Acceptor Concentration Research Articles

Electrically Active Defects Induced by α‐Particle Irradiation in p‐Type Si Surface Barrier Detector

Herein, the investigation of radiation‐induced defects generated in the Al/SiO2/p‐type FZ Si surface barrier detector upon irradiation with α‐particles at room temperature using capacitance−voltage (C−V) and current deep‐level transient spectroscopy (IDLTS) methods is conducted. The carried out C−V measurements indicate the formation of at least 8 × 1012 cm−3 radiation‐induced acceptor traps at the depth fairly close to that where, according to TRIM simulations, the highest concentration of vacancy‐interstitial pairs is created by the incoming α‐particles. The studies conducted by the current DLTS technique allow to relate the observed increase in the acceptor concentration with the near‐midgap level at E V + 0.56 eV. This level can apparently be associated with V2O defects recognized previously to be responsible for the space−charge sign inversion in the irradiated n‐type Si detectors.

Abstract 2872: Methods of assessment of polysialyltransferase inhibitors for treatment of tumor cell dissemination

Abstract Polysialic acid (polySia) decorates the surface of NCAM (neuronal cell adhesion molecule) on neuroendocrine tumors, notably neuroblastoma and small cell lung cancer, and is strongly associated with poor prognosis and aggressive disease in patients in the clinic [1]. PolySia modulates tumor cell-cell and cell-matrix adhesion, migration, invasion and metastasis. SiRNA knockdown of polysialyltransferase (polyST) ST8SiaII, the enzyme primarily responsible for polySia synthesis in tumors, abrogates tumor cell migration and invasion. PolyST is a selective and largely unexplored therapeutic target for neuroblastoma dissemination [1]. While assays are available to assess polyST enzyme activity, there is no methodology available specifically optimized for identification of novel polyST inhibitors. We describe the development of cell-free and cell-based assays that enable assessment of polysialyltransferase inhibition. Development of the HPLC-fluorescence-based enzyme assay includes a comprehensive optimization of assay conditions, including evaluation of metal ion composition, enzyme concentration, substrate and acceptor concentration, temperature, pH and tolerance to DMSO, followed by validation using known polyST inhibitors. Thorough analysis of each of the assay components provided a set of optimized conditions. Under these optimized conditions, the experimentally observed Ki value for CMP, a competitive polyST inhibitor, was strongly correlated with the predicted Ki value, based on the classical Cheng-Prusoff equation [average fold error (AFE) = 1.043]. These results indicate that this assay can provide medium-throughput analysis for enzyme inhibitors with high accuracy. We additionally report optimized HPLC-based and ELISA-based methodologies for assessment of polyST inhibition in neuroblastoma cells, using endoneuraminidase N as control, and assessment of ICT3176 (a polysialylation inhibitor) as a test agent. In conclusion, in vitro cell-free and cell-based assays for accurate measurement of polysialyltransferase (polyST) inhibition are described, specifically designed for routine identification of potential polyST inhibitors, generation of kinetics data and assessment of mode of inhibition, and assessment of effects on cellular polysialylation. Given the considerable and growing interest in the polySTs as important anti-metastatic targets in cancer drug discovery, these are vital tools to enable preclinical identification and evaluation of novel polyST inhibitors for neuroblastoma therapy. [1] Falconer, R.A. et al., Curr. Cancer Drug Targets, 2012, 12, 925-939. Citation Format: Xiaoxiao Guo, Jodie R. Malcolm, Anjana Patel, Marrwa M. Ali, Goreti Ribeiro Morais, Steven D. Shnyder, Paul M. Loadman, Laurence H. Patterson, Robert A. Falconer. Methods of assessment of polysialyltransferase inhibitors for treatment of tumor cell dissemination [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2872.

