Minority and majority carrier traps associated with oxidation induced stacking faults in silicon

Abstract

Majority and minority traps associated with oxidation induced stacking faults (OISFs) have been investigated by deep level transient spectroscopy and minority carrier transient spectroscopy. Electron and hole traps have been characterised in nand p type Si, and the activation energies of all extended defect related traps are found to be dependent on the occupancy of the state associated with the extended defect. Majority and minority carrier traps in n type Si exhibit non-exponential trap filling, which indicates the presence of a significant electrostatic barrier around the OISF. The electrical properties of hole (minority) traps measured by minority carrier transient spectroscopy in n type Si are found to be different from the deep level transient spectroscopy signature of hole (majority) traps in p type Si, and this is explained by examining differences between conditions during the measurements. By examining separately the electron and hole capture properties of OISF related traps, one particular trap can be identified as a recombination centre. The capture cross-section of the OISF related hole trap in n type Si has been measured and it was found that, at low occupancy, the trap capture cross-section is 7 × 10^-14 cm².     

Charge transfer mechanisms between some shallow-trap centres involved in the photochromism of Bi12GeO20

Charge transfers between traps in undoped Bi₁₂GeO₂₀ (BGO) crystals have been investigated so as to complete our previous studies concerning the mechanism of the photochromism in these crystals. Thermally stimulated current measurements as a function of both the temperature at which the crystals are photoexcited and the density of energy used to photoexcite them were carried out between 80 and 350 K. The results show that the detected electron traps, due to their behaviour, can be schematically divided into two families: the shallower ones and the deeper ones. Two of the most important traps among the latter which play the role of electron reservoirs for the fundamental state of the photochromic transitions in the visible spectral range are populated via the former. Hence, the shallower traps act as precursory levels to the filling of the deeper traps.     

Batch and bulk removal of a triarylmethane dye, Fast Green FCF, from wastewater by adsorption over waste materials

De-Oiled Soya, an agricultural waste material and Bottom Ash a waste of power plants, have been used as adsorbents for the removal and recovery of a triarylmethane dye Fast Green FCF from wastewater. Batch studies have been carried by observing the effects of pH, temperature, concentration of the dye, amount of adsorbents, sieve size of adsorbent, contact time, etc. Graphical correlation of various adsorption isotherm models like, Langmuir, Freundlich, Tempkin and Dubinin-Radushkevich have been carried out for both the adsorbents. The adsorption over both the materials has been found endothermic and feasible in nature. Various thermodynamic parameters, such as, Gibb's free energy, entropy and enthalpy of the on-going adsorption process have been calculated. The kinetic studies suggest the process following pseudo first order kinetics and involvement of particle diffusion mechanism. The bulk removal of the dye has been carried out by passing the dye solution through columns of Bottom Ash and De-Oiled Soya and saturation factor of each column has been calculated. Attempts have also been made to recover the dye by eluting dilute NaOH through the columns.     

Process development for the batch and bulk removal and recovery of a hazardous, water-soluble azo dye (Metanil Yellow) by adsorption over waste materials (Bottom Ash and De-Oiled Soya)

Bottom Ash and De-Oiled Soya have been used as adsorbents for the removal of a hazardous azo dye-Metanil Yellow from its aqueous solutions. Adsorption of Metanil Yellow on these adsorbents has been studied as function of time, temperature, concentration and pH. Batch adsorption studies, kinetic studies and column operations enabled extraction of lethal dye from wastewaters. Adsorption equilibrium data confirms both Langmuir and Freundlich isotherm models and monolayer coverage of dye over adsorbents. Kinetic data have been employed to calculate specific rate constants, indicating thereby involvement of first order kinetics in the on-going adsorption and activation energy was determined as 0.813 and 1.060 kJ mol(-1) for Bottom Ash and De-Oiled Soya, respectively. For both adsorbents, the adsorption process has been found governing by film diffusion, over the entire concentration range. Column operations have also been performed for the bulk removal of the dye and also to examine the practical utilization of fixed bed adsorption technique in elimination of dangerous effluent. Saturation factors for Bottom Ash and De-Oiled Soya columns have been calculated as 99.15 and 99.38%, respectively. Attempts have also been made to regenerate the dye from the exhausted columns using aqueous sodium hydroxide as eluent.     

