Thermal neutron detection with Ce doped LiCaAlF6 single crystals

Cerium-doped LiCaAlF₆ (Ce:LiCAF) crystals have been studied as scintillators in application to thermal neutron detection. Three crystals: high-doping Ce:LiCAF, low-doping Ce:LiCAF with 50% enrichment of ⁶Li (both 10 mm×10 mm×2 mm, rectangular) and high-doping Ce:LiCAF with 95% enrichment of ⁶Li (Ø50.8 mm×2 mm, discus) coupled to Photonis XP5300B PMT, were tested. The response of these crystals to neutrons emitted from a paraffin moderated ²³⁸PuBe source has been investigated. Thermal neutron peaks have been found at a Gamma Equivalent Energy (GEE) of ∼2.5 MeV for high-doping Ce:LiCAF (50% ⁶Li), ∼2 MeV for low-doping Ce:LiCAF (50% ⁶Li) and ∼1.9 MeV for high-doping Ce:LiCAF (95% ⁶Li). The light output of Ce:LiCAF was also measured (175-250 phe/MeV from sample to sample). Lithium-6 glass GS20 from Saint Gobain was used as a reference scintillator (Ø50 mm×2 mm, circle). Relative neutron efficiency, normalized to that of GS20 lithium glass, as well as gamma-neutron intrinsic efficiency for all tested samples was calculated. Intrinsic efficiency on thermal neutron detection for small Ce:LiCAF samples was estimated at about 32-35% of that of GS20 and for large Ce:LiCAF sample as about 82% of that of GS20.     

Analysis of four-way two-dimensional liquid chromatography-diode array data: application to metabolomics

Two-dimensional liquid chromatography (2D-LC) is rapidly gaining popularity for the analysis of very complex mixtures, including proteomic and metabolomic samples. It provides an effective strategy for separating such samples, because the resolving power of 2D-LC is far superior to that of traditional single-dimension separations. The present work focuses on the development of data analysis methods for the extremely large data sets, on the order of 10 million data points, generated by 2D-LC with diode-array detection (DAD). Specifically, we have applied and adapted chemometric methods to the analysis of maize seedling digests, focusing on compounds related to the biosynthetic pathways of indole-3-acetic acid, the primary growth regulator in plants. The chemometric techniques of window target testing factor analysis (WTTFA), along with parallel factor analysis - alternating least squares (PARAFAC-ALS) were used to analyze 2D-LC-DAD chromatograms of a sample composed of 26 indolic standards, 2 extracts of mutant orange pericarp maize seedlings, 2 extracts of wild-type maize seedlings, and a blank sample. The indolic compounds studied belonged to six spectrally unique groups, and WTTFA was able to specifically identify the presence or absence of any of the 26 indolic standards in the mutant and wild-type samples. A PARAFAC-ALS algorithm and an ALS algorithm with flexible constraints were successfully applied to resolve the spectrally rank deficient data and to demonstrate the quantitative potential of multivariate curve resolution methods. Using this procedure, 95 total peaks were resolved in the data set analyzed. Of those 95 peaks, 45 were found in both the mutant and wild-type maize samples, 16 peaks were unique to the mutant maize samples, 13 peaks were unique to the wild-type maize samples, and 15 peaks were unique to the standard chromatograms. Of the 26 standards included in the data set, several indole acetic acid conjugates were identified and quantified in the maize samples at levels of approximately 0.3-2 microg/g plant material.     

Electronic structure of Co islands grown on the √3 × √3-Ag/Ge(111) surface

By means of room temperature scanning tunneling spectroscopy (RT STS), we have studied the electronic structure of two different Ag/Ge(111) phases as well as Co islands grown on the √3 × √3-Ag/Ge (111) forming either √13 × √13 or 2 × 2 patterns. The spectrum obtained from 4 × 4-Ag/Ge(111) structure shows the existence of a shoulder at 0.7 V which is also present in the electronic structure of the Ge(111)-c2 × 8 and indicates donation of Ge electrons to electronic states of the Ag-driven phase. However, this fact is not supported by the electronic spectrum taken from the √3 × √3-Ag/Ge (111). The complexity of the Co-√13 × √13 islands bonding with the substrate is mirrored by a large number of peaks in their electronic spectra. The spectra obtained from the Co-2 × 2 islands which had grown on the step differ from those taken from Co-2 × 2 islands located along the edge of the terrace by a number of peaks at negative sample bias. This discrepancy is elucidated in terms of dissimilarities of Co-substrate interaction accompanying Co islands growth on different areas of the stepped surface.     