Extraction of acceptor concentration map from EBIC experiments

Controlling two dimensional doping distributions is an important benefit in order to check processed substrates or specific devices. To achieve this purpose, a new methodology is proposed in order to obtain qualitative maps of acceptor concentration from one EBIC image. Analytical models are used to help in defining the best experimental condition and to check the validity of the approach, and a TCAD simulation is performed on a realistic structure and shows promising results. Then, a measurement is carried out on a device and the epitaxy gradient is clearly visible, as well as the presence of Pwell layers.

Degradation analysis with characteristics and simulations of 265 nm UV-C LED

We report the degradation study on AlGaN-based 265 nm ultraviolet light-emitting diodes (UV-LEDs) under a series of constant current stress. The failure mechanisms were investigated systematically by measuring the optical and electrical characteristics of the LEDs before and after aging. The variation of carrier concentration in the active region was analyzed by capacitance–voltage. Combining the extracted apparent charge distribution profiles with the simulation results of the devices before and after the stress, we found that the change of carrier concentration in the multiple quantum wells was related to the donor diffusion on the n-side. On the p-side, both the acceptor concentration of electron blocking layer (EBL) and the defects in p-GaN contact layer were also found to be under constant change. The reduction of the EBL doping concentration has contributed to an increase of the diode depletion width during the stress. The changes in the LEDs before and after stressing indicate a compensating effect occurred in the p-type EBL close to the quantum wells, which leads to the degradation of the optical power of the 265 nm UV-LEDs.

Numerical study of a high‑performance thin film CIGS solar cell with a-Si and MoTe2 hole transport layer

Ultrathin Cu(InGa)Se2 (CIGS) material has become one of the emerging material in the research of solar cell fields due to its excellent optical, electrical and tunable bandgap properties. In this study, we have described a numerical simulation of ultrathin CIGS solar cell using SCAPS-1D program tool based on WS2 as a buffer layer, CIGS as an absorber layer with a-Si/MoTe2 as a hole transport layer (HTL). The proposed study also reveals that a-Si is better choice for HTL as compared to MoTe2 for CIGS solar cell. The cell parameters such as thickness, defect density and acceptor concentration of CIGS absorber layer have been optimized in proposed work. Based on optimization, the maximum power conversion efficiency (PCE) of 30.17% (Voc =1.093Volts,Jsc=32.41 mA/cm2 and FF=85.12%) has been reached for CIGS solar cell with a-Si HTL. The simulation further analyzed at various operating temperature and series resistance for better understanding of the solar device. All these simulation provide noteworthy manifestation for the fabrication of high efficient ultrathin energy harvesting application.

Interplay of defects in low energy nitrogen implanted ZnO nanorods

We present here an in-depth comprehensive study on the interplay between nitrogen (N) and various point defects in ZnO nanorods (NRs) implanted with 50 keV N ions with fluences from 1 × 1014 to 1 × 1016 ions/cm2 followed by a thermal annealing at 450 °C separately in Ar, O2, and excess Zn ambiences. Detailed X-ray diffractometry results reveal that N implantation induced structural damages increase sharply beyond 1 × 1015 ions/cm2. The Raman scattering analyses are indicative of structural disorders due to various N-related defect complexes. The analyses of X-ray photoelectron spectroscopy (XPS) results validate the incorporation of N at O sublattice forming NO acceptor and NO-VZn acceptor complex in the implanted NRs. Post-implantation annealing in Ar and O2 ambiences causes only NO state, while annealing in excess Zn ambient induces an additional shallow donor (N2)O by substituting N2 at O site. The XPS, Raman scattering, photoluminescence and current-voltage measurement results combiningly illustrate that the post-implantation annealing in O2 and Ar ambiences play a key role to stabilize the N dopants in ZnO NRs via reducing oxygen vacancy and/or preserving the concentration of N-related acceptors. This study would therefore be a benchmark for understanding the role of defects in the N doping in ZnO NRs.

