Ion bombardment of Poly-Allyl-Diglycol-Carbonate (CR-39)

Ion bombardment is thought to have great potential for improving the optical properties of polymeric materials. In this paper, Poly-Allyl-Diglycol-Carbonate (CR-39) polymer samples were bombarded with 320 keV Ar and 130 keV He ions, at different ion fluences. Effects of ion bombardment on the optical properties of CR-39 have been investigated using UV-vis spectrophotometer and photoluminescence (PL) spectroscopy. UV-vis spectra of irradiated samples reveal that the optical band gap decreases with increasing the ion fluence for both Ar and He ions. The width of the tail of localized states in the band gap (E_u) was evaluated using the Urbach edge method. The decrease in the PL intensity with the increase in the ion fluence was observed. This decrease is attributed to ion bombardment induced defects and clusters in the CR-39 which serves as non-radiative centers.     

Study of optical, structural and chemical properties of neutron irradiated PADC film

We have investigated neutron irradiation effects on the optical, structural and chemical properties of polyallyl diglycol carbonate (PADC) polymer, commercially named as CR-39. For this purpose, PADC samples were exposed with 4 MeV Am-Be neutron source at fluences varying from 2.36 × 10⁶ to 5.94 × 10⁷ n/cm². The modifications so induced were analyzed using UV-Visible spectroscopy, X-ray diffraction Measurement (XRD), Photoluminescence (PL) and Fourier Transform infrared (FTIR) spectroscopy in the total attenuation reflection (ATR) mode. UV-Vis spectra of pristine and neutron irradiated PADC polymer sheets exhibit a decreasing trend in optical band gap. This decline in optical band gap with increasing fluence has been discussed on the basis of neutron irradiation induced defects in PADC. The XRD pattern of PADC shows the decreasing intensity of peak positions with increasing in fluence, which suggest that semicrystallinity of PADC changes slightly to amorphous phase after irradiation. At low fluence, crystallinity was found to increase but at higher fluence, it decreased which could be ascribed to neutron- induced defects in the polymer samples. Crystallite size calculated using Scherrer formula indicates a change and reflects the formation of disordered system in the irradiated polymer samples. The PL spectra show that the intensity of PL peak decreased with increase in fluence, which may be due to the disordered system via creation of defects in the irradiated polymer. The FTIR spectrum shows an overall reduction in intensity of the typical bands, indicating the degradation of PADC polymer after irradiation. These results so obtained can be used successfully in dosimetery using well reported protocols.     

Gamma-ray response function of some polymeric nuclear track detectors

The effect of gamma dose on the bulk-etch rate measurements for some gamma-irradiated polymeric nuclear track detectors was extensively studied. Various plastic samples of CR-39 allyl diglycol carbonate, Makrofol-E and Lexan polycarbonates were used and exposed to gamma doses up to 30.0 Mrad. The bulk-etch rate ratioV _BD/V _BO, i.e. the bulk-etch rate of irradiated samples to the unirradiated ones, was measured at the most recommended optimum etching conditions. Fading behaviour of irradiated CR-39 samples was also studied at room temperature and for a duration of up to 8 days. It was found that the etch-rate ratio for the CR-39 specimens was dose-dependent. In contrast, the polycarbonate samples showed an extremely weak response to gamma irradiation. The results of the present work reflected great evidence of the gamma dosimetric potential of CR-39 plastic detectors, which can indeed be recommended as gamma-dosimeters within the studied dose range.     

Optical characterization of electron beam evaporated chloroindium phthalocyanine thin films

In present study, the optical properties of chloroindium phthalocyanine (ClInPc) thin films prepared by electron beam evaporation have been investigated. The optical characteristics of the prepared thin films have been determined using spectrophotometric measurements of the absorbance, transmittance and reflectance at normal incidence in the spectral range 300–1,100 nm. Surface morphology of thin films is studied using field emission scanning electron microscopy. The absorption spectra recorded in UV-Visible region for the deposited films show two well defined intense absorption bands of phthalocyanine molecule; namely the Q-band and the Soret (B-band). The analysis of the spectral behavior of the absorption coefficient in the intrinsic absorption region have been performed to determine the optical band gap energy and type of the electronic transition, which reveals the probability of direct and indirect transitions. Moreover, by studying the absorption coefficient spectra just below the fundamental absorption edge, the width of band tails of localized states (Urbach energy), steepness parameter and width of the defect states have been evaluated. The obtained results of this novel grown ClInPc thin films support the desirable feature for the optoelectronic devices.     

