Scholarly Works, Chemistry

Permanent URI for this collection

https://hdl.handle.net/10919/23843

Research articles, presentations, and other scholarship

Browse

Now showing 1 - 20 of 252

Physical interaction of nitrogen with Pyrex, stainless-steel, and nickel at very low-pressure
Outlaw, R. A.; Brock, F. J.; Wightman, James P. (American Institute of Physics, 1974)
The physical adsorption of nitrogen on the surfaces of Pyrex, 347 stainless steel, and polycrystallinenickel was investigated over the pressure range 1×10−12–3×10−7 Torr and for the temperatures 77.4 and 87.4 °K. The metal surfaces were prepared by vacuum firing, by chemical cleaning, and, following bakeout, by electron impact desorption (EID). Work function measurements were used to indicate changes in the surface condition following electron bombardment, and a mass spectrometer was used to monitor gas composition. The isotherms revealed that the stainless surface was very heterogeneous and that the Pyrex surface area had a roughness factor of 1.7. Nitrogen isotherms were also taken on the metal surfaces after they had been exposed to oxygen. Very little change in physical adsorption on the nickel was detected, presumably because the chemisorbed oxygen was incorporated into the bulk. The chemical adsorption of N2 on nickel at room temperature and below was not observed.
An improved laser-schlieren system for measurement of shock-wave velocity
Bander, J. A.; Sanzone, G. (AIP Publishing, 1974-07)
An improved laser_schlieren system for the measurement of shock_wave velocities has been developed which employs a single detector.Calibration of multiple detectors has been obviated. The system has been shown to yield, in addition to the shock_wave velocity, additional information on the arrival time of the contact surface. Shock_tube performance is compared to the predictions of Mirels' theories.
High-resolution time-of-flight mass spectrometry impulse-field focusing pulse generators
Miller, R. L.; Browder, J. A.; Sanzone, G. (AIP Publishing, 1986-08)
Experiments have shown that the unit mass resolution of conventional Wiley-McLaren time_of_flight (TOF)mass spectrometers can be significantly improved using the technique of impulse_field focusing (IFF). Details of the circuitry used to test the IFF theory are presented. Generators of electrical pulses with nanosecond rise times and 100_V amplitudes are described.
Surface-analysis of gold containing polyimide films
Madeleine, Dennis Gerard; Spillane, S. A.; Taylor, Larry T. (American Institute of Physics, 1987-05)
Polyimide films with metallic surfaces were produced by thermal treatment of solutions containing HAuCl4⋅3H2O, hydrogen tetrachloroaurate trihydrate, and either Ciba–Geigy XU 218, poly[5(6)‐amino‐1‐(4’ phenyl)‐1,3,3 trimethylindane‐3,3’,4,4’‐benzophenonetetracarboxylimide] or BTDA‐ODA, poly [ p, p’‐oxybis (phenylene)‐3,3’,4,4’‐benzophenonetetracarboxylimide]. Scanning electron microscopy indicated that 0.1‐μ particles covered a large portion of the air side surface; whereas, 10‐μ particles covered the glass side surface of these films.Auger electron spectroscopy and x‐ray photoelectron spectroscopy(XPS) indicated that the particles were gold in the metallic state. Model imide compounds were synthesized and used to evaluate the XPS spectra of both unmodified and gold containing films.Surfaceanalysis data suggested that only a small amount of gold was located within the XPS sampling depth and that the observed gold particles resided underneath a polyimide overlayer. The discrete metal particles had an unexpected influence on the photoelectron spectra of the polyimide and the influence was dependent on particle size. A schematic model of the multilayered modified filmsurface was developed and the model further probed by electron flood gun and metal vapor deposition studies.
Raman-scattering and optical studies of argon-etched GaAs surfaces
Feng, G. F.; Zallen, Richard H.; Epp, June Miriam; Dillard, John G. (American Physical Society, 1991-04)
We have studied the structual damage in low-energy argon-ion-bombarded (ion-etched) GaAs using Raman scattering and ultraviolet reflectivity. When combined with post-bombardment sequential chemical etching, the Raman results reveal a graded depth profile of the damage layer, with a nearly linear damage dropoff with depth. The total damage-layer thickness is about 600 angstrom for high-fluence bombardment with 3.89-keV Ar+ ions. The spectral effects produced by argon etching are very different from those produced by high-energy ion implantation. The longitudinal-optic Raman line seen for argon-etched GaAs is not shifted and broadened as in ion-implanted GaAs. More striking are the results of the reflectivity measurements. For argon-etched GaAs, the electronic interband peaks are both broadened and strongly red shifted relative to the crystal peaks; for ion-implanted GaAs, only the broadening occurs. Distinct nanocrystals, which account for the effects seen in ion-implanted GaAs, are evidently absent in argon-etched GaAs. Instead, the damage layer caused by argon etching appears to be characterized by a very high density of point defects, which previous work suggests may be arsenic vacancies.
