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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Lattice defects in semiconducting Hg/1-x/Cd/x/Te alloys. III - Defect structure of undoped Hg0.6Cd0.4Te

Hall effect measurements were carried out on undoped Hg0.6Cd0.4Te crystals quenched to room temperature subsequent to equilibration at temperatures varying from 450 to 720 C under various partial pressures of Hg. The variation of the hole concentration as a function of the partial pressure of Hg indicates that the native acceptor defects are doubly ionized. Native donor defects are found to be negligible in concentration and the p-type to n-type conversion is shown to be due to residual donors and not due to native donor defects. Thermodynamic constant for the incorporation of the doubly ionized native acceptor defect has been established.

Vydyanath, H. R.↗
NASA NTRS1977

Effects of defect recombination centers on radiation damage in solar cells

Defect production in silicon is modeled on a computer by solving a large system of rate equations. The model includes the main, known defects that are stable at operating temperatures of solar cells in outer space; most of these defects are secondary and tertiary defects. The preliminary result shows that the presence of defect recombination centers for primary defects (i.e., vacancy and interstitial) can effectively reduce the production rates of those stable defects and, consequentially, improve the lifetime of solar cells operating in radiation environment. The characteristics of the defect recombination center required for better solar cell performance along with prospective candidates are discussed.

Cheng, L. J.↗
NASA NTRS1971

A study of irradiation-induced defects in silicon using low temperature photoluminescence

Irradiation-induced defects in silicon, using low temperature photoluminescence as a probe of defect properties were investigated. The goal of this research was to gain new understanding of defects which degrade solar cell characteristics in a radiation environment. In this regard, an important aspect of this program was a study of radiation damage and annealing in lithium doped silicon, which is useful in reducing solar cell degradation. Luminescence was used to study defects because this property reveals electron transitions through a number of defect energy levels at any given annealing stage; the luminescence spectra give excellent resolution of many defect energy levels, and these measurements can be used to give defect symmetry in the lattice, impurity dependence, and annealing properties.

Streetman, B. G.↗
NASA NTRS1971

Definition of defect size from ultrasonic inspection.

Attempt to obtain a set of relationships between testing parameters defining the range of defect size that can be associated with a given echo amplitude and defect depth. These relationships allow the user to find the largest defect that will return a signal equal to that from a flat hole of known diameter and depth, and the signal amplitude ratio between worst case and flat hole defects of equal diameter. The variation of the data with defect and testing parameters is shown. The results are obtained analytically, with laboratory corroboration, by calculation of the echo amplitude of the defect shape yielding the smallest return signal, a sphere, and the echo amplitude of the defect shape yielding the largest return signal, a flat hole.

Bennet, S. B.↗
NASA NTRS1981

Effects of artificially produced defects on film thickness distribution in sliding EHD point contacts

The effects of artificially produced dents and grooves on the elastohydrodynamic (EHD) film thickness profile in a sliding point contact were investigated by means of optical interferometry. The defects, formed on the surface of a highly polished ball, were held stationary at various locations within and in the vicinity of the contact region while the disk was rotating. It is shown that the defects, having a geometry similar to what can be expected in practice, can dramatically change the film thickness which exists when no defects are present in or near the contact. This change in film thickness is mainly a function of the position of the defects in the inlet region, the geometry of the defects, the orientation of the defects in the case of grooves, and the depth of the defect relative to the central film thickness.

Cusano, C.↗
NASA NTRS1981

The effects of artificially-produced defects on the film thickness distribution in sliding EHD point contacts

Effects of artificially produced dents and grooves on the elastohydrodynamic film thickness profile in a sliding point contact are investigated using optical interferometry. Defects on the surface of a highly polished ball are held stationary at various locations within the vicinity of the contact region while the disk is rotating. It is shown that defects can dramatically change the film thickness which exists when no defects are present in or near the contact, and it is shown that the change in thickness is mainly a function of the position of the defects in the inlet region, the geometry of the defects, the orientation of the defects in the case of grooves, and the depth of the defect relative to the central film thickness.

