Bruce H Weiller

Aerospace Corporation · Space Materials Laboratory

Embodiments of the present invention provide systems and methods for inhibiting contamination enhanced laser induced damage (CELID) based on fluorinated self- assembled monolayers (F-SAMs) disposed on optics. For example, a coating for inhibiting CELID to an optic disposed in a sealed gas environment or vacuum may include an F-SAM that includes...

A method for sensing hydrogen includes the use of a transduction device with a sensing layer, and means for measuring a mass and/or conductivity change caused by an interaction of a gas with the sensing layer to provide a measure of an amount of hydrogen in the gas. The sensing layer includes polyaniline nanofiber material.

A sensor for detecting phosgene includes a pair of electrodes separated by an electrode gap, and a layer of conducting polymer material positioned over and making electrical contact with the pair of electrodes, the layer of conducting polymer material being modified with an amine such that the electrical resistance of the conducting polymer materia...

We demonstrate vertical graphene-base hot-electron transistors (GB-HETs) with a variety of structures and material parameters. Our GB-HETs exhibit a current saturation with a high current on-off ratio (>105), which result from both the vertical transport of hot electrons across the ultra-thin graphene base and the filtering of hot electrons through...

We explore the feasibility of growing a continuous layer of graphene in pre-patterned substrates, like an engineered silicon wafer, and we apply this as a mold for the fabrication of AFM probes. This fabrication method proves the fabrication of SU-8 devices coated with graphene in a full-wafer parallel technology and with high yield. It also demons...

This paper describes a novel approach for the suppression of contamination enhanced laser damage to optical components by the use of fluorinated coatings that repel organic contaminates. In prior work we studied laser damage thresholds induced by ppm levels of toluene under nanosecond 1.064 μm irradiation of fused silica optics. That work showed th...

To study the effects of hydrocarbon precursor gases, graphene is grown by chemical vapor deposition from methane, ethane, and propane on copper foils. The larger molecules are found to more readily produce bilayer and multilayer graphene, due to a higher carbon concentration and different decomposition processes. Single- and bilayer graphene can be...

Engineering a low-cost graphene-based electronic device has proven difficult to accomplish via a single-step fabrication process. Here we introduce a facile, inexpensive, solid-state method for generating, patterning, and electronic tuning of graphene-based materials. Laser scribed graphene (LSG) is shown to be successfully produced and selectively...

With dark field transmission electron microscopy and select area electron diffraction (SAED) crystallographic grain boundaries in graphene can be easily imaged. We present a complete, quantitative theoretical model of the SAED pattern that allows determination of the number of layers. Grain boundary maps of single and multilayer graphene grown by c...

Graphene's single atomic layer of sp(2) carbon has recently garnered much attention for its potential use in electronic applications. Here, we report a memory application for graphene, which we call graphene flash memory (GFM). GFM has the potential to exceed the performance of current flash memory technology by utilizing the intrinsic properties o...

Growth of graphene on copper (100) single crystals by chemical vapor deposition has been accomplished. The atomic structure of the graphene overlayer was studied using scanning tunneling microscopy. A detailed analysis of moiré superstructures present in the graphene topography reveals that growth occurs in a variety of orientations over the square...

The atomic structure of graphene on polycrystalline copper substrates has been studied using scanning tunneling microscopy. The graphene overlayer maintains a continuous pristine atomic structure over atomically flat planes, monatomic steps, edges, and vertices of the copper surface. We find that facets of different identities are overgrown with gr...

The gas-phase chemical reactions in the Metallorganic Chemical Vapor Deposition (MOCVD) of AlN and TiN have been studied using IR spectroscopy. The products formed from the reaction of trimethyl aluminum (TMA) and NH3 were compared to those from the reaction of TMA with NF3 using a static gas-phase IR cell. Reaction with NH3 is rapid at 25 °C, and...

We have characterized the thresholds for contamination laser induced damage (C-LID) process using toluene as a model contaminant by varying oxygen and toluene concentrations. In the presence of 300 ppm toluene and nitrogen, the damage threshold is (7.8 +/- 1.9) × 103 laser pulses, in synthetic air the damage threshold is (18.0 +/- 2.1) × 103 laser...

