G-Au nanocomposite was characterised by UV-Vis, XRD, FTIR, TEM, XPS and Raman spectroscopy techniques. This G-Au nanocomposite was used to modify glassy carbon electrode (GCE) to fabricate an electrochemical sensor for the selective detection of nitric oxide (NO), a critical cancer biomarker. G-Au modified GCE exhibited an enhanced electrocatalytic response towards the oxidation of NO as compared to other control electrodes. Recent electrochemical detections systems of NO fabricated with graphene in combination with nafion (Yusoff et al. 2015, Anal. Methods.) and cobalt oxide-platinum nanocomposites (Shahid et al. 2015, J. Mater. Chem. A) were resulted in the limit of detection of 11.6 and 1.7 µM, where the linear sweep voltammetry analysis of G-Au modified GCE tested in a linear range of 10-5000 μM with the limit of detection of 0.04 μM (S/N=3).
Furthermore, this enzyme-free G-Au/GCE exhibited an excellent selectivity towards NO in the presence of interferences. The synergistic effect of graphene and AuNPs, which facilitated exceptional electron-transfer processes between the electrolyte and the GCE thereby improving the sensing performance of the fabricated G-Au modified electrode with stable and reproducible responses. This G-Au nanocomposite introduces a new electrode material in the sensitive and selective detection of NO, a prominent biomarker of cancer.
... Another group of scientists prepared ultrathin gold nanocrystals (AuNCs) on a co-reduced GO surface by photo irradiation (LEDs with continuous stirring) in the absence of chemical reductants and surfactants [108]. Also, photo-aided synthesis of graphene-AuNPs was employed to grow AuNPs in AuCl 4´e lectrolyte [109]. This convenient and reliable method has ensured a steady growth rate of AuNPs with well-controlled distribution by using focused laser light. ...
Graphene is a single-atom-thick two-dimensional carbon nanosheet with outstanding chemical, electrical, material, optical, and physical properties due to its large surface area, high electron mobility, thermal conductivity, and stability. These extraordinary features of graphene make it a key component for different applications in the biosensing and imaging arena. However, the use of graphene alone is correlated with certain limitations, such as irreversible self-agglomerations, less colloidal stability, poor reliability/repeatability, and non-specificity. The addition of gold nanostructures (AuNS) with graphene produces the graphene-AuNS hybrid nanocomposite which minimizes the limitations as well as providing additional synergistic properties, that is, higher effective surface area, catalytic activity, electrical conductivity, water solubility, and biocompatibility. This review focuses on the fundamental features of graphene, the multidimensional synthesis, and multipurpose applications of graphene-Au nanocomposites. The paper highlights the graphene-gold nanoparticle (AuNP) as the platform substrate for the fabrication of electrochemical and surface-enhanced Raman scattering (SERS)-based biosensors in diverse applications as well as SERS-directed bio-imaging, which is considered as an emerging sector for monitoring stem cell differentiation, and detection and treatment of cancer.
... Graphenes consist of a small number of atomic carbon layers arranged in a hexagonal lattice. Graphene has unique optical and electrical properties [1][2][3][4][5], making graphenebased systems of vital importance for the creation of the next generation of optical sensors, photovoltaics, and energy storage devices [2][3][4][6][7][8][9][10][11][12][13]. Graphene architectures can take many forms, from carbon flakes [14,15], carbon nanotubes [4,14], horizontal sheets [3,4], and vertical graphene nanosheets (VGNs) [2,4,6,7,[12][13][14][16][17][18][19][20]. ...
... Graphenes are relatively low-loss and transparent optical materials which can provide strong electromagnetic (EM) confinement, making the interaction of graphene with metal nanoparticles of interest for the development of novel plasmonic-based devices [4,6,23]. In particular, decorating graphene with metallic nanostructures has led to the development of new surface enhanced Raman spectroscopy (SERS) systems [7,8,[24][25][26][27]. The metal nanoparticles can focus the light down to nanoscale areas, increasing the SERS signal intensity. ...
Vertical graphene nanosheets have advantages over their horizontal counterparts, primarily due to the larger surface area available in the vertical systems. Vertical sheets can accommodate more functional particles, and, due to the conduction and optical properties of thin graphene, these structures can find niche applications in the development of sensing and energy storage devices. This work is a combined experimental and theoretical study that reports on the synthesis and optical responses of vertical sheets decorated with gold nanoparticles. The findings help in interpreting optical responses of these hybrid graphene structures and are relevant to the development of future sensing platforms.