Cusano, C.↗
NASA NTRS1974

Influence of material quality and process-induced defects on semiconductor device performance and yield

An overview of major causes of device yield degradation is presented. The relationships of device types to critical processes and typical defects are discussed, and the influence of the defect on device yield and performance is demonstrated. Various defect characterization techniques are described and applied. A correlation of device failure, defect type, and cause of defect is presented in tabular form with accompanying illustrations.

Porter, W. A.↗
NASA NTRS1976

The application of an optical Fourier spectrum analyzer on detecting defects in mass-produced satellite photographs

Various defects in mass-produced pictures transmitted to earth from a satellite are investigated. It is found that the following defects are readily detectable via Fourier spectrum analysis: (1) bit slip, (2) breakup causing loss of image, and (3) disabled track at the top of the imagery. The scratches made on the film during mass production, which are difficult to detect by visual observation, also show themselves readily in Fourier spectrum analysis. A relation is established between the number of scratches, their width and depth and the intensity of their Fourier spectra. Other defects that are found to be equally suitable for Fourier spectrum analysis or visual (image analysis) detection are synchronous loss without blurring of image, and density variation in gray scale. However, the Fourier spectrum analysis is found to be unsuitable for detection of such defects as pin holes, annotation error, synchronous loss with blurring of images, and missing image in the beginning of the work order. The design of an automated, real time system, which will reject defective films, is treated.

Athale, R.↗
NASA NTRS1977

The effect of oxidation-expanded defects upon MOS parameters

Implantation of Ne ions was chosen as a means of introducing a uniformly distributed quantitatively controllable and reproducible amount of microdefects at the silicon surface. Each wafer was ion-implanted on one half of its surface, the other half remaining as a control. Seven implant fluences from 1 trillion to 5 by 10 to the 14th power Ne ions/sq cm were used. The fluences, as well as the concentrations of defects expanded by the subsequent gate oxidation, were correlated with seven different MOS parameters. For implant fluences of 10 to the 14th power per sq cm and above, increasing stacking-fault densities were found. The oxide defect density associated with time-dependent breakdown increased significantly with Ne dose. The presence of oxidation-expanded defects drastically increases the surface-generation velocity and decreases the bulk lifetime. Slight increases in flatband voltage and surface-state density occurred only for the wafers having the greatest defect concentrations. Oxidation of a P-containing damaged silicon surface results in a greater pileup of P at the surface than occurs for the oxidation of a similar but undamaged surface. It appears that the expanding defects restrain the diffusion of P inward from the surface.

Prussin, S.↗
NASA NTRS1979

Characterization of defect growth structure in ion plated films by scanning electron microscopy

Copper and gold films (0.2 to 2 microns) were ion plated onto polished 304-stainless-steel surfaces. These coatings were examined by scanning electron microscopy for coating growth defects. Three types of defects were distinguished: nodular growth, abnormal or runaway growth, and spits. The cause and origin for each type of defect was traced. Nodular growth is primarily due to inherent substrate microdefects, abnormal or runaway growth is due to external surface inclusions, and spits are due to nonuniform evaporation. All these defects have adverse effects on the coatings. They induce stresses and produce porosity in the coatings and thus weaken their mechanical properties. Friction and wear characteristics are affected by coating defects, since the large nodules are pulled out and additional wear debris is generated.