Several orders of magnitude of change in resistance are observed upon chemical doping and dedoping of the conducting polymer polyaniline. This large conductivity range can be utilized to make sensitive chemical sensors. Polyaniline, in its nanofiber form, has even greater sensing capabilities due to the small fiber diameters, high surface area, and...

We report the use of polyaniline nanofiber-metal salt composites for the detection of arsine gas (AsH(3)) using the resistance change of the materials. Aqueous dispersions of polyaniline nanofibers facilitate the preparation of metal salt/polyaniline nanofiber composites with the use of water-soluble inorganics. Various composites were tested Inclu...

Polyaniline nanofibers were deposited on either gold or platinum electrodes and used as resistive sensors for the detection of hydrogen. In earlier work (J. Phys. Chem. B 2006, 110, 22266-22270), we showed that hydrogen interacts directly with polyaniline nanofibers to induce a small resistance decrease (-3%) at low concentrations of hydrogen (1%)...

We report the development of useful chemical sensors from chemically converted graphene dispersions using spin coating to create single-layer films on interdigitated electrode arrays. Dispersions of graphene in anhydrous hydrazine are formed from graphite oxide. Preliminary results are presented on the detection of NO(2), NH(3), and 2,4-dinitrotolu...

Reduced graphite oxide (GO) has shown promise as a scalable alternative to mechanically exfoliated specimens. Although many measurements show that reduced GO has properties approaching those of pristine graphene, it has been difficult to quantify the extent to which the graphitic network is restored upon reduction. Raman spectroscopy is widely used...

Contamination-enhanced Laser Induced Damage (CLID) occurs when molecular or particulate contamination, present on or in the vicinity of an optical material, leads to accelerated laser power degradation and premature failure. The physical mechanisms that cause CLID are not sufficiently understood to predict the extent to which a contaminant will cau...

The electrical properties of polyaniline changes by orders of magnitude upon exposure to analytes such as acids or bases, making it a useful material for detection of these analytes in the gas phase. The objectives of this lab are to synthesize different diameter polyaniline nanofibers and compare them as sensor materials. In this experiment polyan...

The electrical properties of the conducting polymer polyaniline change greatly upon exposure to various chemicals. Specifically, polyaniline undergoes doping and dedoping chemistry with acids and bases that result in conductivity changes of over eight orders of magnitude. This large range in conductivity can be utilized to make polyaniline chemical...

A template‐free method for the production of polypyrrole nanofibers is presented. By adding a small amount of bipyrrole into the oxidative polymerization of pyrrole, a drastic change in the morphology of the observed material is observed from large, granular particles to nanofibrils with an average diameter of 20 nm. This simple procedure allows fo...

Copper acetate and related metal salt films react directly with hydrogen sulfide at room temperature to form metal sulfides, resulting in conductivity changes as large as 108. The observed changes in conductivity are related to the solubility product constant (Ksp) and the difference in conductivity between the metal salt and the resulting metal su...

Hydrogen causes a reversible decrease in the resistance of a thin film of camphorsulfonic acid doped polyaniline nanofibers. For a 1% mixture of hydrogen in nitrogen, a 3% decrease in resistance is observed (DeltaR/R = -3%). The hydrogen response is completely suppressed in the presence of humidity. In contrast, oxygen does not inhibit the hydrogen...

A bulk synthetic method that yields uniform polyaniline nanofibers with narrow size distribution, which can be adjusted from 30 to 120 mm, was analyzed. The polyaniline nanofibers used as chemical sensors offers high surface area and small diameter, which facilitates the diffusion of molecules and dopants into the nanofibers. In this experiment, as...

A new sensor for hydrazine detection is reported using conventional polyaniline thin films processed from hexafluoroisopropanol. This and other fluorinated alcohols are shown to react with hydrazine to produce a strong acid. The hydrofluoric acid (HF) protonates the emeraldine base form of polyaniline leading to large increases in conductivity-grea...

The conjugated polymer polyaniline is a promising material for sensors, since its conductivity is highly sensitive to chemical vapors. Nanofibers of polyaniline are found to have superior performance relative to conventional materials due to their much greater exposed surface area. A template-free chemical synthesis is described that produces unifo...

