High Figure Of Merit Value Research Articles

Influence of (Ar + O2) atmosphere and CdCl2 coating heat treatment on physical properties of CdS thin film for solar cell applications

Cadmium sulphide (CdS) thin films have been grown on corning glass substrate by thermal evaporation technique under base pressure 2 × 105 mbar. In this study we investigate the influence of Cadmium chloride (CdCl2) heat treatment and argon and oxygen (Ar + O2) annealing on the structural, morphological optical and electrical properties of CdS thin films to achieve high quality thin films for solar cells applications. X-ray diffraction (XRD), Field Emission scanning electron microscope (FE-SEM) and UV–Vis-NIR spectrophotometer were used to confirm and investigate the different physical properties of CdS films. The quality of CdS thin films crystallinity including the average grain size (Davg), the average lattice strain (εls) and the dislocation density (ρD) were extracted via XRD line broadening analysis. XRD analysis revealed that the samples are polycrystalline in nature with a mixed (hexagonal + cubic) structure and the crystallinity of the films increases with both (Ar + O2) annealing and CdCl2 heat treatment. After (Ar + O2) annealing and CdCl2 heat treatment processes the mean values of the grain size indicating the grain growth of CdS films. The surface morphology of the CdS films was examined by (FE-SEM) analysis; which confirmed the nano-crystalline nature of the CdS films with uniform coverage of the substrate surface; The optical properties of as-deposited, (Ar + O2) annealed and CdCl2 treated CdS films were discussed in detail. The optical energy gap was calculated using Tauc plot extrapolation. It was found to be increased from 2.43 eV for as-deposited film to 2.45 for CdCl2 treated CdS film. Swanepoel method was employed to estimate the thicknesses and extract the refractive index of the CdS films. The Room temperature resistivity decreased from 13.4 Ω cm for as-deposited CdS film to 2 and 0.8 Ω cm for (Ar + O2) annealed and CdCl2 treated CdS films respectively. The CdCl2 treated CdS film has the highest figure of merit value of 29 × 10−4 Ω−1. The obtained results confirm that the CdCl2 heat treatment process in (Ar + O2) atmosphere can enhance the physical properties of CdS thin films as a promising window layer or buffer layer material for CdS/CdTe and Cu(In,Ga)Se2 solar cells.

Room Temperature Deposited Transparent Conducting InZnO:Ga thin films by Non-Reactive RF-Magnetron Sputtering

Transparent-conducting InZnO:Ga (IZO:Ga) thin films have been developed on glass substrate at room temperature (300K) by nonreactive RF-Magnetron sputtering using sintered ceramic disc of InZnO:Ga target (In-10 wt%, Ga -3wt% and Zn -87wt%). The novelty of very thin IZO:Ga films are low resistivity (1.5×10−3Ω.cm) and low sheet resistance (20 Ω/□) with average optical transmittance 86%, large Haze factor (>70%) and high figure of merit value (1.1×1018) respectively. RF-sputtered IZO:Ga films shows amorphous nature, smooth and crack-free surface morphology and topography with predominant metallic phase. Heat treated samples becomes crystalline, topography becomes more aligned (U-type) and surface roughness increases.

The relationship between cancer detection in mammography and image quality measurements

PurposeTo investigate the relationship between image quality measurements and the clinical performance of digital mammographic systems. MethodsMammograms containing subtle malignant non-calcification lesions and simulated malignant calcification clusters were adapted to appear as if acquired by four types of detector. Observers searched for suspicious lesions and gave these a malignancy score. Analysis was undertaken using jackknife alternative free-response receiver operating characteristics weighted figure of merit (FoM). Images of a CDMAM contrast-detail phantom were adapted to appear as if acquired using the same four detectors as the clinical images. The resultant threshold gold thicknesses were compared to the FoMs using a linear regression model and an F-test was used to find if the gradient of the relationship was significantly non-zero. ResultsThe detectors with the best image quality measurement also had the highest FoM values. The gradient of the inverse relationship between FoMs and threshold gold thickness for the 0.25mm diameter disk was significantly different from zero for calcification clusters (p=0.027), but not for non-calcification lesions (p=0.11). Systems performing just above the minimum image quality level set in the European Guidelines for Quality Assurance in Breast Cancer Screening and Diagnosis resulted in reduced cancer detection rates compared to systems performing at the achievable level. ConclusionsThe clinical effectiveness of mammography for the task of detecting calcification clusters was found to be linked to image quality assessment using the CDMAM phantom. The European Guidelines should be reviewed as the current minimum image quality standards may be too low.