Spalvins, T.↗
NASA NTRS1979

Definition of mutually optimum NDI and proof test criteria for 2219 aluminum pressure vessels. Volume 3: Applications to rail defect evaluation

The technique for inspection of railroad rails containing transverse fissure defects was discussed. Both pulse-echo and pitch-catch inspection techniques were used. The pulse-echo technique results suggest that a multiple-scan approach using varying angles of inclination, three-surface scanning, and dual-direction traversing may offer promise of characterization of transverse defects. Because each scan is likely to produce a reflection indicating only a portion of the defect, summing of the individual reflections must be used to obtain a reasonably complete characterization of the defect. The ability of the collimated pitch-catch technique to detect relatively small amounts of flaw growth was shown. The method has a problem in characterizing the portions of the defect near the top surface or web intersection. The work performed was a preliminary evaluation of the prospects for automated mapping of rail flaws.

Schwartzberg, F. R.↗
NASA NTRS1979

Characterization of defect growth structures in ion plated films by scanning electron microscopy

Gold and copper films (0.2-2 micron thick) are ion plated on very smooth stainless steel 304 and mica surfaces. The deposited films are examined by SEM to identify the morphological growth of defects. Three types of coating defects are distinguished: nodular growth, abnormal or runaway growth, and spits. The potential nucleation sites for defect growth are analyzed to determine the cause of defect formation. It is found that nuclear growth is due to inherent surface microdefects, abnormal or runaway growth is due to external surface inclusions, and spits are due to nonuniform evaporation and ejection of droplets. All these defects have adverse effects on the coatings.

Spalvins, T.↗
NASA NTRS1981

Electronic properties of deep-level defects in proton irradiated AlGaAs-GaAs solar cells

Deep level transient spectroscopy and capacitance voltage techniques as well as analysis of the forward current voltage (I-V) characteristics and SEM-EIC data were carried out for proton irradiated GaAs solar cells over a wide range of proton energies and proton fluences. Defect and recombination parameters such as defect energy levels and density, carrier capture cross sections and lifetimes as well as diffusion lengths in the undoped n-GaAs LPE layers were determined. Good correlation between these defect parameters and solar cell performance parameters was obtained for GaAs solar cells irradiated by 200 and 290 KeV protons. It was found that 200 to 290 KeV protons will produce the most defects and damages to the GaAs solar cell structure used. The influence of the low temperature (200 to 400 C) periodic thermal annealing on the deep level defects and the performance of the 200 KeV proton irradiated cells is discussed.

Li, S. S.↗
NASA NTRS1981

Flaw criticality of circular disbond defects in compressive laminates

The compressive behavior of T300/5208 graphite-epoxy laminates containing circular delaminations was studied to determine the flaw criticality of two types of implanted defect, Kapton bag and Teflon film, on several laminate configurations. Defect size was varied. Results, presented in the form of residual strength curves, indicate that the Teflon film defect reduced strength more than the Kapton bad defect in 12-ply samples, but that two laminates (+ or - 45) sub 2s and (90/+ or - 45) sub s were insensitive to any implanted defect. A clear thickness effect was shown to exist for the (o/+ pr 45) sub ns laminate and was attributed to failure mode transition. The analytically predicted buckling loads show excellent agreement with experimental results and are useful in predicting failure mode transition.

Webster, J. D.↗
NASA NTRS1980

Estimation of uncertainty in isotherms deduced from Hugoniots resulting from shockwave generated defects

The problem of how defect concentrations produced in a shock experiment affect the isothermal equation of state is considered. From the few experimental results available that bear directly on this question, it appears the effect could be substantial, i.e., the pressure in material free of defects may be 10-25% lower at a given volume than the isothermal pressure deduced from Hugoniot data on the assumption that defects are negligible in the shocked material. This correction caused by the presence of defects is called the defect pressure.

Ruoff, A. L.↗
NASA NTRS1927

Duralumin - Defects and Failures

It is proposed in this paper to identify some of the defects and failures in duralumin most frequently encountered by the aircraft industry with a view to indicate their importance. The defects and failures in duralumin may be classified into the following groups: 1) defects produced during manufacture; 2) defects produced during fabrication; 3) corrosion and erosion; and 4) fatigue failures. Only the first two will be covered in this report.

DURALUMIN - DEFECTS & FAILURES↗