Self-organized CdSSe quantum dots thin films

Self-organized and strained CdSSe quantum dot (Q-dot) thin films have been grown on ITO-coated glass substrates by novel wet chemical route. The Q-dots are (002) oriented faceted pyramids with average particle size of 7.5 nm. The X-ray diffraction results reveal the formation of a solid solution of CdSSe. Atomic force microscopy is used to investigate the morphology of the nanocrystalline thin films. The energy dispersive X-ray analysis spectrum confirms the presence of Cd, S, and Se in the films. Optical absorption and photoluminescence spectra show the blue shift for quantum dot thin films.     

Optical and dielectric properties of double helix DNA thin films

In this work, the thin film of wheat DNA was deposited by spin-coating technique onto glass substrate, and the optical and dielectric properties of the double helix DNA thin film were investigated. The optical constants such as refractive index, extinction coefficient, dielectric constant, dissipation factor, relaxation time, and optical conductivity were determined from the measured transmittance spectra in the wavelength range 190–1100 nm. Meanwhile, the dispersion behavior of the refractive index was studied in terms of the single oscillator Wemple–DiDomenico (W–D) model, and the physical parameters of the average oscillator strength, average oscillator wavelength, average oscillator energy, the refractive index dispersion parameter and the dispersion energy were achieved. Furthermore, the optical band gap values were calculated by W–D model and Tauc model, respectively, and the values obtained from W–D model are in agreement with those determined from the Tauc model. The analysis of the optical absorption data indicates that the optical band gap E_g was indirect transitions. These results provide some useful references for the potential application of the DNA thin films in fiber optic, solar cell and optoelectronic devices.     

Optical and dielectric properties of thin SiOx films of variable composition

The effect of the composition of amorphous SiO_x films produced by the vacuum evaporation of SiO, on their optical and dielectric properties was investigated. The variation in the composition of the films was achieved by changing the deposition rate and the pressure of the residual gases.The optical band gap was observed to increase from 2.2 to 3.1 eV as the deposition rate was decreased from 50 to 5 Å s^-1 and simultaneously the refractive index, the permittiviity and the dielectric loss factor were found to decrease. The composition and structure of the films were determined from the optical absorption and IR spectroscopy.The experimental results revealed that SiO_x films produced by vacuum evaporation do not comprise a simple mixture of silicon and SiO₂ phases but they have a single-phase structure.     

Optical properties of HgTe colloidal quantum dots

Room temperature photodetection with HgTe colloidal quantum films is reported between 2 and 5 μm for particles of sizes between ~5 and ~12 nm diameter, and photodetection extends to 7 μm at 80 K. The size-tuning of the absorption of HgTe colloidal quantum dots, their optical cross section and the infrared absorption depth of films are measured. The tuning with radius is empirically given by [see formula in text] where R is in nm. The optical cross section of the colloidal dots at 415 nm is approximately proportional to their volume and given by σ(Hg)(415) = 2.6 ± 0.4 10(-17) cm(2)/mercury atom. The size-dependent optical cross section at the band edge ~1.5 10(-15) cm(2) is consistent with the expected oscillator strength of the quantum dots. The absorption depth of HgTe colloidal dot films is short, about 1-2 μm, which is an advantage for thin film devices. These properties agree rather well with the expectation from the k · p model. HgTe colloidal quantum dot thin films show a strong tuning with temperature with a large positive thermal shift between 0.4 and 0.2 meV K(-1), decreasing with decreasing size within the size range studied and this is attributed primarily to electron-phonon effects.     

Optical properties of europium thin films

The optical conductivity of europium was studied between 1.6 and 6.2 eV under static ultrahigh vacuum. It is shown that the total conductivity σ(ω) results from a coupling between frequency-dependent intraband, interband and structure terms. The maxima which are displayed near 2.12 and 4.58 eV are explained by two different mechanisms. The joint density of states is obtained from energy band calculation. In the ultraviolet range the observed peaks agree with the experimental absorption band which is assigned to interband transitions. In the infrared region the structure in the conductivity is thickness dependent and is correlated with granular effects which are explained by means of a refined Maxwell Garnett theory.     

Optical properties of vanadium thin films

The optical constants of vanadium thin films of different thicknesses were determined in the spectral range of 2.5 to 8.5 m. These optical constants were used to evaluate some microcharacteristics of vanadium thin films such as the free charge concentration, the relaxation time, the static conductivity, the electron velocity at the Fermi surface, the mean free path and the specularity parameter.The determination of the microcharacteristics were carried out in conjunction with Drude's theory of free charge carriers as well as with anomalous skin effect theory.     