Growth, thermal, dielectric and mechanical studies of triglycine zinc chloride, a semiorganic nonlinear optical material

Triglycine zinc chloride, a semiorganic material, has been grown by slow solvent evaporation technique from a mixture of aqueous solution of glycine and zinc chloride in 2:1 molar ratio at room temperature. The grown crystal is up to the dimension of 45 × 23 × 18 mm³. Characterization of the crystals was made using single-crystal X-ray diffraction for obtaining unit cell parameters. Powder X-ray diffraction was recorded and the major peaks were indexed. Simultaneous thermogravimetric analysis and differential thermal analysis were carried out for the as grown crystals to determine the thermal stability of the crystal. The crystals were further characterized by UV-Vis-NIR transmission spectrum in the range of 200 to 1100 nm. Dielectric constant and dielectric loss measurements were carried out at different temperatures and frequencies. Mechanical studies were carried out on the as grown crystal.     

Performance test of Si PIN photodiode line scanner for thermal neutron detection

Thermal neutron imaging using Si PIN photodiode line scanner and Eu-doped LiCaAlF₆ crystal scintillator has been developed. The pixel dimensions of photodiode are 1.18 mm (width)×3.8 mm (length) with 0.4 mm gap and the module has 192 channels in linear array. The emission peaks of Eu-doped LiCaAlF₆ after thermal neutron excitation are placed at 370 and 590 nm, and the corresponding photon sensitivities of photodiode are 0.04 and 0.34 A/W, respectively. Polished scintillator blocks with a size of 1.18 mm (width)×3.8 mm (length)×5.0 mm (thickness) were wrapped by several layers of Teflon tapes as a reflector and optically coupled to the photodiodes by silicone grease. JRR-3 MUSASI beam line emitting 13.5 meV thermal neutrons with the flux of 8×10⁵ n/cm² s was used for the imaging test. As a subject for imaging, a Cd plate was moved at the speed of 50 mm/s perpendicular to the thermal neutron beam. Analog integration time was set to be 416.6 μs, then signals were converted by a delta-sigma A/D converter. After the image processing, we successfully obtained moving Cd plate image under thermal neutron irradiation using PIN photodiode line scanner coupled with Eu-doped LiCaAlF₆ scintillator.     

Transparent conductive titanium-doped indium oxide films prepared by a magnetic null discharge sputter source

Titanium-doped indium oxide (ITiO) films were prepared on soda-lime glass substrate using a magnetic null discharge (MND) sputter source. The ITiO thin films containing 10 wt.% Ti showed the minimum resistivity of ρ = 5.5 × 10⁻³ Ω cm. The optical transmittance increases from 70% at 450 nm to 80% at 700 nm in visible spectrum. Photoelectron peaks for In 3d, Ti 2p, O 1s and C 1s were detected for the ITiO film in the binding energy range of 0-1100 eV. The surface roughness of the sample showed a change from 10 nm to 50 nm. The ITiO film used for TCO layer of DSCs exhibited an energy conversion efficiency of about 3.8% at light intensity of 100 mW/cm².     

Charge transport properties of as-grown CZT by traveling heater method

In this present work we have grown Cd_0.9Zn_0.1Te doped with indium by the traveling heater method (THM) technique. Large 2 in diameter CZT ingots of more than 1 kg each were successfully grown by the THM technique in vertical configuration. In order to evaluate our as-grown CZT samples, charge transport characteristics were studied at and below room temperature. The key parameter investigated for as-grown CZT samples was the mobility-trapping time product and its temperature variation. Mobility-trapping time values as high as 9×10⁻³ cm²/V at 30 °C were measured for samples exhibiting resistivities in the 1-2×10¹⁰ Ω cm range. The as-grown samples showed moderately good resolution of 1.5-3.5% at 662 keV when fabricated. The variation of the internal electric field along the depth of the detector was studied for as-grown material to evaluate deformations inside the crystal due to the presence of residual stress or other defects.     

