A.M. El-Naggar

A new method of finding the optical constants of a solid from the reflectance and transmittance spectrograms of its slab

Abstract The reflectance and the transmittance of dielectric (glass) and semiconductor (silicon) slabs are measured and used to calculate, by means of an iteration procedure, the attenuation factor of each sample and the Fresnel reflectance and transmittance of its interface. These three parameters determine the refractive index and the extinction coefficient and their dispersion. The dispersion curves across a wide spectral range, 0.2–3 μm, are used to determine the atomic and quantum constants of both silicon (undoped polycrystalline) and glass (corning).

A new method of determining the optical constants of a thin film from its reflectance and transmittance interferograms in a wide spectral range: 0.2–3 μm

Abstract The wavelength separation of the adjacent maxima and minima of either the reflectance or the transmittance fringes of equal chromatic order (FECO) enables their exact order values to be determined for a thin silicon film. Knowing the film optical thickness accurately to 1–5 parts in 10 4 , its refractive index is deduced accurately to 3 parts in 10 3 . The phase shifts upon reflection at the air/film and the substrate/film interfaces are found from the shifts of the maxima of one interferogram from the minima of the other. The extinction coefficient is calculated from the values obtained for the refractive indices and phase shifts. The data are fitted to the Cauchy dispersion function and the Fermi–Dirac distribution function.

Huge operation by energy gap of novel narrow band gap Tl1−x In1−x B x Se2 (B = Si, Ge): DFT, x-ray emission and photoconductivity studies

It is shown that narrow band gap semiconductors Tl1−x In1−x GexSe2 are able effectively to vary the values of the energy gap. DFT simulations of the principal bands during the cationic substitutions is done. Changes of carrier transport features is explored. Relation with the changes of the near the surface states is explored . Comparison on a common energy scale of the x-ray emission Se Kβ 2 bands, representing energy distribution of the Se 4p states, indicates that these states contribute preliminary to the top of the valence band. The temperature dependence of electrical conductivity and spectral dependence photoconductivity for the Tl1−x In1−x Ge x Se2 and Tl1−x In1−x Si x Se2 single crystals were explored and compared with previously reported Tl1−x In1−x Sn x Se2. Based on our investigations, a model of centre re-charging is proposed. Contrary to other investigated crystals in Tl1−x In1−x Ge x Se2 single crystals for x = 0.1 we observe extraordinarily enormous photoresponse, which exceed more than nine times the dark current. X-ray photoelectron core-level and valence-band spectra for pristine and Ar+-ion irradiated surfaces of Tl1−x In1−x GexSe2 (x = 0.1 and 0.2) single crystals have been studied. These results indicate that the relatively low hygroscopicity of the studied single crystals is typical for the Tl1−x In1−x Ge x Se2 crystals, a property that is very important for handling these quaternary selenides as infrared materials operating at ambient conditions.

Synthesis and structure of novel Ag2Ga2SiSe6 crystals: promising materials for dynamic holographic image recording

Phase diagrams of the AgGaSe2–SiSe2 system were explored by differential thermal analysis (DTA) and X-ray diffraction (XRD) analysis methods for the first time. It was demonstrated that the investigated system forms quaternary compounds of compositions Ag2Ga2SiSe6 and AgGaSiSe4. Ag2Ga2SiSe6 melts at 1042 K and exists in two polymorphous modifications. The crystal structure of the low-temperature modification was determined by the single crystal method (space group I2d (122) and lattice parameters a = 5.9021(1) A, b = 5.9021(1) A, and c = 10.4112(10) A). Additional details (CIF file) regarding the crystal structure investigations are available at the Fachinformationszentrum Karlsruhe. The band gap (Eg) of the Ag2Ga2SiSe6 system was estimated from the fundamental absorption edge and we showed that it decreases with increasing temperature (100–300 K) from 2.13 eV to 1.97 eV. The compound is photosensitive and its spectral dependence on the photoconductivity has two maxima: at λmax1 = 640 nm and λmax2 = 900 nm. For the pristine Ag2Ga2SiSe6 crystal surface, X-ray photoelectron core-level and valence-band spectra were obtained. The X-ray photoelectron valence-band spectrum of Ag2Ga2SiSe6 was compared on a common energy scale with the X-ray emission Se Kβ2 and Ga Kβ2 bands, representing peculiarities of the energy distribution of the Se 4p and Ga 4p states, respectively. The comparison revealed that the principal contributions of the valence Se p and Ga p states occur in the upper and central parts of the valence band, respectively, with significant contributions to other valence band regions. The illumination by the bicolour coherent pulses of the Er:glass nanosecond lasers at different angles led to the formation of the gratings, which are sensitive to the irradiation time.

