Oxygen Contamination Research Articles

Electrical characteristics of amorphous Si:H/crystalline Si0.3Ge0.7 heterojunction solar cells grown on compositionally graded buffer layers

We examined the influence of the processing temperature on hydrogenated amorphous Si/crystalline Si0.3Ge0.7 heterojunction solar cells with a bandgap of 1.0eV, which were grown on Si(001) by solid-source molecular beam epitaxy. Stepwise, compositionally graded buffer Si1−xGex layers were applied to prepare Si0.3Ge0.7 films with low dislocation density. We studied the influence of the annealing temperature applied at the buffer layer on the diode characteristics. The diode factor was minimized to 1.45 at 800°C, and the saturation current density monotonically decreased from 7.5×10−4A/cm2 for an annealing temperature of 650°C to 5.0×10−5A/cm2 for that of 900°C, as a result of the promotion of dislocation annihilation. Consequently, the Si0.3Ge0.7 heterojunction solar cell showed a maximum conversion efficiency of 1.50% when the annealing temperature was 850°C. We also studied the influence of the growth temperature of the p-Si0.3Ge0.7 active layer (absorber) on the cell performance. The short circuit current density increased from 16.03mA/cm2 for 520°C to 20.95mA/cm2 for 600°C. This result corresponded to an improvement of quantum efficiency response in the longer wavelength region due to the reduction of crystal defects caused by oxygen contamination. However, the Si0.3Ge0.7 active layer processed at a higher temperature showed an accumulation of threading dislocations and roughening of the surface, resulting in the degradation of both the open circuit voltage and the fill factor.

Rare-earth free p-type filled skutterudites: Mechanisms for low thermal conductivity and effects of Fe/Co ratio on the band structure and charge transport

A key driver of cost for a thermoelectric generator is the thermoelectric materials themselves, and the heavy reliance on rare earth (RE) elements as fillers, particularly for p-type formulations, represents a strategic risk. In the present study, we have investigated fully filled p-type skutterudites with nominal compositions CaFexCo4−xSb12 (2⩽x⩽3.5) using both experimental and theoretical methods. High purity samples were successfully synthesized using a combined melt-spinning (MS) and spark plasma sintering (SPS) technique. Structural analysis confirmed phase-pure samples with high filling fraction (>90%), homogeneous filler and transition metal distribution, and exceptionally low levels of oxygen contamination. Electrical and thermal transport property measurements revealed large power factors and unexpectedly low thermal conductivities. Electronic band structure calculations found a rapid increase in the density of states at the Fermi level with increasing Fe content. The large power factors observed in this system are attributable to this effect. Maximum zT of 0.9 was achieved in CaFe3CoSb12 at 773K. To understand the low lattice thermal conductivity in these compounds, lattice dynamics calculations were performed. The small size of Ca atoms and their concomitantly weak interactions with the surrounding Sb atoms result in a small force constant between fillers and the host, giving rise to a heretofore unreported low frequency optical phonon mode. This low frequency mode at 7meV is in addition to the previously described mode at 17meV identified by modeling the Ca as a simple harmonic oscillator. The lower energy phonon mode imparted by Ca filling results in a comparable lattice thermal conductivity reduction to early lanthanide species such as La.

Effects of temperature and gas phase impurities on the composition of Co-B alloy surface layers

Layers formed on the surfaces of Co-B melts in vacuum and in a helium atmosphere with oxygen and carbon contamination are purified. It is established that films containing B2O3 and CoO oxides form on the melt surfaces, leading to abnormalities in the temperature dependences of viscosity. It is shown that increasing the boron content in the Co100−xBx alloys lowers the temperature of oxide disappearance. Raising the oxygen content stabilizes oxides, while carbon impurities block their formation.

The question of intrinsic origin of the metal-insulator transition in i-AlPdRe quasicrystal

The icosahedral (i-) AlPdRe is the most resistive quasicrystalline alloy discovered so far. Resistivities ($\rho$) of $1\Omega cm$ at 4K and correlated resistance ratios ($RRR = \rho_{4K}/\rho_{300K}$) of more than 200 are observed in polycrystalline samples. These values are two orders of magnitude larger than for the isomorphous i-AlPdMn phase. We discuss here the controversial microscopic origin of the i-AlPdRe alloy electrical specificity. It has been proposed that the high resistivity values are due to extrinsic parameters, such as secondary phases or oxygen contamination. From comprehensive measurements and data from the literature including electronic transport correlated with micro structural and micro chemical analysis, we show that on the contrary there is mounting evidence in support of an origin intrinsic to the i-phase. Similarly to the other quasicrystalline alloys, the electrical resistivity of the i-AlPdRe samples depends critically on minute changes in the structural quality and chemical composition. The low resistivity in i-AlPdRe single-grains compared to polycrystaline samples can be explained by difference in chemical composition, heterogeneity and thermal treatment.

