Semiconductor Carbon Nanotubes as Ultrafast Switching Materials for Optical Telecommunications

Abstract

proaches based on averaging the optical properties of bulk materials are not applicable to these systems.During the preparation of this paper, a work by Kooij et al. [17] was brought to our attention. In that work, the properties of gold nanoparticle films were studied by spectroscopic ellipsometry, extremely small k values (< 0.15) were found for their nanoparticle films. It is believed that the main reason for the difference between the optical constant reported in that work and those in this paper is that Kooij and co-workers used colloidal gold, and the films studied were of lower coverage compared with those studied here.In summary, thin films of gold nanoparticles were fabricated on a gold substrate by a LBL self-assembly approach using a dithiol as the linking agent. The optical properties of these nanoparticle thin films have been investigated using a variable angle spectroscopic ellipsometer. The refractive indices were obtained from the ellipsometric data by fitting to a Lorentz oscillator dispersion model. The modeled data show good agreement with the experimental results. The refractive indices of nanoparticle films undergo dramatic variation in the range close to the plasmon band. It is suggested that this dramatic variation of refractive index could cause difficulties for studies using conventional ellipsometers at a fixed wavelength and is possibly responsible for the significant discrepancies in refractive indices reported in the literature. Furthermore, it is found that nanoparticle films show unique optical constants different from those of typical metals or insulators. ExperimentalSolutions of gold nanoparticles in toluene were prepared as described previously [4]. Particle sizes measured by TEM were in the range 5 ± 0.6 nm. Gold substrates were prepared by thermal deposition of 150 nm gold layers on to glass microscope slides covered with a 10 nm Cr adhesion layer. The substrates were then cleaned thoroughly with hot piranha solution (30:70 H 2 SO 4 /H 2 O 2 ) for 5 min, then rinsed with water and methanol and dried in a nitrogen stream. The cleaned substrates were then left in a 1 mM 1,9-nonanedithiol toluene solution overnight. The dithiol-functionalized gold substrates were first rinsed with copious amounts of toluene and subsequently ultrasonicated in toluene for 1 min, prior to being immersed in the gold nanoparticle solution for 1 h to form the first nanoparticles layer. Subsequent layers were deposited by repeated alternate immersion in solutions of dithiol and gold nanoparticles, respectively. Rinsing and ultrasonication with toluene were performed between each immersion to remove any nonchemical adsorption.A spectroscopic Beaglehole Picometer ellipsometer was used to study the optical properties of the nanoparticle film and to follow the thickness changes as a function of the number of assembled layers. Refractive indices of the gold substrate were evaluated from a clean gold sample, and were found to be in good agreement with previous reports [14]. For each nanoparticle film, spectr...

Nonlinear optical absorption and reflection of single wall carbon nanotube thin films by Z-scan technique

“…) are greater than those of SWNT/Triton X100 suspension 11 and SWNT/polyvinyl alcohol composite, 2 but are somewhat smaller than those of SWNT film 7,17 and SWNT/SDS suspension 18 .…”

“…We are also indebted to Dr. F. Kobayashi for his technical assistance in the experiments and to the Gene Research Center, Shinshu University, for providing us 6 its facilities. 7 …”

“…[2][3][4] It is believed that SWNTs can be used in the fabrication of optical limiting and switching devices due to their nonlinear optical properties upon absorption [4][5][6] and its fast decay time of less than 1 picoseconds. 2,[7][8][9] These nonlinear properties are related to the third-order nonlinear susceptibility χ (3) , which is considered to be a complex quantity: 10 ( ) ( ) ( 3…”

Carbon nanotubes for ultrafast fibre lasers

“…In 2003, single-walled CNTs (SWNTs) were applied in Erdoped fibre laser for passive mode locking for the first time [41]. SWNTs are a promising candidate for the ultrashort pulse generation because they possess ultrafast excited state carrier dynamic and high optical nonlinearity [42][43][44]. Semiconductor SWNTs (s-SWNTs) are a direct bandgap material having a series of van-Hove singularities in the density of state.…”

Exciton diffusion in semiconducting single-walled carbon nanotubes studied by transient absorption microscopy

“…Hence, understanding the exciton dynamics in SWNTs is important for many optoelectronic applications. Photoemission 7 and transient absorption [8][9][10][11][12][13][14][15] transfer of excitons from semiconducting to metallic tubes. When such channels are eliminated in isolated tubes, the energy relaxation can take several picoseconds, [16][17][18][19][20] and exciton lifetimes of several 10 ps 17,18 to several 100 ps 16,19 have been measured.…”