Electrostatic force microscopy on oriented graphite surfaces: coexistence of insulating and conducting behaviors.

PubMed

Lu, Yonghua; Muñoz, M; Steplecaru, C S; Hao, Cheng; Bai, Ming; Garcia, N; Schindler, K; Esquinazi, P

2006-08-18

We present measurements of the electric potential fluctuations on the surface of highly oriented pyrolytic graphite using electrostatic force and atomic force microscopy. Micrometric domainlike potential distributions are observed even when the sample is grounded. Such potential distributions are unexpected given the good metallic conductivity of graphite because the surface should be an equipotential. Our results indicate the coexistence of regions with "metalliclike" and "insulatinglike" behaviors showing large potential fluctuations of the order of 0.25 V. In lower quality graphite, this effect is not observed. Experiments are performed in Ar and air atmospheres.

Ordered water structure at hydrophobic graphite interfaces observed by 4D, ultrafast electron crystallography

PubMed Central

Yang, Ding-Shyue; Zewail, Ahmed H.

2009-01-01

Interfacial water has unique properties in various functions. Here, using 4-dimensional (4D), ultrafast electron crystallography with atomic-scale spatial and temporal resolution, we report study of structure and dynamics of interfacial water assembly on a hydrophobic surface. Structurally, vertically stacked bilayers on highly oriented pyrolytic graphite surface were determined to be ordered, contrary to the expectation that the strong hydrogen bonding of water on hydrophobic surfaces would dominate with suppressed interfacial order. Because of its terrace morphology, graphite plays the role of a template. The dynamics is also surprising. After the excitation of graphite by an ultrafast infrared pulse, the interfacial ice structure undergoes nonequilibrium “phase transformation” identified in the hydrogen-bond network through the observation of structural isosbestic point. We provide the time scales involved, the nature of ice-graphite structural dynamics, and relevance to properties related to confined water. PMID:19246378

Producing graphite with desired properties

NASA Technical Reports Server (NTRS)

Dickinson, J. M.; Imprescia, R. J.; Reiswig, R. D.; Smith, M. C.

1971-01-01

Isotropic or anisotropic graphite is synthesized with precise control of particle size, distribution, and shape. The isotropic graphites are nearly perfectly isotropic, with thermal expansion coefficients two or three times those of ordinary graphites. The anisotropic graphites approach the anisotropy of pyrolytic graphite.

A scanning tunneling microscope study on an ordered mixed monolayer of bis(4,5-dihydronaphtho[1,2-d])-tetrathiafulvalene and n-tetradecane on highly oriented pyrolytic graphite.

PubMed

Zhao, Miao; Jiang, Peng; Deng, Ke; Jiang, Chao

2010-11-01

Tetrathiafulvalene (TTF) and its derivatives (TTFs) have been successfully used as building blocks to form charge transfer salts and organic semiconductors because of their special structures and rich electron nature. We report the formation of ordered mixed binary-component monolayer consisting of Bis(4,5-dihydronaphtho[1,2-d])tetrathiafulvalene (DH-TTF) and n-tetradecane (n-C14H30) molecules on highly oriented pyrolytic graphite (HOPG) surface. Scanning tunneling microscope (STM) imaging reveals that the two different kinds of molecules can spontaneously form ordered periodic phase separation structures on the substrate, in which ordered DH-TTF double- (or single-) lamella structures are periodically tuned by ordered n-C14H30 double- (or single-) lamella structures. Furthermore, scanning tunneling spectrum (STS) measurements by addressing the individual DH-TTF and n-C14H30 molecules in the ordered monolayer show that the two different kinds of molecules exhibit completely different I(V) characters on the HOPG substrate. The modulated arrangement of the TTF derivative by insulating molecules opens a possible route to construct organic conducting molecule ribbons for potential application in nanodevices.

[Study on the determination of trace gallium in molybdenum-coated pyrolytic graphite tube by electrothermal absorption spectrometry].

PubMed

Huang, Yu-an; Zhou, Fang-qin; Long, Si-hua; Yang, Liu

2004-02-01

The effects on gallium atomization in the pyrolytic graphite tube imposed by different matrix modifiers and different coatings were discussed detailedly in this paper. In the presence of matrix modifier of Ni(NO3)2 the matrix interference was eliminated efficiently. The pyrolytic graphite tubes were coated differently with lanthanum, zirconium, and molybdenum to avoid producing gallium carbide. Results showed that the tube with molybdenum coating was the best. On this basis, the mechanism of gallium atomization in the molybdenum-coated pyrolytic graphite tube using Ni(NO3)2 as a matrix modifier was studied furthermore; in addition, the parameters of the operation were optimized. As a result, a new method improved in many aspects was developed to detect trace gallium in complicated sample of gangue. The outcomes of practical applications indicated that the method could satisfy the requests of analysis and that the manipulations were simple to achieve. The characteristic content, the detection limit, and the adding recoveries were 2.12 x 10(-11) g, 1.4 x 10(-10) g and 97.4%-102.7% respectively, and the relative standard deviation was less than or equal to 3.6% (n = 11).

Molecular orientation of copper phthalocyanine thin films on different monolayers of fullerene on SiO{sub 2} or highly oriented pyrolytic graphite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Chenggong; Wang, Congcong; Liu, Xiaoliang

2015-03-23

The interface electronic structures of copper phthalocyanine (CuPc) have been studied using ultraviolet photoemission spectroscopy as different monolayers of C{sub 60} were inserted between CuPc and a SiO{sub 2} or highly ordered pyrolytic graphite (HOPG) substrate. The results show that CuPc has standing up configuration with one monolayer of C{sub 60} insertion on SiO{sub 2} while lying down on HOPG, indicating that the insertion layer propagates the CuPc-substrate interaction. Meanwhile, CuPc on more than one monolayers of C{sub 60} on different substrates show that the substrate orientation effect quickly vanished. Our study elucidates intriguing molecular interactions that manipulate molecular orientationmore » and donor-acceptor energy level alignment.« less

Electrochemical formation and characterization of Au nanostructures on a highly ordered pyrolytic graphite surface

NASA Astrophysics Data System (ADS)

Gómez, José J. Arroyo; Zubieta, Carolina; Ferullo, Ricardo M.; García, Silvana G.

2016-02-01

The electrochemical formation of Au nanoparticles on a highly ordered pyrolytic graphite (HOPG) substrate using conventional electrochemical techniques and ex-situ AFM is reported. From the potentiostatic current transients studies, the Au electrodeposition process on HOPG surfaces was described, within the potential range considered, by a model involving instantaneous nucleation and diffusion controlled 3D growth, which was corroborated by the microscopic analysis. Initially, three-dimensional (3D) hemispherical nanoparticles distributed on surface defects (step edges) of the substrate were observed, with increasing particle size at more negative potentials. The double potential pulse technique allowed the formation of rounded deposits at low deposition potentials, which tend to form lines of nuclei aligned in defined directions leading to 3D ordered structures. By choosing suitable nucleation and growth pulses, one-dimensional (1D) deposits were possible, preferentially located on step edges of the HOPG substrate. Quantum-mechanical calculations confirmed the tendency of Au atoms to join selectively on surface defects, such as the HOPG step edges, at the early stages of Au electrodeposition.

Neutron transmission measurements of poly and pyrolytic graphite crystals

NASA Astrophysics Data System (ADS)

Adib, M.; Abbas, Y.; Abdel-Kawy, A.; Ashry, A.; Kilany, M.; Kenawy, M. A.

The total neutron cross-section measurements of polycrystalline graphite have been carried out in a neutron wavelength from 0.04 to 0.78 nm. This work also presents the neutron transmission measurements of pyrolytic graphite (PG) crystal in a neutron wavelength band from 0.03 to 0.50 nm, at different orientations of the PG crystal with regard to the beam direction. The measurements were performed using three time-of-flight (TOF) spectrometers installed in front of three of the ET-RR-1 reactor horizontal channels. The average value of the coherent scattering amplitude for polycrystalline graphite was calculated and found to be bcoh = (6.61 ± 0.07) fm. The behaviour of neutron transmission through the PG crystal, while oriented at different angles with regard to the beam direction, shows dips at neutron wavelengths corresponding to the reflections from (hkl) planes of hexagonal graphite structure. The positions of the observed dips are found to be in good agreement with the calculated ones. It was also found that a 40 mm thick PG crystal is quite enough to reduce the second-order contamination of the neutron beam from 2.81 to 0.04, assuming that the incident neutrons have a Maxwell distribution with neutron gas temperature 330 K.

Thermophysical properties of graphite HOPG and HAPG in the solid state and under melting (from 2000 K up to 5000 K)

NASA Astrophysics Data System (ADS)

Savvatimskiy, A. I.; Onufriev, S. V.; Konyukhov, S. A.

2017-11-01

Experiments with HOPG graphite grade showed that the melting temperature of graphite equals 4800-4900 K and that the melting of graphite is possible only at elevated pressures. The data were obtained for resistivity, specific heat and input (Joule) energy up to 5000 K. HAPG (Highly Annealing Pyrolytic Graphite) is a form of highly oriented pyrolytic graphite. HAPG specimens in the form of strips (thickness 30 microns) were placed in a cell (between two plates of glass-sapphire). The specimen temperature was measured by a high speed pyrometer. The heat of fusion for both graphite grades (heated in a confined volume) was less (and specific heat - higher) than for the case with nearly free expansion. A possible reason for the observed effects is discussed in the report.

Synthesis of gold nanoparticles on the surface of pyrolytic graphite using penicillin as a stabilizing reagent and the catalytic oxidation of α-naphthylamine

NASA Astrophysics Data System (ADS)

Song, Y. Z.; Song, Y.; Cheng, Z. P.; Zhou, J. F.; Wei, C.

2013-01-01

Electrochemical synthesis of gold nanoparticles on the surface of pyrolytic graphite using penicillin as a stabilizing reagent was proposed. The gold nanoparticles were characterized by scanning electron microscopy, cyclic voltammetry, IR spectra, UV spectra, and powder X-ray diffraction spectra. The electro-chemical catalysis of penicillin for α-naphthylamine was demonstrated.

Thermal Performance of an Annealed Pyrolytic Graphite Solar Collector

NASA Technical Reports Server (NTRS)

Jaworske, Donald A.; Hornacek, Jennifer

2002-01-01

A solar collector having the combined properties of high solar absorptance, low infrared emittance, and high thermal conductivity is needed for applications where solar energy is to be absorbed and transported for use in minisatellites. Such a solar collector may be used with a low temperature differential heat engine to provide power or with a thermal bus for thermal switching applications. One concept being considered for the solar collector is an Al2O3 cermet coating applied to a thermal conductivity enhanced polished aluminum substrate. The cermet coating provides high solar absorptance and the polished aluminum provides low infrared emittance. Annealed pyrolytic graphite embedded in the aluminum substrate provides enhanced thermal conductivity. The as-measured thermal performance of an annealed pyrolytic graphite thermal conductivity enhanced polished aluminum solar collector, coated with a cermet coating, will be presented.

Scanning tunneling microscopy of the formation, transformation, and property of oligothiophene self-organizations on graphite and gold surfaces.

PubMed

Yang, Zhi-Yong; Zhang, Hui-Min; Yan, Cun-Ji; Li, Shan-Shan; Yan, Hui-Juan; Song, Wei-Guo; Wan, Li-Jun

2007-03-06

Two alkyl-substituted dual oligothiophenes, quarterthiophene (4T)-trimethylene (tm)-octithiophene (8T) and 4T-tm-4T, were used to fabricate molecular structures on highly oriented pyrolytic graphite and Au(111) surfaces. The resulted structures were investigated by scanning tunneling microscopy. The 4T-tm-8T and 4T-tm-4T molecules self-organize into long-range ordered structures with linear and/or quasi-hexagonal patterns on highly oriented pyrolytic graphite at ambient temperature. Thermal annealing induced a phase transformation from quasi-hexagonal to linear in 4T-tm-8T adlayer. The molecules adsorbed on Au(111) surface in randomly folded and linear conformation. Based on scanning tunneling microscopy results, the structural models for different self-organizations were proposed. Scanning tunneling spectroscopy measurement showed the electronic property of individual molecules in the patterns. These results are significant in understanding the chemistry of molecular structure, including its formation, transformation, and electronic properties. They also help to fabricate oligothiophene assemblies with desired structures for future molecular devices.

Low-energy electron diffraction study of potassium adsorbed on single-crystal graphite and highly oriented pyrolytic graphite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ferralis, N.; Diehl, R.D.; Pussi, K.

2004-12-15

Potassium adsorption on graphite has been a model system for the understanding of the interaction of alkali metals with surfaces. The geometries of the (2x2) structure of potassium on both single-crystal graphite (SCG) and highly oriented pyrolytic graphite (HOPG) were investigated for various preparation conditions for graphite temperatures between 55 and 140 K. In all cases, the geometry was found to consist of K atoms in the hollow sites on top of the surface. The K-graphite average perpendicular spacing is 2.79{+-}0.03 A , corresponding to an average C-K distance of 3.13{+-}0.03 A , and the spacing between graphite planes ismore » consistent with the bulk spacing of 3.35 A. No evidence was observed for a sublayer of potassium. The results of dynamical LEED studies for the clean SCG and HOPG surfaces indicate that the surface structures of both are consistent with the truncated bulk structure of graphite.« less

Surface Superstructure of Carbon Nanotubes on Highly Oriented Pyrolytic Graphite Annealed at Elevated Temperatures

NASA Astrophysics Data System (ADS)

An, Bai; Fukuyama, Seiji; Yokogawa, Kiyoshi; Yoshimura, Masamichi

1998-06-01

Carbon nanotubes deposited on highly oriented pyrolytic graphite (HOPG) are annealed in ultra high vacuum. The effect of annealing temperature on the surface morphology of the carbon nanotubes on HOPG is examined by scanning tunneling microscopy. The ring-like surface superstructure of (\\sqrt {3}× \\sqrt {3})R30° of graphite is found on the carbon nanotubes annealed above 1593 K. The tips of the carbon nanotubes are destroyed and the stacking misarrangement between the upper and the lower walls of the tube join with HOPG resulting in the superstructure.

Calibrated work function mapping by Kelvin probe force microscopy

NASA Astrophysics Data System (ADS)

Fernández Garrillo, Pablo A.; Grévin, Benjamin; Chevalier, Nicolas; Borowik, Łukasz

2018-04-01

We propose and demonstrate the implementation of an alternative work function tip calibration procedure for Kelvin probe force microscopy under ultrahigh vacuum, using monocrystalline metallic materials with known crystallographic orientation as reference samples, instead of the often used highly oriented pyrolytic graphite calibration sample. The implementation of this protocol allows the acquisition of absolute and reproducible work function values, with an improved uncertainty with respect to unprepared highly oriented pyrolytic graphite-based protocols. The developed protocol allows the local investigation of absolute work function values over nanostructured samples and can be implemented in electronic structures and devices characterization as demonstrated over a nanostructured semiconductor sample presenting Al0.7Ga0.3As and GaAs layers with variable thickness. Additionally, using our protocol we find that the work function of annealed highly oriented pyrolytic graphite is equal to 4.6 ± 0.03 eV.

Imaging graphite in air by scanning tunneling microscopy - Role of the tip

NASA Technical Reports Server (NTRS)

Colton, R. J.; Baker, S. M.; Driscoll, R. J.; Youngquist, M. G.; Baldeschwieler, J. D.; Kaiser, W. J.

1988-01-01

Atomically resolved images of highly oriented pyrolytic graphite (HOPG) in air at point contact have been obtained. Direct contact between tip and sample or contact through a contamination layer provides a conduction mechanism in addition to the exponential tunneling mechanism responsible for scanning tunneling microscopy (STM) imaging. Current-voltage (I-V) spectra were obtained while scanning in the current imaging mode with the feedback circuit interrupted in order to study the graphite imaging mechanism. Multiple tunneling tips are probably responsible for images without the expected hexagonal or trigonal symmetry. The observations indicate that the use of HOPG for testing and calibration of STM instrumentation may be misleading.

Formation mechanism of graphite hexagonal pyramids by argon plasma etching of graphite substrates

NASA Astrophysics Data System (ADS)

Glad, X.; de Poucques, L.; Bougdira, J.

2015-12-01

A new graphite crystal morphology has been recently reported, namely the graphite hexagonal pyramids (GHPs). They are hexagonally-shaped crystals with diameters ranging from 50 to 800 nm and a constant apex angle of 40°. These nanostructures are formed from graphite substrates (flexible graphite and highly ordered pyrolytic graphite) in low pressure helicon coupling radiofrequency argon plasma at 25 eV ion energy and, purportedly, due to a physical etching process. In this paper, the occurrence of peculiar crystals is shown, presenting two hexagonal orientations obtained on both types of samples, which confirms such a formation mechanism. Moreover, by applying a pretreatment step with different time durations of inductive coupling radiofrequency argon plasma, for which the incident ion energy decreases at 12 eV, uniform coverage of the surface can be achieved with an influence on the density and size of the GHPs.

Coupling Graphene Sheets with Iron Oxide Nanoparticles for Energy Storage and Microelectronics

DTIC Science & Technology

2015-12-18

obtained from three different synthetic methods: (i) electrochemical exfoliation of highly oriented pyrolytic graphite ( HOPG ) [8], (ii) reduction of ...Fe2O3 -Graphene Sheets Graphene sheets are obtained from electrochemical exfoliation of highly oriented pyrolytic graphite ( HOPG ) flake. Two...fringes of ɤ-Fe2O3 nanoparticles in graphene sheet is shown. Typical X-ray diffraction ( XRD ) patterns of the HOPG , exfoliated graphene, PyDop1-ɤ-Fe2O3

Materials International Space Station Experiment-6 (MISSE-6) Atomic Oxygen Fluence Monitor Experiment

NASA Technical Reports Server (NTRS)

Banks, Bruce A.; Miller, Sharon K.; Waters, Deborah L.

