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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Sample mounts for microcrystal crystallography

Sample mounts (10) for mounting microcrystals of biological macromolecules for X-ray crystallography are prepared by using patterned thin polyimide films (12) that have curvature imparted thereto, for example, by being attached to a curved outer surface of a small metal rod (16). The patterned film (12) preferably includes a tapered tip end (24) for holding a crystal. Preferably, a small sample aperture is disposed in the film for reception of the crystal. A second, larger aperture can also be provided that is connected to the sample aperture by a drainage channel, allowing removal of excess liquid and easier manipulation in viscous solutions. The curvature imparted to the film (12) increases the film's rigidity and allows a convenient scoop-like action for retrieving crystals. The polyimide contributes minimally to background and absorption, and can be treated to obtain desired hydrophobicity or hydrophilicity.

Thorne, Robert E.↗
NASA NTRS2009

Sample mounts for microcrystal crystallography

Sample mounts (10) for mounting microcrystals of biological macromolecules for X-ray crystallography are prepared by using patterned thin polyimide films (12) that have curvature imparted thereto, for example, by being attached to a curved outer surface of a small metal rod (16). The patterned film (12) preferably includes a tip end (24) for holding a crystal. Preferably, a small sample aperture is disposed in the film for reception of the crystal. A second, larger aperture can also be provided that is connected to the sample aperture by a drainage channel, allowing removal of excess liquid and easier manipulation in viscous solutions. The curvature imparted to the film (12) increases the film's rigidity and allows a convenient scoop-like action for retrieving crystals. The polyimide contributes minimally to background and absorption, and can be treated to obtain desired hydrophobicity or hydrophilicity.

Thorne, Robert E.↗
NASA NTRS1985

Size and shape dependence of CO adsorption sites on sapphire supported Fe microcrystals

The surface structure and stoichiometry of alumina substrates, as well as the size, growth characteristics, and shape of Fe deposits on sapphire substrates have been investigated by low energy electron diffraction (LEED), Auger electron spectroscopy, electron energy loss spectroscopy, and X-ray photoemission spectroscopy (XPS), as well as work function measurements, in conjunction with transition electron microscopy observations. The substrates used in this work were the following: (1) new, clean Al2O3; (2) same surface amorphized by Ar ion bombardment; (3) same surface regenerated by 650 C annealing; (4) amorphous alumina films on Ta slab; and (5) polycrystal alumina films, obtained by heating amorphous films to 600 C. Substrate cleaning was found to be most effective in producing a reproducible surface upon oxygen RF plasma treatment. The Fe nucleation and growth process was found to depend strongly on the type of substrate surface and deposition conditions. Ar ion bombardment under beam flooding, and subsequent annealing at 650 C was found an effective means to restore the original Al2O3 (1102) surface for renewed Fe deposition.

Papageorgopoulos, C.↗
NASA NTRS1988

Field-induced orientation of nonlevitated microcrystals of superconducting YBa2Cu3O(7-x)

X-ray diffraction patterns of superconducting YBa2Cu3O(7-x) particles which have typical dimensions D of less than 5 microns and do not levitate in an inhomogeneous magnetic field at T less than Tc show marked evidence of particle alignment when powder specimens are subjected to a 0.5-T field at T less than Tc, but reveal random orientation for T greater than Tc. A majority of the particles align preferentially with their antiphase twin boundary planes and a-b planes along the applied field, but a minority align with their b axes along the field.

Solin, S. A.↗
NASA NTRS1988

Enhancement of structure images of interstellar diamond microcrystals by image processing

Image processed high resolution TEM images of diamond crystals found in oxidized acid residues of carbonaceous chondrites are presented. Two models of the origin of the diamonds are discussed. The model proposed by Lewis et al. (1987) supposes that the diamonds formed under low pressure conditions, whereas that of Blake et al (1988) suggests that the diamonds formed due to particle-particle collisions behind supernova shock waves. The TEM images of the diamond presented support the high pressure model.

O'Keefe, Michael A.↗
NASA NTRS2000

A Novel Approach to Solving the Problem of Needle Microcrystals (A Case Study of Ribosome Crystals)

Different morphology crystals (needle, rod-tetragonal and wedge-shaped) were grown from the same solution of ribosome; furthermore, in the same drop using 10- 15% 2-methyl-2,4pentanediol as a precipitant. The crystals appeared in 5-48 hours. Observations of the kinetics of crystals appearance lead to the conclusion that higher supersaturation of ribosome solution produces needle-shaped crystals, while the tetragonal-rod and the wedge-shaped crystals grow at lower supersaturation. The ribosome packing in the crystals was characterized by electron microscopy (EM). An analysis of EM ultrathin sections indicates that the unit cells, with a high degree of probability, are the same in the crystals of different morphology. The data obtained suggests how to shift the process of crystal formation from the needles to the crystals with comparative size in all three dimensions.