Accurate band gap determination of chemically synthesized cobalt ferrite nanoparticles using diffuse reflectance spectroscopy

Optical band gap of cuboidal Cobalt ferrite (CoF) Nanoparticles (NP), synthesized using wet chemical method, was accurately determined, by combining Diffuse Reflectance Spectroscopy (DRS) of the nanopowder, Schuster-Kubelka-Munk (SKM) formalism and the application of a detailed band gap estimation algorithm, using which absorption onsets and corresponding base line segments from the Tauc plots were precisely identified. Structural and compositional characterizations such as XRD, FE-SEM, TEM and EDX, were used to conclude that the NP exhibited cubic crystal structure with an average crystallite size of 14 nm. The values of indirect and direct band gaps were calculated to be 0.79 ± 0.01 eV and 1.5 ± 0.01 eV, respectively. The band gap shift for the nanocrystallites, from the bulk band gap, estimated using the effective mass model, came up to a value of 0.084 eV, which corresponded well to the experimentally obtained direct band gap of CoF NP. The direct and indirect band gap values were found to be well consistent with the partially inverse spinel crystal structure of the NP, emphasized using magnetization measurement.     

Study of optical,structural and chemical properties of neutron irradiated PADC film

We have investigated neutron irradiation effects on the optical, structural and chemical properties of polyallyl diglycol carbonate (PADC) polymer, commercially named as CR-39. For this purpose, PADC samples were exposed with 4 MeV Am–Be neutron source at fluences varying from 2.36 × 10⁶ to 5.94 × 10⁷ n/cm². The modifications so induced were analyzed using UV–Visible spectroscopy, X-ray diffraction Measurement (XRD), Photoluminescence (PL) and Fourier Transform infrared (FTIR) spectroscopy in the total attenuation reflection (ATR) mode. UV–Vis spectra of pristine and neutron irradiated PADC polymer sheets exhibit a decreasing trend in optical band gap. This decline in optical band gap with increasing fluence has been discussed on the basis of neutron irradiation induced defects in PADC. The XRD pattern of PADC shows the decreasing intensity of peak positions with increasing in fluence, which suggest that semicrystallinity of PADC changes slightly to amorphous phase after irradiation. At low fluence, crystallinity was found to increase but at higher fluence, it decreased which could be ascribed to neutron- induced defects in the polymer samples. Crystallite size calculated using Scherrer formula indicates a change and reflects the formation of disordered system in the irradiated polymer samples. The PL spectra show that the intensity of PL peak decreased with increase in fluence, which may be due to the disordered system via creation of defects in the irradiated polymer. The FTIR spectrum shows an overall reduction in intensity of the typical bands, indicating the degradation of PADC polymer after irradiation. These results so obtained can be used successfully in dosimetery using well reported protocols.     

Direct and indirect radiative recombination from Ge

Both direct and indirect band gap transitions are observed in Ge by photoluminescence and electroluminescence. The relative emission intensity of direct band gap transition with respect to indirect band gap transition increases with the increase of the n type doping level, optical pumping power, injection current density, temperature, and strain. The enhancement of direct band gap transition is due to the increase of electron population in the direct valley by reducing the difference between direct and indirect band gaps. The reduction of direct and indirect band gaps can be extracted from the emission spectra with direct and indirect transition models. The defects and the thickness dependent reabsorption are responsible for the relatively strong direct band gap transition in the Ge-on-Si sample as compared to bulk Ge.     

The variation of valence and conduction band edges charge densities with lattice constant in GaP and InP

Valence and conduction band edge charge densities for direct band gap InP and indirect band gap semiconductors GaP are calculated for different values of the lattice constant. These variations affect the bonding properties of these semiconductors and the effect of interstitial impurities.     

Photoelectrical properties of In/n-CuIn5Se8 Schottky barriers

CuIn₅Se₈ homogeneous crystals of n-type conductivity have been grown. Donor centers activation energy has been estimated. In/n-CuIn₅Se₈ Schottky barriers have been created and the first spectral dependencies of quantum efficiency of photoconversion of these structures have been derived. The nature of interband optical transitions has been interpreted and the band gap values for direct and indirect transitions in CuIn₅Se₈ crystals have been determined on the results of analysis of the Schottky barriers photoactive edge absorption. A possibility of utilization of CuIn₅Se₈ crystals in wide-band photoconverters of the optical radiation has been established.     