Modeling the spatial control over point defect spin states via processing variables

Contemporary models that are used to search for solid-state point defects for quantum-information applications tend to focus on the defect’s intrinsic properties rather than the range of conditions in which they will form. In this work, a first-principles based multi-scale device model is used to explore how the conditions (i.e., growth temperature, doping concentration, unintentional impurity concentration) influence the formation of a neutral aluminum vacancy complexed with an oxygen impurity at a neighboring nitrogen site vAl-1ON in an Si/Mg:AlN homojunction. Varying the donor (Si) concentration is predicted to lead to the greatest change in both the maximum height and shape of the (vAl-1ON)0 profile. The shape is found to depend on the acceptor (Mg) concentration as well, and a critical ratio between the acceptor and unintentional impurities below which the (vAl-1ON)0 center would not form was identified. A detailed analysis of the electrostatic potential, electric field, and defect chemistry obtained with the model was used to reveal the underlying causes of these changes. These results show the potential of varying processing parameters to manipulate the local electronic structure as a means to control the properties of point defects for quantum-information applications.

Numerical simulation of Cs2AgBiBr6-based perovskite solar cell with ZnO nanorod and P3HT as the charge transport layers

We carried out simulative investigations on a non-toxic, lead-free perovskite solar cell (PSC), where Cs2AgBiBr6, P3HT, ZnO nanorod, and C were utilized as the absorber layer, hole transport layer, electron transport layer, and back contact, respectively. At 600 nm optimum absorber thickness, the device achieved a maximum power conversion efficiency of 4.48%. The PSC operated optimally when the electron affinities were set at 3.3 eV and 4.6 eV for P3HT and ZnO nanorod, respectively. Moreover, the hole mobility and acceptor concentration of P3HT should be weighed during the choosing of appropriate doping additives and doping levels. Besides, the optimum back contact work function and absorber defect density were found to be 5.2 eV and 1015 cm−3, respectively. We also observed the effect of radiative recombination rates and different charge transport layers on the device's performance. Overall, this study's simulation results will provide insightful guidance towards fabricating an environmentally benign PSC.

Inhibition of Mg activation in p-type GaN caused by thin AlGaN capping layer and impact of designing hydrogen desorption pathway

Thermal activation of a Mg-doped GaN layer with a thin AlGaN capping layer was investigated by means of systematic electrical characterization. Two-dimensional electron gas generated at the AlGaN/GaN interface greatly inhibited activation of the underlying Mg-doped GaN layer. This finding is attributed to the charge states of the interstitial hydrogen atoms being released from the Mg–H complexes and their diffusivity being dependent on the Fermi level position in GaN-based heterostructures. Reasonable electrically active acceptor concentration in Mg-doped GaN was achieved by designing a hydrogen desorption pathway.

Charge Carrier Transport in Van Der Waals Semiconductor InSe Intercalated with RbNO3 Probed by Direct Current Methods

Layered van der Waals (vdW) semiconductors show great promise to overcome limitations imposed by traditional semiconductor materials. The synergistic combination of vdW semiconductors with other functional materials can offer novel working principles and device concepts for future nano- and optoelectronics. Herein, we investigate the influence of the intercalation of semiconducting n-type InSe vdW crystals with ferroelectric rubidium nitrate (RbNO3) on the transport of charge carriers along and across the layers. The apparent maxima in the temperature dependences of the Hall coefficient are explained in the framework of a model that predicts, along with three-dimensional carriers, the existence of two-dimensional ones contributing only to the conductivity along the layers. The revealed increase of the conductivity anisotropy and its activation variation with temperature, which is mainly due to a decrease of the conductivity across the layers, confirm a two-dimensionalization of electron gas in n-InSe after insertion of the ferroelectric. From the numerical analysis, we determined the densities of carriers of both types, concentrations of donors and acceptors, as well as the value of the interlayer barrier.