Method for the conversion of cephalomannine to taxol and for the preparation of n-acyl analogs of taxol
(United States Patent and Trademark Office, 1995-11-28)
The natural product cephalomannine can be converted to the important anticancer natural product taxol by a simple process involving the steps of dihydroxylation to give cephalomannine-diols, diol cleavage, benzoylation at the 2'-position and reaction with a 1,2-diamine. The same process when applied to mixtures of taxol and cephalomannine makes it possible to separate taxol from cephalomannine-diols by simple flash-chromatography after the dihydroxylation step. If the benzoylation step is avoided in the above sequence of conversions, the process leads to the free amine (N-debenzoyltaxol). In addition, the selection of an acylating reagent other than that with the benzoyl group for acylation of the free amine (N-debenzoyltaxol), allows the preparation of taxol analogs with other N-acyl substituents.
Synthesis of sphingosines
(United States Patent and Trademark Office, 1996-01-30)
Provided by the present invention is a process for the biocatalytic synthesis of optically pure sphingosines from achiral starting material. The stereoisomers of sphingosine are prepared from chiral arene diols using stereospecific reaction techniques to obtain the desired sphingosine or derivative thereof.
Synthesis of sphingosines
(United States Patent and Trademark Office, 1996-01-30)
Provided by the present invention is a process for the biocatalytic synthesis of optically pure sphingosines from achiral starting material. The stereoisomers of sphingosine are prepared from chiral arene diols using stereospecific reaction techniques to obtain the desired sphingosine or derivative thereof.
Aryl ethynyl phthalic anhydrides and polymers with terminal or pendant amines prepared with aryl ethynyl phthalic anhydrides
(United States Patent and Trademark Office, 1996-02-20)
Arylethynyl phthalic anhydrides have been synthesized and shown to have particular application as endcappers or pendant groups in high performance/high temperature thermosets which include amine terminal or amine pendant groups.
Metallic material with low melting temperature
(United States Patent and Trademark Office, 1996-04-16)
A gallium-indium-zinc-copper metallic material has been found to exhibit many of the advantageous properties of mercury, such as electrical conductivity, fluidity, and high vaporization temperature. The metallic material is formulated by combining individual components in the presence of aqueous base, isolating the metallic phase, and heating the metallic combination. The metallic material is formulated to have sufficient quantities of each of the individual components such that the metallic material has a solidification temperature below 0.degree. C.
Enhanced nonlinear optical response of an endohedral metallofullerene through metal-to-cage charge transfer
Heflin, James R.; Marciu, D.; Figura, C.; Wang, S.; Burbank, P.; Stevenson, Steven A.; Dom, H. C. (AIP Publishing, 1998-06)
A new mechanism for increasing the third-order nonlinear optical susceptibility, X-(3), is described for endohedral metallofullerenes. A two to three orders of magnitude increase in the nonlinear response is reported for degenerate four-wave mixing experiments conducted with solutions of Er-2@C-82 (isomer III) relative to empty-cage fullerenes. A value of - 8.7x 10(-32) esu is found for the molecular susceptibility, gamma(xyyx), of Er-2@C-82 compared to previously reported values of gamma(xxxx) = 3 x 10(-34) esu and gamma(xyyx) = 4 x 10(-35) esu for C-60. The results confirm the importance of the metal-to-cage charge-transfer mechanism for enhancing the nonlinear optical response in endohedral metallofullerenes. (C) 1998 American Institute of Physics.
Dependence of fluorescence lifetimes of Y2O3 : Eu3+ nanoparticles on the surrounding medium
Meltzer, R. S.; Feofilov, S. P.; Tissue, B.; Yuan, H. B. (American Physical Society, 1999-11)
The radiative lifetime, tau(R), of the D-5(0) metastable excited state of Eu3+ ions in nanocrystalline monoclinic Y2O3 samples is about four times longer than that in the micron size powder of the same material. The Eu3+ radiative lifetime was measured in nanocrystals surrounded with air as well as those immersed in different liquids. It is shown that the radiative lifetime changes with the index of refraction of the immersion medium and provides a unique test of the standard formula relating tau(R) and the oscillator strength. The magnitude of the effect is determined by the "filling factor" (the fraction of the sample volume occupied by nanocrystals) which can therefore be determined. [S0163-1829(99)51144-2].
Evidence for long-range interactions between rare-earth impurity ions in nanocrystals embedded in amorphous matrices with the two-level systems of the matrix