This paper describes the fabrication and characterization of a micromachined, micro hot plate (MHP) sensor substrate for chemical sensor applications. The MHPs were fabricated using a silicon-processing foundry followed by a novel combination of laser and chemical etching of individual die. An IR microscope was used for thermal imaging of the MHP a...

Using a new interfacial polymerization method for the synthesis of polyaniline nanofibers, we have developed nanofiber sensors and compared them to conventional polyaniline sensors. Five different response mechanisms are explored: acid doping (HCl), base dedoping (NH3), reduction (with N2H4), swelling (with CHCl3), and polymer chain conformational...

Polyaniline nanofibers with uniform diameters between 30 and 50 nm can be made in bulk quantities through a facile aqueous/organic interfacial polymerization method at ambient conditions. The nanofibers have lengths varying from 500 nm to several micrometers and form interconnected networks. Thin films made of the nanofibers have superior performan...

Due to the mounting evidence for altered lipoprotein and cholesterol-lipoprotein content in several disease states, there has been an increasing interest in analytical methods for lipoprotein profiling for diagnosis. The separation of low- and high-density lipoproteins (LDL and HDL, respectively) has been recently demonstrated using a microchip cap...

The development of a new assay for lipoproteins by capillary electrophoresis in fused-silica capillaries and in glass microdevices is described in this paper. The separation of low-density (LDL) and high-density (HDL) lipoproteins by capillary zone electrophoresis is demonstrated in fused-silica capillaries with both UV absorption and laser-induced...

This paper demonstrates low density lipoprotein (LDL) analysis in a chip-based system without coatings, and is the continuation of work by Weiller et al. (in this Proceedings). It is shown that peak efficiency can be improved remarkably by adding a small amount of sodium dodecyl sulfate (SDS) to the sample. The method proposed here could be adopted...

This paper describes the development of a new, chip-based assay for lipoproteins by capillary electrophoresis. The separation of low-density (LDL) and high-density (HDL) lipoproteins by capillary zone electrophoresis (CZE) was first demonstrated in fused-silica capillaries with both UV absorption and laser-induced fluorescence (LIF) detection. This...

We have tested a suite of micromachined chemical sensors on STS-93. This experiment is one of several incorporated in the overall Micro/Nano Technology (MNT) Testbed developed at The Aerospace Corporation. The sensors used in this experiment include: (1) a micromachined interferometer for carbon dioxide (CO2) detection, (2) a palladium thin-film se...

Titanium nitride films were deposited from tetrakis(ethylmethylamido)titanium and ammonia at 250-350 degrees C and 0.7-2 Torr by thermal chemical vapor deposition. The effect of process parameters such as deposition temperature, precursor temperature, carrier gas flow, and ammonia flow on the film properties was studied, the apparent activation ene...

The Aerospace Corporation is sponsoring research into the development and use of Nanotechnology Instrumentation in support of Space Launch applications. The intent is to use nanotechnology-based commercial-off-the-shelf components (COTS) micro-electromechanical (MEMS) and in-house developed sensors as basis for a wired or wireless sensors instrumen...

The trace detection of chemicals has become increasingly important to the successful production, launch and operation of spacecraft. Chemical microsensors are inexpensive, lightweight, miniature transducers for the direct detection of trace chemicals. These devices can be integrated with microprocessors and communication to form intelligent systems...

The effect of HNMe(2) on the chemical vapor deposition of TiN from tetrakis(dimethylamido)titanium and NH3 was examined. The growth rates were enhanced almost sevenfold with the addition of HNMe(2). However, HNMe(2) did not have a significant effect on the resistivity, composition, or conformality of the films under the conditions studied. The most...

The gas-phase kinetics of the reaction of tetrakis(dimethylamido)titanium (Ti(NMe(2))(4)) with NH3 have been measured using a flow tube reactor and FTIR spectrometer. Ti(NM(2))(4) reacts rapidly with NH3 in a transamination reaction to form HNMe(2) as a direct product. The bimolecular rate constant for the reaction of Ti(NMe(2))(4) with NH3 at 24 d...

Pentamethylcyclopentadienyliridium(I) complexes are now known to undergo rapid and general oxidative addition reactions with a wide range of carbon-hydrogen bonds, including those in alkanes and isolated alkyl groups. The first part of this paper describes flash kinetic experiments carried out on pentamethylcyclopentadienylrhodium carbonyl complexe...