Surface tension and density of RENE N5® and RENE 90® Ni-based superalloys

The surface tension and density of Ni-based superalloys RENE N5® and RENE 90® have been measured by the pinned drop method at temperatures ranging from 1638 to 1780 K. In order to obtain accurate reliable data, the tests have been performed under a reducing atmosphere to minimize the oxygen contamination. In the temperature ranges investigated, both properties show a linear temperature dependence. With the aim of evaluating the reliability of the data, the present results have been analyzed using different thermodynamic models. The new experimental data for RENE N5® and RENE 90® superalloys were also compared with the corresponding data obtained by different experimental techniques.

Grazing incidence X-ray fluorescence analysis of buried interfaces in periodically structured crystalline silicon thin-film solar cells

We present grazing incidence X-ray fluorescence (GIXRF) experiments on 3D periodically textured interfaces of liquid phase crystallized silicon thin-film solar cells on glass. The influence of functional layers (SiOx or SiOx/SiCx) – placed between glass substrate and silicon during crystallization – on the final carbon and oxygen contaminations inside the silicon was analyzed. Baring of the buried structured silicon surface prior to GIXRF measurement was achieved by removal of the original nano-imprinted glass substrate by wet-chemical etching. A broad angle of incidence distribution was determined for the X-ray radiation impinging on this textured surface. Optical simulations were performed in order to estimate the incident radiation intensity on the structured surface profile considering total reflection and attenuation effects. The results indicate a much lower contamination level for SiOx compared to the SiOx/SiCx interlayers, and about 25% increased contamination when comparing structured with planar silicon layers, both correlating with the corresponding solar cell performances.

Materials characterization of impregnated W and W–Ir cathodes after oxygen poisoning

Electric thrusters use hollow cathodes as the electron source for generating the plasma discharge and for beam neutralization. These cathodes contain porous tungsten emitters impregnated with BaO material to achieve a lower surface work function and are operated with xenon propellant. Oxygen contaminants in the xenon plasma can poison the emitter surface, resulting in a higher work function and increased operating temperature. This could lead directly to cathode failure by preventing discharge ignition or could accelerate evaporation of the BaO material. Exposures over hundreds of hours to very high levels of oxygen can result in increased temperatures, oxidation of the tungsten substrate, and the formation of surface layers of barium tungstates. In this work, we present results of a cathode test in which impregnated tungsten and tungsten–iridium emitters were operated with 100ppm of oxygen in the xenon plasma for several hundred hours. The chemical and morphological changes were studied using scanning electron microscopy, energy dispersive spectroscopy, and laser profilometry. The results provide strong evidence that high concentrations of oxygen accelerate the formation of tungstate layers in both types of emitters, a phenomenon not inherent to normal cathode operation. Deposits of pure tungsten were observed on the W–Ir emitter, indicating that tungsten is preferentially removed from the surface and transported in the insert plasma. A W–Ir cathode surface will therefore evolve to a pure W composition, eliminating the work function benefit of W–Ir. However, the W–Ir emitter exhibited less erosion and redeposition at the upstream end than the pure W emitter.

Oil Sands Steam-Assisted Gravity Drainage Process Water Sample Aging during Long-Term Storage

Technology development activities are routinely performed using process water samples collected and stored for several months while tests are being conducted. The results of the technology development activities are highly correlated to the water composition and properties. Processes such as atmospheric oxygen contamination, microbiological activity, and ultraviolet (UV) oxidation have the potential to act on a sample during long-term storage and modify the properties that may be relevant to technology development testing. These changes are referred to as “aging”. Process water samples collected from a steam-assisted gravity drainage (SAGD) bitumen production plant were subjected to different storage conditions and monitored for nearly 5 months. The sample organic composition and physical characteristics of the water were found to be highly dependent upon storage conditions, particularly atmospheric oxygen exposure. Oxygen exposure appeared to drive abiotic polymerization and precipitation of phenolic species and promote aerobic microbiological activity. These results highlight the importance of excluding oxygen from the sample during collection and storage activities. Sample aging must be accounted for in technology development testing activities.

