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Yang C.-S.,National Tsing Hua University | Yang C.-S.,Lawrence Berkeley National Laboratory | Tang T.-T.,Taiwan Semiconductor Manufacturing Company | Chen P.-H.,National Chiao Tung University | And 4 more authors.
Optics Letters | Year: 2014

Transmittance of the device was as high as ∼75%. Phase shift exceeding φ/2 at 1.0 THz is achieved in a ∼500 μm-thick cell. The driving voltage required for the device operating as a quarter-wave plate was as low as 17.68 V (rms), an improvement of nearly an order of magnitude over previous work. © 2014 Optical Society of America.

Yang C.-S.,National Tsing Hua University | Pan R.-P.,National Chiao Tung University | Yu P.,National Chiao Tung University | Pan C.-L.,National Tsing Hua University | Pan C.-L.,Frontier Research Center on Fundamental and Applied science of Matters
2014 31th URSI General Assembly and Scientific Symposium, URSI GASS 2014 | Year: 2014

Phase shift exceeding 2π at 1.0 THz with high transmittance was achieved in liquid-crystal THz phase shifters of three different designs. Indium-tin-oxide (ITO) nanowhiskers (NWhs) were employed as transparent electrodes. The driving voltage required for a 2π wave plate is as low as 5 Vrms. © 2014 IEEE.

Li M.-C.,National Tsing Hua University | Ho R.-M.,National Tsing Hua University | Ho R.-M.,Frontier Research Center on Fundamental and Applied science of Matters | Lee Y.-D.,National Tsing Hua University
Journal of Materials Chemistry C | Year: 2013

Here, we aim to systematically examine the mechanism of photo-induced pyrene association in pyrene-labeled polymers (PLPs) for optical recording. By taking advantage of polymer glass transition, the associated pyrene moieties can be frozen in the glassy matrix of the PLP to give the emission contrast for optical recording, as evidenced by the phenomenon of room-temperature phosphorescence. In situ time profiles of the fluorescence emission during recording reflect that the association of pyrene moieties in PLPs is a diffusion-controlled process, and it is highly dependent on the mobility of the polymer chain. For crystallizable PLPs, the polymer chain can also be frozen in the crystalline state that inhibits the association of pyrene moieties in PLPs. As a result, Tg and Tm of the PLPs can be exploited as energy barriers for the induction of the association of pyrene moieties in PLPs and the recording capabilities of the PLPs will be dependent upon the thermal properties of the PLPs. This journal is © The Royal Society of Chemistry 2013.

Li C.-L.,National Tsing Hua University | Li M.-C.,National Tsing Hua University | Ho R.-M.,National Tsing Hua University | Ho R.-M.,Frontier Research Center on Fundamental and Applied science of Matters
Macromolecules | Year: 2011

A series of poly(4-vinylpyridine)-b-poly(ε-caprolactone) (P4VP-PCL) diblock copolymers have been synthesized and used for the formation of nanostructures with tunable colors arising from the association of chromophores with P4VP block in P4VP-PCL. The association of chromophores leads to the bathochromical shifts of charge transfer absorption peaks, resulting in the color appearance into the visible region. To achieve the formation of well-defined nanostructured materials, the phase behavior of the mixtures of chromophore/P4VP-PCL was systematically examined. As evidenced by transmission electron microscopy and small-angle X-ray scattering (SAXS), the phase transformation of self-assembled nanostructures can be easily induced by introducing chromophores due to the association of 2-methylidenepropanedinitrile in the chromophores with the lone-pair electron of nitrogen in P4VP block (that is the increase on the effective volume fraction of P4VP, as identified by SAXS experiments through the analysis of one-dimensional correlation function). As a result, by taking advantage of charge transfer and corresponding morphologies from transformation, well-defined nanostructured films resulting from mixing of chromophore and P4VP-PCL offer the possibility to create stimuli-responsive nanomaterials with tunable color. © 2011 American Chemical Society.

Yang C.-S.,National Tsing Hua University | Chang C.-M.,National Tsing Hua University | Chen P.-H.,National Chiao Tung University | Yu P.,National Chiao Tung University | And 2 more authors.
Optics Express | Year: 2013

Indium-tin-oxide (ITO) nanorods (NRs) and nanowhiskers (NWhs) were fabricated by an electron-beam glancing-angle deposition (GLAD) system. These nanomaterials are of interests as transparent conducting electrodes in various devices. Two terahertz (THz) time-domain spectrometers (TDS) with combined spectral coverage from 0.15 to 9.00 THz were used. These allow accurate determination of the optical and electrical properties of such ITO nanomaterials in the frequency range from 0.20 to 4.00 THz. Together with Fourier transform infrared spectroscopic (FTIR) measurements, we found that the THz and far-infrared transmittance of these nanomaterials can be as high as 70% up to 15 THz, as opposed to about 9% for sputtered ITO thin films. The complex conductivities of ITO NRs, NWhs as well films are well fitted by the Drude-Smith model. Taking into account that the volume filling factors of both type of nanomaterials are nearly same, mobilities, and DC conductivities of ITO NWhs are higher than those of NRs due to less severe carrier localization effects in the former. On the other hand, mobilities of sputtered ITO thin films are poorer than ITO nanomaterials because of larger concentration of dopant ions in films, which causes stronger carrier scattering. We note further that consideration of the extreme values of Re{σ} and Im{σ} as well the inflection points, which are functions of the carrier scattering time (τ) and the expectation value of cosine of the scattering angle (γ), provide additional criteria for accessing the accuracy of the extraction of electrical parameters of non-Drude-like materials using THz-TDS. Our studies so far indicate ITO NWhs with heights of ∼1000 nm show outstanding transmittance and good electrical characteristics for applications such as transparent conducting electrodes of THz Devices. © 2013 Optical Society of America.

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