2010-01-01

An atomic oxygen fluence monitor was flown as part of the Materials International Space Station Experiment-6 (MISSE-6). The monitor was designed to measure the accumulation of atomic oxygen fluence with time as it impinged upon the ram surface of the MISSE 6B Passive Experiment Container (PEC). This was an active experiment for which data was to be stored on a battery-powered data logger for post-flight retrieval and analysis. The atomic oxygen fluence measurement was accomplished by allowing atomic oxygen to erode two opposing wedges of pyrolytic graphite that partially covered a photodiode. As the wedges of pyrolytic graphite erode, the area of the photodiode that is illuminated by the Sun increases. The short circuit current, which is proportional to the area of illumination, was to be measured and recorded as a function of time. The short circuit current from a different photodiode, which was oriented in the same direction and had an unobstructed view of the Sun, was also to be recorded as a reference current. The ratio of the two separate recorded currents should bear a linear relationship with the accumulated atomic oxygen fluence and be independent of the intensity of solar illumination. Ground hyperthermal atomic oxygen exposure facilities were used to evaluate the linearity of the ratio of short circuit current to the atomic oxygen fluence. In flight, the current measurement circuitry failed to operate properly, thus the overall atomic oxygen mission fluence could only be estimated based on the physical erosion of the pyrolytic graphite wedges. The atomic oxygen fluence was calculated based on the knowledge of the space atomic oxygen erosion yield of pyrolytic graphite measured from samples on the MISSE 2. The atomic oxygen fluence monitor, the expected result and comparison of mission atomic oxygen fluence based on the erosion of the pyrolytic graphite and Kapton H atomic oxygen fluence witness samples are presented in this paper.

SIKA—the multiplexing cold-neutron triple-axis spectrometer at ANSTO

NASA Astrophysics Data System (ADS)

Wu, C.-M.; Deng, G.; Gardner, J. S.; Vorderwisch, P.; Li, W.-H.; Yano, S.; Peng, J.-C.; Imamovic, E.

2016-10-01

SIKA is a new cold-neutron triple-axis spectrometer receiving neutrons from the cold source CG4 of the 20MW Open Pool Australian Light-water reactor. As a state-of-the-art triple-axis spectrometer, SIKA is equipped with a large double-focusing pyrolytic graphite monochromator, a multiblade pyrolytic graphite analyser and a multi-detector system. In this paper, we present the design, functions, and capabilities of SIKA, and discuss commissioning experimental results from powder and single-crystal samples to demonstrate its performance.

Atomization from a tantalum surface in graphite furnace atomic absorption spectrometry

NASA Astrophysics Data System (ADS)

Gregoire, D. C.; Chakrabarti, C. L.

The mechanism of atom formation of U, V, Mo, Ni, Mn, Cu and Mg atomized from pyrolytic graphite and tantalum metal surfaces has been studied. The mechanism of atom formation for U from a graphite tube atomizer is reported for the first time. The peak absorbance for U and Cu is increased by factors of 59.7 and 2.0, respectively, whereas that of V, Mo and Ni is reduced by several orders of magnitude when they are atomized from a tantalum metal surface. The peak absorbance of Mn and Mg is not appreciably affected by the material of the atomization surface. Interaction of Mn and Mg with the graphite surface and formation of their refractory carbides was found to be negligible. Uranium forms a refractory carbide when heated from a graphite surface.

Quenchable compressed graphite synthesized from neutron-irradiated highly oriented pyrolytic graphite in high pressure treatment at 1500 °C

NASA Astrophysics Data System (ADS)

Niwase, Keisuke; Terasawa, Mititaka; Honda, Shin-ichi; Niibe, Masahito; Hisakuni, Tomohiko; Iwata, Tadao; Higo, Yuji; Hirai, Takeshi; Shinmei, Toru; Ohfuji, Hiroaki; Irifune, Tetsuo

2018-04-01

The super hard material of "compressed graphite" (CG) has been reported to be formed under compression of graphite at room temperature. However, it returns to graphite under decompression. Neutron-irradiated graphite, on the other hand, is a unique material for the synthesis of a new carbon phase, as reported by the formation of an amorphous diamond by shock compression. Here, we investigate the change of structure of highly oriented pyrolytic graphite (HOPG) irradiated with neutrons to a fluence of 1.4 × 1024 n/m2 under static pressure. The neutron-irradiated HOPG sample was compressed to 15 GPa at room temperature and then the temperature was increased up to 1500 °C. X-ray diffraction, high-resolution transmission electron microscopy on the recovered sample clearly showed the formation of a significant amount of quenchable-CG with ordinary graphite. Formation of hexagonal and cubic diamonds was also confirmed. The effect of irradiation-induced defects on the synthesis of quenchable-CG under high pressure and high temperature treatment was discussed.

Transformation of shock-compressed graphite to hexagonal diamond in nanoseconds

PubMed Central

Turneaure, Stefan J.; Sharma, Surinder M.; Volz, Travis J.; Winey, J. M.; Gupta, Yogendra M.

2017-01-01

The graphite-to-diamond transformation under shock compression has been of broad scientific interest since 1961. The formation of hexagonal diamond (HD) is of particular interest because it is expected to be harder than cubic diamond and due to its use in terrestrial sciences as a marker at meteorite impact sites. However, the formation of diamond having a fully hexagonal structure continues to be questioned and remains unresolved. Using real-time (nanosecond), in situ x-ray diffraction measurements, we show unequivocally that highly oriented pyrolytic graphite, shock-compressed along the c axis to 50 GPa, transforms to highly oriented elastically strained HD with the (100)HD plane parallel to the graphite basal plane. These findings contradict recent molecular dynamics simulation results for the shock-induced graphite-to-diamond transformation and provide a benchmark for future theoretical simulations. Additionally, our results show that an earlier report of HD forming only above 170 GPa for shocked pyrolytic graphite may lead to incorrect interpretations of meteorite impact events. PMID:29098183

Transformation of shock-compressed graphite to hexagonal diamond in nanoseconds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Turneaure, Stefan J.; Sharma, Surinder M.; Volz, Travis J.

The graphite-to-diamond transformation under shock compression has been of broad scientific interest since 1961. The formation of hexagonal diamond (HD) is of particular interest because it is expected to be harder than cubic diamond and due to its use in terrestrial sciences as a marker at meteorite impact sites. However, the formation of diamond having a fully hexagonal structure continues to be questioned and remains unresolved. Using real-time (nanosecond), in situ x-ray diffraction measurements, we show unequivocally that highly oriented pyrolytic graphite, shock-compressed along the c axis to 50 GPa, transforms to highly oriented elastically strained HD with the (100)HDmore » plane parallel to the graphite basal plane. These findings contradict recent molecular dynamics simulation results for the shock-induced graphite-to-diamond transformation and provide a benchmark for future theoretical simulations. Additionally, our results show that an earlier report of HD forming only above 170 GPa for shocked pyrolytic graphite may lead to incorrect interpretations of meteorite impact events.« less

Transformation of shock-compressed graphite to hexagonal diamond in nanoseconds

DOE PAGES

Turneaure, Stefan J.; Sharma, Surinder M.; Volz, Travis J.; ...

2017-10-27

The graphite-to-diamond transformation under shock compression has been of broad scientific interest since 1961. The formation of hexagonal diamond (HD) is of particular interest because it is expected to be harder than cubic diamond and due to its use in terrestrial sciences as a marker at meteorite impact sites. However, the formation of diamond having a fully hexagonal structure continues to be questioned and remains unresolved. Using real-time (nanosecond), in situ x-ray diffraction measurements, we show unequivocally that highly oriented pyrolytic graphite, shock-compressed along the c axis to 50 GPa, transforms to highly oriented elastically strained HD with the (100)HDmore » plane parallel to the graphite basal plane. These findings contradict recent molecular dynamics simulation results for the shock-induced graphite-to-diamond transformation and provide a benchmark for future theoretical simulations. Additionally, our results show that an earlier report of HD forming only above 170 GPa for shocked pyrolytic graphite may lead to incorrect interpretations of meteorite impact events.« less

Cyclic fatigue-crack propagation, stress-corrosion, and fracture-toughness behavior in pyrolytic carbon-coated graphite for prosthetic heart valve applications.

PubMed

Ritchie, R O; Dauskardt, R H; Yu, W K; Brendzel, A M

1990-02-01

Fracture-mechanics tests were performed to characterize the cyclic fatigue, stress-corrosion cracking, and fracture-toughness behavior of a pyrolytic carbon-coated graphite composite material used in the manufacture of cardiac valve prostheses. Testing was carried out using compact tension C(T) samples containing "atomically" sharp precracks, both in room-temperature air and principally in a simulated physiological environment of 37 degrees C Ringer's lactate solution. Under sustained (monotonic) loads, the composite exhibited resistance-curve behavior, with a fracture toughness (KIc) between 1.1 and 1.9 MPa square root of m, and subcritical stress-corrosion crack velocities (da/dt) which were a function of the stress intensity K raised to the 74th power (over the range approximately 10(-9) to over 10(-5) m/s). More importantly, contrary to common perception, under cyclic loading conditions the composite was found to display true (cyclic) fatigue failure in both environments; fatigue-crack growth rates (da/dN) were seen to be a function of the 19th power of the stress-intensity range delta K (over the range approximately 10(-11) to over 10(-8) m/cycle). As subcritical crack velocities under cyclic loading were found to be many orders of magnitude faster than those measured under equivalent monotonic loads and to occur at typically 45% lower stress-intensity levels, cyclic fatigue in pyrolytic carbon-coated graphite is reasoned to be a vital consideration in the design and life-prediction procedures of prosthetic devices manufactured from this material.

Structural Analysis of Pyrolytic Graphite Optics for the HiPEP Ion Thruster

NASA Technical Reports Server (NTRS)

Meckel, Nicole; Polaha, Jonathan; Juhlin, Nils

2006-01-01

The long lifetime requirements of interplanetary exploration missions is driving the need to develop long-life components for the electric propulsion thrusters that are being targeted for these missions. One of the primary life-limiting components of ion thrusters are the optics, which are continuously eroded during the operation of the thruster. Pyrolytic graphite optics are being considered for the High Power Electric Propulsion (HiPEP) ion thruster because of their very high resistance to erosion. This paper describes the structural analysis of the HiPEP pyrolytic graphite. A description of the development of the grid model, as well as the development of the effective properties and stress concentrations in the apertured area of the grids is included. An evaluation of the use of curved grids shows that the increased stiffness (compared to flat grids) prevents intergrid impact during launch, however, the residual stresses introduced by curving the grids pushes the resulting peak stresses beyond the critical stress. As a result, flat grids are recommended as the design solution. Thermally induced grid displacements during normal thruster operation are also presented.

Diffraction of real and virtual photons in a pyrolytic graphite crystal as source of intensive quasimonochromatic X-ray beam

NASA Astrophysics Data System (ADS)

Bogomazova, E. A.; Kalinin, B. N.; Naumenko, G. A.; Padalko, D. V.; Potylitsyn, A. P.; Sharafutdinov, A. F.; Vnukov, I. E.

2003-01-01

A series of experiments on the parametric X-rays radiation (PXR) generation and radiation soft component diffraction of relativistic electrons in pyrolytic graphite (PG) crystals have been carried out at the Tomsk synchrotron. It is shown that the experimental results with PG crystals are explained by the kinematic PXR theory if we take into account a contribution of the real photons diffraction (transition radiation, bremsstrahlung and PXR photons as well). The measurements of the emission spectrum of channeled electrons in the photon energy range much smaller than the characteristic energy of channeling radiation have been performed with a crystal-diffraction spectrometer. For electrons incident along the <1 1 0> axis of a silicon crystal, the radiation intensity in the energy range 30⩽ ω⩽360 keV exceeds the bremsstrahlung one almost by an order of magnitude. Different possibilities to create an effective source of the monochromatic X-ray beam based on the real and virtual photons diffraction in the PG crystals have been considered.

Nitrogen: Unraveling the Secret to Stable Carbon-Supported Pt-Alloy Electrocatalysts

DTIC Science & Technology

2013-10-01

materials reveal broad N1s spectra, indicative of formation of multiple functionalities including but not limited to pyridinic, graphitic and pyrrolic ...network along with nitrogen substitutional defects, while high-dosage increases vacancy agglomerations and pyridinic and pyrrolic nitrogen defects...Article Online highly oriented pyrolytic graphite (HOPG) surface. Simulated defects included pyridinic (Npyridinic), pyrrolic (Npyrrolic), graphitic

Preparation of pyrolytic carbon coating on graphite for inhibiting liquid fluoride salt and Xe135 penetration for molten salt breeder reactor

NASA Astrophysics Data System (ADS)

Song, Jinliang; Zhao, Yanling; He, Xiujie; Zhang, Baoliang; Xu, Li; He, Zhoutong; Zhang, DongSheng; Gao, Lina; Xia, Huihao; Zhou, Xingtai; Huai, Ping; Bai, Shuo

2015-01-01

A fixed-bed deposition method was used to prepare rough laminar pyrolytic carbon coating (RLPyC) on graphite for inhibiting liquid fluoride salt and Xe135 penetration during use in molten salt breeder reactor. The RLPyC coating possessed a graphitization degree of 44% and had good contact with graphite substrate. A high-pressure reactor was constructed to evaluate the molten salt infiltration in the isostatic graphite (IG-110, TOYO TANSO CO., LTD.) and RLPyC coated graphite under 1.01, 1.52, 3.04, 5.07 and 10.13 × 105 Pa for 12 h. Mercury injection and molten-salt infiltration experiments indicated the porosity and the salt-infiltration amount of 18.4% and 13.5 wt% under 1.52 × 105 Pa of IG-110, which was much less than 1.2% and 0.06 wt% under 10.13 × 105 Pa of the RLPyC, respectively. A vacuum device was constructed to evaluate the Xe135 penetration in the graphite. The helium diffusion coefficient of RLPyC coated graphite was 2.16 × 10-12 m2/s, much less than 1.21 × 10-6 m2/s of the graphite. Thermal cycle experiment indicated the coatings possessed excellent thermal stability. The coated graphite could effectively inhibit the liquid fluoride salt and Xe135 penetration.

3-Dimensional atomic scale structure of the ionic liquid-graphite interface elucidated by AM-AFM and quantum chemical simulations

NASA Astrophysics Data System (ADS)

Page, Alister J.; Elbourne, Aaron; Stefanovic, Ryan; Addicoat, Matthew A.; Warr, Gregory G.; Voïtchovsky, Kislon; Atkin, Rob

2014-06-01

In situ amplitude modulated atomic force microscopy (AM-AFM) and quantum chemical simulations are used to resolve the structure of the highly ordered pyrolytic graphite (HOPG)-bulk propylammonium nitrate (PAN) interface with resolution comparable with that achieved for frozen ionic liquid (IL) monolayers using STM. This is the first time that (a) molecular resolution images of bulk IL-solid interfaces have been achieved, (b) the lateral structure of the IL graphite interface has been imaged for any IL, (c) AM-AFM has elucidated molecular level structure immersed in a viscous liquid and (d) it has been demonstrated that the IL structure at solid surfaces is a consequence of both thermodynamic and kinetic effects. The lateral structure of the PAN-graphite interface is highly ordered and consists of remarkably well-defined domains of a rhomboidal superstructure composed of propylammonium cations preferentially aligned along two of the three directions in the underlying graphite lattice. The nanostructure is primarily determined by the cation. Van der Waals interactions between the propylammonium chains and the surface mean that the cation is enriched in the surface layer, and is much less mobile than the anion. The presence of a heterogeneous lateral structure at an ionic liquid-solid interface has wide ranging ramifications for ionic liquid applications, including lubrication, capacitive charge storage and electrodeposition.In situ amplitude modulated atomic force microscopy (AM-AFM) and quantum chemical simulations are used to resolve the structure of the highly ordered pyrolytic graphite (HOPG)-bulk propylammonium nitrate (PAN) interface with resolution comparable with that achieved for frozen ionic liquid (IL) monolayers using STM. This is the first time that (a) molecular resolution images of bulk IL-solid interfaces have been achieved, (b) the lateral structure of the IL graphite interface has been imaged for any IL, (c) AM-AFM has elucidated molecular level structure immersed in a viscous liquid and (d) it has been demonstrated that the IL structure at solid surfaces is a consequence of both thermodynamic and kinetic effects. The lateral structure of the PAN-graphite interface is highly ordered and consists of remarkably well-defined domains of a rhomboidal superstructure composed of propylammonium cations preferentially aligned along two of the three directions in the underlying graphite lattice. The nanostructure is primarily determined by the cation. Van der Waals interactions between the propylammonium chains and the surface mean that the cation is enriched in the surface layer, and is much less mobile than the anion. The presence of a heterogeneous lateral structure at an ionic liquid-solid interface has wide ranging ramifications for ionic liquid applications, including lubrication, capacitive charge storage and electrodeposition. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr01219d

Precision blackbody sources for radiometric standards.