The structural and electro-optical characteristics of AZO/Cr:Cu/AZO transparent conductive film

A novel triple-layered transparent conductive film, AZO/Cr:Cu/AZO (ACCA), was presented in the paper. The structural and electro-optical properties of the ACCA film were discussed. The thickness of the middle metal layer was constant and those of the AZO layers were varied. The ACCA film shows an obvious ZnO (002) c-axis preferential growth. No diffraction peaks related to Cr and Cu were observed through x-ray diffraction analysis. The middle Cr:Cu layer showed a thickness of 8.16nm with a continuous and amorphous structure by the observation of a high-resolution transmission electron microscopy (HR-TEM). For the electro-optical characteristic, a best figure of merit (FOM) value of 3.54×10−3Ω−1 with a corresponding transmittance of 85% was obtained at the thickness of 116nm of ACCA film. The high FOM value of the film is due to the improvement of conductivity and small sacrifices of transparency.

High ZT in p-Type (PbTe)1–2x(PbSe)x(PbS)x Thermoelectric Materials

Lead chalcogenide thermoelectric systems have been shown to reach record high figure of merit values via modification of the band structure to increase the power factor or via nanostructuring to reduce the thermal conductivity. Recently, (PbTe)1-x(PbSe)x was reported to reach high power factors via a delayed onset of interband crossing. Conversely, the (PbTe)1-x(PbS)x was reported to achieve low thermal conductivities arising from extensive nanostructuring. Here we report the thermoelectric properties of the pseudoternary 2% Na-doped (PbTe)1-2x(PbSe)x(PbS)x system. The (PbTe)1-2x(PbSe)x(PbS)x system is an excellent platform to study phase competition between entropically driven atomic mixing (solid solution behavior) and enthalpy-driven phase separation. We observe that the thermoelectric properties of the PbTe-PbSe-PbS 2% Na doped are superior to those of 2% Na-doped PbTe-PbSe and PbTe-PbS, respectively, achieving a ZT ≈2.0 at 800 K. The material exhibits an increased the power factor by virtue of valence band modification combined with a very reduced lattice thermal conductivity deriving from alloy scattering and point defects. The presence of sulfide ions in the rock-salt structure alters the band structure and creates a plateau in the electrical conductivity and thermopower from 600 to 800 K giving a power factor of 27 μW/cmK(2). The very low total thermal conductivity values of 1.1 W/m·K of the x = 0.07 composition is accounted for essentially by phonon scattering from solid solution defects rather than the assistance of endotaxial nanostructures.

Sputtering pressure dependent composition and dielectric properties in Bi1.5MgNb1.5O7 thin films deposited at room temperature by RF magnetron sputtering

Bismuth magnesium niobate (Bi1.5MgNb1.5O7, BMN) thin films with cubic pyrochlore phase and a highly [111] orientation were deposited by radio frequency magnetron sputtering at different pressures and crystallized at 700 °C in oxygen atmosphere. For low temperature deposition, the sputtering pressure has significant influence on the surface roughness and composition of the BMN thin film. The film deposited at 4.0 Pa has the closest stoichiometric composition and a lowest surface roughness, which exhibits large dielectric constant and low dielectric loss (158 and 0.0046 at 1 MHz, respectively). The dielectric tunability and the figure of merit (FOM) value are 16.4 % and 36 at a dc bias field of 0.8 MV/cm. The relative large dielectric constant, low dielectric loss, and high FOM value suggest that BMN thin films have potential application for tunable microwave device.