Flash kinetic spectroscopy with infrared detection is used to probe C-H activation of cyclohexane-d(0) and -d(12) by intermediates generated upon ultraviolet irradiation of Cp*Rh(CO)(2) (Cp* = C-5(CH3)5) in liquid rare gas (Rg = Kr or Xe) solution at low temperature (163-193 K). Upon UV photolysis, a new C-O stretching band (at 1946.5 cm(-1) in Kr...

We have been investigating several chemical microsensor technologies for the detection of chemicals found in propellant and rocket exhaust plumes and as contaminants for satellite components. In this work we have developed a catalytic metal sensor for the detection of H2 contamination in electronic device packages. The sensor is based on the resist...

Photolysis of M(CO)6 (M = Cr and W) in low-temperature, rare-gas solutions leads to the formation of transient organometallic complexes between M(CO)5 and weak ligands, including CO2, N2O, Xe and Kr. Time-resolved IR spectroscopy was used to capture IR spectra of the complexes over the temperature range of 150 to 200 K. A detailed kinetic investiga...

We have been investigating kinetics issues associated with the development of a new chemical laser in the green based on the b-X transition of NF at 529 nm. The proposed scheme involves energy pooling of NF(a1(Delta) ) with I*(2P1/2) to form NF(b1(Sigma) ). The kinetics of NF(a) and NF(X) have a strong impact on the relative populations of NF(X) an...

The reaction of Cp*Rh(CO)Xe (Cp* = C5Me5) with CO was studied using time-resolved IR spectroscopy of liquid rare gas solutions. IR spectra for Cp*Rh(CO)Xe were obtained using pulsed UV laser photolysis of Cp*Rh-(CO)2 in liquid Xe and a rapid-scan FTIR spectrometer with 0.09-s time resolution. Assignment to the Xe complex was confirmed from the simi...

This paper explores the use of a flow-tube reactor coupled to an FTIR spectrometer to study gas-phase chemical reactions in CVD systems. We show that our apparatus can generate reliable kinetics data by reproducing the literature rate constant for the reaction between O3 and isobutene. We present data from this apparatus on two technologically impo...

The gas-phase chemical reaction between Ti(NMe2)4 and NH3 is a critical step in the Metallorganic Chemical Vapor Deposition (MOCVD) of TiN at low temperatures. We have examined this reaction using a flow-tube reactor coupled to an FTIR spectrometer. A sliding injector provides control over the reaction time and the kinetics of reactive species can...

IR spectra for complexes between Xe and Kr and M(CO)5 (M = Cr, W) have been obtained using laser photolysis of M(CO)6 and rapid-scan FTIR spectroscopy of liquid rare-gas solutions. The Kr complexes have lifetimes of approximately 0.1 s at 150 K in liquid Kr while W(CO)5Xe has a lifetime of approximately 1.5 min at 170.0 K in liquid Xe. W(CO)5Xe rea...

The kinetics of NF(a 1 Δ) and NF(X 3 Σ - ) have been examined using excimer laser photolysis of NF 2 in premixed samples to produce both species. NF(a) was detected by its emission to the ground state, and NF(X) was detected by laser-induced fluorescence.

The kinetics of NF(a1DELTA) and NF(X3SIGMA-) have been examined using excimer laser photolysis of NF2 in premixed samples to produce both species. NF(a) was detected by its emission to the ground state, and NF(X) was detected by laser-induced fluorescence. The rate constants obtained for quenching of NF(a) by NF3, I2, and O2 are (7.4 +/- 0.7) X 10(...

The fast, near-resonant energy pooling between electronically excited NF(a1DELTA) and (I*(P1/2))-P-2 to form NF(b1SIGMA+) has been investigated at 448 K using pulsed I* laser optical pumping. These reagents were obtained from 193-nm photolysis of HI in the presence of NF2 and buffer gas mixtures. During the saturating I* laser pulse, analysis of th...

The fast, near-resonant energy pooling between electronically excited NF(a¹Δ) and I*(²P1/2) to form NF(b¹Σ+) has been investigated at 448 K using pulsed I* laser optical pumping. These reagents were obtained from 193-nm photolysis of HI in the presence of NF2 and buffer gas mixtures. During the saturating I* laser pulse, analysis of the NF(b1Σ⁺) ti...