Room temperature deposition of ZnSe thin films by successive ionic layer adsorption and reaction (SILAR) method

The zinc selenide (ZnSe) thin films are deposited onto glass substrate using relatively simple and inexpensive successive ionic layer adsorption and reaction (SILAR) method. The films are deposited using zinc acetate sodium selenosulphate precursors. The concentration, pH, immersion and rinsing times and number of immersion cycles have been optimized to obtain good quality ZnSe thin films. The X-ray diffraction (XRD) study and scanning electron microscopy (SEM) studies reveals nanocrystalline nature alongwith some amorphous phase present in ZnSe thin films. Energy dispersive X-ray (EDAX) analysis shows that the films are Se deficient. From optical absorption data, the optical band gap ‘E_g’ for as-deposited thin film was found to be 2.8 eV and electrical resistivity in the order of 10⁷ Ω cm.     

A comparative study of EVA with and without thermal history for different lamination process parameters

In more than 80% of the worldwide photovoltaic (PV) modules, mostly very fragile and 200 μm thick, crystalline silicon solar cells are encapsulated into ethylene-vinyl acetate (EVA) foils, which bond the module components together, provide physical protection, electrical insulation and a barrier for moisture ingress. The understanding of what can happen with EVA during its transport, storage and lamination process is necessary to optimize the quality of the PV module for its long exposure to outdoor weather conditions. Achieving a proper cross-link density of over 70%, it is essential to overcome the cold flow of EVA and to make the module durable. In this work, the feasibility of the use of differential scanning calorimetry (DSC) compared with the solvent extraction (SE) method by toluene were evaluated in order to provide structural information on the EVA curing kinetics and the cross-link density. DSC tests were performed on a DTA DuPont1600 tester. The temperature range for the test was from −50 °C to 200 °C, with the heating rate of 10 °C/min, and the endothermic and exothermic peaks were evaluated. Toluene solvent extractions were performed on the same set of samples that were analyzed by DSC. The measured cross-link density shows a direct dependence on the pre-lamination conditions of EVA, which is in good agreement with the data obtained with the DSC method.     

Influence of Sb/As soak times on the structural and optical properties of GaAsSb/GaAs interfaces

The effects of Sb/As soak times, prior to growth of GaAsSb on GaAs were investigated by High Resolution X-Ray Diffraction (HRXRD) and photoluminescence (PL). Multiple quantum well samples with soak times of 0 s, 30 s and 60 s were grown at 500 °C with nominally identical Sb and As fluxes. HRXRD results show that a 30 s soak minimizes diffuse scattering seen around superlattice peaks in the reciprocal space maps, an effect attributed to corrugations in the GaAs-GaAsSb interface. An inferred band diagram calculated using a four band k.p model and modified taking into account the HRXRD results was used to explain PL spectra taken for each sample at 80 K. It is concluded that an optimum soak time exists for GaASb growth on GaAs, determined by the growth conditions.     

The equivalence of Tucker3 and Parafac models with two components

This study investigates similarities and differences between Tucker3 models with two components for each mode and Parafac models with two components. If the core array of the 2 × 2 × 2 Tucker3 model is of rank 2 the solutions contain exactly the same information, but they do not when the rank of the core array is three. Two illustrative applications show the effect the different core arrays have on the solutions and their interpretability.     

Development of amorphous carbon protective coatings on poly(vinyl)chloride

The great versatility of polymers has promoted their application in a series of ordinary situations. The development of specific devices from polymers, however, requires modifications to fit specific stipulations. In this work the surface properties of thin films grown onto polyvinylchloride (PVC) were investigated. Hydrogenated amorphous carbon films were deposited onto commercial PVC plates from acetylene and argon plasmas excited by radiofrequency (13.56 MHz, 70 W) power. The proportion of acetylene in the gas feed was varied against that of argon, keeping the total pressure constant at 2.5 Pa. Deposition time was 1800 s. Film elemental composition was analyzed by X-ray photoelectron spectroscopy, XPS. Water contact angle measurements were performed using the sessile drop technique. The root mean squared roughness was derived from 50 × 50 µm² surface topographic images, acquired by scanning probe microscopy. Nanoindentation and pin-on-disk techniques were employed on the determination of film hardness and sliding wear, respectively. Oxidation resistance was obtained through the etching rate of the samples in oxygen radiofrequency (1.3 Pa, 50 W) plasmas. From XPS analysis it was detected oxygen and nitrogen contamination in all the samples. It was also found that sp³/sp² ratio depends on the proportion of argon in the plasma. At lower argon concentrations, hardness, wear and oxidation resistances were all improved with respect to the uncoated PVC. In such conditions, the surface wettability is low indicating a moderate receptivity to water. This combination of properties, ascribed to a balance between the ion bombardment and deposition processes, is suitable for materials exposed to rigorous weathering conditions.     