The Effect of Microstructure on the Thermoelectric Properties of Polycrystalline Higher Manganese Silicides

In order to obtain single-phase higher manganese silicides (HMS) and investigate the effect of sintering conditions on the thermoelectric properties of a HMS system, HMS compounds were synthesized using a vacuum induction melting method and sintered using spark plasma sintering (SPS) and hot pressing methods. Single-phase HMS with a small amount of second phases was obtained in all of the HMS samples produced. Changes in the electrical conductivity and Seebeck coefficient of the HMS were observed when the sintering temperature was changed, which can be attributed to the presence of the second phases. Similar changes of thermoelectric properties were observed in both the SPS and hot-pressed samples. However, the electrical conductivity and Seebeck coefficient of HMS samples (SPS-HMS) were higher than those of the hot-pressed samples, which can be attributed to SPS's shorter holding time and its ability to control the diffusion rate. The SPS-HMS sample sintered at 1123 K (1123 K SPS-HMS) had a higher figure of merit than any other sample although the sample had a lower power factor. The high value of the figure of merit of the sample can be attributed to its low thermal conductivity. The highest figure of merit value of 0.41 was measured at 850 K in the 1123 K SPS-HMS, which is comparable to the results reported earlier. The results of the present study can be used to optimize the fabrication process of HMS thermoelectric materials.

Enhanced mobility in visible-to-near infrared transparent Al-doped ZnO films

A novel technique of depositing multilayered films by introducing metal Zn layers in between Al-doped ZnO (AZO) films by using RF and DC magnetron sputtering has been proposed to enhance the electrical conductivity through mobility enhancement. The multilayered Zn/AZO films when annealed at 823K, not only maintains high transparency in the visible-to-near infrared region but also shows very high mobility of 46cm2/Vs which is thirteen times more than that of the AZO film and resistivity as low as 2.43×10−4Ω-cm. The highest figure of merit value is 8.6×10−2Ω−1 which is more than double to that of the value of AZO film suggesting that these Zn/AZO films are very promising for solar cell applications.

Phase separation as a key to a thermoelectric high efficiency

This work elucidates the possible reasons for the outstanding, but never reproduced thermoelectric properties of the doped Ti(0.5)Zr(0.25)Hf(0.25)NiSn Heusler compounds. The structural investigations done via synchrotron X-ray diffraction measurements and scanning electron microscope measurements, which clearly show that the microstructure consists of three temperature stable C1(b) phases with possible semi-coherent interfaces, are presented. The exceptional thermoelectric properties are due to this intrinsic phase separation. It is possible to reproduce the high Figure of Merit values with ZT = 1.2 at 830 K. Furthermore, the influence of doping different elements on the Sn position in this Heusler material system is investigated.

Effect of spark plasma sintering temperature on thermoelectric properties of Bi2S3 polycrystal

Abstract

The dielectric and tunable properties of Mn doped (Ba0.6Sr0.4)0.925K0.075TiO3 thin films fabricated by sol-gel method

( Ba 0.6 Sr 0.4 ) 92.5 % K 7.5 % TiO 3 (BSKT) thin films doped by Mn from 0 to 6 mol % were fabricated by the sol-gel method on a Pt/TiO2/SiO2/Si substrate. The structure and surface morphology of Mn-doped BSKT thin films were investigated as a function of Mn concentration by x-ray diffraction and scanning electron microscopy. The dielectric measurements were conducted on metal-insulator-metal capacitors at the frequency from 100 Hz to 1 MHz at room temperature. It was found that the Mn concentration in Mn doped BSKT thin films has a strong influence on material properties including surface morphology and dielectric and tunable properties. Increasing Mn content leads to simultaneous decreasing of surface roughness, dielectric constant, and tunability of Mn doped BSKT films. However the dielectric loss of Mn doped BSKT decreases first and then increases with the increase in Mn dopant. The effects of Mn doping on the microstructure and dielectric and tunable properties of Mn doped BSKT thin films were analyzed. (Ba0.6Sr0.4)92.5%K7.5%TiO3 thin films show the highest dielectric constant and tunability to be 1040 and 73.6%, respectively. However, the 1 mol % Mn doped BSKT thin films with the smallest dielectric loss and upper tunability are the best choice for tunable device applications for its highest figure of merit value of 37.5.