PubMed

Sapritsky, V I; Khlevnoy, B B; Khromchenko, V B; Lisiansky, B E; Mekhontsev, S N; Melenevsky, U A; Morozova, S P; Prokhorov, A V; Samoilov, L N; Shapoval, V I; Sudarev, K A; Zelener, M F

1997-08-01

The precision blackbody sources developed at the All-Russian Institute for Optical and Physical Measurements (Moscow, Russia) and their characteristics are analyzed. The precision high-temperature graphite blackbody BB22p, large-area high-temperature pyrolytic graphite blackbody BB3200pg, middle-temperature graphite blackbody BB2000, low-temperature blackbody BB300, and gallium fixed-point blackbody BB29gl and their characteristics are described.

Carbon Materials Research

DTIC Science & Technology

2006-08-01

carbon would be highly oriented pyrolytic graphite ( HOPG ), which is formed by depositing one atom at a time on a surface utilizing the pyrolysis of a... of the crystallites, and baking to 2800 K produces a polycrystalline graphite part that has high strength and conductivity. To make isotropic...pitch fibers) or flexible (Graphoil®), as well as anisotropic ( HOPG ) or isotropic ( polycrystalline graphite ). In addition, porosity, lubricity

A high-performance ternary Si composite anode material with crystal graphite core and amorphous carbon shell

NASA Astrophysics Data System (ADS)

Sui, Dong; Xie, Yuqing; Zhao, Weimin; Zhang, Hongtao; Zhou, Ying; Qin, Xiting; Ma, Yanfeng; Yang, Yong; Chen, Yongsheng

2018-04-01

Si is a promising anode material for lithium-ion batteries, but suffers from sophisticated engineering structures and complex fabrication processes that pose challenges for commercial application. Herein, a ternary Si/graphite/pyrolytic carbon (SiGC) anode material with a structure of crystal core and amorphous shell using low-cost raw materials is developed. In this ternary SiGC composite, Si component exists as nanoparticles and is spread on the surface of the core graphite flakes while the sucrose-derived pyrolytic carbon further covers the graphite/Si components as the amorphous shell. With this structure, Si together with the graphite contributes to the high specific capacity of this Si ternary material. Also the graphite serves as the supporting and conducting matrix and the amorphous shell carbon could accommodate the volume change effect of Si, reinforces the integrity of the composite architecture, and prevents the graphite and Si from direct exposing to the electrolyte. The optimized ternary SiGC composite displays high reversible specific capacity of 818 mAh g-1 at 0.1 A g-1, initial Coulombic efficiency (CE) over 80%, and excellent cycling stability at 0.5 A g-1 with 83.6% capacity retention (∼610 mAh g-1) after 300 cycles.

Microrobot with passive diamagnetic levitation for microparticle manipulations

NASA Astrophysics Data System (ADS)

Feng, Lin; Zhang, Shengyuan; Jiang, Yonggang; Zhang, Deyuan; Arai, Fumihito

2017-12-01

In this paper, an innovative microrobot with passive diamagnetic levitation is presented. Based on theoretical analysis, finite element method simulation, and experiments, the shape of pyrolytic graphite is redesigned, which improves the stability of passive diamagnetic levitation significantly. Therefore, passive diamagnetic levitation is able to be applied for 3-D control of the microrobot. Compared with the traditional microrobots driven by permanent magnets in a microfluidic chip, the microrobot made of pyrolytic graphite and driven by magnetic force has two advantages, no friction and 3-D control, which is able to expand the scope of the microrobot applications. Finally, the microrobot with passive diamagnetic levitation was demonstrated by being encapsulated in a microfluidic chip for microparticle manipulations.

SPM observation of slow highly charged ion induced nanodots on highly orientated pyrolytic graphite

NASA Astrophysics Data System (ADS)

Mitsuda, Y.; Nakamura, B. E. O'Rourke1 N.; Kanai, Y.; Ohtani, S.; Yamazaki, Y.

2007-03-01

We have observed nanodots on a highly orientated pyrolytic graphite (HOPG) surface produced by highly charged ion impacts using a scanning tunneling microscope. Previous measurements have con.rmed the dominant role of the potential energy or the incident ion charge state on the size and height of the observed nanodots. The present results extend these previous measurements to much lower kinetic energy. It appears that there is no observable influence on the lateral size of the nanodots due to the incident ion kinetic energy down to approximately 200 eV. In contrast some slight reduction in the nanodot height was observed as the kinetic energy was reduced.

Bactericidal activity of self-assembled palmitic and stearic fatty acid crystals on highly ordered pyrolytic graphite.

PubMed

Ivanova, Elena P; Nguyen, Song Ha; Guo, Yachong; Baulin, Vladimir A; Webb, Hayden K; Truong, Vi Khanh; Wandiyanto, Jason V; Garvey, Christopher J; Mahon, Peter J; Mainwaring, David E; Crawford, Russell J

2017-09-01

The wings of insects such as cicadas and dragonflies have been found to possess nanostructure arrays that are assembled from fatty acids. These arrays can physically interact with the bacterial cell membranes, leading to the death of the cell. Such mechanobactericidal surfaces are of significant interest, as they can kill bacteria without the need for antibacterial chemicals. Here, we report on the bactericidal effect of two of the main lipid components of the insect wing epicuticle, palmitic (C16) and stearic (C18) fatty acids. Films of these fatty acids were re-crystallised on the surface of highly ordered pyrolytic graphite. It appeared that the presence of two additional CH 2 groups in the alkyl chain resulted in the formation of different surface structures. Scanning electron microscopy and atomic force microscopy showed that the palmitic acid microcrystallites were more asymmetric than those of the stearic acid, where the palmitic acid microcrystallites were observed to be an angular abutment in the scanning electron micrographs. The principal differences between the two types of long-chain saturated fatty acid crystallites were the larger density of peaks in the upper contact plane of the palmitic acid crystallites, as well as their greater proportion of asymmetrical shapes, in comparison to that of the stearic acid film. These two parameters might contribute to higher bactericidal activity on surfaces derived from palmitic acid. Both the palmitic and stearic acid crystallite surfaces displayed activity against Gram-negative, rod-shaped Pseudomonas aeruginosa and Gram-positive, spherical Staphylococcus aureus cells. These microcrystallite interfaces might be a useful tool in the fabrication of effective bactericidal nanocoatings. Nanostructured cicada and dragonfly wing surfaces have been discovered to be able physically kill bacterial cells. Here, we report on the successful fabrication of bactericidal three-dimensional structures of two main lipid components of the epicuticle of insect wings, palmitic (C16) and stearic (C18) acids. After crystallisation onto highly ordered pyrolytic graphite, both the palmitic and stearic acid films displayed bactericidal activity against both Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus cells. The simplicity of the production of these microcrystallite interfaces suggests that a fabrication technique, based on solution deposition, could be an effective technique for the application of bactericidal nanocoatings. Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Fabrication and Vibration Results of 30-cm Pyrolytic Graphite Ion Optics

NASA Technical Reports Server (NTRS)

DePano, Michael K.; Hart, Stephen L.; Hanna, Andrew A.; Schneider, Analyn C.

2004-01-01

Boeing Electron Dynamic Devices, Inc. is currently developing pyrolytic graphite (PG) grids designed to operate on 30-cm NSTAR-type thrusters for the Carbon Based Ion Optics (CBIO) program. The PG technology effort of the CBIO program aims to research PG as a flightworthy material for use in dished ion optics by designing, fabricating, and performance testing 30-cm PG grids. As such, PG grid fabrication results will be discussed as will PG design considerations and how they must differ from the NSTAR molybdenum grid design. Surface characteristics and surface processing of PG will be explored relative to effects on voltage breakdown. Part of the CBIO program objectives is to understand the erosion of PG due to Xenon ion bombardment. Discussion of PG and CC sputter yields will be presented relative to molybdenum. These sputter yields will be utilized in the life modeling of carbon-based grids. Finally, vibration results of 30-cm PG grids will be presented and compared to a first-order model generated at Boeing EDD. Performance testing results of the PG grids will not be discussed in this paper as it has yet to be completed.

The theory of cyclic voltammetry of electrochemically heterogeneous surfaces: comparison of different models for surface geometry and applications to highly ordered pyrolytic graphite.

PubMed

Ward, Kristopher R; Lawrence, Nathan S; Hartshorne, R Seth; Compton, Richard G

2012-05-28

The cyclic voltammetry at electrodes composed of multiple electroactive materials, where zones of one highly active material are distributed over a substrate of a second, less active material, is investigated by simulation. The two materials are assumed to differ in terms of their electrochemical rate constants towards any given redox couple. For a one-electron oxidation or reduction, the effect on voltammetry of the size and relative surface coverages of the zones as well as the rate constant of the slower zone are considered for systems where it is much slower than the rate constant of the faster zones. The occurrence of split peak cyclic voltammetry where two peaks are observed in the forward sweep, is studied in terms of the diffusional effects present in the system. A number of surface geometries are compared: specifically the more active zones are modelled as long, thin bands, as steps in the surface, as discs, and as rings (similar to a partially blocked electrode). Similar voltammetry for the band, step and ring models is seen but the disc geometry shows significant differences. Finally, the simulation technique is applied to the modelling of highly-ordered pyrolytic graphite (HOPG) surface and experimental conditions under which it may be possible to observe split peak voltammetry are predicted.

Structure-Property Relationships in Surface-Modified Ceramics. NATO advanced Science Institutes, Series E: Applied Sciences, Volume 170

DTIC Science & Technology

1989-01-01

channelling and scanning electron microscopy (SEM) of highly oriented pyrolytic graphite ( HOPG ), comparative scratch testing results and some ideas on...electrode graphite , HOPG and carbon fibers also show enhanced wear resistance followoing irradiation (6), the extent of which depends upon the initial...literature dealing with damage effects and physical property changes following neutron irradiation of graphite (single and polycrystalline ) in nuclear

Pyrolytic Carbon Nanosheets for Ultrafast and Ultrastable Sodium-Ion Storage.

PubMed

Cho, Se Youn; Kang, Minjee; Choi, Jaewon; Lee, Min Eui; Yoon, Hyeon Ji; Kim, Hae Jin; Leal, Cecilia; Lee, Sungho; Jin, Hyoung-Joon; Yun, Young Soo

2018-04-01

Na-ion cointercalation in the graphite host structure in a glyme-based electrolyte represents a new possibility for using carbon-based materials (CMs) as anodes for Na-ion storage. However, local microstructures and nanoscale morphological features in CMs affect their electrochemical performances; they require intensive studies to achieve high levels of Na-ion storage performances. Here, pyrolytic carbon nanosheets (PCNs) composed of multitudinous graphitic nanocrystals are prepared from renewable bioresources by heating. In particular, PCN-2800 prepared by heating at 2800 °C has a distinctive sp 2 carbon bonding nature, crystalline domain size of ≈44.2 Å, and high electrical conductivity of ≈320 S cm -1 , presenting significantly high rate capability at 600 C (60 A g -1 ) and stable cycling behaviors over 40 000 cycles as an anode for Na-ion storage. The results of this study show the unusual graphitization behaviors of a char-type carbon precursor and exceptionally high rate and cycling performances of the resulting graphitic material, PCN-2800, even surpassing those of supercapacitors. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Graphite, graphene and the flat band superconductivity

NASA Astrophysics Data System (ADS)

Volovik, G. E.

2018-04-01

Superconductivity has been observed in bilayer graphene [1,2]. The main factor, which determines the mechanism of the formation of this superconductivity is the "magic angle" of twist of two graphene layers, at which the electronic band structure becomes nearly flat. The specific role played by twist and by the band flattening, has been earlier suggested for explanations of the signatures of room-temperature superconductivity observed in the highly oriented pyrolytic graphite (HOPG), when the quasi two-dimensional interfaces between the twisted domains are present. The interface contains the periodic array of misfit dislocations (analogs of the boundaries of the unit cell of the Moire superlattice in bilayer graphene), which provide the possible source of the flat band. This demonstrates that it is high time for combination of the theoretical and experimental efforts in order to reach the reproducible room-temperature superconductivity in graphite or in similar real or artificial materials.

Online time-differential perturbed angular correlation study with an 19O beam - Residence sites of oxygen atoms in highly oriented pyrolytic graphite

NASA Astrophysics Data System (ADS)

Sato, W.; Ueno, H.; Watanabe, H.; Miyoshi, H.; Yoshimi, A.; Kameda, D.; Ito, T.; Shimada, K.; Kaihara, J.; Suda, S.; Kobayashi, Y.; Shinohara, A.; Ohkubo, Y.; Asahi, K.

2008-01-01

The online time-differential perturbed angular correlation (TDPAC) method was applied to a study of the physical states of a probe 19F, the β- decay product of 19O (t1/2 = 26.9 s), implanted in highly oriented pyrolytic graphite. The observed magnitude of the electric field gradient at the probe nucleus, ∣Vzz∣ = 2.91(17) × 1022 V m-2, suggests that the incident 19O atoms are stabilized at an interlayer position with point group C3v. Exhibiting observed TDPAC spectra having a clear sample-to-detector configuration dependence, we demonstrate the applicability of the present online method with a short-lived radioactive 19O beam.

Observation of Persistent Currents in Finely Dispersed Pyrolytic Graphite

NASA Astrophysics Data System (ADS)

Saad, M.; Gilmutdinov, I. F.; Kiiamov, A. G.; Tayurskii, D. A.; Nikitin, S. I.; Yusupov, R. V.

2018-01-01

The trapped magnetic flux in the finely ground pyrolytic graphite sample annealed at 670 K in air has been observed. Flux trapping occurs on cooling of the sample from room temperature to 10 K in a magnetic field of 1 T. The magnitude and sign of the induced trapped moment remain unchanged when the applied magnetic field is varied within ±1 T at T K. The trapped magnetic flux is manifested in the displacement of the magnetization curve relative to that of the sample cooled in zero field. Displacement magnitude gradually decreases with the temperature increase up to 350 K, not reaching zero. The set of experimental observations probably reflects the presence in the sample of a granular high-temperature superconducting phase.

Molecular beam epitaxy growth of SrO buffer layers on graphite and graphene for the integration of complex oxides

DOE PAGES

Ahmed, Adam S.; Wen, Hua; Ohta, Taisuke; ...

2016-04-27

Here, we report the successful growth of high-quality SrO films on highly-ordered pyrolytic graphite (HOPG) and single-layer graphene by molecular beam epitaxy. The SrO layers have (001) orientation as confirmed by X-ray diffraction (XRD) while atomic force microscopy measurements show continuous pinhole-free films having rms surface roughness of <1.5 Å. Moreover, transport measurements of exfoliated graphene, after SrO deposition, show a strong dependence between the Dirac point and Sr oxidation. As a result, the SrO is leveraged as a buffer layer for more complex oxide integration via the demonstration of (001) oriented SrTiO3 grown atop a SrO/HOPG stack.

Molecular beam epitaxy growth of SrO buffer layers on graphite and graphene for the integration of complex oxides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahmed, Adam S.; Wen, Hua; Ohta, Taisuke

Here, we report the successful growth of high-quality SrO films on highly-ordered pyrolytic graphite (HOPG) and single-layer graphene by molecular beam epitaxy. The SrO layers have (001) orientation as confirmed by X-ray diffraction (XRD) while atomic force microscopy measurements show continuous pinhole-free films having rms surface roughness of <1.5 Å. Moreover, transport measurements of exfoliated graphene, after SrO deposition, show a strong dependence between the Dirac point and Sr oxidation. As a result, the SrO is leveraged as a buffer layer for more complex oxide integration via the demonstration of (001) oriented SrTiO3 grown atop a SrO/HOPG stack.

SPM observation of nano-dots induced by slow highly charged ions

NASA Astrophysics Data System (ADS)

Nakamura, Nobuyuki; Terada, Masashi; Nakai, Yoichi; Kanai, Yasuyuki; Ohtani, Shunsuke; Komaki, Ken-ichiro; Yamazaki, Yasunori

2005-05-01

We have observed nano-dots on a highly oriented pyrolytic graphite (HOPG) surface produced by highly charged ion impacts with a scanning probe microscope. In order to clarify the role of potential and kinetic energies in surface modification, we have measured the kinetic energy and incident ion charge dependences of the dot size. The results showed that the potential energy or the incident ion charge has strong influence on the surface modification rather than the kinetic energy.

A new oxidation based technique for artifact free TEM specimen preparation of nuclear graphite

NASA Astrophysics Data System (ADS)

Johns, Steve; Shin, Wontak; Kane, Joshua J.; Windes, William E.; Ubic, Rick; Karthik, Chinnathambi

2018-07-01

Graphite is a key component in designs of current and future nuclear reactors whose in-service lifetimes are dependent upon the mechanical performance of the graphite. Irradiation damage from fast neutrons creates lattice defects which have a dynamic effect on the microstructure and mechanical properties of graphite. Transmission electron microscopy (TEM) can offer real-time monitoring of the dynamic atomic-level response of graphite subjected to irradiation; however, conventional TEM specimen-preparation techniques, such as argon ion milling itself, damage the graphite specimen and introduce lattice defects. It is impossible to distinguish these defects from the ones created by electron or neutron irradiation. To ensure that TEM specimens are artifact-free, a new oxidation-based technique has been developed. Bulk nuclear grades of graphite (IG-110 and NBG-18) and highly oriented pyrolytic graphite (HOPG) were initially mechanically thinned to ∼60 μm. Discs 3 mm in diameter were then oxidized at temperatures between 575 °C and 625 °C in oxidizing gasses using a new jet-polisher-like set-up in order to achieve optimal oxidation conditions to create self-supporting electron-transparent TEM specimens. The quality of these oxidized specimens were established using optical and electron microscopy. Samples oxidized at 575 °C exhibited large areas of electron transparency and the corresponding lattice imaging showed no apparent damage to the graphite lattice.