Karpova, Elizaveta A.↗
NASA NTRS2004

Microcrystals and Amorphous Material in Comets and Primitive Meteorites: Keys to Understanding Processes in the Early Solar System

Comets, fine-grained matrices of chondrites, and chondritic interplanetary dust particles (IDPs) are each composed of both crystalline and amorphous silicates. The primitive solar nebula, in which comets and asteroids accreted, was formed from the collapsed core of a Giant Molecular Cloud, that, in turn, condensed from materials present in the interstellar medium (ISM). Despite observations that reveal the presence of crystalline magnesium silicate minerals in the shells of very high mass-loss-rate stars [1,2], typical silicate grains in the ISM are most likely to be amorphous, given their relatively long residence time in such a high radiation environment. An upper limit of ~3% crystalline grains can be derived from their non-detection in spectra of ISM solids [3]. If the vast majority of grains that enter the primitive solar nebula are amorphous, then the observation of crystalline dust in comets and primitive chondrite matrices indicates the action of specific processes required to transform the amorphous starting materials into the crystals that are observed.

Nuth, J. A.↗
NASA NTRS1989

Raman intensity as a probe of concentration near a crystal growing in solution

The feasibility of using Raman spectral scattering signals for measurements of concentration profiles near a crystal interface during growth or dissolution is discussed. With KH2PO4 (KDP) as a test material, optical multichannel analyzer (OMA) detection of a solute Raman vibrational band provided direct quantification of solute concentration with band intensity. The intersection of incident laser and Raman collection optics provided 3-D selective point measurements of the solution concentration field. Unlike many other techniques, the Raman band intensity is not sensitive to the typical temperature variations. Precision calibration of Raman intensity versus KDP concentration with less than 1 pct standard deviation error levels was demonstrated. A fiber optic, which sampled incident laser intensity and coupled it to the OMA, provided a fully synchronized monitor of fluctuations in laser power to correlate with observed Raman signals. With 1 W of laser power at the sample, good data statistics required eight repeated data collections at approximately 2.5 min collection. The accumulated time represents the concentration measurement time at one spatial location. Photomicroscopy documented a 30 micrometer diameter by 200 micrometer of laser Raman scattering region in the solution near the crystal surface. The laser beam was able to approach up to 25 micrometer from the crystal surface. However, a crystal surface reflected intensity contribution was weakly detectable. Nucleated microcrystals were seen in the crystal-growing solution. These microcrystals convect right up to the crystal surface and indicate no quiet diffusion region under normal gravity conditions. Translation of the solution cell with respect to the optics caused systematic intensity errors.

Wilkinson, R. Allen↗
NASA NTRS1969

Laser action from a terbium beta-ketoenolate at room temperature

Laser activity is achieved in a solution of terbium tris at room temperature in a liquid solvent of acetonitrile or p-dioxane. After precipitation, the microcrystals of hydrated tris chelate are filtered, washed in distilled water, and dried. They show no signs of deterioration after storage.

Bjorklund, S.↗
NASA NTRS1973

Uranium concentration and distribution in six peridotite inclusions of probable mantle origin

Fission-track activation was used to investigate uranium concentration and distribution in peridotite inclusions in alkali basalt from six localities. Whole-rock uranium concentrations range from 24 to 82 ng/g. Most of the uranium is uniformly distributed in the major silicate phases - olivine, orthopyroxene, and clinopyroxene. Chromian spinels may be classified into two groups on the basis of their uranium content - those which have less than 10 ng/g and those which have 100 to 150 ng/g U. In one sample accessory hydrous phases, phlogopite and hornblende, contain 130 and 300 ng/g U, respectively. The contact between the inclusion and the host basalt is usually quite sharp. Glassy or microcrystalline veinlets found in some samples contain more than 1 microgram/g. Very little uranium is associated with microcrystals of apatite. These results agree with some earlier investigators, who have concluded that suboceanic peridotites contain too little uranium to account for normal oceanic heat flow by conduction alone.

Haines, E. L.↗
NASA NTRS1978

The tektite problem

Small glassy pebbles, called tektites, are found in widely scattered locations around the world. These tektites appear much like volcanic glass obsidian, but their chemical composition is different from that of any terrestrial lava and they contain far less water and none of obsidian's characteristic microcrystals. No one has ever found the mother lode of a field of tektites. They cannot, therefore, be the product of terrestrial volcanism. Recently acquired knowledge about the moon's surface confirms earlier indications that tektites cannot be bits of lunar soil propelled to the earth by the impact of meteorites on the moon. According to one of two remaining possibilities tektites are bits of terrestrial sedimentary rock excavated by meteorites striking the earth's surface, melted by the heat of impact, and congealed into glass as they travel above the atmosphere to the scattered sites where they are found. The other possibility is that tektites are the remains of gobs of lava fired at the earth by volcanic activity on the moon.