Optimization of exposure parameters in full field digital mammography

Optimization of exposure parameters (target, filter, and kVp) in digital mammography necessitates maximization of the image signal-to-noise ratio (SNR), while simultaneously minimizing patient dose. The goal of this study is to compare, for each of the major commercially available full field digital mammography (FFDM) systems, the impact of the selection of technique factors on image SNR and radiation dose for a range of breast thickness and tissue types. This phantom study is an update of a previous investigation and includes measurements on recent versions of two of the FFDM systems discussed in that article, as well as on three FFDM systems not available at that time. The five commercial FFDM systems tested, the Senographe 2000D from GE Healthcare, the Mammomat Novation DR from Siemens, the Selenia from Hologic, the Fischer Senoscan, and Fuji's 5000MA used with a Lorad M-IV mammography unit, are located at five different university test sites. Performance was assessed using all available x-ray target and filter combinations and nine different phantom types (three compressed thicknesses and three tissue composition types). Each phantom type was also imaged using the automatic exposure control (AEC) of each system to identify the exposure parameters used under automated image acquisition. The figure of merit (FOM) used to compare technique factors is the ratio of the square of the image SNR to the mean glandular dose. The results show that, for a given target/filter combination, in general FOM is a slowly changing function of kVp, with stronger dependence on the choice of target/filter combination. In all cases the FOM was a decreasing function of kVp at the top of the available range of kVp settings, indicating that higher tube voltages would produce no further performance improvement. For a given phantom type, the exposure parameter set resulting in the highest FOM value was system specific, depending on both the set of available target/filter combinations, and on the receptor type. In most cases, the AECs of the FFDM systems successfully identified exposure parameters resulting in FOM values near the maximum ones, however, there were several examples where AEC performance could be improved.

TU‐B‐M100J‐01: Optimizing Mammography Image Quality and Dose: X‐Ray Spectrum and Exposure Parameter Selection

Optimization of exposure parameters (target, filter, and kVp) in digital mammography necessitates maximization of the image signal‐to‐noise ratio (SNR), while simultaneously minimizing patient dose. The goal of this talk is to compare, for each of the major commercially available full field mammography (FFDM) systems, the impact of the selection of technique factors on image SNR and radiation dose for a range of breast thickness and tissue types. The comparison will be based on the results of a multi‐center phantom study. The five commercial FFDM systems tested, the Senographe 2000D from GE Healthcare, the Mammomat Novation from Siemens, and the Selenia from Hologic, the Fischer Senoscan, and Fuji's 5000MA used with a Lorad M‐IV mammography unit, are located at five different university test sites. Performance was assessed using all available x‐ray target and filter combinations and nine different phantom types (three compressed thicknesses, and three tissue composition types). Each phantom type was also imaged using the automatic exposure control (AEC) of each system to identify the exposure parameters used under automated image acquisition. The figure of merit (FOM) used to compare technique factors is the ratio of the square of the image SNR to the mean glandular dose (MGD). The results show that, for a given target/filter combination, in general FOM is a slowly changing function of kVp, with stronger dependence on the choice of target/filter combination. In all cases the FOM was a decreasing function of kVp at the top of the available range of kVp settings, indicating that higher tube voltages would produce no further performance improvement. For a given phantom type, the exposure parameter set resulting in the highest FOM value was system‐specific, depending on both the set of available target/filter combinations, and on the receptor type. Noise performance differed noticeably among the FFDM systems and played an important role in determining relative FOM values. In most cases, the AECs of the FFDM systems successfully identified exposure parameters resulting in FOM values near the maximum ones, however there were several examples where AEC performance could be improved.Educational Objectives:1. become familiar with the effect of changing kVp, target material, and filtration on the mean glandular dose for a variety of breast.2. become familiar with the effect of changing kVp, target material, and filtration on image signal and noise for specific commercial FFDM systems.3. learn how the exposure technique factors selected for a variety of breast types by the AECs of current FFDM systems compare with the technique factors resulting in optimal FOM values.