Meltzer, R. S.; Yen, W. M.; Zheng, H. R.; Feofilov, S. P.; Dejneka, M. J.; Tissue, B. M.; Yuan, H. B. (American Physical Society, 2001-09)
The low-temperature homogeneous broadening of the electronic transitions of Eu3+ and Pr3+ rare-earth impurity ions in Y2O3 and LaF3 nanocrystals embedded into amorphous materials (polymer and oxyfluoride glass ceramics) was studied with hole-burning and fluorescence line narrowing techniques. It is-shown that the homogeneous linewidth is determined by the interaction of the impurity ions contained in the nanocrystals with the two-level systems (TLS's) of the surrounding glass matrix. A comparison of the experiments with a calculation provides direct evidence for the long-range nature of the interaction with the TLS's.
Low-resistance films of polyimides with impregnated copper sulfide
Rowe, R. V. A.; Kunita, M. H.; Porto, M. F.; Muniz, E. C.; Rubira, A. F.; Nery, R. C.; Radovanovic, E.; Taylor, Larry T.; Nazem, N. (Cambridge University Press, 2001-11)
Surface modification of polyimides has been used to obtain better interaction with an inorganic material. Copper sulfide incorporation onto the surface of commercial Kapton (R) polyimide showed that treatment with base was necessary for adherence of the copper sulfide to the polymeric matrix. The optimized conditions for composite preparation, obtained by response surface methodology, was pH 1.4 at 80 degreesC for 3.67 h. Using these conditions, we obtained electrical resistance as low as 1.0 ohm for CuS\Kapton (R) composites. These optimized conditions were used to prepare other low-resistance polyimide composites. The resulting composites were analyzed by photoelectron spectroscopy. The presence of S(2p) and Cu(2p) peaks demonstrated the incorporation of copper sulfide onto the polyimide surface. Scanning electron microphotographs and the images from atomic force microscopy showed a homogeneous CuS distribution in all composites.
Measurement of 3-alkyl-2-methoxypyrazine by headspace solid-phase microextraction in spiked model wines
Hartmann, Peter J.; McNair, Harold M.; Zoecklein, Bruce W. (American Society for Enology and Viticulture, 2002)
The effect of wine matrix ingredients and conditions on the headspace sampling of 3-alkyl-2-methoxypyrazines was investigated with solid-phase microextraction (SPME) and capillary gas chromatography, using a nitrogen phosphorus detector. Changes in the recovery of 3-ethyl-, isopropyl-, sec-butyl-, and isobutyl-2-methoxypyrazines from the static headspace of synthetic wine matrices spiked with 5 mug/L of each analyte were investigated and reported as a function of SPME fiber type, extraction time, and temperature. The influence of pH, ethanol, phenolics, and oak was studied. Divinylbenzene/carboxen/polyclimethylsiloxane (PDMS) SPME fibers at an extraction temperature of 50degreesC for 30 minutes with 30% (w/v) added sodium chloride resulted in the highest analyte recoveries. Although PDMS (100 mum) SPME fibers at an extraction temperature of 35degreesC for 30 minutes with 30% (w/v) added sodium chloride resulted in lower analyte recoveries, the fiber remained functional for 50 to 75 analyses after other coatings deteriorated. Changing the sample ethanol concentration from 0 to 20% (v/v) resulted in an exponential decrease in the recovered analytes. Below pH 2, there was extensive loss of the analytes in the headspace. No measurable impact on alkyl-methoxypyrazine headspace concentrations was observed with exposures to selected phenolics and to oak.
Transience of plasma surface modification as an adhesion promoter for polychlorotrifluorethylene
Subrahmanyan, Sumitra; Dillard, John G.; Love, B. J.; Romand, M.; Charbonnier, M. (American Institute of Physics, 2002-05-01)
Poly (chlorotrifluoroethylene) (PCTFE) and other fluoropolymers are increasingly used as inner layer dielectrics. However, these polymers have low surface energies and correspondingly poor adhesive proper-ties. Results are presented on the use of a low-pressure ammonia plasma to enhance the surface bondability of PCTFE. The plasma modified PCTFE film surfaces were characterized by x-ray photoelectron spectroscopy and contact angle measurements, Surface modified films exhibited improved adhesion to electroless copper deposits (180degrees peel test) compared to coated PCTFE controls and that underwent no plasma exposure. Annealing studies were conducted between 30 and 100 degreesC to examine the stability of the plasma-modified surfaces. For samples annealed below T-g. contact angle measurements indicated that the plasma-introduced groups remained bound on the surface for four weeks. For specimens annealed above Tg, the surface functionalities were absorbed within the bulk and surface rearrangement occurred within 10 h of annealing time. As a result of rearrangement, the benefit of adhesion enhancement by plasma is lost and the adhesion to copper is reduced. (C) 2002 American Vacuum Society.
Between the Scylla of hidebound conservatism and the Charybdis of mindless speculation
Bauer, Henry H. (Inter-Research, 2004)