Molecular beam epitaxial re-growth of CdTe, CdTe/CdMgTe and CdTe/CdZnTe double heterostructures on CdTe/InSb(1 0 0) substrates with As cap

Molecular beam epitaxial growth on CdTe substrates is challenging since the CdTe film crystalline and optical quality is limited by residual defects including threading dislocations and stacking faults. This remains an obstacle in spite of exhausting variables including pre-growth substrate preparation as well as epitaxial growth conditions including thermal oxide desorption, growth temperature, and II/VI flux ratios. We propose a new technique to re-grow structures with low defect densities and high optical and structural quality on InSb substrates. The “CdTe virtual wafer” is made by growing a thin CdTe film on an InSb(100) substrate which is then covered with a thin As cap layer to prevent oxidation of the CdTe surface. The As cap can be removed by thermal desorption at about 300C leaving a clean CdTe surface for subsequent epitaxial growth. This method eliminates the need for chemical etching of CdTe substrates which has been found to lead to an atomically rough surface with residual Carbon and Oxygen contamination. XRD and SEM characterization show a smooth transition from the buffer CdTe to re-grown CdTe layer with identical crystalline quality as for virtual wafer. Steady-state PL and time-resolved PL from CdTe/CdMgTe double heterostructures show substantial improvement in luminescence intensity and carrier lifetime comparable to values for identical samples grown without exposure to atmosphere. We will also report on CdTe/CdZnTe double heterostructures grown on virtual wafers compared to identical structures on conventional CdTe(211)B substrates.

Structural and Magnetic Characterization of Single‐phase Sponge‐like Bulk α′′‐Fe16N2

Abstract Improvements of the two‐step reaction sequence starting from γ‐Fe2O3 enabled us to synthesize α′′‐Fe16N2 in single phase according to the applied diffraction methods. Simultaneous Rietveld refinements were carried out on powder X‐ray and neutron diffraction data. Scanning electron microscopy images of the in situ formed α‐Fe and α′′‐Fe16N2 indicate the formation of pores during reduction and ammonolysis reaction, respectively, resulting in a sponge‐like morphology of the α′′‐Fe16N2 particles and simultaneously a large surface area facilitating a complete reaction at comparably low temperatures of 125 °C. The large surface area is susceptible to the sorption of impurities and indeed chemical analysis reveals significant oxygen and hydrogen contamination of the sample. From EDX measurements in combination with the results of chemical analysis a sorption of humidity to the surface seems to be more likely to explain this contamination than an incorporation of oxygen into the bulk of the sample. Magnetization measurements on the bulk sample of α′′‐Fe16N2 did not reveal any indication for the presence of a proposed giant magnetic effect.

Structural properties of In2Se3 precursor layers deposited by spray pyrolysis and physical vapor deposition for CuInSe2 thin-film solar cell applications

The structural properties of In2Se3 precursor thin films grown by chemical spray pyrolysis (CSP) and physical vapor deposition (PVD) methods were compared. This is to investigate the feasibility to substitute PVD process of CuInSe2 (CISe) films by CSP films as precursor layer, thus decreasing the production cost by increasing material-utilization efficiency. Both films of 1μm thickness were deposited at the same substrate temperature of 380°C. X-ray diffraction and Raman spectra confirm the formation of γ-In2Se3 crystalline phase for both films. The PVD and CSP films exhibited (110) and (006) preferred orientations, respectively. The PVD films showed a smaller full width at half maximum value (0.09°) compared with CSP layers (0.1°). Films with the same crystalline phase but with different orientations are normally used in the preparation of high quality CISe films by 3-stage process. Scanning electron microscope cross-section images showed an important difference in grain size with well-defined larger grains of size 1–2μm in the PVD films as compared to CSP layers (600nm). Another important characteristic that differentiates the two precursor films is the oxygen contamination. X-ray photoelectron spectroscopy showed the presence of oxygen in CSP films. The oxygen atoms could be bonded to indium by replacing Se vacancies, which are formed during CSP deposition. Taking account of the obtained results, such CSP films can be used as precursor layer in a PVD process in order to produce CISe absorber films.

Availability of a containerless polymer gel detector and a gelatin container

We considered an availability of the polymer gel detector without container but with a plastic wrap under assumption of the low oxygen transmissivity of a sheet of plastic wrap. And a gelatin container was also examined for a gel detector. These samples can be made easily and this containerless polymer gel detector well works without any artifacts by means of wrapping with a thin plastic sheet. Nevertheless, there is still room for improvement on preventing oxygen contamination. Combination with a gelatin container and a polymer gel detector and/or Gafchromic films has a various potential for extension of 3D dosimetry.