Process development for the removal and recovery of hazardous dye erythrosine from wastewater by waste materials-Bottom Ash and De-Oiled Soya as adsorbents

Erythrosine is a water-soluble xanthene class of dye. It is widely used as colorant in foods, textiles, drugs and cosmetics. It is highly toxic, causes various types of allergies, thyroid activities, carcinogenicity, DNA damage behaviour, neurotoxicity and xenoestrogen nature in the humans and animals. The photochemical and biochemical degradation of the erythrosine is not recommended due to formation of toxic by-products. The present paper is an attempt to remove erythrosine from wastewater using adsorption over Bottom Ash-a power plant waste and De-Oiled Soya-an agricultural waste. Under the batch studies, effect of concentration of dye, temperature, pH of the solution, dosage of adsorbents, sieve size of adsorbents, etc., have been studied for the uptake of the dye over both adsorbents. The adsorption process verifies Langmuir and Freundlich adsorption isotherms in both the cases and based on the data different thermodynamic parameters have been evaluated. Batch studies also include kinetic measurements, rate constant study, mass transfer behaviour and establishment of mechanistic pathway for both the cases. For the bulk removal of the dye column operations have been carried out and breakthrough capacities of the Bottom Ash and De-Oiled Soya columns have been calculated. Attempts have also been made for the recovery of the adsorbed dye from exhausted columns by eluting dilute NaOH and more than 90% of the dye was recovered.     

Antibacterial and photocatalytic activities of TiO2 nanotubes

TiO₂ nanotubes have been prepared by anodisation of titanium foil and their antibacterial activities have been tested against Gram-positive bacteria (Bacillus atrophaeus) while photocatalytic activity was tested for the degradation of the methyl orange dye. We found that the annealing temperature strongly affected antibacterial activity and photocatalytic dye degradation, as well as the production of reactive oxygen species under illumination. However, different trends were observed for dye degradation and antibacterial activity dependence on the annealing temperature. The relationship between annealing conditions, crystal structure, reactive oxygen species generation, dye degradation and antibacterial activity is discussed.     

Carrier trapping and delocalization in PbI2-containing CdI2 crystals

Two pairs of electron and hole traps have been identified in PbI₂-containing CdI₂ crystals in the range 80–305 K using a combination of thermally stimulated and photoinduced depolarization of a photoelectret state. The electron traps are identified as Pb⁺ centers in nanocrystalline 2H- and 4H-PbI₂ inclusions in the CdI₂ lattice. One of the hole centers is assumed to be a Pb²⁺ vacancy. All of the traps in the binary crystalline system are related to the presence of PbI₂ impurities as a consequence of the formation of heterojunctions between the CdI₂ matrix and nanocrystalline PbI₂ inclusions. We have calculated the energy distribution for filled traps.     

Servo control of an optical trap

A versatile optical trap has been constructed to control the position of trapped objects and ultimately to apply specified forces using feedback control. While the design, development, and use of optical traps has been extensive and feedback control has played a critical role in pushing the state of the art, few comprehensive examinations of feedback control of optical traps have been undertaken. Furthermore, as the requirements are pushed to ever smaller distances and forces, the performance of optical traps reaches limits. It is well understood that feedback control can result in both positive and negative effects in controlled systems. We give an analysis of the trapping limits as well as introducing an optical trap with a feedback control scheme that dramatically improves an optical trap's sensitivity at low frequencies.     

Studies on the adsorption kinetics and isotherms for the removal and recovery of Methyl Orange from wastewaters using waste materials

De-Oiled Soya a waste of Soya oil industries and Bottom Ash a waste of thermal power plants have been used as effective adsorbent for recovery and removal of hazardous dye Methyl Orange from wastewater. During the studies effects of amount of dye and adsorbents, pH, sieve sizes, column studies etc. have been carried out. Adsorption of the dye over both the adsorbents has been monitored through Langmuir and Freundlich adsorption isotherm models and feasibility of the process is predicted in both the cases. Different thermodynamic parameters like Gibb's free energy, enthalpy and entropy of the undergoing process are also evaluated through these adsorption models. The kinetic studies confirm the first order process for the adsorption reaction and also play an important role in finding out half-life of the adsorption process and rate constants for both the adsorbents. It is also found that over the entire concentration range the adsorption on Bottom Ash takes place via particle diffusion process, while that of De-Oiled Soya undergoes via film diffusion process. In order to establish the practical utility of the developed process, attempts have been made for the bulk removal of the dye through column operations. For the two columns saturation factors are found as 98.61 and 99.8%, respectively, for Bottom Ash and De-Oiled Soya with adsorption capacity of each adsorbent as 3.618 and 16.664 mg/g, respectively. The dye recovery has been achieved by eluting dil. NaOH through the exhausted columns.     

Thermoluminescence of CaS:Ag:Dy phosphors

CaS phosphors co-activated with varying concentrations of Ag and Dy have been prepared and their thermoluminescence behaviour is studied in the temperature range of 300°K to 443°K. The activation energies corresponding to the glow peaks have been evaluated by four different methods. The effect of addition of activators on general features of glow curves and on distribution of traps is discussed. Conclusions are drawn regarding the nature and origin of traps and about the type of kinetics involved in the thermoluminescence process.     