Okeefe, J. A.↗
NASA NTRS1980

Nitridation of silicon /111/ - Auger and LEED results

Clean silicon (111) (7x7) surfaces at up to 1050 C have been reacted with nitrogen ions and neutrals produced by a low energy ion gun. The LEED patterns observed are similar to those previously reported for reaction of silicon (111) (7x7) with NH3. The nitrogen KLL peak exhibits no shift or change in shape with nitride growth. At the same time the magnitude of the elemental silicon LVV peak at 92 eV decreases progressively as a new peak at 84 eV increases. The position of both peaks appears to be independent of the degree of nitridation. Since the Auger spectra are free of oxygen and other impurities, these features can be attributed only to silicon, nitrogen, and their reaction products. Characteristic features of the Auger spectra are related to LEED observations and to the growth of microcrystals of Si3N4.

Delord, J. F.↗
NASA NTRS1986

Did template-directed nucleation precede molecular replication?

It is proposed that mononucleotides incorporated into the surfaces of microcrystals of inorganic phosphates such as hydroxyapatite can act as templates to assemble complementary mononucleotides from solution, and that the phosphate groups of the assembled nucleotides can facilitate nucleation of a second hydroxyapatite crystal. This would provide a mechanism of replication that is subject to natural selection. The possible role of a replicating system of this kind in the origins of life on the earth is discussed.

Orgel, Leslie E.↗
NASA NTRS1987

Heat's on to develop high-temperature materials

An evaluation is made of the state-of-the-art and foreseeable development prospects in high temperature engineering materials applicable to advanced heat engines and other aerothermodynamically affected structures. Attention is given to monocrystal- and microcrystal-producing metal solidification processes, soft oxide and chemically stable fluoride high temperature solid lubricants, polyimide and other high temperature polymers for propulsion system applications, high strength/toughness ceramics for heat engine structural components, thermal barrier coatings, and metal-matrix composites employing refractory matrices as well as reinforcing fibers.

Gray, Hugh R.↗
NASA NTRS1988

Preliminary investigations into solutal flow about growing tetragonal lysozyme crystals

A series of preliminary experiments were done to investigate solutal flow about growing lysozyme crystals and its effects. Density-gradient-driven flow was observed using a schlieren optical system. Crystals used ranged from 0.3 to 1.72 mm across the (110) face, and protein concentrations were from 3.7 to 23.7 mg/ml. The convective plume velocities were found to be from 10 to 50 microns/s, which correlated with those predicted to occur based upon a diffusive-convective model. When microcrystals of lysozyme, less than 20 microns across the (110) face were subjected to directed solution flows, the growth rate was found to rapidly decrease over the 8-20 h course of the experiment. Solution flow rates used ranged from 18 to 40 microns/s, and protein concentrations were from 7.3 to 11.7 mg/ml, conditions typical of larger (greater than 0.5 mm) crystals in the terminal phases of a typical crystal growth procedure.

Pusey, Marc↗
NASA NTRS1996

The Effect of Gravity Axis Orientation on the Growth of Phthalocyanine Thin Films

Experimentally, many of the functions of electrical circuits have been demonstrated using optical circuits and, in theory, all of these functions may be accomplished using optical devices made of nonlinear optical materials. Actual construction of nonlinear optical devices is one of the most active areas in all optical research being done at this time. Physical vapor transport (PVT) is a promising technique for production of thin films of a variety of organic and inorganic materials. Film optical quality, orientation of microcrystals, and thickness depends critically on type of material, pressure of buffer gas and temperature of deposition. An important but understudied influence on film characteristics is the effect of gravity-driven buoyancy. Frazier, Hung, Paley, Penn and Long have recently reported mathematical modelling of the vapor deposition process and tested the predictions of the model on the thickness of films grown by PVT of 6-(2-methyl-4-nitroanilino)-2,4-hexadiyn-l-ol (DAMNA). In an historic experiment, Debe, et. al. offered definitive proof that copper phthalocyanine films grown in a low gravity environment are denser and more ordered than those grown at 1 g. This work seeks to determine the influence on film quality of gravity driven buoyancy in the low pressure PVT film growth of metal-free phthalocyanine.

Pearson, Earl F.↗
NASA NTRS1996

Synthesis and Characterization of a Chitosan Derivative for Electro-Optical Applications

Chitin is a naturally occurring polymer of alpha(1-4) poly N-acetylglucosamine found primarily in the shells of crustaceans and insects. This polymer is chemically and thermally stable and physically durable as a consequence of hydrogen bonding which causes the alignment and ordering of the polymer chains into microcrystals which aggregate into sheets with chiral nematic order. Industry has attempted to take advantage of chitin's properties and low cost (chitin is a waste product of the shellfish industry) to produce durable fibers and other products. This has been largely unsuccessful because of chitin's non reactivity and insolubility. Chitosan is the deacetylation product of chitin and retains many of the structural properties of chitin. Unlike chitin, chitosan is soluble in aqueous solution at reduced pH making it easier to be processed into fibers and films than chitin. Chitosan and its derivatives are now used in such commercial applications as wound dressings, waste water treatment, and in pharmaceuticals. In this study, we have synthesized a chitosan derivative, N-para-nitrophenyl chitosan (NPNPC), as a model material with potential applications in electro optics.

Prastofer, Thomas↗