A new oxidation based technique for artifact free TEM specimen preparation of nuclear graphite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johns, Steve; Shin, Wontak; Kane, Joshua J.

Graphite is a key component in designs of current and future nuclear reactors whose in-service lifetimes are dependent upon the mechanical performance of the graphite. Irradiation damage from fast neutrons creates lattice defects which have a dynamic effect on the microstructure and mechanical properties of graphite. Transmission electron microscopy (TEM) can offer real-time monitoring of the dynamic atomic-level response of graphite subjected to irradiation; however, conventional TEM specimen-preparation techniques, such as argon ion milling itself, damage the graphite specimen and introduce lattice defects. It is impossible to distinguish these defects from the ones created by electron or neutron irradiation. Thus,tomore » ensure that TEM specimens are artifact-free, a new oxidation-based technique has been developed. Bulk nuclear grades of graphite (IG-110 and NBG-18) and highly oriented pyrolytic graphite (HOPG) were initially mechanically thinned to ~60μm. Discs 3mm in diameter were then oxidized at temperatures between 575°C and 625°C in oxidizing gasses using a new jet-polisher-like set-up in order to achieve optimal oxidation conditions to create self-supporting electron-transparent TEM specimens. The quality of these oxidized specimens were established using optical and electron microscopy. Samples oxidized at 575°C exhibited large areas of electron transparency and the corresponding lattice imaging showed no apparent damage to the graphite lattice.« less

A new oxidation based technique for artifact free TEM specimen preparation of nuclear graphite

DOE PAGES

Johns, Steve; Shin, Wontak; Kane, Joshua J.; ...

2018-04-03

Graphite is a key component in designs of current and future nuclear reactors whose in-service lifetimes are dependent upon the mechanical performance of the graphite. Irradiation damage from fast neutrons creates lattice defects which have a dynamic effect on the microstructure and mechanical properties of graphite. Transmission electron microscopy (TEM) can offer real-time monitoring of the dynamic atomic-level response of graphite subjected to irradiation; however, conventional TEM specimen-preparation techniques, such as argon ion milling itself, damage the graphite specimen and introduce lattice defects. It is impossible to distinguish these defects from the ones created by electron or neutron irradiation. Thus,tomore » ensure that TEM specimens are artifact-free, a new oxidation-based technique has been developed. Bulk nuclear grades of graphite (IG-110 and NBG-18) and highly oriented pyrolytic graphite (HOPG) were initially mechanically thinned to ~60μm. Discs 3mm in diameter were then oxidized at temperatures between 575°C and 625°C in oxidizing gasses using a new jet-polisher-like set-up in order to achieve optimal oxidation conditions to create self-supporting electron-transparent TEM specimens. The quality of these oxidized specimens were established using optical and electron microscopy. Samples oxidized at 575°C exhibited large areas of electron transparency and the corresponding lattice imaging showed no apparent damage to the graphite lattice.« less

One-step formation of straight nanostripes from a mammal lipid-oleamide directly on highly oriented pyrolytic graphite.

PubMed

Zhang, Renjie; Möhwald, Helmuth; Kurth, Dirk G

2009-02-17

Hierarchical nanostructures are obtained directly on highly oriented pyrolytic graphite (HOPG) by spin coating of dilute chloroform solution of 9-Z-octadecenamide (oleamide), a natural lipid with cis-CdC- conformation, existing in the cerebrospinal fluid of mammal animals and being an additive for medical use and food packaging. Straight separated nanostripes with a length of 70-300 nm exist in the topmost layer and compact nanostripes in the bottom layer contacting HOPG. Compact nanostripes have a periodicity spacing of 3.8 nm, indicating H-bonding between two rows of oleamide molecules. The orientation of the hierarchical nanostructures differs by n60 degrees+/-8 degrees (n=1 or 2), reflecting the epitaxial ordering along theHOPGsubstrate. The nanostripes are stable against annealing.Amolecular packing scheme for the nanostructures is proposed, where the -C=C bond angle in oleamide is 120 degrees and the plane of the carbon skeleton lies parallel to the HOPG substrate. Nanostripes in the topmost layer are formed from separated rows of oleamide molecules, due to the short-range surface potential of the substrate. The scheme involves direct influence ofHOPGon the orientation of oleamide molecules to form nanostripes without any purposely added saturated alkanes and H-bonds between amide groups in adjacent two rows of oleamide molecules.

Stability of Nanobubbles Formed at the Interface between Cold Water and Hot Highly Oriented Pyrolytic Graphite.

PubMed

An, Hongjie; Tan, Beng Hau; Zeng, Qingyun; Ohl, Claus-Dieter

2016-11-01

For the wider application of nanobubbles, a simple and reproducible nucleation process is not readily available. Here we describe a method for nucleating nanobubbles using only the most basic of conditions: depositing cold water at 4 °C on heated highly oriented pyrolytic graphite substrates. This method thus avoids the need, as in previous studies, to use secondary liquids, salts, or electrolysis to nucleate the nanobubbles and provides a pure system in which the properties of nanobubbles can be studied. The nanobubbles generated with this method are observed to survive for at least 5 days, barely changing their contact angles or heights after the first few hours. The stability of the nanobubbles in our system is discussed within the framework of some recently published theories.

Multiferroic BiFeO3 thin films and nanodots grown on highly oriented pyrolytic graphite substrates

NASA Astrophysics Data System (ADS)

Shin, Hyun Wook; Son, Jong Yeog

2017-12-01

Multiferroic BiFeO3 (BFO) thin films and nanodots are deposited on highly oriented pyrolytic graphite (HOPG) substrates via a pulsed laser deposition technique, where the HOPG surface has a honeycomb lattice structure made of carbon atoms, similar to graphene. A graphene/BFO/HOPG capacitor exhibited multiferroic properties, namely ferroelectricity (a residual polarization of 26.8 μC/cm2) and ferromagnetism (a residual magnetization of 1.1 × 10-5 emu). The BFO thin film had high domain wall energies and demonstrated switching time of approximately 82 ns. An 8-nm BFO nanodot showed a typical piezoelectric hysteresis loop with an effective residual piezoelectric constant of approximately 110 pm/V and exhibited two clearly separated current curves depending on the ferroelectric polarization direction.

The electrophoretic deposition of ZnO on highly oriented pyrolytic graphite

NASA Astrophysics Data System (ADS)

Ghalamboran, Milad; Jahangiri, Mojtaba; Yousefiazari, Ehsan

2017-12-01

Intensive research has been conducted on ZnO thin and thick films in recent years. Such layers, used in different electronic devices, are deposited utilizing various methods, but electrophoretic deposition (EPD) has been chosen because of the advantages like low energy consumption, economical superiority, ecofriendliness, controllability, and high deposition rate. Here, we report electrophoretically depositing ZnO layers onto highly oriented pyrolytic graphite. Well-dispersed and stable ZnO suspensions are used for the deposition of continuous and even layers of ZnO on the substrate. ZnO powder is dispersed in acetone. The electric field applied is in the 250 V/cm to 2000 V/cm range. The morphology of the deposits are studied by SEM at the different stages of the deposition process.

Window for radiation detectors and the like

DOEpatents

Sparks, C.J. Jr.; Ogle, J.C.

1975-10-28

An improved x- and gamma-radiation and particle transparent window for the environment-controlling enclosure of various types of radiation and particle detectors is provided by a special graphite foil of a thickness of from about 0.1 to 1 mil. The graphite must have very parallel hexagonal planes with a mosaic spread no greater than 5$sup 0$ to have the necessary strength in thin sections to support one atmosphere or more of pressure. Such graphite is formed by hot- pressing and annealing pyrolytically deposited graphite and thereafter stripping off layers of sufficient thickness to form the window.

Atomic resolution images of graphite in air

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grigg, D.A.; Shedd, G.M.; Griffis, D.

One sample used for proof of operation for atomic resolution in STM is highly oriented pyrolytic graphite (HOPG). This sample has been imaged with many different STM`s obtaining similar results. Atomic resolution images of HOPG have now been obtained using an STM designed and built at the Precision Engineering Center. This paper discusses the theoretical predictions and experimental results obtained in imaging of HOPG.

Atomic intercalation to measure adhesion of graphene on graphite

PubMed Central

Wang, Jun; Sorescu, Dan C.; Jeon, Seokmin; Belianinov, Alexei; Kalinin, Sergei V.; Baddorf, Arthur P.; Maksymovych, Petro

2016-01-01

The interest in mechanical properties of two-dimensional materials has emerged in light of new device concepts taking advantage of flexing, adhesion and friction. Here we demonstrate an effective method to measure adhesion of graphene atop highly ordered pyrolytic graphite, utilizing atomic-scale ‘blisters' created in the top layer by neon atom intercalates. Detailed analysis of scanning tunnelling microscopy images is used to reconstruct atomic positions and the strain map within the deformed graphene layer, and demonstrate the tip-induced subsurface translation of neon atoms. We invoke an analytical model, originally devised for graphene macroscopic deformations, to determine the graphite adhesion energy of 0.221±0.011 J m−2. This value is in excellent agreement with reported macroscopic values and our atomistic simulations. This implies mechanical properties of graphene scale down to a few-nanometre length. The simplicity of our method provides a unique opportunity to investigate the local variability of nanomechanical properties in layered materials. PMID:27796294

The Erosion of Diamond and Highly Oriented Pyrolytic Graphite After 1.5 Years of Space Exposure

NASA Technical Reports Server (NTRS)

De Groh, Kim K.; Banks, Bruce A.

2018-01-01

Polymers and other oxidizable materials on the exterior of spacecraft in the low Earth orbit (LEO) space environment can be eroded due to reaction with atomic oxygen (AO). Therefore, in order to design durable spacecraft, it is important to know the LEO AO erosion yield (Ey, volume loss per incident oxygen atom) of materials susceptible to AO reaction. The Polymers Experiment was developed to determine the AO Ey of various polymers and other materials flown in ram and wake orientations in LEO. The experiment was flown as part of the Materials International Space Station Experiment 7 (MISSE 7) mission for 1.5 years on the exterior of the International Space Station (ISS). As part of the experiment, a sample containing Class 2A diamond (100 plane) and highly oriented pyrolytic graphite (HOPG, basal and edge planes) was exposed to ram AO and characterized for erosion. The materials were salt-sprayed prior to flight to provide isolated sites of AO protection. The Ey of the samples was determined through post-flight electron microscopy recession depth measurements. The experiment also included a Kapton H witness sample for AO fluence determination. This paper provides an overview of the MISSE 7 mission, a description of the flight experiment, the characterization techniques used, the mission AO fluence, and the LEO Ey results for diamond and HOPG (basal and edge planes). The data is compared to the Ey of pyrolytic graphite exposed to four years of space exposure as part of the MISSE 2 mission. The results indicate that diamond erodes, but with a very low Ey of 1.58 +/- 0.04 x 10(exp -26) cm(exp 3)/atom. The different HOPG planes displayed significantly different amounts of erosion from each other. The HOPG basal plane had an Ey of 1.05 +/- 0.08 x 10(exp -24) cm(exp 3)/atom while the edge plane had a lower Ey of only 5.38 +/- 0.90 x 10(exp -25) -cm(exp 3)/atom. The Ey data from this ISS spaceflight experiment provides valuable information for understanding of chemistry and chemical structure dependent modeling of AO erosion.

Nuclear fuel elements and method of making same

DOEpatents

Schweitzer, Donald G.

1992-01-01

A nuclear fuel element for a high temperature gas nuclear reactor that has an average operating temperature in excess of 2000.degree. C., and a method of making such a fuel element. The fuel element is characterized by having fissionable fuel material localized and stabilized within pores of a carbon or graphite member by melting the fissionable material to cause it to chemically react with the carbon walls of the pores. The fissionable fuel material is further stabilized and localized within the pores of the graphite member by providing one or more coatings of pyrolytic carbon or diamond surrounding the porous graphite member so that each layer defines a successive barrier against migration of the fissionable fuel from the pores, and so that the outermost layer of pyrolytic carbon or diamond forms a barrier between the fissionable material and the moderating gases used in an associated high temperature gas reactor. The method of the invention provides for making such new elements either as generally spherically elements, or as flexible filaments, or as other relatively small-sized fuel elements that are particularly suited for use in high temperature gas reactors.

Electrochemical detection of DNA damage induced by acrylamide and its metabolite at the graphene-ionic liquid-Nafion modified pyrolytic graphite electrode.

PubMed

Qiu, Yanyan; Qu, Xiangjin; Dong, Jing; Ai, Shiyun; Han, Ruixia

2011-06-15

A new electrochemical biosensor for directly detecting DNA damage induced by acrylamide (AA) and its metabolite was presented in this work. The graphene-ionic liquid-Nafion modified pyrolytic graphite electrode (PGE) was prepared, and then horseradish peroxidase (HRP) and natural double-stranded DNA were alternately assembled on the modified electrode by the layer-by-layer method. The PGE/graphene-ionic liquid-Nafion and the construction of the (HRP/DNA)(n) film were characterized by electrochemical impedance spectroscopy. With the guanine signal in DNA as an indicator, the damage of DNA was detected by differential pulse voltammetry after PGE/graphene-ionic liquid-Nafion/(HRP/DNA)(n) was incubated in AA solution or AA+H(2)O(2) solution at 37°C. This method provides a new model to mimic and directly detect DNA damage induced by chemical pollutants and their metabolites in vitro. The results indicated that, in the presence of H(2)O(2), HRP was activated and catalyzed the transformation of AA to glycidamide, which could form DNA adducts and induce more serious damage of DNA than AA. In order to further verify these results, UV-vis spectrophotometry was also used to investigate DNA damage induced by AA and its metabolites in solution and the similar results were obtained. Copyright © 2011 Elsevier B.V. All rights reserved.

Determining the phonon energy of highly oriented pyrolytic graphite by scanning tunneling microscope light emission spectroscopy

NASA Astrophysics Data System (ADS)

Uehara, Yoichi; Michimata, Junichi; Watanabe, Shota; Katano, Satoshi; Inaoka, Takeshi

2018-03-01

We have investigated the scanning tunneling microscope (STM) light emission spectra of isolated single Ag nanoparticles lying on highly oriented pyrolytic graphite (HOPG). The STM light emission spectra exhibited two types of spectral structures (step-like and periodic). Comparisons of the observed structures and theoretical predictions indicate that the phonon energy of the ZO mode of HOPG [M. Mohr et al., Phys. Rev. B 76, 035439 (2007)] can be determined from the energy difference between the cutoff of STM light emission and the step in the former structure, and from the period of the latter structure. Since the role of the Ag nanoparticles does not depend on the substrate materials, this method will enable the phonon energies of various materials to be measured by STM light emission spectroscopy. The spatial resolution is comparable to the lateral size of the individual Ag nanoparticles (that is, a few nm).

Optical motion control of maglev graphite.

PubMed

Kobayashi, Masayuki; Abe, Jiro

2012-12-26

Graphite has been known as a typical diamagnetic material and can be levitated in the strong magnetic field. Here we show that the magnetically levitating pyrolytic graphite can be moved in the arbitrary place by simple photoirradiation. It is notable that the optical motion control system described in this paper requires only NdFeB permanent magnets and light source. The optical movement is driven by photothermally induced changes in the magnetic susceptibility of the graphite. Moreover, we demonstrate that light energy can be converted into rotational kinetic energy by means of the photothermal property. We find that the levitating graphite disk rotates at over 200 rpm under the sunlight, making it possible to develop a new class of light energy conversion system.

Electrochemical Control of Peptide Self-Organization on Atomically Flat Solid Surfaces: A Case Study with Graphite.

PubMed

Seki, Takakazu; So, Christopher R; Page, Tamon R; Starkebaum, David; Hayamizu, Yuhei; Sarikaya, Mehmet

2018-02-06

The nanoscale self-organization of biomolecules, such as proteins and peptides, on solid surfaces under controlled conditions is an important issue in establishing functional bio/solid soft interfaces for bioassays, biosensors, and biofuel cells. Electrostatic interaction between proteins and surfaces is one of the most essential parameters in the adsorption and self-assembly of proteins on solid surfaces. Although the adsorption of proteins has been studied with respect to the electrochemical surface potential, the self-assembly of proteins or peptides forming well-organized nanostructures templated by lattice structure of the solid surfaces has not been studied in the relation to the surface potential. In this work, we utilize graphite-binding peptides (GrBPs) selected by the phage display method to investigate the relationship between the electrochemical potential of the highly ordered pyrolytic graphite (HOPG) and peptide self-organization forming long-range-ordered structures. Under modulated electrical bias, graphite-binding peptides form various ordered structures, such as well-ordered nanowires, dendritic structures, wavy wires, amorphous (disordered) structures, and islands. A systematic investigation of the correlation between peptide sequence and self-organizational characteristics reveals that the presence of the bias-sensitive amino acid modules in the peptide sequence has a significant effect on not only surface coverage but also on the morphological features of self-assembled structures. Our results show a new method to control peptide self-assembly by means of applied electrochemical bias as well as peptide design-rules for the construction of functional soft bio/solid interfaces that could be integrated in a wide range of practical implementations.

Interfacial nanobubbles on atomically flat substrates with different hydrophobicities.

