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provide more hot spots, which are introduced by the electromagnetic mechanism (EM). By the virtue of their larger specific surface area and periodic structure, 3D SERS substrates can effectively amplify the optical field around metal nanoparticles (NPs), thereby enhancing the Raman signal. Moreover, the 3D structure of these substrates is beneficial for the enrichment of probe molecules around metal nanoparticles; as a result, one can still obtain a high Raman signal, even under an ultralow concentration. Consequently, an increasing number of researchers are now focusing on the design and fabrication of 3D SERS substrates.To make full use of the merits of the 3D structure, SERS substrates based on 2D materials and metal nanoparticles have been combined and proposed. [23,24] In these 3D SERS substrates, the 3D structure can fully utilize the 3D focal volume of the incident beam and increase the density of the metal nanoparticles. Furthermore, introduction of the 2D material can act as an atomically thick SERS substrate, [25] perfect absorbent layer of molecules, [26] excellent sub-nanometer spacer, [27] and passivation layer for metal, [28,29] and introduce enhancements via a chemical mechanism (CM). Previously, a 3D SERS substrate based on graphene covering a pyramid-shaped Au structure was reported to achieve high enhancement. [30] While the integration of graphene and pyramid-shaped Au was successfully implemented, this 3D SERS substrate was not flexible and did not meet with the requirements when detecting probe molecules on an arbitrary curvilinear surface.Therefore, transformation of these stiff 3D substrates into flexible structures via using various methods has been investigated extensively. Leem et al. reported 3D crumpled graphene-AuNPs hybrid structures for SERS applications using a mechanical self-assembly strategy on a thermally activated polymer. [31] Similarly, Lee et al. fabricated a rippled graphene structure on a polystyrene substrate using a thermal rippling process and demonstrated the increased plasmonic coupling and higher density of the hot spots on the rippled nanostructure. [32] Kumar et al. presented a flexible SERS sensor by depositing Ag on structured polydimethylsiloxane using a Taro leaf as the template and achieved highly sensitive detection for malachite green. [33] Moreover, to fabricate a flexible 3D SERS substrate, the transfer printing technique, [34] shadow Substrate design has attracted much interest in development of an effective surface enhanced Raman scattering (SERS) sensor. A flexible SERS substrate with excellent performance needs to be sensitive to details of the preparation process; this sensitivity represents a significant challenge for practical applications as opposed to laboratory research applications. Here, a 3D flexible plasmonic structure, AgNPs@MoS 2 /pyramidal polymer (polymethyl methacrylate), is fabricated using a simple and lowcost method. Using experiments and theoretical simulations, the SERS performance of the proposed substrate is assessed in terms of ...

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We demonstrate that continuous, uniform graphene films can be directly synthesized on quartz substrates using a two-temperature-zone chemical vapor deposition system and that their layers can be controlled by adjusting the precursor partial pressure. Raman spectroscopy and transmission electron microscopy confirm the formation of monolayer graphene with a grain size of ∼100 nm. Hall measurements show a room-temperature carrier mobility above 1500 cm2 V(-1) s(-1). The optical transmittance and conductance of the graphene films are comparable to those of transferred metal-catalyzed graphene. The method avoids the complicated and skilled post-growth transfer process and allows the graphene to be directly incorporated into a fully functional biosensor for label-free detection of adenosine triphosphate (ATP). This device shows a fast response time of a few milliseconds and achieves a high sensitivity to ATP molecules over a very wide range from 0.002 to 5 mM.

ZnO thin films were grown on sapphire substrates at a growth temperature of 400 °C by Nd:yttrium–aluminum–garnet (Nd:YAG 1064 nm) pulsed-laser deposition. The effects of oxygen pressure on the structure, stoichiometric composition and optical properties of ZnO thin films were investigated in detail. X-ray diffraction (XRD) shows that the crystal quality is highest for the ZnO film grown at a pressure of 10 mTorr. Optical transmittance, electronic properties and Raman spectra show the increase in the stoichiometric composition ratio of ZnO films with increasing oxygen pressure owing to the reduction in the number of oxygen vacancies (VO) and Zn interstitials (Zni). Photoluminescence (PL) spectra reveal that the UV-emission properties have greater dependence on the stoichiometriy of ZnO films than on the crystal quality. A blue-light emission peak at about 465 nm (E g=2.66 eV) was observed in the PL spectra of ZnO thin films fabricated at various oxygen pressures. This emission peak was ascribed to the electronic transition from the donor energy level of the Zn interstitials to the acceptor energy level of the Zn vacancies (VZn) rather than the oxygen vacancies.