Identification of p53 gene by using CdSe/ZnS conjugation and hybridization

Recently Quantum Dots (QDs) have been of great interest due to their unique optical properties such as size-dependent, symmetric, narrow, and stable emissions, allowing for prolonged observation and multiplexing. We have prepared oligonucleotide conjugated to QD as a probe to detect p53 tumor suppressor gene related to hereditary cancer. QDs with carboxyl functional group have been conjugated to thiol-modified oligo nucleotides, which have been used as a hybridization probe for p53 gene. Target gene was added and hybridized with the QD bound probe. The conjugation of QD and thiolated oligonucleotide was stained by gel electrophoresis using Etrium Bromide (EtBr) as intercalating dye. Fluorescence resonance energy transfer (FRET) has been observed between QD and intercalating dye (Propidium Iodide) after hybridization of target and probe. FRET efficiency was increased with the increase of dye and DNA concentration. This shows the possibility of specific detection of low concentration of unlabeled complimentary DNA via quantum dots.     

Batch and bulk removal of hazardous dye, indigo carmine from wastewater through adsorption

An inexpensive adsorption method has been developed for the removal of indigo carmine, a highly toxic indigoid class of dye from wastewater. Waste materials--bottom ash, a power plant waste and de-oiled soya, an agricultural waste--have been used as adsorbents. Attempts have been made through batch and bulk removal of the dye and both the adsorbents have been found to exhibit good efficiency to adsorb indigo carmine. Under batch technique effect of temperature, pH, concentration, dosage of adsorbents, sieve size of adsorbents, etc. have been observed. The dye uptake on to both the adsorbents is found to validate Langmuir and Freundlich adsorption isotherms models. Different thermodynamic parameters, like Gibb's free energy, enthalpy and entropy of the on-going adsorption process have also been evaluated. Batch technique has also been employed for the kinetic measurements and the adsorption follows a first order rate kinetics for both the adsorbents. The kinetic investigations also reveal for both the adsorbents film diffusion and particle diffusion mechanisms are operative in the lower and higher concentration ranges, respectively. Under the bulk removal, indigo carmine has been adsorbed through the column beds of bottom ash and de-oiled soya and more than 90% of the dye material has been recovered by eluting dilute NaOH solution through exhausted columns.     

Majority carrier capture rates for transition metal impurities in germanium

The carrier capture cross-sections of deep levels in semiconductors are important parameters determining the properties of devices. Therefore not only the electrical levels of the transition metal impurities in germanium have been identified with DLTS but also the capture cross-sections have been directly determined by means of the DLTS amplitude as a function of the DLTS filling pulse duration. Due to the accurate fitting method the temperature dependence of these cross-sections could be measured. For the electron traps the empirical rule for phonon-assisted capture was observed, while for the hole traps a cross-section inversely proportional to the temperature was measured. Comparing the observed values it might be predicted that Ni and Co are the most efficient lifetime killers in p-type germanium, while Cr and Hf are the least efficient.     

Analysis of MIS equivalent electrical circuit of Au/Pd/Ti-SiO2-GaAs structure based on DLTS measurements

In this paper MIS equivalent electrical circuit of Au/Pd/Ti-SiO₂-GaAs has been analyzed by a comparison of the results obtained from admittance and DLTS spectroscopy. Two groups of peaks with different magnitude and different gate voltage dependence have been observed in DLTS and admittance spectra. Based on the analysis of the peaks behavior, it has been concluded that they are associated with the response of bulk traps and interface states, respectively. In order to characterize bulk traps and interface states responsible for the occurrence of two groups of peaks in normalized conductance spectra we have used the equivalent circuit with two CPE-R branches. The time constant values estimated for both peaks from admittance analysis have been compared with the time constant determined from DLTS analysis. Some discrepancies have been noted between the time constants obtained for interface states whereas the time constants for bulk traps were compatible. It has been also demonstrated that when conductance peaks overlap, the admittance experimental data can be fitted by the equivalent electrical model with only one CPE-R branch. However, in this case incomplete information about the analyzed process has been obtained despite the fact that all model validity criteria can be fulfilled and the model seems to be correct.     

Saturation Characteristics of Cr(4)+:YAG Crystals and Dye Films for Passive Q Switches

Measurements of the saturated transmission and the undepleted ground-state population density of both Cr(4+):YAG crystals and dye films as saturable absorbers have been experimentally attempted to understand the additional unsaturated losses in a high Q state. The saturated transmission of a saturable absorber is less than its maximum at a high saturation fluence because of the undepleted ground-state population density. Higher saturated transmission and lower undepleted ground-state population density have been observed for Cr(4+):YAG crystals than have been observed for dye films at high optical densities.     