PubMed

Wang, Xingya; Zhao, Binyu; Ma, Wangguo; Wang, Ying; Gao, Xingyu; Tai, Renzhong; Zhou, Xingfei; Zhang, Lijuan

2015-04-07

The dependence of the morphology of interfacial nanobubbles on atomically flat substrates with different wettability ranges was investigated by using PeakForce quantitative nanomechanics. Interfacial nanobubbles were formed and imaged on silicon nitride (Si3N4), mica, and highly ordered pyrolytic graphite (HOPG) substrates that were partly covered by reduced graphene oxide (rGO). The contact angles and sizes of those nanobubbles were measured under the same conditions. Nanobubbles with the same lateral width exhibited different heights on the different substrates, with the order Si3N4≈mica>rGO>HOPG, which is consistent with the trend of the hydrophobicity of the substrates. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Magnetotransport in two dimensional electron systems under microwave excitation and in highly oriented pyrolytic graphite

NASA Astrophysics Data System (ADS)

Ramanayaka, Aruna N.

This thesis consists of two parts. The first part considers the effect of microwave radiation on magnetotransport in high quality GaAs/AlGaAs heterostructure two dimensional electron systems. The effect of microwave (MW) radiation on electron temperature was studied by investigating the amplitude of the Shubnikov de Haas (SdH) oscillations in a regime where the cyclotron frequency o c and the MW angular frequency o satisfy 2o ≤ o c ≤ 3.5o. The results indicate negligible electron heating under modest MW photoexcitation, in agreement with theoretical predictions. Next, the effect of the polarization direction of the linearly polarized MWs on the MW induced magnetoresistance oscillation amplitude was investigated. The results demonstrate the first indications of polarization dependence of MW induced magnetoresistance oscillations. In the second part, experiments on the magnetotransport of three dimensional highly oriented pyrolytic graphite (HOPG) reveal a non-zero Berry phase for HOPG. Furthermore, a novel phase relation between oscillatory magneto- and Hall- resistances was discovered from the studies of the HOPG specimen. INDEX WORDS: Two dimensional electron systems, Magnetoresistance, Microwave induced magnetoresistance oscillations, Graphite, Quantum Hall effect, Hall effect, Resistivity rule, Shubnikov de Haas effect, Shubnikov de Haas oscillation.

Feasibility of intercalated graphite railgun armatures

NASA Technical Reports Server (NTRS)

Gaier, James R.; Gooden, Clarence E.; Yashan, Doreen; Naud, Steven

1990-01-01

Graphite intercalation compounds may provide an excellent material for the fabrication of electro-magnetic railgun armatures. As a pulse of power is fed into the armature the intercalate could be excited into the plasma state around the edges of the armature, while the bulk of the current would be carried through the graphite block. Such an armature would have the desirable characteristics of both diffuse plasma armatures and bulk conduction armatures. In addition, the highly anisotropic nature of these materials could enable the electrical and thermal conductivity to be tailored to meet the specific requirements of electromagnetic railgun armatures. Preliminary investigations were performed in an attempt to determine the feasibility of using graphite intercalation compounds as railgun armatures. Issues of fabrication, resistivity, stability, and electrical current spreading are addressed for the case of highly oriented pyrolytic graphite.

Electrochemical modification of a pyrolytic graphite sheet for improved negative electrode performance in the vanadium redox flow battery

NASA Astrophysics Data System (ADS)

Kabir, Humayun; Gyan, Isaiah O.; Francis Cheng, I.

2017-02-01

The vanadium redox flow battery is a promising technology for buffering renewable energies. It is recognized that negative electrode is the limitation in this device where there are problems of slow heterogeneous electron transfer (HET) of V3+/2+ and parasitic H2 evolution. Any methods aimed at addressing one of these barriers must assess the effects on the other. We examine electrochemical enhancement of a common commercially available material. Treatment of Panasonic pyrolytic graphite sheets is through oxidation at 2.1 V vs. Ag/AgCl for 1 min in 1 M H2SO4. This increases the standard HET rate for V3+/2+ from 3.2 × 10-7 to 1 × 10-3 cm/s, one of the highest in literature and shifts voltammetric reductive peak potential from -1.0 V to -0.65 V in 50 mM V3+ in 1 M H2SO4. Infrared analysis of the surfaces indicates formation of Csbnd OH, Cdbnd O, and Csbnd O functionalities. These groups catalyze HET with V3+/2+ as hypothesized by Skyllas-Kasacos. Also of significance is that electrode modification decreases the fraction of the current directed towards H2 evolution. This proportion decreases by two orders of a magnitude from 12% to 0.1% as measured at the respective voltammetric peak potentials of -1.0 V (pristine) and -0.65 V (modified).

Transformation of shock-compressed graphite to hexagonal diamond in nanoseconds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Turneaure, Stefan J.; Sharma, Surinder M.; Volz, Travis J.

2017-10-01

The graphite-to-diamond transformation under shock compression has been of broad scientific interest since 1961. The formation of hexagonal diamond (HD) is of particular interest because it is expected to be harder than cubic diamond and due to its use in terrestrial sciences as a marker at meteorite impact sites. However, the formation of diamond having a fully hexagonal structure continues to be questioned and remains unresolved. Using real-time (nanosecond), in situ x-ray diffraction measurements, we show unequivocally that highly oriented pyrolytic graphite, shock-compressed along the c axis to 50 GPa, transforms to highly oriented elastically strained HD with the (100)HDmore » plane parallel to the graphite basal plane.« less

Surface analysis of model systems: From a metal-graphite interface to an intermetallic catalyst

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kwolek, Emma J.

This thesis summarizes research completed on two different model systems. In the first system, we investigate the deposition of the elemental metal dysprosium on highly-oriented pyrolytic graphite (HOPG) and its resulting nucleation and growth. The goal of this research is to better understand the metal-carbon interactions that occur on HOPG and to apply those to an array of other carbon surfaces. This insight may prove beneficial to developing and using new materials for electronic applications, magnetic applications and catalysis.

Semiconductor cooling apparatus

NASA Technical Reports Server (NTRS)

Banks, Bruce A. (Inventor); Gaier, James R. (Inventor)

1993-01-01

Gas derived graphite fibers generated by the decomposition of an organic gas are joined with a suitable binder. This produces a high thermal conductivity composite material which passively conducts heat from a source, such as a semiconductor, to a heat sink. The fibers may be intercalated. The intercalate can be halogen or halide salt, alkaline metal, or any other species which contributes to the electrical conductivity improvement of the graphite fiber. The fibers are bundled and joined with a suitable binder to form a high thermal conductivity composite material device. The heat transfer device may also be made of intercalated highly oriented pyrolytic graphite and machined, rather than made of fibers.

Electrochemical Functionalization of Graphene at the Nanoscale with Self-Assembling Diazonium Salts.

PubMed

Xia, Zhenyuan; Leonardi, Francesca; Gobbi, Marco; Liu, Yi; Bellani, Vittorio; Liscio, Andrea; Kovtun, Alessandro; Li, Rongjin; Feng, Xinliang; Orgiu, Emanuele; Samorì, Paolo; Treossi, Emanuele; Palermo, Vincenzo

2016-07-26

We describe a fast and versatile method to functionalize high-quality graphene with organic molecules by exploiting the synergistic effect of supramolecular and covalent chemistry. With this goal, we designed and synthesized molecules comprising a long aliphatic chain and an aryl diazonium salt. Thanks to the long chain, these molecules physisorb from solution onto CVD graphene or bulk graphite, self-assembling in an ordered monolayer. The sample is successively transferred into an aqueous electrolyte, to block any reorganization or desorption of the monolayer. An electrochemical impulse is used to transform the diazonium group into a radical capable of grafting covalently to the substrate and transforming the physisorption into a covalent chemisorption. During covalent grafting in water, the molecules retain the ordered packing formed upon self-assembly. Our two-step approach is characterized by the independent control over the processes of immobilization of molecules on the substrate and their covalent tethering, enabling fast (t < 10 s) covalent functionalization of graphene. This strategy is highly versatile and works with many carbon-based materials including graphene deposited on silicon, plastic, and quartz as well as highly oriented pyrolytic graphite.

Microcontact Printing Patterning of an HOPG Surface by an Inverse Electron Demand Diels-Alder Reaction.

PubMed

Zhu, Jun; Hiltz, Jonathan; Tefashe, Ushula M; Mauzeroll, Janine; Lennox, R Bruce

2018-06-21

The chemical modification of an sp 2 hybridized carbon surface in a controllable manner is very challenging but also crucial for many applications. An inverse electron demand Diels-Alder (IEDDA) reaction using microcontact printing technique is introduced to spatially control the modification of a highly ordered pyrolytic graphite (HOPG) surface under ambient conditions. The covalent modification was characterized by Raman spectroscopy, XPS, and SECM. Tetrazine derivatives can effectively react with an HOPG surface and with microcontact printing methods resulting in spatially patterned surfaces being produced with micrometer-scale resolution. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cyclic fatigue and fracture in pyrolytic carbon-coated graphite mechanical heart-valve prostheses: role of small cracks in life prediction.

PubMed

Dauskardt, R H; Ritchie, R O; Takemoto, J K; Brendzel, A M

1994-07-01

A fracture-mechanics based study has performed to characterize the fracture toughness and rates of cyclic fatigue-crack growth of incipient flaws in prosthetic heart-valve components made of pyrolytic carbon-coated graphite. Such data are required to predict the safe structural lifetime of mechanical heart-valve prostheses using damage-tolerant analysis. Unlike previous studies where fatigue-crack propagation data were obtained using through-thickness, long cracks (approximately 2-20 mm long), growing in conventional (e.g., compact-tension) samples, experiments were performed on physically small cracks (approximately 100-600 microns long), initiated on the surface of the pyrolytic-carbon coating to simulate reality. Small-crack toughness results were found to agree closely with those measured conventionally with long cracks. However, similar to well-known observations in metal fatigue, it was found that based on the usual computations of the applied (far-field) driving force in terms of the maximum stress intensity, Kmax, small fatigue cracks grew at rates that exceeded those of long cracks at the same applied stress intensity, and displayed a negative dependency on Kmax; moreover, they grew at applied stress intensities less than the fatigue threshold value, below which long cracks are presumed dormant. To resolve this apparent discrepancy, it is shown that long and small crack results can be normalized, provided growth rates are characterized in terms of the total (near-tip) stress intensity (incorporating, for example, the effect of residual stress); with this achieved, in principle, either form of data can be used for life prediction of implant devices. Inspection of the long and small crack results reveals extensive scatter inherent in both forms of growth-rate data for the pyrolytic-carbon material.

Auger mediated positron sticking on graphene and highly oriented pyrolytic graphite

NASA Astrophysics Data System (ADS)

Chirayath, V. A.; Chrysler, M.; McDonald, A.; Lim, Z.; Shastry, K.; Gladen, R.; Fairchild, A.; Koymen, A.; Weiss, A.

Positron annihilation induced Auger electron spectroscopy (PAES) measurements on 6-8 layers graphene grown on polycrystalline copper and the measurements on a highly oriented pyrolytic graphite (HOPG) sample have indicated the presence of a bound surface state for positrons. Measurements carried out with positrons of kinetic energies lower than the electron work function for graphene or HOPG have shown emission of low energy electrons possible only through the Auger mediated positron sticking (AMPS) process. In this process the positron makes a transition from a positive energy scattering state to a bound surface state. The transition energy is coupled to a valence electron which may then have enough energy to get ejected from the sample surface. The positrons which are bound to surface state are highly localized in a direction perpendicular to surface and delocalized parallel to it which makes this process highly surface sensitive and can thus be used for characterizing graphene or graphite surfaces for open volume defects and surface impurities. The measurements have also shown an extremely large low energy tail for the C KVV Auger transition at 263eV indicative of another physical process for low energy emission. This work was supported by NSF Grant No. DMR 1508719 and DMR 1338130.

Relationship between microstructure and tribological behavior of CFRC composites

NASA Astrophysics Data System (ADS)

de Souza, Maria Aparecida Miranda; Pardini, Luiz Claudio

2017-12-01

Carbon fiber reinforced carbon (CFRC) composites were initially introduced in spacecraft propulsion area and quickly started to be applied in aircraft braking systems, replacing conventional metallic systems, thanks to their excellent tribological properties. Each company develops their own CFRC composite production system, the information is unique to each manufacturer, and little is reported in the literature. In this work, tribological characterizations of three commercial CFRC composites are performed using a pin-on-disc tribometer. The results showed that the pairs assembled with pyrolytic matrix composites of rough or smooth laminar texture with graphitization index between 18 and 40% has an average COF between 0.15 and 0.25, while the pairs assembled with mixed pairs, pyrolytic matrix and glassy matrix, or pair of glassy matrix display average COF between 0.10 and 0.15. Wear which can reach a rate 9 times higher to the tribological pair of glassy composite when compared to a pyrolytic composite.

On the fractography of overload, stress corrosion, and cyclic fatigue failures in pyrolytic-carbon materials used in prosthetic heart-valve devices.

PubMed

Ritchie, R O; Dauskardt, R H; Pennisi, F J

1992-01-01

A scanning electron microscopy study is reported of the nature and morphology of fracture surfaces in pyrocarbons commonly used for the manufacture of mechanical heart-valve prostheses. Specifically, silicon-alloyed low-temperature-isotropic (LTI)-pyrolytic carbon is examined, both as a coating on graphite and as a monolithic material, following overload, stress corrosion (static fatigue), and cyclic fatigue failures in a simulated physiological environment of 37 degrees C Ringer's solution. It is found that, in contrast to most metallic materials yet in keeping with many ceramics, there are no distinct fracture morphologies in pyro-carbons which are characteristic of a specific mode of loading; fracture surfaces appear to be identical for both catastrophic and subcritical crack growth under either sustained or cyclic loading. We conclude that caution should be used in assigning the likely cause of failure of pyrolytic carbon heart-valve components using fractographic examination.

Huyen Dinh | NREL

Science.gov Websites

.; Dinh, H.N. T. Gennett and R. O' (2013). "Nitrogen: unraveling the secret to stable carbon .; Gennett, (2011). "Tuning carbon-based fuel cell catalyst support structures via nitrogen pyrolytic graphite doped with nitrogen." J Phys Chem (C 2011 115:28); pp. 13676-13684. Dinh, H.N.; Ren

Wearable strain sensors based on thin graphite films for human activity monitoring

NASA Astrophysics Data System (ADS)

Saito, Takanari; Kihara, Yusuke; Shirakashi, Jun-ichi

2017-12-01

Wearable health-monitoring devices have attracted increasing attention in disease diagnosis and health assessment. In many cases, such devices have been prepared by complicated multistep procedures which result in the waste of materials and require expensive facilities. In this study, we focused on pyrolytic graphite sheet (PGS), which is a low-cost, simple, and flexible material, used as wearable devices for monitoring human activity. We investigated wearable devices based on PGSs for the observation of elbow and finger motions. The thin graphite films were fabricated by cutting small films from PGSs. The wearable devices were then made from the thin graphite films assembled on a commercially available rubber glove. The human motions could be observed using the wearable devices. Therefore, these results suggested that the wearable devices based on thin graphite films may broaden their application in cost-effective wearable electronics for the observation of human activity.

ICP-MS measurement of silver diffusion coefficient in graphite IG-110 between 1048K and 1284K

NASA Astrophysics Data System (ADS)

Carter, L. M.; Seelig, J. D.; Brockman, J. D.; Robertson, J. D.; Loyalka, S. K.

2018-01-01

Silver-110m has been shown to permeate intact silicon carbide and pyrolytic carbon coating layers of the TRISO fuel particles during normal High Temperature Gas-Cooled Reactor (HTGR) operational conditions. The diffusion coefficients for silver in graphite IG-110 measured using a release method designed to simulate HTGR conditions of high temperature and flowing helium in the temperature range 1048-1253 K are reported. The measurements were made using spheres milled from IG-110 graphite that were infused with silver using a pressure vessel technique. The Ag diffusion was measured using a time release technique with an ICP-MS instrument for detection. The results of this work are:

Orientation-free and differentially pumped addition of a low-flux reactive gas beam to a surface analysis system.

PubMed

Harthcock, Colin; Jahanbekam, Abdolreza; Eskelsen, Jeremy R; Lee, David Y

2016-11-01

We describe an example of a piecewise gas chamber that can be customized to incorporate a low flux of gas-phase radicals with an existing surface analysis chamber for in situ and stepwise gas-surface interaction experiments without any constraint in orientation. The piecewise nature of this gas chamber provides complete angular freedom and easy alignment and does not require any modification of the existing surface analysis chamber. In addition, the entire gas-surface system is readily differentially pumped with the surface chamber kept under ultra-high-vacuum during the gas-surface measurements. This new design also allows not only straightforward reconstruction to accommodate the orientation of different surface chambers but also for the addition of other desired features, such as an additional pump to the current configuration. Stepwise interaction between atomic oxygen and a highly ordered pyrolytic graphite surface was chosen to test the effectiveness of this design, and the site-dependent O-atom chemisorption and clustering on the graphite surface were resolved by a scanning tunneling microscope in the nm-scale. X-ray photoelectron spectroscopy was used to further confirm the identity of the chemisorbed species on the graphite surface as oxygen.

Imaging surface nanobubbles at graphite-water interfaces with different atomic force microscopy modes.

PubMed

Yang, Chih-Wen; Lu, Yi-Hsien; Hwang, Ing-Shouh

2013-05-08

We have imaged nanobubbles on highly ordered pyrolytic graphite (HOPG) surfaces in pure water with different atomic force microscopy (AFM) modes, including the frequency-modulation, the tapping, and the PeakForce techniques. We have compared the performance of these modes in obtaining the surface profiles of nanobubbles. The frequency-modulation mode yields a larger height value than the other two modes and can provide more accurate measurement of the surface profiles of nanobubbles. Imaging with PeakForce mode shows that a nanobubble appears smaller and shorter with increasing peak force and disappears above a certain peak force, but the size returns to the original value when the peak force is reduced. This indicates that imaging with high peak forces does not cause gas removal from the nanobubbles. Based on the presented findings and previous AFM observations, the existing models for nanobubbles are reviewed and discussed. The model of gas aggregate inside nanobubbles provides a better explanation for the puzzles of the high stability and the contact angle of surface nanobubbles.