The kinetics of the reactions of NF(X) with NF(X), NF2, and NF3 were studied, using UV photolysis (248 nm) of NF2 to produce NF(X) and laser-induced fluorescence (LIF) to monitor the time dependence of NF(X) as a function of reactant density. The rate constant for the reaction of NF(X) with NF2, measured under pseudofirst order conditions, is 2.40...

The reaction of Fen (n = 7-27) clusters with H2O and D2O are studied in a continuous flow reactor coupled with a laser-vaporization cluster source and the reaction products are detected via laser ionization and time-of-flight mass spectrometry.

The study of gas phase chemical reactions of neutral metal clusters with simple molecules has become feasable due to the development of the pulsed fast flow reactor and the low pressure continuous flow tube reactor. In both devices a laser vaporization cluster source is coupled to the flow tube reactor. An inert carrier gas enables both cluster for...

The photochemical reaction of the dihydride (I) with a variety of organic substrates, e.g. (II) (9 examples) in liquid xenon leads to oxidative addition products of the type (III).

The reactions of neutral iron clusters Fe{sub 7--27} with water are studied in a laser-vaporization cluster source coupled to a continuous-flow reactor. Reaction products are detected via laser ionization and time-of-flight mass spectrometry. The reactions of room-temperature clusters with H{sub 2}O show adsorbate decomposition and hydrogen desorpt...

Since the first demonstration of the intermolecular oxidative addition of alkane C-H bonds to transition-metal centers, there have been many studies of the mechanism of this reaction. While these studies have illuminated many aspects of the C-H activation process, they do not provide direct information about the reactive intermediates or the potent...

Chemical change is a science of intermediates. Reactive molecules and fragments guide the chemistry of multicomponent systems and determine the stereospecific outcomes of individual reactions. Organometallic chemistry is among the richest of all for its transient species. Metal-centered intermediates variously appear and disappear via oxidative add...

The new short-lived complex cis-Cr(CO)/sub 4/(C/sub 2/H/sub 4/)/sub 2/ is observed by time-resolved IR absorption spectrometry after pulsed laser photolysis of gaseous mixtures of Cr(CO)/sub 5/(C/sub 2/H/sub 4/) and C/sub 2/H/sub 4/. No evidence is found for associated production of trans-Cr(CO)/sub 4/(C/sub 2/H/sub 4/)/sub 2/. cis-Cr(CO)/sub 4/(C/...

The new short-lived complex cis-Cr(CO)/sub 4/(C/sub 2/H/sub 4/)/sub 2/ is observed by time-resolved IR absorption spectrometry after pulsed laser photolysis of gaseous mixtures of Cr(CO)/sub 5/(C/sub 2/H/sub 4/) and C/sub 2/H/sub 4/. No evidence is found for associated production of trans-Cr(CO)/sub 4/(C/sub 2/H/sub 4/)/sub 2/. cis-Cr(CO)/sub 4/(C/...

Evidence is presented for structural changes in iron clusters in the Fe13 to Fe23 size range. Abrupt changes with cluster size are found for several chemical properties, including reactivity with hydrogen and binding energies of ammonia and water. These changes often come at the same cluster sizes, pointing to a common origin—fundamental changes in...

The new short-lived complex cis-Cr(CO)4(C2H4)2 is observed by time-resolved IR absorption spectrometry after pulsed laser photolysis of gaseous mixtures of Cr(CO)5(C2H4) and C2H4. No evidence is found for associated production of trans-Cr(CO)4(C2H4)2. cis-Cr(CO)4(C2H4)2 reacts with CO to re-form Cr(CO)5(C2H4) by dissociative substitution. From the...

Pulsed laser photolysis of mixtures of (I) and C2H4 yields the transient gas-phase complexes (II) and (III).

The title compound is unstable and reacts with CO by dissociative substitution.

Fe(CO)3(C2H4)2 with CO at 297 K to form Fe(CO)4(C2H4).

Olefin complexes of metal carbonyl fragments have theoretical importance and play a role in numerous catalytic systems. Theory suggests an interesting trend in bond strengths for the bis-olefin and diene complexes of the 16-electron group VI (group 6) carbonyl fragments. Bis-olefin complexes of M(CO)/sub 4/ (M = Cr, Mo, W) are generally thought to...

