Gold and silver nanoparticles and nanostructures exhibit plasmon resonances that result in strong scattering and absorption of light, as well as enhanced optical fi elds near the metal surface. The resonant fi eld enhancement dramatically enhances the weak Raman scattering signals from molecules near the metal surface. [ 1 ] This effect, called surface enhanced Raman scattering (SERS), has been widely pursued as a molecular sensing technology over the past decade. [ 2 , 3 ] SERS is non-destructive, suffi ciently sensitive for single molecule detection, and provides inherent molecular specifi city since it yields molecular vibrational spectra. While fi eld enhancement occurs over an entire nanostructure surface, SERS signals are strongest from small gaps between nanoparticles referred to as "hot spots" where the fi eld enhancement is maximal. [ 4 , 5 ] Most SERS work to date has focused on detection with substrates that are designed to maximize the density, sensitivity, and reproducibility of hot spots in order to give the strongest possible SERS signal. Many substrates have been developed which refl ect the variety of nanofabrication, synthesis, and assembly strategies that have emerged over the past decade. These include semiconducting nanowires, [ 6 ] aggregated colloids, [ 7 , 8 ] colloidal lithography, [ 9 , 10 ] soft lithography, [ 11 , 12 ] e-beam lithography, [ 13 ] and colloidal assembly. [ 14 , 15 ] Most of the substrates consist of nanostructured gold or silver on a fl at substrate. Some reports describe substrates with increased surface roughness to increase the number of hot spots, including aligned carbon nanotube substrates that support silver nanoparticles. [ 16 ] These substrates were found to provide highly sensitive detection. However, optical scattering and light collection occur in a three dimensional focal volume. Therefore, to maximize the quantity of scattered light generated and detected, SERS substrates should contain hot spots in a large three dimensional volume that is matched to the optics of the SERS instrumentation. Three dimensional substrates have been fabricated and tested based on porous silicon, microfabricated silicon, and porous gold. [17][18][19][20] These have indeed improved the detection limit for small molecules like trinitrotoluene (TNT). Therefore, it is desirable to create densely packed metal nanostructures with nanogaps to form plentiful hot spots for better SERS performance. [21][22][23] In the present study, we describe the fabrication of a structurally tunable 3D SERS substrate based on vertically aligned CNTs. Vertically aligned CNTs provide a new paradigm to realize three dimensional SERS substrates with high nanoparticle density. The vertically aligned CNTs were synthesized on a SiO 2 substrate by water-assisted chemical vapor deposition (CVD). The resulting vertically aligned CNTs were several millimeters long and were composed of a mixture of double-and triple-walled nanotubes. [ 24 , 25 ] A gold fi lm (50 nm thickness) was deposited on top of the CN...

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We propose a water vapor treatment to direct the formation of single-walled carbon nanotubes (SWNTs) into a self-assembled microhoneycomb network (μ-HN) for the application to SWNT-Si solar cells. The μ-HN consists of vertical aggregated SWNT walls and a buckypaper bottom. This hierarchical structure exhibits lower sheet resistance and higher optical transmittance compared with buckypaper. The pristine μ-HN SWNT-Si solar cell shows a record-high fill factor of 72% as well as a power conversion efficiency (PCE) of 6% without optimizing the diameter or height of the vertically aligned SWNTs. The PCE remains stable for weeks under ambient condition, and a PCE exceeding 10% is achieved in the dry state after dilute nitric acid treatment.

ABSTRACT:We fabricated polymer-laminated, transparent, all-carbon-nanotube field-effect transistors (CNTFETs), making use of the flexible yet robust nature of single-walled carbon nanotubes (SWNTs). All components of the FET (active channel, electrodes, dielectric layer, and substrate) consist of carbon-based materials. The use of a plastic substrate that is considerably thinner than those used in other flexible CNT-FETs allowed our devices to be highly deformable without degradation of electrical properties. Using this approach, flexible, transparent CNT-FET devices able to withstand a 1 mm bending radius were realized. a) Author to whom correspondence should be addressed. E-mail: maruyama@photon.t.u-tokyo.ac.jp 2 Field-effect transistors (FETs) based on single-walled carbon nanotubes (SWNTs), [1][2][3][4][5][18][19][20] or ITO 6,7,[13][14][15][16] as the electrode material. The use of Au diminishes the optical transparency, whereas brittle ITO limits the mechanical flexibility of the device. 21,22 To simultaneously improve upon both of these aspects, carbon nanotube FETs (CNT-FETs) employing SWNTs 8 or graphene [9][10][11][12] for all electrodes (source, drain, and gate) have recently been reported.These metal-free devices can realize both optical transparency and mechanical robustness, but flexibility is typically sacrificed by fabricating the devices on thick plastic substrates. As suggested by Hur et al. 2and Cao et al.,8 combining SWNTs with a thin, flexible material could lead to devices that are able to be wrinkled like paper. 23In this study, we demonstrate the realization of all-CNT-FETs in which all channels and electrodes (source, drain, and gate) are composed of SWNTs, and the substrate and dielectric layer are made of poly(vinyl alcohol) (PVA). The devices are fabricated using a simple transfer process followed by lamination using polymer sheets, and exhibit extreme flexibility and robustness to mechanical deformation.A schematic illustrating the layered structure of the all-CNT-FET is shown in Fig. 1(a). To fabricate the device, a Si wafer was cut into 2 pieces, and on one of these pieces a 1 square inch active layer (S/D electrodes and channel) was prepared. On the other piece, a 0.5 × 1 inch global gate electrode was prepared. The larger substrate was patterned using standard photolithography processes (exposure and development). After patterning, Co catalyst (thickness: 0.5 nm) was deposited onto both the photolithography-defined and non-patterned substrates using a thermal evaporator. The patterned substrate was then washed by dipping into acetone to remove residual resist (lift-off), rinsed with isopropyl alcohol (IPA), and dried using a nitrogen gun. SWNTs were then synthesized on both substrates using the alcohol catalytic chemical vapor deposition (ACCVD) 3 method. 24Details regarding the synthesis procedure have been described elsewhere. [25][26][27] This approach enables us to synthesize both the channels and S/D electrodes in a single CVD step. 28The device substrate and dielectric lay...

Changing the carbon feedstock from pure ethanol to a 5 vol % mixture of acetonitrile in ethanol during the growth of vertically aligned single-walled carbon nanotubes (SWNTs) reduces the mean diameter of the emerging SWNTs from approximately 2 to 1 nm. We show this feedstock-dependent change is reversible and repeatable, as demonstrated by multilayered vertically aligned SWNT structures. The reversibility of this process and lack of necessity for catalyst modification provides insight into the role of nitrogen in reducing the SWNT diameter.