A rapid, facile and label-free sensing strategy is developed for the detection of dopamine (DA) in the real samples by exploiting nitrogen-doped graphene quantum dots (N-GQDs) decorated on Au nanoparticles ([email protected]). The as-grown [email protected] exhibits strong blue fluorescence at room temperature and the fluorescence intensity is drastically quenched in presence of DA in neutral medium. The mechanistic insight into the DA sensing by [email protected] is explored here by careful monitoring of the evolution of the interaction of Au NPs and N-GQDs with DA under different conditions through electron microscopic and spectroscopic studies. The highly sensitive and selective detection of DA over a wide range is attributed to the unique core-shell structure formation with [email protected] hybrids. The quenching mechanism involves the ground state complex formation as well as electron transfer from N-GQDs. The presence of Au NPs in [email protected] hybrids accelerates the quenching process (~14 fold higher than bare N-GQDs) by the formation of stable dopamine-o-quinone (DQ) in the present detection scheme. The fluorescence quenching follows the linear Stern-Volmer plot in the range 0–100 μM, establishing its efficacy as a fluorescence-based DA sensor with a limit of detection (LOD) 430 nM. Further, based on the systematic change in the intensity of absorption peak of [email protected] with DA concentration, the well-known Hill equation is introduced for the sensing of DA in the range 0–10 μM with detection limit 40 nM. The proposed sensing method has a high selectivity towards DA over a wide range of common biological molecules as well as metal ions. The quenching in [email protected] fluorescence intensity makes it possible to determine the spiked DA in human serum in the linear range from 0.0 to 80.0 μM with the limit of detection (LOD) 590 nM, which is ~27 fold lower than the lowest abnormal concentration of DA in serum (16 μM). This sensing scheme is also successively applied to trace DA in Brahmaputra river water sample with LOD 480 nM including its satisfactory recovery (95–112%). Our studies reveal a novel sensing pathway for DA through the core-shell structure formation and it is highly promising for the design of efficient biological and environmental sensor.
Binding graphene with auxiliary nanoparticles for plasmonics, photovoltaics, and/or optoelectronics, while retaining the trigonal-planar bonding of sp2 hybridized carbons to maintain its carrier-mobility has remained a challenge. The conventional nanoparticle-incorporation route for graphene is to create nucleation/attachment sites via ‘carbon-centered’ covalent functionalization, which changes the local hybridization of carbon atoms from trigonal-planar sp2 to tetrahedral sp3. This disrupts the lattice planarity of graphene, thus dramatically deteriorating its mobility and innate superior properties. Here, we show large-area, vapor-phase, ‘ring-centered’ hexahapto (η6) functionalization of graphene to create nucleation-sites for silver nanoparticles (AgNPs) without disrupting its sp2 character. This is achieved by the grafting of chromium tricarbonyl [Cr(CO)3] with all six carbon atoms (sigma-bonding) in the benzenoid ring on graphene to form an (η6-graphene)Cr(CO)3 complex. This non-destructive functionalization preserves the lattice continuum with a retention in charge carrier mobility (9% increase at 10 K); and with AgNPs attached on graphene/n-Si solar cells, we report an ~11-fold plasmonic-enhancement in the power conversion efficiency (1.24%).
The subject matter of this article is the use of nanomaterials as tools (i.e. sorbents in microextraction techniques, optical sensors, vibrational spectroscopies, etc.) for the characterization and/or determination of nanoanalytes (analysis of the nanoworld). The so-called Third Way is the combination of the two classical approaches of analytical nanoscience and nanotechnology (AN&N), namely, the use of nanotools and determination of nanoanalytes, looking for synergies between the two nanoparticles involved in the same analytical process. After an overview of AN&N, the definition, the objectives, and the types of Third Way processes in AN&N are outlined. Moreover, examples of analytical methodologies involving the use of nanotools (i.e. sorbents in (micro)extraction techniques) for the determination of nanomaterials involving different analytical techniques (i.e. optical sensors and vibrational spectroscopies) are systematically presented. Last but not least, a critical approach to the future of these analytical nanotechnological mixed processes is discussed.
In recent years, there has been a growing interest in using graphene as a synthesis platform for polymers, zero-dimensional (0D) materials, one-dimensional materials (1D), and two-dimensional (2D) materials. Here, we report the investigation of the growth of germanium nanowires (GeNWs) and germanium nanocrawlers (GeNCs) on single-layer graphene surfaces. GeNWs and GeNCs are synthesized on graphene films by gold nanoparticles catalyzed vapor-liquid-solid growth mechanism. The addition of hydrogen chloride gas (HCl) at the nucleation step increased the propensity toward GeNCs growth on the surface. As the time lag before HCl introduction during the nucleation step increased, a significant change in the number of out-of-plane GeNWs versus in-plane GeNCs was observed. The nucleation temperature and time played a key role in the formation of GeNCs as well. The fraction of GeNCs (NCs) decreased from 0.95 ± 0.01 to 0.66 ± 0.07 when the temperature was kept at 305°C for 15 sec versus maintained at 305°C throughout the process, respectively. GeNCs exhibit <112> as the preferred growth direction whereas GeNWs exhibit both <112> and <110> as the preferred growth directions. Finally, our growth model suggests a possible mechanism for the preference of an in-plane GeNC growth on graphene versus GeNW on SiO2. These findings open up unique opportunities for fundamental studies of crystal growth on graphene, as well as enable exploration of new electronic interfaces between group IV materials and graphene, potentially toward designing new geometries for hybrid materials sensors.