Neutron irradiation induced defects in oxides and their impact on the oxide properties

Understanding the irradiation-induced defects in oxides is of interest for a wide range of applications. ZnO is an interesting oxide with mixed ionic and covalent bonding that contains a variety of point defect structures—making it an excellent model for studying irradiation-induced defects and their impact on properties. Here, we investigate the effects of neutron irradiation on the formation of defects and on the structural, optical, and electrical properties of ZnO single crystals. We observe the formation of vacancies and voids via positron annihilation spectroscopy. Neutron irradiation led to a significant deterioration of the ZnO structure and formed a high concentration of point defects, vacancy clusters, and voids with large disparities in their structure across variable irradiation times. It also led to significant changes in the optical properties and sample color. Irradiation for 444 h induced a high concentration of Cu acceptors as well as a high concentration of Ga donors. Temperature-dependent Hall effect measurements revealed the competing production of donors and acceptors and showed an increase in the slope of the carrier freeze-out curve with increasing irradiation dose. This work demonstrates the combined effects of neutron irradiation in producing a wide range of structural defects, impurities, and dopants in oxides and their enormous impact on modifying the oxide structure and both the optical and electronic properties. It particularly emphasizes the importance of considering the production of new impurities and dopants during the neutron irradiation of oxides.

Effect of MoS2 interlayer on performances of copper-barium-tin-sulfur thin film solar cells via theoretical simulation

Cu2BaSn(S,Se)4 (CBTSSe) solar cells are emerging photovoltaic devices due to their high theoretical efficiencies of ~31%, environment-friendly and earth-abundant composition, low density of non-recombination defects, and so on. However, the record efficiency of CBTSSe solar cell is only 5.2%, showing the importance of studying their performance via numerical analysis to further enhance their practical efficiencies. In this paper, the effect of absorber and buffer layers on performances of Cu2BaSnS4 (CBTS) solar cells are firstly systematically studied via the SCAPS-1D software to provide a platform for the study of the effect of MoS2 interlayer on the performances of CBTS solar cells. The highest PCE of CBTS solar cell with a 30 nm CdS buffer layer is 11.87%. The PCE of CBTS solar cell with a 0.8 μm CBTS absorb layer is 12.51%, indicating that the CBTS solar cell is a potential low-cost solar cell due to its large optical absorption coefficient (α > 104 cm−1). The efficiency of CBTS solar cell is improved to 16.47% when the carrier concentration of CBTS is 1016 cm−3. The relationship between the performance of solar cell and the band gap, thickness, donor concentration, acceptor concentration of MoS2 interlayer is systematically investigated on the basis of the optimized efficiency. It is found that MoS2 interlayer plays an important role in the performance of CBTS solar cell. The p-type MoS2 has a beneficial effect on the efficiency improvement while the n-type MoS2 has a negative effect on the efficiency enhancement. The highest PCE of CBTS solar cell is as high as 18.28% when the thickness and the acceptor concentration of MoS2 are 4 nm and 1019 cm−3, respectively. Our simulation result provides a promising research direction to further improve the actual efficiency of the CBTS solar cell.

Electronic structure of cubic boron arsenide probed by scanning tunneling spectroscopy

The unusually high lattice thermal conductivity of semiconducting cubic boron arsenide (BAs) has motivated studies of the bulk electronic band structure of BAs for its potential use as an active layer material in electronic devices. However, the surface electronic structure of BAs remains to be investigated. Scanning tunneling spectroscopy (STS) is employed here to probe the electronic structure of as-grown and in situ cleaved surfaces of BAs single crystals. The bandgap measured at several interior locations of the cleaved surface is about 2.1 eV, close to our calculated bulk bandgap value of 2.05 eV. In comparison, the measured bandgap within several micrometers from the two edges of the cleaved surface decreases to about 1.9 eV. This decrease is attributed to tunneling from an increased concentration of shallow acceptors. Several of the tunneling peaks observed by STS within the bandgap are close to the calculated energy levels for bulk lattice defects and substitutional impurities. In contrast to some other III–V compound semiconductors where surface relaxation prevents intrinsic surface states from appearing in the bulk bandgap, some measured tunneling peaks in the BAs bulk bandgap can contain contributions from intrinsic surface states calculated for boron dangling bonds.