Using fast atomic source and low-energy plasma ions for polymer surface modification

A systematic study was carried out to characterize the effects of argon atomic beam irradiation and low-energy argon ions in plasma for polystyrene (PS) surface modification. The PS samples were exposed to a 1.5 keV, argon atomic beam from a fast atomic source (FAS) at different exposure times. The low-energy (1.5 eV) argon plasma ions were achieved in a two-stage RF discharge and PS samples were exposed to plasma for different times and powers. The surface characterization of these atomic beam and plasma modified PS samples was carried out using X-ray photoelectron spectroscopy. For FAS, the results showed a rapid increase (from 0.01 to 0.18) in oxygen-to-carbon ratio (O/C) at the surface of PS with first 10 s exposure time while further increase in exposure time up to 500 s showed about 50% decrease in O/C. Therefore, first few seconds of atomic beam irradiation useful to increase the O/C at the PS surface whereas at higher irradiation time the surface etching may took places and it could have advantage in surface cleaning. A comparison of O/C with FAS and plasma ions showed FAS is more effective way to achieve oxygen incorporation at PS surface relatively to low-energy flux plasma ions.     

Enhanced characterization of ITO films deposited on PET by RF superimposed DC magnetron sputtering

Tin-doped indium oxide (ITO) films were deposited on polyethylene terephthalate substrates by RF superimposed DC magnetron sputtering using an ITO target composed of In₂O₃ (90 wt.%):SnO₂ (10 wt.%). The total sputtering power was maintained at 70 W and the power ratio of RF/(RF + DC) was varied from 0 to 100% in steps of 25%. The discharge voltage and deposition rate decreased with increasing RF/(RF + DC) power ratio. The ITO film deposited at a 50% RF portion of the total power showed the lowest resistivity (3.18 × 10^− 4 Ωcm), high transmittance (87.5%) and relatively good mechanical durability, which was evaluated using bending and scratch tests.     

Hot wire configuration for depositing device grade nano-crystalline silicon at high deposition rate

The University of Barcelona is developing a pilot-scale hot wire chemical vapor deposition (HW-CVD) set up for the deposition of nano-crystalline silicon (nc-Si:H) on 10 cm × 10 cm glass substrate at high deposition rate. The system manages 12 thin wires of 0.15-0.2 mm diameter in a very dense configuration. This permits depositing very uniform films, with inhomogeneities lower than 2.5%, at high deposition rate (1.5-3 nm/s), and maintaining the substrate temperature relatively low (250 °C). The wire configuration design, based on radicals’ diffusion simulation, is exposed and the predicted homogeneity is validated with optical transmission scanning measurements of the deposited samples. Different deposition series were carried out by varying the substrate temperature, the silane to hydrogen dilution and the deposition pressure. By means of Fourier transform infrared spectroscopy (FTIR), the evolution in time of the nc-Si:H vibrational modes was monitored. Particular importance has been given to the study of the material stability against post-deposition oxidation.     

Using response surface methodology to assess the effects of iron and spent mushroom substrate on arsenic phytotoxicity in lettuce (Lactuca sativa L.)

The effects of iron (Fe) and spent mushroom substrate (SMS) arsenic (As) phytotoxicity towards lettuce in artificial soils were investigated to separate the adverse soil parameters relating to As toxicity using a response surface methodology. SMS induced the root elongation of lettuce in both control and As-treated soils. However, in phytotoxicity test using a median effective concentration (EC₅₀) of As, Fe and the interaction between both parameters (Fe*SMS) significantly affected EC₅₀, which explained 71% and 23% of the response, respectively. The refined model was as follows: EC₅₀ of As (mg kg⁻¹) = 10.99 + 60.03 × Fe − 10.50 × Fe*SMS. The results confirmed that the soil parameters relating to the As mobility in soils were important factors affecting its toxicity. In conclusion, Fe significantly reduced the As phytotoxicity. However, although SMS enhanced the root elongation, SMS in As-treated soils decreased EC₅₀ of As on the root growth via its interaction with Fe. Despite the limitations of the artificial soils and range of parameters studied, the application of this statistical tool can be considered a powerful and efficient technique for interpretation and prediction of the complicated results caused by the interactions between many factors within the soil environments.     