Growth of graphene films on Cu catalyst in hydrogen plasma using polymethylmethacrylate as carbon source

Owing to its excellent electronic characteristics and wide spectrum of potential applications, graphene has attracted intense attention by not only scientists but also engineers. Growth of graphene films on copper foils using gaseous carbon sources has been emphasized previously due to the high quality/price ratio. In this study, we reported the synthesis of graphene films on copper substrate converting from a solid carbon source (polymethylmethacrylate) with help of hydrogen plasma. The effects of substrate temperature and microwave power on the growth of graphene have been investigated. Raman spectroscopic data indicated that high microwave power and substrate temperature would benefit the growth of high quality graphene films. X-ray photoelectron spectroscopic results implied that the synthesized graphene films were in high purity with small amount of oxygen contaminations. Transmission electron microscopy data suggested that the synthesized graphene films are polycrystalline and its atomic arrangement is in short-range order.

Microstructure and Stress Corrosion Cracking of Dissimilar Metal Weld 16MND5/309L/308L/Z2CND18-12N Used for Connecting Reactor Pressure Vessel to Piping in Nuclear Power Plants

The microstructure and stress corrosion cracking (SCC) in simulated primary water at 290°C of a dissimilar metal weld 16MND5/309L/308L/Z2CND18-12N made in China were studied for reliability and lifetime assessment and management of relevant pressurized water reactor (PWR) nuclear power plants. Results of microstructure characterization showed that the base metal of the low alloy steel (LAS) 16MND5 was upper-bainitic and stainless steel (SS) Z2CND18-12N was equiaxial austenitic grains, the bulk weld metal of SS 308L was austenite with dendritic structures plus δ-ferrite islands. The interfaces areas around 16MND5/309L and 308L/Z2CND18-12N exhibited apparent fusion lines with complicated microstructure/chemical composition changes, especially the former. The area between the 16MND5 base metal and the bulk weld metal was made up of three parts, that is, the heat-affect zone of 16MND5, fusion line and transition zone. There was a thin martensitic layer along the fusion line, which possessed the highest micro-hardness among the weld. The transition zone was an austenitic layer within which Cr% and Ni% changed significantly. SCC test results showed that this area around 16MND5/309L was the most susceptible to SCC among the weld. Both intergranular and transgranular SCC occurred in this area when tested in at high electrode potential which is mainly related to bad water chemistry with high oxygen contamination. The crack mechanism and the significance in engineering are discussed.

High-Energy Ball Milling and Hot Pressing of the Ni-48Ti-2Sn and Ni-45Ti-5Sn Powder Mixtures

This work presents the results on the high-energy ball milling and hot pressing of Ni-48Ti-2Sn and Ni-45Ti-5Sn (at-%) powder mixtures. The milling process was performed in a planetary ball mill using stainless steel vial (225 mL) and hardened steel balls (19 mm diameter), rotary speed of 300 rpm, and a ball-to-powder weight ratio of 10:1. Samples were collected into the vial after different milling times: 60, 180 and 300 min. In the sequence, wet milling (isopropyl alcohol) was adopted up to 720 min in order to increase the powder yield into the vials. The as-milled and hot-pressed samples were characterized by X-ray diffraction, electron scanning microscopy, and energy dispersive spectrometry. Results indicated that the ductile particles were promptly cold-welded during the initial milling times. XRD patterns of the Ni-48Ti-2Sn powder mixture indicated that the peaks of Ni, Ti and Sn disappeared after milling for 3h. Following, peaks of NiTi and Ni4Ti3 were preferentially formed during milling of Ni-Ti-Sn powders. A large amount of fine powders was yielded into the vial after wet milling for 720 min only. No significant carbon or oxygen contamination was detected by EDS analysis. Hot pressing produced homogeneous and dense samples which presented microstructures containing a large amount of the NiTi compound.

Infrared-transparent glass ceramics: An exploratory study

In this work, the vision and need for a fully ceramized long-wave infrared (LWIR)-transmitting glass ceramic have been articulated. Three sulfide systems were explored including two with La2S3 in hopes of imparting strong bonds from this refractory sulfide, and two containing GeS2 in hopes of widening the glass-forming region. Attempts were made to produce glasses in the Ga2S3–La2S3–(ZnS,CaS) system, the GeS2–La2S3 system, and the GeS2–Ga2S3–CdS system. Water quenching produced glasses of Ga2S3–La2S3–CaS and GeS2–Ga2S3–CdS. Microstructural and thermal analyses were used to explore nucleation and growth in these systems and infrared transmission and mechanical hardness showed potential for LWIR window use. The GeS2–Ga2S3–CdS system showed good LWIR transmission and pre-crystallized hardness superior to chemical vapor deposited ZnS. The Ga2S3–La2S3 glasses did not appear to be viable candidates at this time due to a small temperature window between crystallization and glass transition temperatures and problems with oxygen contamination in the La2S3 source. Suggestions are made for two alternative methods for producing fully ceramized LWIR-transmitting glass ceramics.