Radiobiological quality of high dose rate interstitial brachytherapy treatments of carcinoma of the cervix

Summary Aim The aim of the present study was to apply the Figure of Merit (FOM) concept to High Dose Rate (HDR) interstitial brachytherapy treatments delivered for carcinoma of the cervix at the Kidwai Memorial Institute of Oncology, Bangalore, in order to evaluate the radiobiological quality of the implants. Materials/Methods Twenty seven patients received external beam radiotherapy, as 50 Gy in 25 fractions over five weeks, followed by interstitial brachytherapy by the HDR template technique on a Gammamed HDR machine. Doses were delivered 5mm from the periphery of the implant along the transverse plane. Points in the bladder and rectum, receiving the maximum dose rate, were used for the evaluation of total dose received by these critical organs. BED and FOM values were evaluated for all patients. Results Two patients had a rectal FOM value greater than 10. A FOM bladder value of higher than 10 was observed in six patients. Only in one patient were FOM values for both the rectum and bladder found to be above 10. The relationship between FOM values for the rectum and the bladder indicated that most FOM values were clustered near the initial portion of the scattergram obtained. For one patient the rectal FOM value was above 10, while the FOM for the bladder was significantly smaller. In another patient, having a high FOM value for the bladder, the FOM value for the rectum was also above the critical value of 10. Conclusions Good physical optimization can lead to good radiobiological optimization, as observed in our study. Radiobiology can not improve a bad quality implant. HDR interstitial brachytherapy, which gives better geometrical sparing for critical normal organs such as the rectum and bladder, should be the treatment of choice for patients with carcinoma of the cervix. In optimizing treatment for a patient, the maximizing of FOM should be supplemented by a comparison of reference BED values and new treatments for the tumour, rectum and bladder.

Structural and dielectric properties of Ba(ZrxTi1−x)O3 thin films prepared by the sol–gel process

The Ba(ZrxTi1−x)O3 (BZT) thin films were prepared by deposition of relevant materials on LaNiO3-coated silicon substrates by the sol–gel process. The films thus prepared show a (100) preferred orientation in structure and vary with zirconium content. With the addition of Zr, the grain sizes of films were found to decrease, whereas their microstructure became dense. The changes in the films' grain sizes and microstructure were attributed to the addition of Zr to the BaTiO3 lattice. Dielectric constant measurements revealed that the thin films show a relaxor behaviour and have a diffuse phase transition characteristic when x is 0.35. The hysteresis loops of the dielectric properties of films measured at room temperature were considered to be the result of the polarization state of the domains in these films in both the ferroelectric or paraelectric state. This leads to a distribution of Curie temperatures. The highest figure of merit value, K, was found for the BZT thin film with a very low dielectric constant. This indicates that BZT films have the potential to be used as microwave tunable devices with superior performance.

Distribution of tritiated cyclandelate (3,5,5-Trimethylcyclohexyl mandelate) — A vasoactive drug: Preliminary observations by liquid scintillation spectrometry

Tritiated cyclandelate (a vasoactive drug) uptake, distribution and elimination by organ and fluid specimens of the rat following intragastric and intraperitoneal administrations, was detected and quantitated by the method of liquid scintillation spectrometry. The best results achievable without the use of a Packard Tri-carb Sample Oxidizer or a Beckman Biological Material Oxidizer considering tissue dissolubility, reduced quenching, phase separation and chemiluminescence and increased efficiency, were obtained with the procedure described in this study for the preparation of biological specimens for liquid scintillation counting. The effective half life values of tritiated cyclandelate in various biological specimens range from 2·8 to 4·l days. The majority of specimens showed maximal uptake at 1 hr while brain, diaphragm, stomach and vein showed maximal levels at 24 hr. Afterwards, the levels gradually declined in a non-linear manner over the period of 28 days when levels were negligible. Organ/plasma ratios were greatest in vein, brain, diaphragm, stomach and kidney. All organ/plasma ratios remained essentially unchanged during the first week except brain which showed diminishing ratios between 1 and 7 days before assuming rather constant ratios for the remaining 21 days. The functional significance of this observation in brain tissue is presently not understood but is under consideration. Tritiated cyclandelate levels were greater in all specimens at each time interval in rats that received multiple (five daily) doses compared with those that received a single dose. Execution of the plan to study the pharmacokinetics of tritiated cyclandelate in humans is greatly facilitated by the high figure of merit values of urine, plasma and whole blood, specimens which are obtainable with minimal inconvenience for subject under study.