Bioactive coating on a cobalt base alloy by heat treatment

A method to promote a bioactive surface on the cobalt base alloy ASTM F-75 was tested. A set of cylindrical samples was obtained using the investment casting technique and packed in a mixture composed of 70% β-tricalcium phosphate and 30% bioactive glass and then heat treated for 1 h at 1220 °C. To characterize the in vitro bioactivity, a set of heat treated metallic specimens was immersed in a simulated body fluid with an ionic concentration nearly equal to that of human blood plasma (SBF) for 7, 10 and 21 days and in a more concentrated solution (1.5 SBF). After heat treatment, fine agglomerates homogeneously distributed, containing Ca, P, O and Na were observed on the metallic surface. After immersion of the samples in simulated body fluids, a thicker layer identified as apatite was formed on the samples immersed in SBF for 21 days and on all samples immersed in 1.5 SBF.     

Proteomic profile analysis and biomarker discovery from mass spectra using independent component analysis combined with uncorrelated linear discriminant analysis

A strategy based on Independent Component Analysis (ICA) and Uncorrelated linear discriminant analysis (ULDA) was proposed for proteomic profile analysis and potential biomarker discovery from proteomic mass spectra of cancer and control samples. The method mainly includes 3 steps: (1) ICA decomposition for the mass spectra; (2) selection of discriminatory independent components (ICs) using nonparametric Mann-Whitney U-test; and (3) selection of special peaks (m/z locations) as potential biomarkers by executing of ULDA on a mass spectra data set which was reconstructed with the m/z locations that collected from the selected discriminatory ICs. A colorectal cancer data set and an ovarian cancer data set were analyzed with the proposed method. As results, 9 and 10 m/z locations were selected as potential biomarkers for the colorectal and ovarian cancer data set respectively. The classification results of ULDA using the selected potential biomarkers yielded better results than fisher discriminant analysis (FDA) and principal component analysis (PCA), and could distinguish the disease samples from healthy controls on the independent test sets with 100% of sensitivities and specificities for the colorectal cancer dataset and 100% of sensitivity and 96.77% of specificity for the ovarian cancer dataset.     

Novel thermoelectric materials based on boron-doped silicon microchannel plates

The thermoelectric properties of boron-doped silicon microchannel plates (MCPs) were investigated. The samples were prepared by photo-assisted electrochemical etching (PAECE). The Seebeck coefficient and electrical resistivity at room temperature (25 °C) were measured to determine the thermoelectric properties of the samples. In order to decrease the very high resistivity, boron doping was introduced and by modulating the doping time, a series of samples with different resistivity as well as Seebeck coefficient were obtained. Boron doping changed the electrical resistivity of the samples from 1.5 × 10⁵ Ω cm to 5.8 × 10⁻³ Ω cm, and the absolute Seebeck coefficient deteriorated relatively slightly from 674 μV/K to 159 μV/K. According to the Seebeck coefficient and electrical conductivity, the power factor was calculated and a peak value of 4.7 × 10⁻¹ mW m⁻¹ K⁻² was obtained. The results indicate that silicon MCPs doped with boron are promising silicon-based thermoelectric materials.     

Spectroscopic, thermal and mechanical behavior of allylthiourea cadmium chloride single crystals

Allylthiourea cadmium chloride, a promising non-linear optical material was grown from aqueous solution by slow evaporation technique. Single crystal X-ray diffraction studies reveal that the crystal is trigonal structure with R3C space group. The spectroscopic properties were investigated by recording the Fourier transform infrared and optical absorption spectra. The dielectric studies of the sample were carried out at varying temperatures in the frequency range from 50 Hz to 5 MHz. The thermal properties were studied using thermogravimetric analyses and photopyroelectric technique. It is evident from the thermal studies that the decomposition of the crystal begins around 200 °C. The microhardness test conducted on the grown crystal suggests that the crystal has a relatively high mechanical strength. The second harmonic generation efficiency of the crystal was studied and found to be nearly 1.5 times that of urea.