Pyrolytic Carbon Coatings on Aligned Carbon Nanotube Assemblies and Fabrication of Advanced Carbon Nanotube/Carbon Composites

NASA Astrophysics Data System (ADS)

Faraji, Shaghayegh

Chemical vapor deposition (CVD) is a technique used to create a pyrolytic carbon (PyC) matrix around fibrous preforms in carbon/carbon (C/C) composites. Due to difficulties in producing three-dimensional carbon nanotube (CNT) assemblies, use of nanotubes in CVD fabricated CNT/C composites is limited. This dissertation describes efforts to: 1) Study the microstructure of PyC deposited on CNTs in order to understand the effect of microstructure and morphology of carbon coatings on graphitization behavior of CNT/PyC composites. This understanding helped to suggest a new approach for controlled radial growth of CNTs. 2) Evaluate the properties of CNT/PyC structures as a novel form of CNT assemblies with resilient, anisotropic and tunable properties. PyC was deposited on aligned sheets of nanotubes, drawn from spinnable CNT arras, using CVD of acetylene gas. At longer deposition times, the microstructure of PyC changed from laminar turbostratic carbon to a disordered carbon. For samples with short PyC deposition times (up to 30 minutes), deposited carbon layer rearranged during graphitization treatment and resulted in a crystalline structure where the coating and original tube walls could not be easily differentiated. In contrast, in samples with longer carbon deposition durations, carbon layers close to the surface of the coating remained disordered even after graphitization thermal treatment. Understanding the effect of PyC microstructure transition on graphitization behavior of CNT/PyC composites was used to develop a new method for controlled radial growth of CNTs. Carbon coated aligned CNT sheets were graphitized after each short (20 minutes) carbon deposition cycle. This prevented development of disorder carbon during subsequent PyC deposition cycles. Using cyclic-graphitization method, thick PyC coating layers were successfully graphitized into a crystalline structure that could not be differentiated from the original nanotube walls. This resulted into radial growth of CNTs, from 40 to 100 nm. Infiltration of PyC into stacked layered sheets of aligned CNTs produced resilient foam-like materials that exhibited complete recovery from 90% compressive strain. PyC coated the junctions between nanotubes and also increased their surface roughness. These changes were assumed to be responsible for the resiliency of the, once inelastic, assembly of nanotubes. While nanotubes' alignment resulted in anisotropic properties of the foams, variation in PyC infiltration duration was used to tune the foams' properties. Further investigation into properties of these foams showed promising results for their application as pressure/strain sensor and selective liquid absorbers for oil spill clean ups. Finally, CNT foams were used as novel substrates for growth of secondary nanotube assemblies. In order to achieve that, foams were first coated with alumina buffer layers using atomic layer deposition (ALD) method. New nanotubes were further grown inside the foams by CVD of acetylene over iron nano-particles. Super low density and highly porous structure of the foams allowed for diffusion of catalyst along with growth gasses into their bulk, which resulted in growth of secondary nanotubes throughout the thickness of the foams. The thickness of the alumina buffer layer was shown to influence CNT nucleation density and growth uniformity across the thickness of the foams. Compressive mechanical testing of the foams showed an order of magnitude increase in compression strength after secondary CNT growth.

Effect of mechanical and electrical stimuli in conductive atomic force microscopy with noble metal-coated tips

NASA Astrophysics Data System (ADS)

Zade, Vishal; Kang, Hung-Sen; Lee, Min Hwan

2018-01-01

Conductive atomic force microscopy has been widely employed to study the localized electrical properties of a wide range of substrates in non-vacuum conditions by the use of noble metal-coated tips. However, quantitative characterization of the electrical properties was often precluded by unpredictable changes in the tip apex morphology, and/or electronic transport characteristics of undesired oxide overcoats on the tip. In this paper, the impact of mechanical and electrical stimuli on the apex geometry of gold coated tips and electrical conduction properties at the tip-substrate contact is discussed by choosing gold and highly ordered pyrolytic graphite as the representative tip and substrate materials, respectively.

Integrated Thermal Modules for Cooling Silicon and Silicon Carbide Power Modules

DTIC Science & Technology

2007-06-11

analyses, bench tests, and motor tests comprise the program. The ITMs, in place of standard heatsinks, use a highly conductive pyrolytic graphite to...passively cool power modules. Initial results show that even simple ITMs can lower chip temperatures by 20 deg. C and 10 deg. C with engine oil and

Voltammetric studies of hemoglobin-coated polystyrene latex bead films on pyrolytic graphite electrodes.

PubMed

Sun, Hong; Hu, Naifei

2004-08-01

A novel hemoglobin (Hb)-coated polystyrene (PS) latex bead film was deposited on pyrolytic graphite (PG) electrode surface. In the first step, positively charged Hb molecules in pH 5.0 buffers were adsorbed on the surface of negatively charged, 500 nm diameter PS latex beads bearing sulfate groups by electrostatic interaction. The aqueous dispersion of Hb-coated PS particles was then deposited on the surface of PG electrodes and, after evaporation of the solvent, Hb-PS films were formed. The Hb-PS film electrodes exhibited a pair of well-defined, quasi-reversible cyclic voltammetric (CV) peaks at about -0.36 V vs. SCE in pH 7.0 buffers, characteristic of Hb heme Fe(III)/Fe(II) redox couples. Positions of Soret absorption band of Hb-PS films suggest that Hb retains its near-native structure in the films in its dry form and in solution at medium pH. The Hb in PS films was also acted as a catalyst to catalyze electrochemical reduction of various substrates such as trichloroacetic acid (TCA), nitrite, oxygen and hydrogen peroxide.

Electrodeposition of platinum on highly oriented pyrolytic graphite. Part I: electrochemical characterization.

PubMed

Lu, Guojin; Zangari, Giovanni

2005-04-28

The electrochemical deposition of Pt on highly oriented pyrolytic graphite (HOPG) from H2PtCl6 solutions was investigated by cyclic voltammetry and chronoamperometry. The effects of deposition overpotential, H2PtCl6 concentration, supporting electrolyte, and anion additions on the deposition process were evaluated. Addition of chloride inhibits Pt deposition due to adsorption on the substrate and blocking of reduction sites, while SO4(2-) and ClO4- slightly promote Pt reduction. By comparing potentiostatic current-time transients with the Scharifker-Hills model, a transition from progressive to instantaneous nucleation was observed when increasing the deposition overpotential. Following addition of chloride anions the fit of experimental transients with the instantaneous nucleation mode improves, while the addition of SO4(2-) induces only small changes. Chloride anions strongly inhibit the reduction process, which is shifted in the cathodic direction. The above results indicate that the most appropriate conditions for growing Pt nanoparticles on HOPG with narrow size distribution are to use an H2PtCl6 solution with HCl as supporting electrolyte and to apply a high cathodic overpotential.

Formation of Nanocones on Highly Oriented Pyrolytic Graphite by Oxygen Plasma

PubMed Central

Vesel, Alenka; Eleršič, Kristina; Modic, Martina; Junkar, Ita; Mozetič, Miran

2014-01-01

Improvement in hemocompatibility of highly oriented pyrolytic graphite (HOPG) by formation of nanostructured surface by oxygen plasma treatment is reported. We have showed that by appropriate fine tuning of plasma and discharge parameters we are able to create nanostructured surface which is densely covered with nanocones. The size of the nanocones strongly depended on treatment time. The optimal results in terms of material hemocompatibility were obtained after treatment with oxygen plasma for 15 s, when both the nanotopography and wettability were the most favorable, since marked reduction in adhesion and activation of platelets was observed on this surface. At prolonged treatment times, the rich surface topography was lost and thus also its antithrombogenic properties. Chemical composition of the surface was always more or less the same, regardless of its morphology and height of the nanocones. Namely, on all plasma treated samples, only a few atomic percent of oxygen was found, meaning that plasma caused mostly etching, leading to changes in the surface morphology. This indicates that the main preventing mechanism against platelets adhesion was the right surface morphology. PMID:28788553

Highly sensitive protein detection by combination of atomic force microscopy fishing with charge generation and mass spectrometry analysis.

PubMed

Ivanov, Yuri D; Pleshakova, Tatyana; Malsagova, Krystina; Kozlov, Andrey; Kaysheva, Anna; Kopylov, Arthur; Izotov, Alexander; Andreeva, Elena; Kanashenko, Sergey; Usanov, Sergey; Archakov, Alexander

2014-10-01

An approach combining atomic force microscopy (AFM) fishing and mass spectrometry (MS) analysis to detect proteins at ultra-low concentrations is proposed. Fishing out protein molecules onto a highly oriented pyrolytic graphite surface coated with polytetrafluoroethylene film was carried out with and without application of an external electric field. After that they were visualized by AFM and identified by MS. It was found that injection of solution leads to charge generation in the solution, and an electric potential within the measuring cell is induced. It was demonstrated that without an external electric field in the rapid injection input of diluted protein solution the fishing is efficient, as opposed to slow fluid input. The high sensitivity of this method was demonstrated by detection of human serum albumin and human cytochrome b5 in 10(-17) -10(-18) m water solutions. It was shown that an external negative voltage applied to highly oriented pyrolytic graphite hinders the protein fishing. The efficiency of fishing with an external positive voltage was similar to that obtained without applying any voltage. © 2014 FEBS.

Ultra-thin passivating film induced by vinylene carbonate on highly oriented pyrolytic graphite negative electrode in lithium-ion cell

NASA Astrophysics Data System (ADS)

Matsuoka, O.; Hiwara, A.; Omi, T.; Toriida, M.; Hayashi, T.; Tanaka, C.; Saito, Y.; Ishida, T.; Tan, H.; Ono, S. S.; Yamamoto, S.

We investigated the influence of vinylene carbonate, as an additive molecule, on the decomposition phenomena of electrolyte solution [ethylene carbonate (EC)—ethyl methyl carbonate (EMC) (1:2 by volume) containing 1 M LiPF 6] on a highly oriented pyrolytic graphite (HOPG) negative electrode by using cyclic voltammetry (CV) and atomic force microscopy (AFM). Vinylene carbonate deactivated reactive sites (e.g. radicals and oxides at the defects and the edge of carbon layer) on the cleaved surface of the HOPG negative electrode, and prevented further decomposition of the other solvents there. Further, vinylene carbonate induced an ultra-thin film (less than 1.0 nm in thickness) on the terrace of the basal plane of the HOPG negative electrode, and this film suppressed the decomposition of electrolyte solution on the terraces of the basal plane. We consider that this ultra-thin passivating film is composed of a reduction product of vinylene carbonate (VC), and might have a polymer structure. These induced effects might explain how VC improves the life performance of lithium-ion cells.

Crystallographic order and decomposition of [MnIII 6CrIII]3+ single-molecule magnets deposited in submonolayers and monolayers on HOPG studied by means of molecular resolved atomic force microscopy (AFM) and Kelvin probe force microscopy in UHV

NASA Astrophysics Data System (ADS)

Gryzia, Aaron; Volkmann, Timm; Brechling, Armin; Hoeke, Veronika; Schneider, Lilli; Kuepper, Karsten; Glaser, Thorsten; Heinzmann, Ulrich

2014-02-01

Monolayers and submonolayers of [Mn III 6 Cr III ] 3+ single-molecule magnets (SMMs) adsorbed on highly oriented pyrolytic graphite (HOPG) using the droplet technique characterized by non-contact atomic force microscopy (nc-AFM) as well as by Kelvin probe force microscopy (KPFM) show island-like structures with heights resembling the height of the molecule. Furthermore, islands were found which revealed ordered 1D as well as 2D structures with periods close to the width of the SMMs. Along this, islands which show half the heights of intact SMMs were observed which are evidences for a decomposing process of the molecules during the preparation. Finally, models for the structure of the ordered SMM adsorbates are proposed to explain the observations.

Atomic intercalation to measure adhesion of graphene on graphite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jun; Sorescu, Dan C.; Jeon, Seokmin

The interest in mechanical properties of layered and 2D materials has reemerged in light of device concepts that take advantage of flexing, adhesion and friction in such systems. Here we provide an effective measurement of the nanoscale elastic adhesion of a graphene sheet atop highly ordered pyrolytic graphite (HOPG) based on the analysis of atomic intercalates in graphite. Atomic intercalation is carried out using conventional ion sputtering, creating blisters in the top-most layer of the HOPG surface. Scanning tunneling microscopy coupled with image analysis and density functional theory are used to reconstruct the atomic positions and the strain map withinmore » the deformed graphene sheet, as well as to demonstrate subsurface diffusion of the ions creating such blisters. To estimate the adhesion energy we invoke an analytical model originally devised for macroscopic deformations of graphene. This model yields a value of 0.221 ± 0.011 J/m -2 for the adhesion energy of graphite, which is in surprisingly good agreement with reported experimental and theoretical values. This implies that macroscopic mechanical properties of graphene scale down to at least a few nanometers length. The simplicity of our method, compared to the macroscale characterization, enables analysis of elastic mechanical properties in two-dimensional layered materials and provides a unique opportunity to investigate the local variability of mechanical properties on the nanoscale.« less

Atomic intercalation to measure adhesion of graphene on graphite

DOE PAGES

Wang, Jun; Sorescu, Dan C.; Jeon, Seokmin; ...

2016-10-31

The interest in mechanical properties of layered and 2D materials has reemerged in light of device concepts that take advantage of flexing, adhesion and friction in such systems. Here we provide an effective measurement of the nanoscale elastic adhesion of a graphene sheet atop highly ordered pyrolytic graphite (HOPG) based on the analysis of atomic intercalates in graphite. Atomic intercalation is carried out using conventional ion sputtering, creating blisters in the top-most layer of the HOPG surface. Scanning tunneling microscopy coupled with image analysis and density functional theory are used to reconstruct the atomic positions and the strain map withinmore » the deformed graphene sheet, as well as to demonstrate subsurface diffusion of the ions creating such blisters. To estimate the adhesion energy we invoke an analytical model originally devised for macroscopic deformations of graphene. This model yields a value of 0.221 ± 0.011 J/m -2 for the adhesion energy of graphite, which is in surprisingly good agreement with reported experimental and theoretical values. This implies that macroscopic mechanical properties of graphene scale down to at least a few nanometers length. The simplicity of our method, compared to the macroscale characterization, enables analysis of elastic mechanical properties in two-dimensional layered materials and provides a unique opportunity to investigate the local variability of mechanical properties on the nanoscale.« less

Self-assembled monolayers of shape-persistent macrocycles on graphite: interior design and conformational polymorphism.

PubMed

Vollmeyer, Joscha; Eberhagen, Friederike; Höger, Sigurd; Jester, Stefan-S

2014-01-01

Three shape-persistent naphthylene-phenylene-acetylene macrocycles of identical backbone structures and extraannular substitution patterns but different (empty, apolar, polar) nanopore fillings are self-assembled at the solid/liquid interface of highly oriented pyrolytic graphite and 1,2,4-trichlorobenzene. Submolecularly resolved images of the resulting two-dimensional (2D) crystalline monolayer patterns are obtained by in situ scanning tunneling microscopy. A concentration-dependent conformational polymorphism is found, and open and more dense packing motifs are observed. For all three compounds alike lattice parameters are found, therefore the intermolecular macrocycle distances are mainly determined by their size and symmetry. This is an excellent example that the graphite acts as a template for the macrocycle organization independent from their specific interior.

Self-assembled PCBM bilayers on graphene and HOPG examined by AFM and STM

NASA Astrophysics Data System (ADS)

Li, Yanlong; Chen, Chuanhui; Burton, John; Park, Kyungwha; Heflin, James R.; Tao, Chenggang

2018-05-01

In this work we report fabrication and characterization of phenyl-C61-butyric acid methyl ester (PCBM) bilayer structures on graphene and highly oriented pyrolytic graphite (HOPG). Through careful control of the PCBM solution concentration (from 0.1 to 2 mg ml-1) and the deposition conditions, we demonstrate that PCBM molecules self-assemble into bilayer structures on graphene and HOPG substrates. Interestingly, the PCBM bilayers are formed with two distinct heights on HOPG, but only one unique representative height on graphene. At elevated annealing temperatures, edge diffusion allows neighboring vacancies to merge into a more ordered structure. This is, to the best of our knowledge, the first experimental realization of PCBM bilayer structures on graphene. This work could provide valuable insight into fabrication of new hybrid, ordered structures for applications to organic solar cells.

Self-assembled PCBM bilayers on graphene and HOPG examined by AFM and STM.

PubMed

Li, Yanlong; Chen, Chuanhui; Burton, John; Park, Kyungwha; Heflin, James R; Tao, Chenggang

2018-05-04

In this work we report fabrication and characterization of phenyl-C61-butyric acid methyl ester (PCBM) bilayer structures on graphene and highly oriented pyrolytic graphite (HOPG). Through careful control of the PCBM solution concentration (from 0.1 to 2 mg ml -1 ) and the deposition conditions, we demonstrate that PCBM molecules self-assemble into bilayer structures on graphene and HOPG substrates. Interestingly, the PCBM bilayers are formed with two distinct heights on HOPG, but only one unique representative height on graphene. At elevated annealing temperatures, edge diffusion allows neighboring vacancies to merge into a more ordered structure. This is, to the best of our knowledge, the first experimental realization of PCBM bilayer structures on graphene. This work could provide valuable insight into fabrication of new hybrid, ordered structures for applications to organic solar cells.