Structural and optical properties of novel optoelectronic Tl1−xIn1−xSixSe2 single crystals

Principal optical properties of Tl1−xIn1−xSixSe2 solid state crystalline alloys were studied. The influence of the x on the principal optical and structural features was explored. Temperature features of the band energy gap are studied. The possible explanation of the observed behavior is given within a framework of the Urbach rule approach. The role of intrinsic defective sub-system and anharmonic electron–phonon interaction is discussed. A possible application of the titled materials for the infrared optoelectronic is discussed. The replacement of In atoms by Sn is evaluated. Additionally studies of influence of x on the optoelectronic features is done. The formation of the positive charged ions (donors) and negatively charged ions is explored within the introduced intrinsic defect models.

IR laser induced spectral kinetics of AgGaGe3Se8:Cu chalcogenide crystals.

The possibility to operate by optical spectra near the absorption edge gap was discovered for the AgGaGe3Se8:Cu semiconducting chalcogenide crystals under influence of microsecond CO2 laser with pulse energy 60 mJ operating at wavelength 10.6 μm. An occurrence of substantial photoinduced optical density was observed at wavelengths in the spectral range of 610-620 nm. Introducing of Cu ions leads to substantial spectral asymmetry in the observed spectra. The process achieves its maximum value after the 80-120 s of CO2 laser treatment and relaxes with almost irreversible changes after the same time. The contribution of thermo heating did not exceed 5-6%. Only the irreversible changes of the samples surface topography were observed during the CO2 laser treatment, which do not influence the treatment. So the surface states do not play a principal role and the effect is prevailingly originated from the. The observed effect may be used for control of the CO2 laser power density.

A simple method of measuring and applying the dispersion of thin films

Abstract The position and the separation of the adjacent maxima and minima of the interference bands of an amorphous hydrogenated silicon film doped with aluminum are used to determine the order value unambiguously, the optical thickness to accuracy ranging from eight parts in 10 5 to one part in 10 3 , and the refractive index accurately to ±0.03 across a wide spectral interval 0.5–2.5 μm. The dependence of the film dispersion on the doping concentration is expressed in terms of a polynomial dispersion function whose coefficients vary with the doping concentration.

Rectal misoprostol for myomectomy: A randomised placebo-controlled study

Uterine leiomyomas are the most common benign tumours in women. Misoprostol, which is widely used in the treatment and prevention of postpartum haemorrhage in obstetrics, may decrease intra‐operative bleeding in abdominal myomectomies when haemorrhage constitutes a challenging problem.

Study of deep levels in Schottky/CuInSe2 single-crystal devices by deep-level transient spectroscopy measurements

Deep-level transient spectroscopy (DLTS) measurements performed on Schottky/CuInSe2 diodes are reported. So far, Cd(Zn)S has been used as a window n-type layer to prepare CuInSe2 diodes. The diffusion of such a layer introduced defects into Cd(Zn)S-CuInSe2 diodes. Thus, the importance of using Schottky diodes lies in the elimination of the window n-type layer diffusion into CuInSe2 material to reveal the intrinsic properties of the semiconductor. A comparison between previously reported defect states in Cd(Zn)S-CuInSe2 and those found in Schottky/CuInSe2 is made.The defect concentration is calculated as well as the capture cross-section. Some of the defect levels agree with previously published data. A common feature exhibited in all the measured samples is that the capacitance transient is non-exponential, and the DLTS spectrum is relatively broad, due to the contribution of two or more closely spaced levels.

Laser induced infrared spectral shift of the MgB2:Cr superconductor films

During illumination of the MgB2:Cr2O3 films it was established substantial spectral shift of the infrared spectra in the vicinity of 20-50cm(-1). The excitations were performed by nanosecond Er:glass laser operating at 1.54μm and by microsecond 10.6μm CO2 laser. The spectral shifts of the IR maxima were in opposite spectral directions for the two types of lasers. This one observed difference correlates well with spectral shift of their critical temperatures. The possible explanation is given by performance of DFT calculations of the charge density redistribution and the time kinetics of the photovoltaic response. To understand the kinetics of the photoinduced processes the time kinetics of photoresponse was done for the particular laser wavelengths.