Investigation of size dependent structural and optical properties of thin films of CdSe quantum dots

Cadmium selenide (CdSe) quantum dots were grown on indium tin oxide substrate using wet chemical technique for possible application as light emitting devices. The structural, morphological and luminescence properties of the as deposited thin films of CdSe Q-dot have been investigated, using X-ray diffraction, transmission electron microscopy, atomic force microscopy and optical and luminescence spectroscopy. The quantum dots have been shown to deposit in an organized array on ITO/glass substrate. The as grown Q-dots exhibited size dependent blue shift in the absorption edge. The effect of quantum confinement also manifested as a blue shift of photoluminescence emission. It is shown that the nanocrystalline CdSe exhibits intense photoluminescence as compared to the large grained polycrystalline CdSe films.     

Broadband antireflection properties of thin heterogeneous dielectric films

New exactly solvable flexible models of inhomogeneous thin film with smooth and deep variations of dielectric susceptibility epsilon(z) are presented. Formation of cutoff frequencies of such films (as well as the broadband antireflection), controlled by the profiles epsilon(z), is shown. The crucial role of gradients of epsilon(z) in the optics of strongly inhomogeneous media is emphasized.     

Optical properties of AgGaSe2 thin films

AgGaSe₂ films were grown using the flash evaporation technique on glass substrates at various substrate temperatures. The optical absorption of these films in the energy range 1.4–1.9 eV was studied and the films were found to possess direct band gap material. The photoconductivity of the AgGaSe₂ films was studied as a function of (i) light intensity, (ii) temperature and (iii) response times. The photoconductivity response spectra of the AgGaSe₂ films were utilized to determine the band gap energies as a function of the substrate temperature. The implications are discussed.     

Optical properties of Langmuir-Blodgett polydiacetylene thin films

The colour phase transition of Langmuir-Blodgett polydiacetylene (LB PDA) films is investigated as a function of annealing temperature. A new reversible colour change is observed for a short annealing time. Such a reversible property has not previously been reported in LB PDA films. The X-ray diffraction patterns show that the reversible property is closely related to the layer structure of the LB films. Furthermore, the ratio of the line intensities of the Raman peaks due to C≡C and C=C stretch modes changes with the annealing temperature. The colour phase transition of the LB PDA films is correlated with this ratio. Such phase transitions have also been observed in laser-annealed points of LB PDA films. From these results, a new optical device based on LB PDA films is proposed. Furthermore, the electrical properties of ion-irradiated LB PDA films are briefly reported.     

Optical properties of CulnSe2 thin films

The optical constants of vacuum-deposited CulnSe₂ films were determined from the measured transmittance and reflectance at normal incidence of light in the wavelength range 500 to 2000 nm. The analysis of the experimental points of the absorption coefficient revealed the existence of two optical transition processes: an allowed direct transition withE _g=1.03±0.01 eV and a forbidden direct transition withE _f=1.254±0.001 eV. The optical constants of the films were independent of the substrate temperature.On leave to the Kingdom of Saudi Arabia.     

Optical properties of porous helical thin films

Porous dielectric thin films, composed of isolated helical columns, are fabricated by the glancing angle deposition technique. The selective reflection of circularly polarized light and the optical rotation of linearly polarized light are investigated as a function of film material and helical morphology. The strongest chiral optical response is observed for titanium-dioxide films because of its large refractive index. Optical rotatory powers as high as 4.5 degrees are observed in 830-nm-thick helical films. By tailoring the pitch of the helical columns, the wavelength dependence of the circular reflection band is tuned to preferentially reflect red, green, or blue light, a promising quality for display applications.     

Optical and photocatalytic properties of arginine-stabilized cadmium sulfide quantum dots

Currently, environmental pollution caused by organic compounds leads to severe negative consequences in the human society. Therefore, the removal of these pollutants from aqueous media has become one of the most important issues in environmental science. In the present study, CdS QDs were successfully prepared under aqueous conditions using l-arginine as the stabilizing agent. Optical property determination results reveal that the CdS QDs exhibited strong absorption and photoluminescence in a visible wavelength region. Moreover, the CdS QDs could effectively degrade two organic dyes under visible light irradiation. This suggested that the CdS QDs prepared in this work might be used as the potential photocatalyst to effectively treat the organic pollutants under visible light irradiation.