Dependence of LTX plasma performance on surface conditions as determined by in situ analysis of plasma facing components

The Materials Analysis and Particle Probe (MAPP) diagnostic has been implemented on the Lithium Tokamak Experiment (LTX) at PPPL, providing the first in situ X-ray photoelectron spectroscopy (XPS) surface characterization of tokamak plasma facing components (PFCs). MAPP samples were exposed to argon glow discharge conditioning (GDC), lithium evaporations, and hydrogen tokamak discharges inside LTX. Samples were analyzed with XPS, and alterations to surface conditions were correlated against observed LTX plasma performance changes. Argon GDC caused the accumulation of nm-scale metal oxide layers on the PFC surface, which appeared to bury surface carbon and oxygen contamination and thus improve plasma performance. Lithium evaporation led to the rapid formation of a lithium oxide (Li2O) surface; plasma performance was strongly improved for sufficiently thick evaporative coatings. Results indicate that a 5h argon GDC or a 50nm evaporative lithium coating will both significantly improve LTX plasma performance.

Citrate gel synthesis of aluminum-doped lithium lanthanum titanate solid electrolyte for application in organic-type lithium–oxygen batteries

Aluminium doped lithium lanthanum titanate (A-LLTO) powders with various excess Li2O content are synthesized using a simple citrate gel method. The obtained A-LLTO powders show an agglomerated form, composed of nano-sized particles of 20–50 nm. The morphology and conductivity of the A-LLTO ceramics are largely affected by the content of excess Li2O. The highest total ionic conductivity of 3.17 × 10−4 S cm−1 is achieved for the A-LLTO sample containing 20% excess Li2O, exhibiting a vacancy content of 6%, and a total activation energy of 0.358 eV. The A-LLTO can act as a membrane to protect lithium metal from oxygen and other contaminants diffused through the oxygen electrode part. The Li–O2 cell employing the A-LLTO solid electrolyte shows a good cycle life of longer than 100 discharge-charge cycles, under the constant capacity mode of 300 mAh g−1.

PO-0684 Effects Of Endotracheal Suctioning In Newborn Preterm Infants Weighing Between 500 And 1500 G

Objective To observe different ways of implementing the techniques of aspiration of preterm infants and verify factors associated with changes in oxygen saturation and contamination of equipment. Methods An observational, prospective, descriptive study. The aspirations of the endotracheal tube in infants with birth weights between 500 and 1500 g were observed during two procedures; morning and evening. Results We evaluated 32 infants with a mean weight of 942 g and a mean gestational age of 28 weeks (64 aspiration procedures). During aspiration 61% of children had hypoxemia. The saturation drops were more related to the aspiration held by a single professional, also when they were made more than three disconnections of the fan and when disconnections occurred beyond fifteen seconds. The pre – oxygenation did not decrease significantly during the procedure hypoxia and preterm – oxygen showed hyperoxia from third minute of recovery. The aspiration held by two professionals joined the adequate pre – oxygenation, decreased number and duration of disconnections ventilation, and less contamination of materials. The use of saline during suctioning in less than 1 ml volume was associated with significant decreases saturation. Conclusions The aspiration of the endotracheal tube can lead to hypoxemia. To minimise episodes is important that it be performed by two professionals that meet the care disconnecting the system less than 3 times and use less than 15 seconds. Also pre-oxygenation should be done with caution and the use of less than 1 ml volume of saline solution leads to negative consequences for the patient.

Impact of copper overpressure on the synthesis of hexagonal boron nitride atomic layers.

Hexagonal boron nitride (h-BN) atomic layers are synthesized on polycrystalline copper foils via a novel chemical vapor deposition (CVD) process that maintains a vapor-phase copper overpressure during growth. Compared to h-BN films grown without a copper overpressure, this process results in a >10× reduction of 3-dimensional BN fullerene-like surface features, a reduction of carbon and oxygen contamination of 65% and 62%, respectively, an increase in h-BN grain size of >2×, and an 89% increase in electrical breakdown strength.