Direct-Write Copper via Vacuum Cold Spray: Comparing Process Parameters, Line Profiles and Electrical Resistivity

We use cosmological constraints from current data sets and a figure of merit\n(FoM) approach to probe any deviations from general relativity (GR) at\ncosmological scales. The FoM approach is used to study the constraining power\nof various combinations of data sets on modified gravity (MG) parameters. We\nuse recently refined HST-COSMOS weak-lensing tomography data, ISW-galaxy cross\ncorrelations from 2MASS and SDSS LRG surveys, matter power spectrum from\nSDSS-DR7 (MPK), WMAP7 temperature and polarization spectra, BAO from 2DF and\nSDSS-DR7, and Union2 compilation of supernovae, in addition to other bounds\nfrom H_0 measurements and BBN. We use 3 parametrizations of MG parameters that\nenter the perturbed field equations. In order to allow for variations with\nredshift and scale, the first 2 parametrizations use recently suggested\nfunctional forms while the third is based on binning methods. Using the first\nparametrization, we find that CMB + ISW + WL provides the strongest constraints\non MG parameters followed by CMB+WL or CMB+MPK+ISW. Using the second\nparametrization or binning methods, CMB+MPK+ISW consistently provides some of\nthe strongest constraints. This shows that the constraints are parametrization\ndependent. We find that adding up current data sets does not improve\nconsistently uncertainties on MG parameters due to tensions between best-fit MG\nparameters preferred by different data sets. Furthermore, some functional forms\nimposed by the parametrizations can lead to an exacerbation of these tensions.\nNext, unlike some studies that used the CFHTLS lensing data, we do not find any\ndeviation from GR using the refined HST-COSMOS data, confirming previous claims\nin those studies that their result may have been due to some systematic effect.\nFinally, we find in all cases that the values corresponding to GR are within\nthe 95% confidence level contours for all data set combinations. (abridged)\n

SiC-MoSi2 composite powders was prepared by wet milling with MoSi2 powders and SiC loose grinding ball in alcohol solution. Vacuum cold spray (VCS) process was used to deposit SiC-MoSi2 electric conducting composite coatings. The microstructure of the VCS SiC-MoSi2 composite coatings were characterized by scanning electron microscopy. The electrical resistance of the coatings was measured using a four-point probe method. The effects of the deposition parameters on the electrical resistivity of the composite coatings were investigated. The electrical properties of the coatings at elevated temperatures in air and Ar gas atmospheres were also explored. The results show that the electrical resistivity of SiC-MoSi2 coatings decreases with increasing He gas flow rates ranged from 3 to 6 L/min. The electrical resistivity increases with the increase in heat treatment temperature due to “pesting” behavior of MoSi2. The electric conductive property of the VCS SiC-MoSi2 coating is significantly improved after heat treatment at 1000 °C for 3 h in Ar protective atmosphere without oxidation. A minimum resistivity of the heat treated coating is 0.16 Ω · cm.

A new test technique and apparatus have been developed for measuring the thermoelectric (TE) performance of the quantum well (QW) thin films. Innovative, nanotechnology Si/SiGe QW TE thin film materials have been developed that appear to demonstrate significantly higher Seebeck coefficients and lower electrical resistivities that show the power factor, Seebeck coefficient squared divided by resistivity, to be many times higher than for the state-of-the-art TE materials such as Bi2Te3, PbTe, TAGS or SiGe bulk materials. The power factor values were derived from QW films deposited on very electrically resistive Si substrates. Since the electrical resistance of the Si substrate is so high (> 100 times the QW film sample resistance) it acts like an insulator and the Seebeck and resistivity values that are measured are essentially those of the QW films. The measurement of thermal conductivity of QW films to obtain efficiency and the Figure of Merit, ZT, is much more difficult to measure and spurred this new experimental approach. This test was designed to determine if the QW materials are significantly better in ZT and efficiency than state-of-the-art TE materials such as Bi2Te3. As with the Seebeck and resistivity measurements, the presence of the Si substrate complicates the performance analysis. This test setup was designed to minimize the influence of the substrate. The technique developed allows the N or P sample to be measured as a thermoelectric couple with a copper wire as the other leg. During the test, the electrical output of the test sample and the imposed temperature difference are recorded simultaneously. The measured temperature difference, along with measured electrical properties at the steady-state conditions, is used to calculate the conversion efficiency by two different methods. Three separate QW samples were tested in the new test apparatus. A bulk Bi2Te3 sample was also tested to compare the QW performance with a state-of-the-art bulk TE material. From the experimental data, it was found that the QW samples exhibited conversion efficiencies which were approximately three times higher than the efficiency of the bulk Bi2Te3 material. Also, the experimentally measured properties of the Bi2Te3 sample were in good agreement with the published properties of the material, thus providing additional confirmation of this new test technique. Another confirmation of a higher ZT is that maximum efficiency and maximum power peaks exist at considerably different loads, whereas these peaks both occur near matched loads for Bi2Te3 alloys. The new test apparatus has been used effectively to measure the power factor of the QW thin films deposited on silicon substrates, and this power factor is significantly higher than for the state-of-the-art bulk TE materials.

