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The electrical properties of carbon nanostructures have been greatly stimulating to use in the nanotechnology for electronic components. In this paper, we study the AC and DC electrical conductivity responses of multi-walled carbon nanotube films, prepared by the vacuum filtration methods, with noncontact terahertz time-domain spectroscopy (THz- TDS) approach utilizing the extrapolation analysis as well as probe-in line technique.

The direct metallic or semiconducting characterization of carbon nanotubes (CNTs) in the high-frequency is one of the key issues to use them in the different state-to-the-art applications. In this work, the terahertz surface conductivity and transmission of carbon nanostructures thin-film utilizing terahertz time-domain spectroscopy (THz-TDS) have been studied. We have also compared the achieved results of single-walled carbon nanotubes thin-film surface conductivity with pervious study as a function of frequency. However, we have improved the obtained conductivity of carbon nanostructures from the microwave to terahertz range by THz-TDS technique with high signal-to-noise ratio.

In this paper, we report on the optical and electrical properties of single-walled (SWNT) and multi-walled (MWNT) carbon nanotube thin-films investigated by terahertz time-domain spectroscopy. Our study focuses on the absorption and dispersion properties of the single-walled and multi-walled carbon nanotubes in frequency range of 0.1-2 THz. The results show that the single-walled carbon nanotubes thin-films have the great frequency-dependent of the power absorption coefficient, the index of the refraction and conductivity compared to the multi-walled carbon nanotubes thinfilms because more mobile carries of carbon nano-structure as well as effective of carbon nanotubes length and diameter.

Propagation of terahertz waves in segmented waveguides (1 -D photonic crystal) is experimentally demonstrated. Data are well fitted using a modified FDTD method. Dispersion curves of the first guided modes are determined.

Narrow band resonant reflection of a polarized focused beam from a single-crystal silicon grid is demonstrated at terahertz frequencies with an efficiency close to 100 %. A spectral width of less than 7 μm at a resonance wavelength of 570 μm is achieved with a 4 mm-waist beam which overlaps with only ~10 grid periods. This compact reflection filter is a scale model of what can be expected at optical frequencies, but also represents a new type of compact terahertz device.

The far infrared behavior of doped semiconductors is dominating by the free carrier response and it is well described by the simple Drude model. As the free carriers can be photogenerated in high resistivity semiconductors, the electromagnetic response of these semiconductors can be changed, via laser excitation, from a dielectric behavior to a metallic one. Using terahertz time-domain spectroscopy, we have checked this Drude-like behavior with several silicon wafers of different doping, and with a high resistivity silicon sample photo-excited by a Ti:Sa laser beam. Then we benefited of this effect to photo-modify the transmission of a photonic band-gap crystal in the terahertz range. The photonic band-gap crystal is a woodpile structure, which exhibits a complete forbidden band around 265 GHz. Silicon- made defects are introduced in interstitial sites of the lattice of the photonic crystal in order to create a defect mode inside the photonic band-gap of the crystal. This defect mode then acts as a narrow bandpass filter at the frequency of 253 GHz. Under 400-mW laser excitation power, the resonance peak associated to the defect mode completely vanishes.

In this paper we have characterised the refractive index and absorption coefficient of negative photoresist NANOTM xp su 8 from 0. 1 - 1 .6 THz using terahertz time-domain spectroscopy. Over the measured frequency range it was found that therefractive index (n) is a relatively flat function of frequency, decreasing from 1 .8 to 1 .7. The value of absorption coefficient(a) is seen to increase in a linear fashion over the given frequency range, being 25 cm1 at 1 THz. From this data we haveextracted functions of dielectric constant (er) and dielectric loss tangent (tan(s)) versus frequency, quantities which will be ofuse for future terahertz circuit design. In addition to these measurements, we have demonstrated two novel applications ofSU-8. Firstly, we have fabricated membrane-like features by using a multi-exposure photolithographic technique on a singlelayer of SU-8, and secondly we have utilised a thin layer of SU-8 (0.4 tim) as a patternable adhesion layer as part of asemiconductor epitaxial lift-off (ELO) process designed to transfer 111-V semiconductor epitaxial layers onto lower loss hostsubstrates.Keywords: SU-8 negative photoresist, terahertz time-domain spectroscopy, micromachining, microstructuring, membranestructures, epitaxial lift-off techniques

THz time-domain spectroscopy is a powerful and fast technique for measuring the optical constants of materials over a wide frequency range. In this paper, we analyze the weight of the different error terms on the optical constants determination. The different sources of noise are taken into account in a phenomenological way and the noise power can be expressed as a second order polynomial function of the complex transmission coefficient modulus (rho) of the sample under test. Then, for given experimental conditions, the accuracy on the optical constants determination depends on (rho) . In the case of optically thick sample, the echoes of the THz pulse, caused by multiple reflections into the sample, are temporally well separated and can be time- windowed. For each echo, (rho) can be measured and it depends on the echo number. We demonstrate that the precision on the optical constants is greatly enhanced using the pth echo, the value of p depending on the material refractive index and absorption. Moreover, as the coefficients of the polynomial function can be easily experimentally evaluated, quantitative information on the sources of noise is deduced.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

THz time-domain spectroscopy is a powerful and fast technique for measuring the complex dielectric constant of materials over a wide range of frequencies. This technique can be applied to the characterization of anisotropic materials only if the polarization of the THz beam impinging on the sample is perfectly known. In this paper, we show that the polarization of the THz beam radiated by a standard THz antenna, composed of a photoconductive switch and an extended hemispherical lens, is frequency dependent. We experimentally observe that the polarization of the THz field is linear but its direction varies over more than 10 degrees in the 100 GHz - 1 THz range. This variation can be attributed to a slight misalignment of the antenna. Using a thick slide of a highly anisotropic material acting as a polarization temporal separator, the incident THz pulse is divided into two pulses with orthogonal linear polarizations. By temporal windowing, we keep only one of the two linear polarizations, and thus free ourselves from the response of emitting antenna in terms of polarization. Then, a precise characterization of any anisotropic sample along one of its optical axis becomes possible.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.