On the nature of photosensitivity gain in Ga2O3 Schottky diode detectors: Effects of hole trapping by deep acceptors

Lightly n-type doped Ga2O3 layers grown by Halide Vapor Phase Epitaxy (HVPE) on bulk n+-Ga2O3 substrates were subjected to irradiation with fast reactor neutrons, 20 MeV protons, or treatment in high ion density Ar plasma. These treatments lead to a marked increase in the concentration of deep acceptors in the lower half of the bandgap. These acceptors have optical ionization thresholds near 2.3 eV and 3.1 eV. There is a simultaneous strong enhancement of the photocurrent of Schottky diodes fabricated on these layers in the UV spectral range, and a large increase in the Electron Beam Induced Current (EBIC) collection efficiency. The gain in photocurrent at −10 V reached 18 times for neutron and proton irradiated samples, and 104 times for the plasma treated samples. Similar increases in gain were observed in the EBIC current collection efficiency for beam energy 4 keV. With such beam energy, the electron–hole pairs are generated well within the space charge region. The results are explained by assuming that the capture of photoinduced or electron-beam-induced holes by the deep acceptors gives rise to a decrease in the effective Schottky barrier height and an increase of the electron current flow that is responsible for the observed high gain. The reported observation could form a basis for radical improvement of photosensitivity of Ga2O3-based solar-blind photodetectors. However, the photocurrent build-up and decay times in this mechanism are inherently long, on the order of some seconds.

Extremely high-efficient activation of acceptor boron introduced by ion implantation at room temperature with various doping concentrations in epitaxially synthesized diamond films by chemical vapor deposition

We homoepitaxially synthesized a pure diamond film on type Ib base substrates by microwave plasma-assisted special chemical vapor deposition method and then doped B impurity atoms by the ion implantation technique with various doping concentrations from 2×1017 to 2×1019 cm−3 at room temperature followed by activation annealing at 1300 °C. The electrical properties of specific resistance, carrier concentration, Hall mobility, and conductive carrier type were analyzed by Hall effect measurements based on the van der Pauw method at sample temperatures from 77 to 873 K. We consequently realized excellent B-doping in the CVD-synthesized diamond film with a low compensation ratio and perfect doping efficiency and confirmed p-type conduction at almost all temperature ranges for the measured samples. In very lightly doped diamond, we observed first the existence of deep acceptor levels located near 1.85 eV with respect to the valence band maximum and proposed a conduction mechanism based on hopping conduction in deep acceptor levels. We showed the availability of this doping process to high-efficient B doping with various acceptor concentrations in diamond. The great success achieved in the activation of acceptor B implanted in diamond with various doping concentrations should definitely contribute to the progress in the application of diamond-based power semiconductor devices.

Electrical properties and structural defects of p-type GaN layers grown by halide vapor phase epitaxy

The electrical properties and structural defects of p-type GaN layers with Mg concentrations from 8.0 × 1018 to 8.3 × 1019 cm−3 grown by halide vapor phase epitaxy (HVPE) were investigated. In all samples, p-type conduction was confirmed at room temperature. The hole concentration at room temperature decreased in a heavily Mg-doped sample. By analyzing the results of Hall-effect measurements at various temperatures, the acceptor concentration decreased in a heavily Mg-doped sample, whereas the compensating donor concentration increased. These results affect the decrease in the hole concentration. The hole mobility decreased with increasing acceptor concentration. In the heavily Mg-doped sample, pyramidal inversion domains (PIDs) were formed. The size of each PID in an HVPE-grown sample is in good agreement with that Mg-doped GaN layers grown by metalorganic vapor phase epitaxy (MOVPE). Thus, the formation mechanism of PIDs in HVPE-grown samples is possibly the same as that in MOVPE-grown samples. Energy-dispersive X-ray spectroscopy shows that Mg atoms accumulate in PIDs, which suggests that Mg atoms in PIDs are electrically inactive, inhibiting the increase in the acceptor concentration. These results are useful guidelines for fabricating p-type GaN layers with higher hole concentrations by HVPE.