Evaluating electrolyte additives for lithium-ion cells: A new Figure of Merit approach

NTO/Ag/NTO multilayer transparent conducting electrodes for photovoltaic applications tuned by low energy ion implantation

Electrical and mechanical properties of nano-structured TiN coatings deposited by vacuum cold spray

TiN coatings on Al2O3 substrates were fabricated by vacuum cold spray (VCS) process using ultrafine starting ceramic powders of 20 nm in size at room temperature (RT). Microstructure analysis of the samples was carried out by scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. Sheet resistance of the VCS TiN coatings was measured with a four-point probe. The effects of microstructure on the electrical properties of the coatings were investigated. It was found that the sheet resistance and electrical resistivity of TiN coatings were significantly associating with the spray distance, nozzle traversal speed, and deposition chamber pressure. A minimum sheet resistance of 127 Ω was achieved. The microstructural changes can be correlated to the electrical resistivity of TiN coatings.

Sub-micro-structured titanium nitrides (TiN) coatings on Al2O3 substrates were fabricated by vacuum cold spray (VCS) process using ceramic powders, which were ball-milled at room temperature. The microstructure features and crystal structures of the VCS TiN coatings were analyzed by scanning electron microscopy and X-ray diffraction. The adhesion between the coating and the substrate was evaluated with a scratch tester. The sheet resistance of the VCS TiN coatings was measured by using a four-point probe method. The effects of nozzle traverse speed on the microstructure, adhesion to substrate and electrical properties of the coatings were investigated. It was found that the adhesion improves greatly with the nozzle traverse speed increasing from 5 to 15mm/s, and the electrical resistivity levels of the coatings is decreased significantly. The resistivity of sub-micron-structured TiN coatings is substantially lower than those of nano-structured ones fabricated by the same VCS process. And a minimum resistivity of 1.16×10-4 Ω·m is achieved.

Vacuum cold spraying (VCS) has emerged as an environmentally sustainable method for fabricating ceramic and metal films. A high particle impact velocity is a critical factor in the deposition of metal particles during the VCS process, which can be significantly enhanced through gas preheating. This study employs Computational Fluid Dynamics (CFD) simulations to investigate the substantial impact of gas preheating temperature on particle impact velocity and temperature. Elevating the gas temperature leads to higher particle impact velocity, resulting in severe deformation and the formation of dense copper films. The experimental results indicate improvements in both film compactness and electrical properties with gas preheating. Remarkably, the electrical resistivity of the copper film deposited at a gas preheating temperature of 350 °C was measured at 4.4 × 10−8 Ω·m. This study also examines the evolution of cone-shaped pits on the surface of copper films prepared on rough substrates. VCS demonstrates a self-adaptive repair mechanism when depositing metal films onto rough ceramic substrates, making it a promising method for ceramic surface metallization.