Enhancement of nonlinear optical susceptibility of CuPc films by ITO layer

In the present study, the Copper Phthalocyanine (CuPc)/ITO thin film was fabricated using thermal evaporation method. The structural property was analyzed by X-ray diffraction study and confirms that the thin film has been preferentially grown along (200) plane. The atomic force microscope study was carried out on deposited film and quality of thin films is assessed by calculating the roughness of the films. The direct and indirect band gap, linear and nonlinear optical characteristics of grown films were calculated by using UV–Vis–NIR spectrometer studies. The calculated values of the first direct and indirect band gaps (E_g1(d) & E_g1(ind)) are 1.879 and 1.644 eV as a fundamental gap, while the values of second direct and indirect band gap (E_g2(d) & E_g2(ind)) are 1.660 and 1.498 eV as an onset gap for CuPc. The values of nonlinear refractive index (n₂) and third order nonlinear optical susceptibility (χ³) are found to be 5 × 10⁻⁸ and 8 × 10⁻⁹ (theoretical) and 5.2 × 10⁻⁸ and 1.56 × 10⁻⁷ (experimental) respectively. The optical band and third order nonlinear properties suggest that the as-prepared films are may be applied in optoelectronic and nonlinear applications.     

First-principles optical calculations of AsNMg3 and SbNMg3

The structural, electronic and optical properties of antiperovskite semiconductors AsNMg₃ and SbNMg₃ have been studied using the full-potential augmented plane wave plus local-orbital (APW+lo) method. The exchange correlation has been treated using the generalized gradient approximation (GGA). The equilibrium lattice constant and other structural properties have been determined. The AsNMg₃ is found to be a direct band gap semiconductor while SbNMg₃ is indirect. The results for electronic band structures, density of states, charge densities as well as optical properties are presented and discussed.     

Influence of gamma radiation on the optical properties of ZnSe nanocrystalline thin films

The effect of gamma (γ) irradiation on the absorption spectra and the optical energy bandwidth of ZnSe nanocrystalline thin films have been studied. Thin films of different thicknesses from 20 to 120 nm were deposited by Inert gas condensation technique at constant temperature of 300 K and under pressure 2 × 10⁻³ Torr of Argon gas flow. The optical transmission (T) and optical reflection (R) in the wavelength range 190–2,500 nm of ZnSe nanocrystalline thin films were measure for unirradiated and irradiated films. The dependence of the absorption coefficient α on photon energy hν was determined for different γ-doses irradiated films. The ZnSe thin films show direct allowed interband transition by γ-doses. Both the absorption coefficient (α) and optical energy bandwidth were found to be γ-dose dependent. The optical energy band width has been decreased by irradiated of γ-doses. The E_gn values of irradiated thin films by 34.5 Gy of γ-doses were recovered to nearly their initial values after 100 days at 300 K.     

CR-39 as a gamma dosimeter: Dielectric and infrared studies

The relative permittivity, , and dielectric loss factor, tan , were measured in the frequency range 50–10⁵ Hz for the solid state track detector CR-39 irradiated with -rays (5–100 kGy). The variation of and tan with -dose have been interpreted in terms of structural changes as emphasized from infrared spectra. A mathematical model has been introduced describing the use of CR-39 as a dielectric dosimeter.     

Oscillatory band gap behavior in small diameter Si-clathrate nanowires

Electronic structure analysis of small cagelike silicon nanowires is carried out and reveals many surprising features. The band gap values for all the nanowires are found to be smaller than their bulk counterparts. The most intriguing aspect appears to be the alternating sequence of direct and indirect band gaps as the diameter changes. This is attributed to the type of surface geometry. We illustrate this with two well-known clathrate forms as well as a new hexagonal clathrate structure with a direct band gap in the optical region.     

Synthesis and characterization of thin films of poly(3-methyl thiophene) by rf-plasma polymerization

To facilitate synthesis of poly(3-methyl thiophene) thin film by RF-plasma polymerization process, suitable modifications have been done in a RF-sputtering set up. The deposition rate is found to be 3.33 nm/min. The synthesized films are characterized by FTIR, XRD, Ellipsometry, UV-Visible absorption spectroscopy and SEM. From FTIR, the formation of poly(3-methyl thiophene) has been confirmed. It is found that the synthesized polymer is cross-linked. XRD shows the amorphous nature of the prepared polymer film. The optical band gap has been estimated to be 2.14 eV from UV-visible absorption spectrum. Thickness of the polymer films has been measured to be 2000 Å by ellipsometry.     