Spectroscopic investigation of the wettability of multilayer graphene using highly ordered pyrolytic graphite as a model material.

PubMed

Ashraf, Ali; Wu, Yanbin; Wang, Michael C; Aluru, Narayana R; Dastgheib, Seyed A; Nam, SungWoo

2014-11-04

We report the intrinsic water contact angle (WCA) of multilayer graphene, explore different methods of cleaning multilayer graphene, and evaluate the efficiency of those methods on the basis of spectroscopic analysis. Highly ordered pyrolytic graphite (HOPG) was used as a model material system to study the wettability of the multilayer graphene surface by WCA measurements. A WCA value of 45° ± 3° was measured for a clean HOPG surface, which can serve as the intrinsic WCA for multilayer graphene. A 1 min plasma treatment (100 W) decreased the WCA to 6°, owing to the creation of surface defects and functionalization by oxygen-containing groups. Molecular dynamics simulations of water droplets on the HOPG surface with or without the oxygen-containing defect sites confirmed the experimental results. Heat treatment at near atmospheric pressure and wet chemical cleaning methods using hydrofluoric acid and chloroform did not change the WCA significantly. Low-pressure, high-temperature annealing under argon and hydrogen reduced the WCA to 54°, close to the intrinsic WCA of HOPG. Raman spectroscopy and atomic force microscopy did not show any significant change for the HOPG surface after this treatment, confirming low-pressure, high-temperature annealing as an effective technique to clean multilayer graphene without damaging the surface. Time-of-flight secondary ion mass spectrometry indicated the existence of hydrocarbon species on the surface of the HOPG sample that was exposed to air for <5 min and the absence of these impurities in the bulk. X-ray photoelectron spectroscopy analyses of the sample surfaces after the different cleaning techniques were performed to correlate the WCA to the surface chemistry. X-ray photoelectron spectroscopy results revealed that the WCA value changed drastically, depending on the amounts of oxygen-containing and hydrocarbon-containing groups on the surface.

Sound velocities in highly oriented pyrolytic graphite shocked to 18 GPa: Orientational order dependence and elastic instability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lucas, Marcel; Winey, J. M.; Gupta, Y. M.

Previous reports of rapid phase transformation above 18 GPa [Erskine and Nellis, Nature 349, 317 (1991)] and large elastic waves below 18 GPa [Lucas et al., J. Appl. Phys. 114, 093515 (2013)] for shock-compressed ZYB-grade highly-oriented pyrolytic graphite (HOPG), but not for less oriented ZYH-grade HOPG, indicated a link between the orientational order dependence of the HOPG response above and below the phase transformation stress. To gain insight into this link and into the mechanical response of HOPG shocked to peak stresses approaching the phase transformation onset, the compressibility of ZYB- and ZYH-grade HOPG in the shocked state was examinedmore » using front surface impact experiments. Particle velocity histories and sound velocities were measured for peak stresses reaching 18 GPa. Although the locus of the measured peak stress-particle velocity states is indistinguishable for the two grades of HOPG, the measured sound velocities in the peak state reveal significant differences between the two grades. Specifically, 1) The measured sound velocities are somewhat higher for ZYH-grade HOPG, compared to ZYB-grade HOPG. 2) The measured sound velocities for ZYH-grade HOPG increase smoothly with compression, whereas those for ZYB-2 grade HOPG exhibit a significant reduction in the compression dependence from 12 GPa to 17 GPa and an abrupt increase from 17 GPa to 18 GPa. 3) The longitudinal moduli, determined from the measured sound velocities, are smaller than the calculated bulk moduli for ZYB-grade HOPG shocked to peak stresses above 15 GPa, indicating the onset of an elastic instability. The present findings demonstrate that the softening of the longitudinal modulus (or elastic instability) presented here is linked to the large elastic waves and the rapid phase transformation reported previously – all observed only for shocked ZYB-grade HOPG. The elastic instability in shocked ZYB-grade HOPG is likely a precursor to the rapid phase transformation observed above 18 GPa for this HOPG grade.« less

Sound velocities in highly oriented pyrolytic graphite shocked to 18 GPa: Orientational order dependence and elastic instability

DOE PAGES

Lucas, Marcel; Winey, J. M.; Gupta, Y. M.

2015-12-28

Previous reports of rapid phase transformation above 18 GPa [Erskine and Nellis, Nature 349, 317 (1991)] and large elastic waves below 18 GPa [Lucas et al., J. Appl. Phys. 114, 093515 (2013)] for shock-compressed ZYB-grade highly-oriented pyrolytic graphite (HOPG), but not for less oriented ZYH-grade HOPG, indicated a link between the orientational order dependence of the HOPG response above and below the phase transformation stress. To gain insight into this link and into the mechanical response of HOPG shocked to peak stresses approaching the phase transformation onset, the compressibility of ZYB- and ZYH-grade HOPG in the shocked state was examinedmore » using front surface impact experiments. Particle velocity histories and sound velocities were measured for peak stresses reaching 18 GPa. Although the locus of the measured peak stress-particle velocity states is indistinguishable for the two grades of HOPG, the measured sound velocities in the peak state reveal significant differences between the two grades. Specifically, 1) The measured sound velocities are somewhat higher for ZYH-grade HOPG, compared to ZYB-grade HOPG. 2) The measured sound velocities for ZYH-grade HOPG increase smoothly with compression, whereas those for ZYB-2 grade HOPG exhibit a significant reduction in the compression dependence from 12 GPa to 17 GPa and an abrupt increase from 17 GPa to 18 GPa. 3) The longitudinal moduli, determined from the measured sound velocities, are smaller than the calculated bulk moduli for ZYB-grade HOPG shocked to peak stresses above 15 GPa, indicating the onset of an elastic instability. The present findings demonstrate that the softening of the longitudinal modulus (or elastic instability) presented here is linked to the large elastic waves and the rapid phase transformation reported previously – all observed only for shocked ZYB-grade HOPG. The elastic instability in shocked ZYB-grade HOPG is likely a precursor to the rapid phase transformation observed above 18 GPa for this HOPG grade.« less

Ion sputter textured graphite electrode plates

NASA Technical Reports Server (NTRS)

Curren, A. N.; Forman, R.; Sovey, J. S.; Wintucky, E. G. (Inventor)

1983-01-01

A specially textured surface of pyrolytic graphite exhibits extremely low yields of secondary electrons and reduced numbers of reflected primary electrons after impingement of high energy primary electrons. Electrode plates of this material are used in multistage depressed collectors. An ion flux having an energy between 500 iV and 1000 iV and a current density between 1.0 mA/sq cm and 6.0 mA/sq cm produces surface roughening or texturing which is in the form of needles or spires. Such textured surfaces are especially useful as anode collector plates in high tube devices.

The nucleation and growth of uranium on the basal plane of graphite studied by scanning tunneling microscopy

NASA Astrophysics Data System (ADS)

Tench, R. J.

1992-11-01

For the first time, nanometer scale uranium clusters were created on the basal plane of highly oriented pyrolytic graphite by laser ablation under ultra-high vacuum conditions. The physical and chemical properties of these clusters were investigated by scanning tunneling microscopy (STM) as well as standard surface science techniques. Auger electron and X-ray photoelectron spectroscopies found the uranium deposit to be free of contamination and showed that no carbide had formed with the underlying graphite. Clusters with sizes ranging from 42 to 630 sq A were observed upon initial room temperature deposition. Surface diffusion of uranium was observed after annealing the substrate above 800 K, as evidenced by the decreased number density and the increased size of the clusters. Preferential depletion of clusters on terraces near step edges as a result of annealing was observed. The activation energy for diffusion deduced from these measurements was found to be 15 Kcal/mole. Novel formation of ordered uranium thin films was observed for coverages greater than two monolayers after annealing above 900 K. These ordered films displayed islands with hexagonally faceted edges rising in uniform step heights characteristic of the unit cell of the P-phase of uranium. In addition, atomic resolution STM images of these ordered films indicated the formation of the (beta)-phase of uranium. The chemical properties of these surfaces were investigated and it was shown that these uranium films had a reduced oxidation rate in air as compared to bulk metal and that STM imaging in air induced a polarity-dependent enhancement of the oxidation rate.

Room temperature stable single molecule rectifiers with graphite electrodes

NASA Astrophysics Data System (ADS)

Rungger, Ivan; Kaliginedi, V.; Droghetti, A.; Ozawa, H.; Kuzume, A.; Haga, M.; Broekmann, P.; Rudnev, A. V.

In this combined theoretical and experimental study we present new molecular electronics device characteristics of unprecedented stability at room temperature by using electrodes based on highly oriented pyrolytic graphite with covalently attached molecules. To this aim, we explore the effect of the anchoring group chemistry on the charge transport properties of graphite/molecule contacts by means of the scanning tunneling microscopy break-junction technique and ab initio simulations. The theoretical approach to evaluate the conductance is based on density functional theory calculations combined with the non-equilibrium Greens function technique, as implemented in the Smeagol electron transport code. We also demonstrate a strong bias dependence and rectification of the single molecule conductance induced by the anchoring chemistry in combination with the very low density of states of graphite around the Fermi energy. We show that the direction of tunneling current rectification can be tuned by anchoring group chemistry.

On the thermodynamic path enabling a room-temperature, laser-assisted graphite to nanodiamond transformation

NASA Astrophysics Data System (ADS)

Gorrini, F.; Cazzanelli, M.; Bazzanella, N.; Edla, R.; Gemmi, M.; Cappello, V.; David, J.; Dorigoni, C.; Bifone, A.; Miotello, A.

2016-10-01

Nanodiamonds are the subject of active research for their potential applications in nano-magnetometry, quantum optics, bioimaging and water cleaning processes. Here, we present a novel thermodynamic model that describes a graphite-liquid-diamond route for the synthesis of nanodiamonds. Its robustness is proved via the production of nanodiamonds powders at room-temperature and standard atmospheric pressure by pulsed laser ablation of pyrolytic graphite in water. The aqueous environment provides a confinement mechanism that promotes diamond nucleation and growth, and a biologically compatible medium for suspension of nanodiamonds. Moreover, we introduce a facile physico-chemical method that does not require harsh chemical or temperature conditions to remove the graphitic byproducts of the laser ablation process. A full characterization of the nanodiamonds by electron and Raman spectroscopies is reported. Our model is also corroborated by comparison with experimental data from the literature.

Phonon-assisted indirect transitions in angle-resolved photoemission spectra of graphite and graphene

NASA Astrophysics Data System (ADS)

Ayria, Pourya; Tanaka, Shin-ichiro; Nugraha, Ahmad R. T.; Dresselhaus, Mildred S.; Saito, Riichiro

2016-08-01

Indirect transitions of electrons in graphene and graphite are investigated by means of angle-resolved photoemission spectroscopy (ARPES) with several different incident photon energies and light polarizations. The theoretical calculations of the indirect transition for graphene and for a single crystal of graphite are compared with the experimental measurements for highly-oriented pyrolytic graphite and a single crystal of graphite. The dispersion relations for the transverse optical (TO) and the out-of-plane longitudinal acoustic (ZA) phonon modes of graphite and the TO phonon mode of graphene can be extracted from the inelastic ARPES intensity. We find that the TO phonon mode for k points along the Γ -K and K -M -K' directions in the Brillouin zone can be observed in the ARPES spectra of graphite and graphene by using a photon energy ≈11.1 eV. The relevant mechanism in the ARPES process for this case is the resonant indirect transition. On the other hand, the ZA phonon mode of graphite can be observed by using a photon energy ≈6.3 eV through a nonresonant indirect transition, while the ZA phonon mode of graphene within the same mechanism should not be observed.

The low temperature oxidation of lithium thin films on HOPG by O 2 and H 2O

DOE PAGES

Wulfsberg, Steven M.; Koel, Bruce E.; Bernasek, Steven L.

2016-04-16

Lithiated graphite and lithium thin films have been used in fusion devices. In this environment, lithiated graphite will undergo oxidation by background gases. In order to gain insight into this oxidation process, thin (< 15 monolayer (ML)) lithium films on highly ordered pyrolytic graphite (HOPG) were exposed in this paper to O 2(g) and H 2O (g) in an ultra-high vacuum chamber. High resolution electron energy loss spectroscopy (HREELS) was used to identify the surface species formed during O 2(g) and H 2O (g) exposure. Auger electron spectroscopy (AES) was used to obtain the relative oxidation rates during O 2(g)more » and H 2O (g) exposure. AES showed that as the lithium film thickness decreased from 15 to 5 to 1 ML, the oxidation rate decreased for both O 2(g) and H 2O (g). HREELS showed that a 15 ML lithium film was fully oxidized after 9.7 L (L) of O 2(g) exposure and Li 2O was formed. HREELS also showed that during initial exposure (< 0.5 L) H 2O (g), lithium hydride and lithium hydroxide were formed on the surface of a 15 ML lithium film. Finally, after 0.5 L of H 2O (g) exposure, the H 2O (g) began to physisorb, and after 15 L of H 2O (g) exposure, the 15 ML lithium film was not fully oxidized.« less

The low temperature oxidation of lithium thin films on HOPG by O 2 and H 2O

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wulfsberg, Steven M.; Koel, Bruce E.; Bernasek, Steven L.

Lithiated graphite and lithium thin films have been used in fusion devices. In this environment, lithiated graphite will undergo oxidation by background gases. In order to gain insight into this oxidation process, thin (< 15 monolayer (ML)) lithium films on highly ordered pyrolytic graphite (HOPG) were exposed in this paper to O 2(g) and H 2O (g) in an ultra-high vacuum chamber. High resolution electron energy loss spectroscopy (HREELS) was used to identify the surface species formed during O 2(g) and H 2O (g) exposure. Auger electron spectroscopy (AES) was used to obtain the relative oxidation rates during O 2(g)more » and H 2O (g) exposure. AES showed that as the lithium film thickness decreased from 15 to 5 to 1 ML, the oxidation rate decreased for both O 2(g) and H 2O (g). HREELS showed that a 15 ML lithium film was fully oxidized after 9.7 L (L) of O 2(g) exposure and Li 2O was formed. HREELS also showed that during initial exposure (< 0.5 L) H 2O (g), lithium hydride and lithium hydroxide were formed on the surface of a 15 ML lithium film. Finally, after 0.5 L of H 2O (g) exposure, the H 2O (g) began to physisorb, and after 15 L of H 2O (g) exposure, the 15 ML lithium film was not fully oxidized.« less

Supercooling of Hydrogen on Template Materials to Deterministically Seed Ignition-Quality Solid Fuel Layers

DOE PAGES

Shin, S. J.; Zepeda-Ruiz, L. A.; Lee, J. R. I.; ...

2016-09-01

In this study, we explored templating effects of various materials for hydrogen (H 2 and D 2) solidification by measuring the degree of supercooling required for liquid hydrogen to solidify below each triple point. The results show high supercooling (>100 mK) for most metallic, covalent, and ionic solids, and low supercooling (<100 mK) for van der Waals (vdW) solids. We attribute the low supercooling of vdW solids to the weak interaction of the substrate and hydrogen. Highly ordered pyrolytic graphite showed the lowest supercooling among materials that are solid at room temperature, but did not exhibit a templating effect withinmore » a fill-tube and capsule assembly.« less

Bandgap engineering through nanocrystalline magnetic alloy grafting on reduced graphene oxide.

PubMed

De, D; Chakraborty, M; Majumdar, S; Giri, S

2014-09-28

High conductivity and the absence of ferromagnetism in pristine graphene fail to satisfy primary criteria for possible technological application in spintronics. Opening of the bandgap in graphene is primarily desirable for such applications. We report a simplified and novel approach of controlled grafting of a magnetic alloy on reduced graphene oxide. This eventually leads to ferromagnetism of the stable hybrid material at room temperature, with a large moment (∼1.2 μB) and a remarkable decrease in conductivity (∼10 times) compared to highly ordered pyrolytic graphite. Our model band-structure calculation indicates that the combined effect of controlled vacancies and impurities attributed to the nanocrystalline alloy grafting leads to a promising step toward band gap engineering.

Structural Transformation of Guanine Coordination Motifs in Water Induced by Metal ions and Temperature.

PubMed

Li, Wei; Jin, Jing; Liu, Xiaoqing; Wang, Li

2018-06-15

The transformation effects of metal ions and temperature on the DNA bases guanine (G) metal-organic coordination motifs in water have been investigated by scanning tunneling microcopy (STM). The G molecules form an ordered hydrogen-bonded structure at the water- highly oriented pyrolytic graphite (HOPG) interface. The STM observations reveal that the canonical G/9H form can be transformed into the G/(3H, 7H) tautomer by increasing the temperature of the G solution to 38.6oC. Moreover, metal ions bind with G molecules to form G4Fe13+, G3Fe32+ and the heterochiral intermixed G4Na1+ metal-organic networks after the introduction of the alkali-metal ions in cellular environment.

Thermally stable laminating resins

NASA Technical Reports Server (NTRS)

Jones, R. J.; Vaughan, R. W.; Burns, E. A.

1972-01-01

Improved thermally stable laminating resins were developed based on the addition-type pyrolytic polymerization. Detailed monomer and polymer synthesis and characterization studies identified formulations which facilitate press molding processing and autoclave fabrication of glass and graphite fiber reinforced composites. A specific resin formulation, termed P10P was utilized to prepare a Courtaulds HMS reinforced simulated airfoil demonstration part by an autoclave molding process.