The impact of phantom size and shape in brachytherapy dosimetry was assessed using Monte Carlo methods in liquid water for and point sources. This is needed since differences in published dosimetry data, both measurements and simulations, employ a variety of phantom sizes and shapes which can cause dose differences exceeding 30% near the phantom periphery. Spheres of radius, , were examined to determine the equivalent spherical phantom size to a variety of cylinder and cube sizes, and , respectively. These sizes ranged from . The equivalent for a given size cylinder or cube was determined using a figure of merit (FOM) function to minimize differences between radial dose functions, . Using the FOM approach, a linear fit was obtained for the equivalent for a given size cylinder or cube. The equivalent phantom for a cylinder, of diameter and length , is a sphere of in radius and the equivalent phantom for a cube of on each side is a sphere of 17.5 in radius. When normalizing all results to for comparisons of phantom shape, the absolute dose rates were equivalent within 0.1% for for both and . Correlation factors to permit comparisons of unbounded data for in 20 published datasets resulted in agreement generally within 2%. Residual differences with four datasets were attributed to methodological uncertainties in the published references.

Effect of composition and deposition temperature on the characteristics of Ga doped ZnO thin films

Copper-graphite composites were made by a powder metallurgical method. Two starting graphite powders, either with or without copper coating, were each mixed individually with copper metal powder in a conical flask using a mechanical stirrer at 3600 rev min−1 for a period of 6 min. The method of copper coating graphite particles is described. The copper-graphite powder mixture was of nominal composition 8 wt-% graphite. Small cylindrical specimens of 8mm diameter and 12mm length were obtained by die compaction using a unidirectional hydraulic press at ambient temperature over a pressure range of 400-1200 MPa. For comparison, parallel specimens made of pure copper powders were consolidated and pressed under identical conditions. In this investigation, an attempt has been made to study the particle properties and behaviour which influence the consolidation of mixes of copper and graphite (coated or uncoated) powders. The green density values of compacts at various pressures are reported. It was found that the Konopicky-Shapiro equation can be applied to the compaction of copper-graphite powder mixes. When sintering at 1000°C, it was found that copper coated graphite compacts were fully sintered in a shorter time than uncoated compacts. The sintered specimens were mirror polished using a standard technique before being examined metallographically. Copper coated graphite composites possessed high relative density and low electrical resistivity very close to the corresponding values of pure copper, however uncoated graphite composites showed lower relative density and higher electrical resistivity values. Compression measurements showed that the yield and ultimate strengths of coated graphite composites were much higher than those of uncoated specimens. PM/0745

Enhancement of thermoelectric figure of merit by doping Dy in La 0.1Sr 0.9TiO 3 ceramic

Various Figures of Merits (FoMs) are used in order to evaluate the quality of x-ray images. A new Figure of Merit (FoM) is presented, which is based on analysis of data extracted from line profiles within the image. This FoM is referred as Line Contrast (LC). In order to evaluate its performance, the proposed FoM along with Contrast to Noise Ratio (CNR) and Contrast Michelson are applied in simulated Brain CT images and the resulting FoM values are compared. Brain CT images are created using the XRAYImagingSimulator, an in-house developed software platform for x-ray imaging simulation. A 3D brain phantom especially modified for x-ray imaging that contains volumes of gray, white, skull and cerebrospinal fluid was used. Presented Dual Energy CT images were produced with the low/high energy combination of 100/110 keV monochromatic beams. All images were evaluated using CNR, Contrast Michelson and LC FoM, both with and without the simulated presence of noise. Initial results from the application of FoMs show that LC comes into full accordance with visual assessment and that it overpasses the traditionally used CNR and Contrast Michelson. Initial results are presented here, while further studies on the evaluation of the proposed FoM are in progress.

The thermoelectric properties of magnesium silicide (Mg2Si) samples prepared by use of an atmospheric plasma spray (APS) were compared with those of samples prepared from the same feedstock powder by use of the conventional hot-pressing method. The characterization performed included measurement of thermal conductivity, electrical conductivity, Seebeck coefficient, and figure of merit, ZT. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDX) were used to assess how phase and microstructure affected the thermoelectric properties of the samples. Hall effect measurements furnished carrier concentration, and measurement of Hall mobility provided further insight into electrical conductivity and Seebeck coefficient. Low temperature and high velocity APS using an internal-powder distribution system achieved a phase of composition similar to that of the feedstock powder. Thermal spraying was demonstrated in this work to be an effective means of reducing the thermal conductivity of Mg2Si; this may be because of pores and cracks in the sprayed sample. Vacuum-annealed APS samples were found to have very high Seebeck coefficients. To further improve the figure of merit, carrier concentration must be adjusted and carrier mobility must be enhanced.