CR-39 acceptance test and optimisation for fast neutron dosimetry applications

The ENEA fast neutron dosemeter is based on a planar PADC (poly allyl diglycol carbonate) placed in a polyethylene holder. The CR-39 (registered trademark of PPG Industries Inc.) material, produced by Intercast Europe S.p.A., has been used in the routine of the Individual Monitoring Service (IMS) since 1998. Since then, acceptance tests on average sheet background track density and sheet neutron sensitivity have been made on new batches as a quality control within a quality assurance programme of the IMS of ENEA-Institute for Radiation Protection (IRP). Dosemeters were irradiated with a 241Am-Be source at ENEA-IRP and processed through a chemical etching procedure (pre-etching with 40% KOH water solution 6.25 N and 60% ethyl alcohol at 70 degrees C followed by 12 h of etching in 6.25 N KOH water solution). In this paper we present the analysis of acceptance testing data for more than 30 sheets of CR-39 plastic produced in 1998, 1999 and 2000. Moreover, we compare the performance of sheets of CR-39 of standard composition with that of sheets of CR-39 with the addition of DOP (dioctylphthalate), in different concentrations, on the hasis of average background density, neutron sensitivity and background fluctuation that limit the lower detectable dose. This study demonstrates the need for acceptance tests to assure the quality of the dosimetric performance of these dosemeters, which is considerably dependent on the quality of the CR-39 plastic.     

Influence of substitutional doping on the electronic properties of carbon nanotubes with Stone Wales defects: density functional calculations

Abstract

In this work, we implemented density function theory to investigate the structural and the electronic properties of nitrogen doped single walled carbon nanotube under different orientations of Stone Wales defect. We have found that, the doped defected structures are more stable than the non-doped defected structures. Furthermore, doping defected carbon nanotubes with a nitrogen atom has significantly narrowed the band gap and slightly shifted the Fermi level toward the conduction band. Moreover, nitrogen substitution creates new band levels just above the Fermi level which exemplifies an n-type doping. However, the induced band gap is indirect band gap compared to direct band gap as in pristine carbon nanotubes. Furthermore, the electronic and structural properties of nitrogen doped carbon nanotube with Stone Wales defects is crucially affected by the dopant site as well as the orientations of Stone Wales defects.     

(001)面双轴应变锗材料的能带调控

本文基于形变势理论构建(001)面双轴应变Ge材料的能带结构模型。计算结果表明(001)面双轴应变可以将Ge的能带从以L能谷为导带底的间接带半导体调控到以Δ4能谷为导带底的间接带半导体或者以Г能谷为导带底的直接带半导体。同时室温下Ge的带隙与应变的关系可用四段函数来表示:当压应变将Ge材料调控为以Г能谷为导带底的间接带半导体后,每增加1%的压应变,禁带宽度将线性减小约78.63meV;当张应变将Ge材料调控为直接带半导体后,张应变每增加1%,禁带宽度将线性减小约177.98meV;应变介于-2.06%和1.77%时,Ge将被调控为以L能谷为导带底的间接带半导体,禁带宽度随着压应变每增加1%而增加11.66meV,随着张应变每增加1%而线性减小约88.29meV。该量化结果可为研究和设计双轴应变Ge材料及其器件提供理论指导和实验依据。     

Role of Ni<Superscript>2+</Superscript> Ions in Magnetite Nano-particles Synthesized by Co-precipitation Method

In the present work, nickel-doped iron oxide (Ni_xFe_3?x O ₄) nanoparticles with different concentration of nickel (x = 0, 0.05, 0.1, and 0.15) have been prepared by co-precipitation method. These prepared nanoparticles have been characterized by using x-ray diffractometer, thermo gravimetric analysis and differential scanning calorimetry, Fourier transform infrared spectroscopy, scanning electron microscopy, vibrating sample magnetometer, and UV-Visible spectroscopy to study their structural, thermal, morphological, magnetic, and optical properties, respectively. The x-ray diffraction confirms the formation of single-phase inverse spinel cubic structure of NiFe₃ O ₄ nanoparticles. Crystallite size has been estimated by the full width at half maximum of the most intense x-ray diffraction peak where vibrational and stretching modes of metal-oxygen bonds in 872 cm are shown in Fourier transform infrared spectra which confirms the formation of nanoparticles. The thermal analysis revealed that the transition temperature and stability increases with increasing Ni concentration. The surface morphology indicated that the particles are spherical in shape with some agglomeration. The magnetic measurement revealed that the coercivity and anisotropy increases with nickel doping in magnetite nanoparticles. The optical analysis revealed that direct and indirect both types of band gap increases when the particle size decreases because the absorption spectra shift toward smaller wavelength. The blue shift confirms the formation of nanoparticles.