Aloke Jain

Polarization-dependent photocurrent in thin film polydiacetylene single crystals

Investigations of the anisotropic photocurrent behaviour, as a function of laser intensity and sample temperature, in thin film polydiacetylene single crystals are reported. These polydiacetylenes, PTS (poly-(2,4-hexadiyne-1,6-diol bis(p-toluenesulphonate))) and BTFP (poly-bis-(4-n-butyl-2,3,5,6-tetra-fluorophenyl) butadiyne), have similar one-dimensional electronic band structures. However, the polarization and temperature-dependent photocurrent have completely different behaviour for PTS and BTFR. These results indicate that photocurrent behaviour in these quasi-one-dimensional semiconductors is strongly influenced by the nature and organization of the side groups.

A simple experiment for determining Verdet constants using alternating current magnetic fields

A simple experiment suitable for a senior undergraduate and graduate laboratory on the measurement of Faraday rotation using ac magnetic fields is described. The apparatus was used to measure the wavelength dependence of Verdet constants for several materials. A concentration-dependent study on ferric chloride water solution was also carried out to demonstrate that the diamagnetic and paramagnetic contributions to Faraday rotation have opposite signs.

Determination of Electron and Hole Mobility of Regioregular Poly(3‐hexylthiophene) by the Time of Flight Method

Time of flight method (TOF) is used to measure the electron and hole mobility of a spin coated regioregular poly(3‐hexylthiophene) (P3HT) film. We find that both electron and hole have the same mobility (about 3.8∼3.9×10−4 cm2/Vs) at an applied field of 120 kV/cm. It is demonstrated in this paper that the electron‐hole recombination process may prevent the electron transport in the material due to the fact that the carrier recombination time is much shorter than the transit time.

Enhanced performance of polythiophene derivative based light emitting diodes by addition of europium and ruthenium complexes

Abstract Fabrication of polymer light emitting diodes (PLEDs) from a urethane containing processable polythiophene derivative, poly[2-(3-thienyl) ethanol n -butoxy carbonylmethyl urethane], (PURET) and its composites with luminescent Ruthenium (II) and Europium (III) complexes is discussed. Enhanced electroluminescence (EL) performance was observed, when 1% by weight of europium (III) or ruthenium (II) complexes were added to the PURET polymer. Multi-layered devices with polyaniline as a hole injecting layer and tris-8-hydroxyquinoline-aluminum as an electron injecting layer have also been fabricated. PLEDs from PURET polymer have a threshold voltage of 3.6 V and emit an orange-red light with a brightness of about 500 cd/m 2 under forward bias of 9 V, upon the addition of 1% of europium (III) thenoyl trifluoroacetonate complex to the polymer.

A new guest-host system : towards stable second-order optical nonlinearity

Abstract A new guest-host system based on the azo dye disperse red 1 and phenyl siloxane polymer has been investigated. The second order susceptibility of the polymer cured at 200° C was found to be stable at room temperature and decayed to 60% of its original value after being maintained at a temperature of 100°C for nearly 30 hours. The linear and second-order nonlinear optical (NLO) properties of this material are measured and reported. Curing at higher temperature is expected to lead to greater stability of NLO properties.

Dispersions of the third-order nonlinear optical susceptibilities χ1111(3)(ω;ω,0,0) and χ2211(3)(ω;ω,0,0) of a polydiacetylene film

Abstract The dispersions of the in-plane components χ 1111 (3) ( ω ; ω ,0,0) and χ 2211 (3) ( ω ; ω ,0,0) of a spin coated polydiacetylene film (poly(4-BCMU)) were determined through electroabsorption spectroscopy with interdigital electrodes. The maximum values of real part and imaginary part of χ 1111 (3) ( ω ; ω ,0,0) are 1.69×10 −10 esu and 1.24×10 −10 esu, respectively, and the maximum values of real part and imaginary part of χ 2211 (3) ( ω ; ω ,0,0) are 6.2×10 −11 esu and 4.2×10 −11 esu, respectively. The spectra of these two components are similar, and the ratio of χ 1111 (3) ( ω ; ω ,0,0) to χ 2211 (3) ( ω ; ω ,0,0) is found to be 2.8, very close to 3, indicating an in-plane isotropy.

Cerenkov type phase-matched second harmonic generation in polymeric channel waveguides

Abstract Fabrication of polymer channel waveguides by etching on glass is reported. Results on second harmonic generation (SHG) in the Cerenkov mode from stable poled polymeric channel waveguides are presented. The waveguide conversion efficiency for doubling of Nd:YAG laser beam was estimated to be 0.1%/W with a total efficiency of 4.9×10 −7 %/W.

Steady-state photoconductivity in a novel solution-cast polydiacetylene film

Abstract Steady-state photoconductivity in solution-cast thin films of a polydiacetylene, ((8-butoxy carbonyl)methyl urethanyl)-1-(5-pyrimidyl)-octa-1,3-diyne (PDA-BPOD), has been investigated as a function of light intensity, applied electric field, incident wavelength and temperature. This newly synthesized polydiacetylene is characterized by a conjugating aromatic side group which is expected to play a role in the electronic properties of the system. The results are interpreted within the framework of one-dimensional Onsager theory of geminate recombination. The photoconductivity action spectrum shows a peak at 1.9 eV and direct band-to-band transition above 2.4 eV.

Photoinduced charge-carrier generation and transport in thin-film polydiacetylene single crystals

Abstract The photocurrent behavior in polydiacetylene single crystals of PTS (poly-(2,4-hexadiyne-1,6-diol bis-( p -toluenesulfonate)) and MADF (poly-(1-(3-(methylamino)phenyl)-4-(3,5-bis(trifluoromethyl)-phenyl)butadiyne)) has been investigated as a function of incident light polarization and intensity by using the steady-state photoconductivity technique. The polarization dependence of the photocurrent has completely different behavior for the polydiacetylenes PTS and MADF. These results show for the first time that the photocurrent behavior in these quasi-one-dimensional single crystals is very sensitive to the nature and organization of the side groups. The charge-carrier drift velocity of a PTS single crystal has been investigated by using transient photoconductivity in single- and dual-gap transmission-line configurations. The results from these two experiments are consistent, and give a drift velocity of the order of 10 6 cm s −1 . The drift velocity is independent of applied electric field in the range 8000–15 000 V cm −1 .

A Simple Technique for Submicron Scale Patterning of Silver Using Visible Light Interference

A novel, one step and simple methodology for the fabrication of submicron scale silver patterns is demonstrated. The photosensitivity of an organic silver salt has been utilized for this purpose of fabrication. The silver-organometallic compound is converted to metallic silver selectively in the illuminated regions. Surface morphology was studied by scanning electron microscopy (SEM). Energy dispersion spectroscopy (EDS) shows the presence of silver in the developed film. X-ray photoelectron spectroscopy (XPS) confirms the formation of metallic silver. Feature sizes of the order of 200 nm have been achieved using this technique.