The ‘quality’ of a scientific publication is not an absolute but must be assessed in relation to a journal’s mission. It should be judged primarily by its disciplined intellectual rigor, bearing in mind what course the publication aims to take, as between the Scylla of hidebound conservatism and the Charybdis of mindless speculation. One commonly applied measure of the ‘quality’ of a periodical, perhaps most overtly in the social sciences, is its rejection rate: the higher that rate, the higher the presumed quality. In the natural sciences, a somewhat similar criterion is invoked, perhaps less overtly and certainly less quantitatively, when kudos comes for being published in journals ‘hard to get into’, such as Nature or Science or the Journal of the American Chemical Society. But consider the professed, or implicitly taken-for-granted, aim of these ‘top’ journals. Actually, there are 2 aims: that what gets published should be ground breaking; and that what gets published should not be in error. But it seems not to be commonly understood that these aims are incompatible. The first implies a willingness to be often wrong, at least to some degree, because it is always difficult to judge the validity of something that is without precedent. On the other hand, the second places high barriers in the way of anything so novel as to call into question ideas that have hitherto been widely accepted. Between these 2 incompatible aims, no journal can avoid making its own choice, at least implicitly, in which direction to lean. The judgment of a journal’s quality should then be based upon how well it performs its chosen task, not according to whether one agrees or differs with the journal’s aim of emphasizing novelty over reliability or vice versa.
Influence of buried hydrogen-bonding groups within monolayer films on gas-surface energy exchange and accommodation
Ferguson, M. K.; Lohr, J. R.; Day, Brian Scott; Morris, J. R. (American Physical Society, 2004-02-20)
Self-assembled monolayers (SAMs) of carbonyl-containing alkanethiols on gold are employed to explore the influence of hydrogen-bonding interactions on gas-surface energy exchange and accommodation. H-bonding, COOH-terminated SAMs are found to produce more impulsive scattering and less thermal accommodation than non-H-bonding, COOCH3-terminated monolayers. For carbamate-functionalized SAMs of the form Au/S(CH2)(16)OCONH(CH2)(n-1)CH3, impulsive scattering decreases and accommodation increases as the H-bonding group is positioned farther below the terminal CH3.
Scanning near-field optical microscopy utilizing silicon nitride probe photoluminescence
Lulevich, Valentin; Ducker, William A. (AIP Publishing, 2005-11)
We describe a simple method for performing high-resolution scanning near-field optical microscopy (SNOM). A commercial Si3N4 tip is illuminated by an intense light source, which causes the tip to emit redshifted (inelastically scattered) light. Part of the redshifted light passes through a sample, allowing transmission light microscopy. By simple modification of a commercial atomic force microscopes (AFM), we are able to image many different samples with high-resolution optical microscopy, achieving 20-30 nm lateral resolution for the best samples. The high resolution of the technique is not only due to the high curvature of the AFM tip, but also to the fact that the intensity of inelastically scattered light transmitted through the sample decays exponentially with the separation between the tip and the sample (decay length similar to 100 nm). We envisage applications to transmission SNOM, spectroscopic imaging, and imaging of fluorescently labeled bioconjugates. The collection of the optical image does not interfere with the normal operation of the AFM, so deflection, height, or other modes of operation can be captured simultaneously. (c) 2005 American Institute of Physics.
An atomic force microscope tip as a light source
Lulevich, V.; Honig, Christopher D. F.; Ducker, William A. (AIP Publishing, 2005-12-01)
We present a simple method for causing the end of a silicon nitride atomic force microscope (AFM) tip to emit light, and we use this emitted light to perform scanning near-field optical microscopy. Illumination of a silicon nitride AFM tip by blue (488 nm) or green (532 nm) laser light causes the sharp part of the tip to emit orange light. Orange light is emitted when the tip is immersed in either air or water; and while under illumination, emission continues for a period of many hours without photobleaching. By careful alignment of the incident beam, we can arrange the scattered light to decay as a function of the tip-substrate separation with a decay length of 100-200 nm. The exponential decay of the intensity means that the emitted light is dominated by contributions from parts of the tip that are near the sample, and therefore the emitted orange light can be used to capture high-resolution near-field optical images in air or water. (c) 2005 American Institute of Physics.

Browse

Browsing Scholarly Works, Chemistry by Issue Date

Results Per Page

Sort Options