Selective and efficient extraction of cationic dyes from industrial effluents through polymer inclusion membrane

• Selective and efficient extraction of cationic dyes. • Initial study by liquid-liquid extraction using EDC as complexing agent. • Synthesis of highly efficient and selective EDC-PIM for extraction of cationic dyes. • A novel, economical, green, robust and easy-to-use PIM-system. • Application of EDC-PIM to real industrial effluents. Cationic dyes are widely used colorants in textile and other related industries. These dyes are highly toxic for marine life and make a major fraction of the industrial effluents. In this study, we report the synthesis of ester derivative of calix[4]arene (EDC) impregnated polymer inclusion membrane (PIM) and employed it for the transfer of cationic dyes between two aqueous phases. EDC forms inclusion complex with cationic dyes having 1:1 M ratio as revealed by the Job’s plot, the log/log plot, and the Benesi-Hildebrand methods while using methylene blue (MB) as a model cationic dye. EDC was used as carrier with cellulose triacetate (CTA) as a base polymer, and 2-nitrophenyl octyl ether (2-NPOE) as a plasticizer for the synthesis of EDC-PIM. Membranes were characterized by Fourier Transform Infrared spectroscopy (FT-IR), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), Brunauer–Emmett–Teller (BET), and Barrett-Joyner-Halenda (BJH) analysis. The extraction performance of the synthesized PIM was optimized by varying different external parameters including pH of the donor and the acceptor phases, temperature, stirring speed, and concentration of EDC and dye while using MB as a model cationic dye. More than 90% extraction was achieved under optimized conditions which is 4.5-fold more than EDC-free-PIM. The extraction efficiency of the EDC-PIM remained similar after ten consecutive cycles that demonstrates its reusability potential in context of economical industrial applications. Finally, the synthesized EDC-PIM was used for selective extraction of other cationic dyes (basic red and nile blue) at the optimized conditions from the real industrial effluents. The extraction efficiency of the EDC-PIM was reproducible in all cases. The reusability and robustness of the EDC-PIM makes it an excellent candidate for retrieving cationic dyes from the industrial effluents.

Synthesis of fucosylated oligosaccharides with α-L-fucosidase from Thermotoga maritima immobilized on Eupergit® CM.

Fucosylated oligosaccharides present in human milk perform various biological functions that benefit infants' health. These compounds can be also obtained by enzymatic synthesis. In this work, the effect of the immobilization of α-L-fucosidase from Thermotoga maritima on the synthesis of fucosylated oligosaccharides was studied, using lactose and 4-nitrophenyl-α-L-fucopyranoside (pNP-Fuc) as acceptor and donor substrates, respectively, and Eupergit® CM as an immobilization support. The enzyme was immobilized with 90% efficiency at pH 8 and ionic strength of 1.5M. Immobilization decreased enzyme affinity for the donor substrate as shown by a 1.5-times higher KM value and a 22-times decrease of the kcat/KM ratio in comparison to the unbound enzyme. In contrast, no effect was observed on the synthesis/hydrolysis ratio (rs/rh) when α-L-fucosidase was immobilized. Also, the effect of initial concentration of substrates was studied. An increase of the acceptor concentration improved the yields of fucosylated oligosaccharides regardless enzyme immobilization. The synthesis yields of 38.9 and 40.6% were obtained using Eupergit® CM-bound or unbound enzyme, respectively, and 3.5mM pNP-Fuc and 146mM lactose. In conclusion, α-L-fucosidase from Thermotoga maritima was efficiently immobilized on Eupergit® CM support without affecting the synthesis of fucosylated oligosaccharides.