The transient gas-phase complexes, cis-Fe(CO)â(CâHâ)â, trans-Fe(CO)â(CâHâ)â, and Fe(CO)(CâHâ)â, are observed by time-resolved IR absorption spectrometry after pulsed laser photolysis of mixtures of Fe(CO)â(CâHâ)â and CâHâ. The isomers of Fe(CO)â(CâHâ)â relax by two, parallel dissociate substitution pathways to reform Fe(CO)â(CâHâ)â. From the CO and...

Gas-phase Fe(CO)3(C2H4)2is observed to react thermally with CO at 297 K to form Fe(CO)4(C2H4) by the mechanism of dissociative substitution. From the CO and ethylene pressure dependencies of the observed reaction rate, the unimolecular decay constant for Fe(CO)3(C2H4) is found to be 2.9 ± 0.3 X 10-3 s-1. In addition, the elementary branching ratio...

The catalytic cycle for the water gas shift reaction is initiated under mild conditions (5-65 degree C) by the pulsed laser (337 nm) irradiation of M(CO)//6 (M equals Cr, W) in basic water/methanol solution. CO is supplied to the reaction as NaO//2CH. The cycle displays conventional saturation behavior in formate substrate concentration. The format...

Die Stereochemie der Umlagerung von (2S)-a-Lysin (I) unter der Einwirkung der Titelspezies in (3 S)-β-Lysin (II) wird anhand von Versuchen mit deuterierten Analogen (Darstellung beschrieben) eingehend untersucht.

The stereochemistry of lysine 2,3-aminomutase in Clostridium subterminale strain SB4 has been elucidated. Deuterium NMR has been used to show that the transformation of (2S)-α-lysine to (3S)-,β-lysine proceeds with transfer of the 3-pro-R hydrogen of α-lysine to the 2-pro-R position of β-lysine. The 3-pro-S hydrogen of α-lysine is retained at C-3 o...

(2RS,3S)-[4-13C]Valine was diazotized and converted to (2RS, 3S)-[4-13C]-2-bromoisovaleric acid, which on reduction with Zn/HCl gave (3S)-[4-13C] isovaleric acid. This was converted to (3S)-[4-13C] isovaleraldehyde, which was converted by a Strecker synthesis to (2RS,4S)-[5-13C] leucine. Resolution via the N-acetate then gave (2S,4S) and (2R,4S)-[5...

Die Einwirkung des Titelenzyms - aus Clostridium SB4 (zellfreier Extrakt) - auf L-Lysin führt zu einer gleichzeitigen Wanderung des H-Atoms am C-3 zu C-2 und der NHz-Gruppe am C-2 zu C-3 unter jeweiliger Konfigurationsinversion, wie anhand der Überführung der deuterierten Substrate (Ia)-(Ic) in die umgelagerten Derivate (II) gezeigt wird.

An electronic nose to be used as an air quality monitor in human habitats in space has been developed at the Jet Propulsion Laboratory. This device is capable of detecting, identifying and quantifying several organic and inorganic chemical species which might be present as contaminants in spacecraft air. The complete portable device, including sens...

The chemical reactions of neutral iron clusters with DâO are studied in a continuous flow tube reactor by molecular beam sampling and time-of-flight mass spectrometry with laser photoionization. Product distributions are invariant to a four-fold change in reaction time demonstrating that equilibrium is attained between free and adsorbed DâO. The ob...

Gas-phase Fe(CO)â(CâHâ)â is observed to react thermally with CO at 297 K to form Fe(CO)â(CâHâ) by the mechanism of dissociative substitution. From the CO and ethylene pressure dependencies of the observed reaction rate, the unimolecular decay constant for Fe(CO)â(CâHâ) is found to be 2.9 +/- 0.3 x 10⁻³ s⁻¹. In addition, the elementary branchi...

Olefin complexes of metal carbonyl fragments have theoretical importance and play a role in numerous catalytic systems. Theory suggests an interesting trend in bond strengths for the bis-olefin and diene complexes of the 16-electron group VI (group 6) carbonyl fragments. Bis-olefin complexes of M(CO)â (M = Cr, Mo, W) are generally thought to be mor...