Infrared reflection–absorption spectroscopy applied to a merocyanine dye J-aggregate deposited on transparent electrodes based on zinc oxide

Effectiveness of the infrared reflection–absorption spectroscopy (IR-RAS) using transparent electrodes made of Ga-doped ZnO as metal substrates has been demonstrated. For a merocyanine dye with and without a metallic cation, differences in the IR-RAS spectrum have been clearly observed, even when the quantity of the material is restricted to the monolayer level. Referring to the visible transmission spectra of the samples, which can be measured thanks to the transparency of the substrates, chelation of the metallic cation by the carboxyl group belonging to a dye molecule and the keto group belonging to an adjacent dye molecule has been regarded as a promising candidate for the J-aggregation driver.     

Removal of Alizarin Violet 3R (anthraquinonic dye) from aqueous solutions by natural coagulants

In this paper the ability of two natural products in removing dyes has been tested. After a preliminary screening for dye removal capacity, a tannin-based coagulant called ACQUAPOL C-1 and a vegetal protein extract derived from Moringa oleifera seed have been fully studied. The influence of several parameters such as pH, temperature or initial dye concentration (IDC) have been tested and the behavior of both coagulants has been compared. pH results to be an interesting variable and dye removal decreases as pH increases. This effect is higher in ACQUAPOL C-1 than in M. oleifera seed extract. Temperature seems not to be so affecting parameter, while IDC appears to be a very important variable in q_c capacity, which is higher as IDC increases. Langmuir isotherm model fits very well in both cases of ACQUAPOL C-1 and M. oleifera seed extract dye removal.     

Adsorption of reactive dye from an aqueous solution by chitosan: isotherm, kinetic and thermodynamic analysis

The adsorption of Remazol black 13 (Reactive) dye onto chitosan in aqueous solutions was investigated. Experiments were carried out as function of contact time, initial dye concentration (100-300mg/L), particle size (0.177, 0.384, 1.651mm), pH (6.7-9.0), and temperature (30-60 degrees C). The equilibrium adsorption data of reactive dye on chitosan were analyzed by Langmuir and Freundlich models. The maximum adsorption capacity (qm) has been found to be 91.47-130.0mg/g. The amino group nature of the chitosan provided reasonable dye removal capability. The kinetics of reactive dye adsorption nicely followed the pseudo-first and second-order rate expression which demonstrates that intraparticle diffusion plays a significant role in the adsorption mechanism. Isotherms have also been used to obtain the thermodynamic parameters such as free energy, enthalpy and entropy of adsorption. The positive value of the enthalpy change (0.212kJ/mol) indicated that the adsorption is endothermic process. The results indicate that chitosan is suitable as adsorbent material for adsorption of reactive dye form aqueous solutions.     

Molecular boxes on a molecular printboard: encapsulation of anionic dyes in immobilized dendrimers

Fifth-generation poly(propylene imine) dendrimers, modified with 64 apolar adamantyl groups, have been immobilized on cyclodextrin host monolayers ("molecular printboards") on glass by supramolecular microcontact printing. The immobilized dendrimers retain their guest-binding properties and function as "molecular boxes" that can be filled with fluorescent dye molecules from solution. Alternatively, part of the immobilized dendrimers were filled with dye molecules by cross-microcontact printing while the remaining, empty dendrimers were filled with a different dye from solution, resulting in alternating patterns of dye molecules. In addition, we demonstrate that encapsulation of dyes in immobilized dendrimers is reversible: immobilized molecular boxes can be filled with a dye, emptied, and subsequently refilled with a different dye.     

Photodegradation of direct yellow-12 using UV/H2O2/Fe2+

A detailed investigation of photodegradation of direct yellow-12 (DY12) using UV/H(2)O(2)/Fe(2+) has been carried out in a photochemical reactor. Experiments studied degradation as a function of concentration, decolorization and reduction in chemical oxygen demand (COD). The effect of operating parameters, such as UV, pH, amount of Fenton's reagent (H(2)O(2) and FeSO(4)), and amount of DY12 dye has also been determined. It has been observed that simultaneous utilization of UV irradiation with Fenton's reagent increases the degradation rate of DY12 dye. The dye quickly losses its color and there is an appreciable decrease in COD value, indicating that the dissolved organic have been oxidized. The kinetics of degradation of the dye in dilute aqueous solutions follows pseudo-first order kinetics. Final products detected at the end of the reaction include NO(3)(-), NO(2)(-), N(2)O, NO(2), SO(2), CO(2) and CO. Results indicate that dye degradation is dependent upon pH, UV-intensity, concentration of Fenton's reagent and dye. Acidic pH has been found to be more suitable in comparison to neutral and alkaline. The optimum concentration of Fenton's reagent (H(2)O(2)/Fe(2+)) was found as 1500/500 mg l(-1) for 50 mg l(-1) DY12 dye in water at pH 4. The results indicate that the treatment of DY12 dye wastewater with UV/Fe(2+)/H(2)O(2) system is efficient.