Microbial Degradation of Citric Acid in Low Level Radioactive Waste Disposal: Impact on Biomineralization Reactions

Organic complexants are present in some radioactive wastes and can challenge waste disposal as they may enhance subsurface mobility of radionuclides and contaminant species via chelation. The principal sources of organic complexing agents in low level radioactive wastes (LLW) originate from chemical decontamination activities. Polycarboxylic organic decontaminants such as citric and oxalic acid are of interest as currently there is a paucity of data on their biodegradation at high pH and under disposal conditions. This work explores the biogeochemical fate of citric acid, a model decontaminant, under high pH anaerobic conditions relevant to disposal of LLW in cementitious disposal environments. Anaerobic microcosm experiments were set up, using a high pH adapted microbial inoculum from a well characterized environmental site, to explore biodegradation of citrate under representative repository conditions. Experiments were initiated at three different pH values (10, 11, and 12) and citrate was supplied as the electron donor and carbon source, under fermentative, nitrate-, Fe(III)- and sulfate- reducing conditions. Results showed that citrate was oxidized using nitrate or Fe(III) as the electron acceptor at > pH 11. Citrate was fully degraded and removed from solution in the nitrate reducing system at pH 10 and pH 11. Here, the microcosm pH decreased as protons were generated during citrate oxidation. In the Fe(III)-reducing systems, the citrate removal rate was slower than in the nitrate reducing systems. This was presumably as Fe(III)-reduction consumes fewer moles of citrate than nitrate reduction for the same molar concentrations of electron acceptor. The pH did not change significantly in the Fe(III)-reducing systems. Sulfate reduction only occurred in a single microcosm at pH 10. Here, citrate was fully removed from solution, alongside ingrowth of acetate and formate, likely fermentation products. The acetate and lactate were subsequently used as electron donors during sulfate-reduction and there was an associated decrease in solution pH. Interestingly, in the Fe(III) reducing experiments, Fe(II) ingrowth was observed at pH values recorded up to 11.7. Here, TEM analysis of the resultant solid Fe-phase indicated that nanocrystalline magnetite formed as an end product of Fe(III)-reduction under these extreme conditions. PCR-based high-throughput 16S rRNA gene sequencing revealed that bacteria capable of nitrate Fe(III) and sulfate reduction became enriched in the relevant, biologically active systems. In addition, some fermentative organisms were identified in the Fe(III)- and sulfate-reducing systems. The microbial communities present were consistent with expectations based on the geochemical data. These results are important to improve long-term environmental safety case development for cementitious LLW waste disposal.

Förster energy transfer mechanism and color tunability in three binary conjugated polymer blends

The energy transfer mechanism from poly(9,9-dioctylfluorene-2,7-diyl) (PFO) to poly 9,9-dioctylfluorene-alt-benzothiadiazole (F8BT) and to poly(2-methoxy-5(2-ethylhexyl)-1,4 -phenylenevinylene (MEH-PPV), and from F8BT to MEH-PPV were comprehensively investigated. The concentrations of the donors in their binary blends were kept constant, while the acceptor concentration was carefully varied before reaching the complete emission quenching. The binary blend thin films were prepared using the solution blending method before they were spin-coated onto glass substrate. The UV–Vis absorption and emission spectra showed color emission shift towards the acceptor emission, confirming the energy transfer. These spectra were used to calculate important energy transfer parameters, such as the Förster radius (Ro), the distance between donor and acceptor molecules (RDA), energy transfer rate (kET), energy transfer efficiency (η), energy transfer probability (PDA), quenching constant (Ksv) and quenching rate constant (kq). The spectra also indicated that at high acceptor content the creation of excimer due to the molecule aggregation resulted in a red shift of the acceptor emission. In addition, the CIE coordinates proved the tunability of the color-emission. Finally, based on the calculated parameters, energy transfer mechanism in the three binary blends were suggested.