Atomic Oxygen Erosion Yield Predictive Tool for Spacecraft Polymers in Low Earth Orbit

NASA Technical Reports Server (NTRS)

Bank, Bruce A.; de Groh, Kim K.; Backus, Jane A.

2008-01-01

A predictive tool was developed to estimate the low Earth orbit (LEO) atomic oxygen erosion yield of polymers based on the results of the Polymer Erosion and Contamination Experiment (PEACE) Polymers experiment flown as part of the Materials International Space Station Experiment 2 (MISSE 2). The MISSE 2 PEACE experiment accurately measured the erosion yield of a wide variety of polymers and pyrolytic graphite. The 40 different materials tested were selected specifically to represent a variety of polymers used in space as well as a wide variety of polymer chemical structures. The resulting erosion yield data was used to develop a predictive tool which utilizes chemical structure and physical properties of polymers that can be measured in ground laboratory testing to predict the in-space atomic oxygen erosion yield of a polymer. The properties include chemical structure, bonding information, density and ash content. The resulting predictive tool has a correlation coefficient of 0.914 when compared with actual MISSE 2 space data for 38 polymers and pyrolytic graphite. The intent of the predictive tool is to be able to make estimates of atomic oxygen erosion yields for new polymers without requiring expensive and time consumptive in-space testing.

Nanoscale electrochemical patterning reveals the active sites for catechol oxidation at graphite surfaces.

PubMed

Patel, Anisha N; McKelvey, Kim; Unwin, Patrick R

2012-12-19

Graphite-based electrodes (graphite, graphene, and nanotubes) are used widely in electrochemistry, and there is a long-standing view that graphite step edges are needed to catalyze many reactions, with the basal surface considered to be inert. In the present work, this model was tested directly for the first time using scanning electrochemical cell microscopy reactive patterning and shown to be incorrect. For the electro-oxidation of dopamine as a model process, the reaction rate was measured at high spatial resolution across a surface of highly oriented pyrolytic graphite. Oxidation products left behind in a pattern defined by the scanned electrochemical cell served as surface-site markers, allowing the electrochemical activity to be correlated directly with the graphite structure on the nanoscale. This process produced tens of thousands of electrochemical measurements at different locations across the basal surface, unambiguously revealing it to be highly electrochemically active, with step edges providing no enhanced activity. This new model of graphite electrodes has significant implications for the design of carbon-based biosensors, and the results are additionally important for understanding electrochemical processes on related sp(2)-hybridized materials such as pristine graphene and nanotubes.

Mono- and multilayers of molecular spoked carbazole wheels on graphite

PubMed Central

Aggarwal, A Vikas; Kalle, Daniel; Höger, Sigurd

2014-01-01

Summary Self-assembled monolayers of a molecular spoked wheel (a shape-persistent macrocycle with an intraannular spoke/hub system) and its synthetic precursor are investigated by scanning tunneling microscopy (STM) at the liquid/solid interface of 1-octanoic acid and highly oriented pyrolytic graphite. The submolecularly resolved STM images reveal that the molecules indeed behave as more or less rigid objects of certain sizes and shapes – depending on their chemical structures. In addition, the images provide insight into the multilayer growth of the molecular spoked wheels (MSWs), where the first adlayer acts as a template for the commensurate adsorption of molecules in the second layer. PMID:25550744

Mono- and multilayers of molecular spoked carbazole wheels on graphite.

PubMed

Jester, Stefan-S; Aggarwal, A Vikas; Kalle, Daniel; Höger, Sigurd

2014-01-01

Self-assembled monolayers of a molecular spoked wheel (a shape-persistent macrocycle with an intraannular spoke/hub system) and its synthetic precursor are investigated by scanning tunneling microscopy (STM) at the liquid/solid interface of 1-octanoic acid and highly oriented pyrolytic graphite. The submolecularly resolved STM images reveal that the molecules indeed behave as more or less rigid objects of certain sizes and shapes - depending on their chemical structures. In addition, the images provide insight into the multilayer growth of the molecular spoked wheels (MSWs), where the first adlayer acts as a template for the commensurate adsorption of molecules in the second layer.

Photodeposition of Gold, Platinum, or Silver onto Titanium Dioxide Nanoparticles at Steps of Highly Oriented Pyrolytic Graphite

NASA Astrophysics Data System (ADS)

Taing, James

The photodeposition of gold, platinum, or silver nanoparticles selectively onto isolated titanium dioxide (TiO2) nanoparticles created metal/TiO2 photocatalysts and heterogeneous catalysts, and validated the photocatalytic property of the semiconductor. The isolated and ordered TiO2 nanoparticles permitted clear observations of the stability, and changes in morphology, of the particles in various experimental conditions. The fabrication of TiO2 nanoparticles at the steps of highly oriented pyrolytic graphite (HOPG), utilizing physical vapor deposition, required heating the graphite substrate to a minimum of 800 °C. The production of a photocurrent, and plating of gold nanoparticles, confirmed the photocatalytic property of the TiO2 nanoparticles on HOPG when utilized as a photoelectrode in a two half-cell setup. Employing sodium chloride (1.0 M) as an electrolyte resulted in an increase/decrease of the photocurrent with the addition of gold cations to the half-cell without/with the TiO2 nanoparticles. A poor distribution of gold nanoparticles, roughly 40-45 nm wide, deposited around few of the TiO2 nanoparticles. A lower concentration of sodium chloride (0.1 M) resulted in a coalescence of Au nanoparticles, roughly 10 nm, around many TiO2 nanoparticles. Using sodium nitrate as an electrolyte resulted in a rapid decay in the photocurrent and a growth of an unidentified material on the TiO2 nanoparticles. The unidentified material hindered the reduction of gold cations introduced midway through the experiment. With gold cations present at the onset of the experiment, disperse gold nanoparticles (˜5-10 nm) deposited around the TiO2 nanoparticles. In the absence of additional electrolyte, many disperse gold nanoparticles less than 5 nm deposited onto the TiO2 nanoparticles. More platinum than gold selectively deposited onto the TiO2 nanoparticles. On the contrary, less silver selectively deposited onto the TiO2 nanoparticles. Scanning electron microscopy and atomic force microscopy determined the morphology and distribution of the TiO2 nanoparticles and metal/TiO 2 nanocomposites. Energy dispersive X-ray spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy identified the composition of the materials.

Toward tunable doping in graphene FETs by molecular self-assembled monolayers

NASA Astrophysics Data System (ADS)

Li, Bing; Klekachev, Alexander V.; Cantoro, Mirco; Huyghebaert, Cedric; Stesmans, André; Asselberghs, Inge; de Gendt, Stefan; de Feyter, Steven

2013-09-01

In this paper, we report the formation of self-assembled monolayers (SAMs) of oleylamine (OA) on highly oriented pyrolytic graphite (HOPG) and graphene surfaces and demonstrate the potential of using such organic SAMs to tailor the electronic properties of graphene. Molecular resolution Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM) images reveal the detailed molecular ordering. The electrical measurements show that OA strongly interacts with graphene leading to n-doping effects in graphene devices. The doping levels are tunable by varying the OA deposition conditions. Importantly, neither hole nor electron mobilities are decreased by the OA modification. As a benefit from this noncovalent modification strategy, the pristine characteristics of the device are recoverable upon OA removal. From this study, one can envision the possibility to correlate the graphene-based device performance with the molecular structure and supramolecular ordering of the organic dopant.In this paper, we report the formation of self-assembled monolayers (SAMs) of oleylamine (OA) on highly oriented pyrolytic graphite (HOPG) and graphene surfaces and demonstrate the potential of using such organic SAMs to tailor the electronic properties of graphene. Molecular resolution Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM) images reveal the detailed molecular ordering. The electrical measurements show that OA strongly interacts with graphene leading to n-doping effects in graphene devices. The doping levels are tunable by varying the OA deposition conditions. Importantly, neither hole nor electron mobilities are decreased by the OA modification. As a benefit from this noncovalent modification strategy, the pristine characteristics of the device are recoverable upon OA removal. From this study, one can envision the possibility to correlate the graphene-based device performance with the molecular structure and supramolecular ordering of the organic dopant. Electronic supplementary information (ESI) available: AFM images of self-assembled monolayers of OA on HOPG; AFM height image of the graphene surface on a SiC substrate; high resolution STM image of a self-assembled monolayer of OA on HOPG; transfer curves of a graphene FET with and without baking steps; transfer curves of a graphene FET under high vacuum conditions; transfer curves of a graphene FET and its Raman response before and after OA treatment; transfer curves of a graphene FET before and after rinsing with n-hexane. See DOI: 10.1039/c3nr01255g

Understanding the Growth Mechanism of GaN Epitaxial Layers on Mechanically Exfoliated Graphite

NASA Astrophysics Data System (ADS)

Li, Tianbao; Liu, Chenyang; Zhang, Zhe; Yu, Bin; Dong, Hailiang; Jia, Wei; Jia, Zhigang; Yu, Chunyan; Gan, Lin; Xu, Bingshe; Jiang, Haiwei

2018-04-01

The growth mechanism of GaN epitaxial layers on mechanically exfoliated graphite is explained in detail based on classic nucleation theory. The number of defects on the graphite surface can be increased via O-plasma treatment, leading to increased nucleation density on the graphite surface. The addition of elemental Al can effectively improve the nucleation rate, which can promote the formation of dense nucleation layers and the lateral growth of GaN epitaxial layers. The surface morphologies of the nucleation layers, annealed layers and epitaxial layers were characterized by field-emission scanning electron microscopy, where the evolution of the surface morphology coincided with a 3D-to-2D growth mechanism. High-resolution transmission electron microscopy was used to characterize the microstructure of GaN. Fast Fourier transform diffraction patterns showed that cubic phase (zinc-blend structure) GaN grains were obtained using conventional GaN nucleation layers, while the hexagonal phase (wurtzite structure) GaN films were formed using AlGaN nucleation layers. Our work opens new avenues for using highly oriented pyrolytic graphite as a substrate to fabricate transferable optoelectronic devices.

Understanding the Growth Mechanism of GaN Epitaxial Layers on Mechanically Exfoliated Graphite.

PubMed

Li, Tianbao; Liu, Chenyang; Zhang, Zhe; Yu, Bin; Dong, Hailiang; Jia, Wei; Jia, Zhigang; Yu, Chunyan; Gan, Lin; Xu, Bingshe; Jiang, Haiwei

2018-04-27

The growth mechanism of GaN epitaxial layers on mechanically exfoliated graphite is explained in detail based on classic nucleation theory. The number of defects on the graphite surface can be increased via O-plasma treatment, leading to increased nucleation density on the graphite surface. The addition of elemental Al can effectively improve the nucleation rate, which can promote the formation of dense nucleation layers and the lateral growth of GaN epitaxial layers. The surface morphologies of the nucleation layers, annealed layers and epitaxial layers were characterized by field-emission scanning electron microscopy, where the evolution of the surface morphology coincided with a 3D-to-2D growth mechanism. High-resolution transmission electron microscopy was used to characterize the microstructure of GaN. Fast Fourier transform diffraction patterns showed that cubic phase (zinc-blend structure) GaN grains were obtained using conventional GaN nucleation layers, while the hexagonal phase (wurtzite structure) GaN films were formed using AlGaN nucleation layers. Our work opens new avenues for using highly oriented pyrolytic graphite as a substrate to fabricate transferable optoelectronic devices.

Alternate electrode materials for the SP100 reactor

NASA Astrophysics Data System (ADS)

Randich, E.

1992-05-01

This work was performed in response to a request by the Astro-Space Division of the General Electric Co. to develop alternate electrodes materials for the electrodes of the PD2 modules to be used in the SP100 thermoelectric power conversion system. Initially, the project consisted of four tasks: (1) development of a ZrB2 (C) CVD coating on SiMo substrates; (2) development of a ZrB2 (C) CVD coating on SiGe substrates; (3) development of CVI W for porous graphite electrodes; and (4) technology transfer of pertinent developed processes. The project evolved initially into developing only ZrB2 coatings on SiGe and graphite substrates, and later into developing ZrB2 coatings only on graphite substrates. Several sizes of graphite and pyrolytic carbon-coated graphite substrates were coated with ZrB2 during the project. For budgetary reasons, the project was terminated after half the allotted time had passed. Apart from the production of coated specimens for evaluation, the major accomplishment of the project was the development of the CVD processing to produce the desired coatings.

AFM visualization at a single-molecule level of denaturated states of proteins on graphite.

PubMed

Barinov, Nikolay A; Prokhorov, Valery V; Dubrovin, Evgeniy V; Klinov, Dmitry V

2016-10-01

Different graphitic materials are either already used or believed to be advantageous in biomedical and biotechnological applications, e.g., as biomaterials or substrates for sensors. Most of these applications or associated important issues, such as biocompatibility, address the problem of adsorption of protein molecules and, in particular the conformational state of the adsorbed protein molecule on graphite. High-resolution AFM demonstrates highly oriented pyrolytic graphite (HOPG) induced denaturation of four proteins of blood plasma, such as ferritin, fibrinogen, human serum albumin (HSA) and immunoglobulin G (IgG), at a single molecule level. Protein denaturation is accompanied by the decrease of the heights of protein globules and spreading of the denatured protein fraction on the surface. In contrast, the modification of HOPG with the amphiphilic oligoglycine-hydrocarbon derivative monolayer preserves the native-like conformation and provides even more mild conditions for the protein adsorption than typically used mica. Protein unfolding on HOPG may have universal character for "soft" globular proteins. Copyright © 2016 Elsevier B.V. All rights reserved.

In-situ observation of the chemical erosion of graphite in the scrape-off-layer of TEXTOR

NASA Astrophysics Data System (ADS)

Philipps, V.; Vietzke, E.; Erdweg, M.

1989-04-01

A sniffer probe system has been used to investigate the chemical erosion during interaction of the TEXTOR scrape-off plasma with a pyrolytic graphite plate at temperatures up to 1400 °C. Floating potential conditions as well as 200 V bias has been applied at plasma ion fluxes of about 10 18ions/cm 2 sec.Methane formation was found to be 8 × 10 -3 CH 4/H and 1.5 × 10 -2 CD 4/D + for room temperature graphite and floating potential increasing by a factor of two at temperature around 500 °C. Biasing the graphite decreases the methane yield at room temperature and increase it in the maximum temperature range. CO formation due to chemical interaction of oxygen ions with the graphite reaches ratios between 3 and 6 × 10 -2 CO/D(H) near the limiter edge under normal TEXTOR scrape-off conditions and exceeds the chemical hydro-(deu-tero-carbon formation significantly. The results are discussed in view of the present status of hydro-(deutero-)carbon formation on graphite and carbon impurity observations made in fusion experiments.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wertsching, Alan Kevin; Trantor, Troy Joseph; Ebner, Matthias Anthony

A method and device for producing secure, high-density tritium bonded with carbon. A substrate comprising carbon is provided. A precursor is intercalated between carbon in the substrate. The precursor intercalated in the substrate is irradiated until at least a portion of the precursor, preferably a majority of the precursor, is transmutated into tritium and bonds with carbon of the substrate forming bonded tritium. The resulting bonded tritium, tritium bonded with carbon, produces electrons via beta decay. The substrate is preferably a substrate from the list of substrates consisting of highly-ordered pyrolytic graphite, carbon fibers, carbon nanotunes, buckministerfullerenes, and combinations thereof.more » The precursor is preferably boron-10, more preferably lithium-6. Preferably, thermal neutrons are used to irradiate the precursor. The resulting bonded tritium is preferably used to generate electricity either directly or indirectly.« less

[AFM fishing of proteins under impulse electric field].

PubMed

Ivanov, Yu D; Pleshakova, T O; Malsagova, K A; Kaysheva, A L; Kopylov, A T; Izotov, A A; Tatur, V Yu; Vesnin, S G; Ivanova, N D; Ziborov, V S; Archakov, A I

2016-05-01

A combination of (atomic force microscopy)-based fishing (AFM-fishing) and mass spectrometry allows to capture protein molecules from solutions, concentrate and visualize them on an atomically flat surface of the AFM chip and identify by subsequent mass spectrometric analysis. In order to increase the AFM-fishing efficiency we have applied pulsed voltage with the rise time of the front of about 1 ns to the AFM chip. The AFM-chip was made using a conductive material, highly oriented pyrolytic graphite (HOPG). The increased efficiency of AFM-fishing has been demonstrated using detection of cytochrome b5 protein. Selection of the stimulating pulse with a rise time of 1 ns, corresponding to the GHz frequency range, by the effect of intrinsic emission from water observed in this frequency range during water injection into the cell.

Ultrafast compression of graphite observed with sub-ps time resolution diffraction on LCLS

NASA Astrophysics Data System (ADS)

Armstrong, Michael; Goncharov, A.; Crowhurst, J.; Zaug, J.; Radousky, H.; Grivickas, P.; Bastea, S.; Goldman, N.; Stavrou, E.; Belof, J.; Gleason, A.; Lee, H. J.; Nagler, R.; Holtgrewe, N.; Walter, P.; Pakaprenka, V.; Nam, I.; Granados, E.; Presher, C.; Koroglu, B.

2017-06-01

We will present ps time resolution pulsed x-ray diffraction measurements of rapidly compressed highly oriented pyrolytic graphite along its basal plane at the Materials under Extreme Conditions (MEC) sector of the Linac Coherent Light Source (LCLS). These experiments explore the possibility of rapid (<100 ps time scale) material transformations occurring under very highly anisotropic compression conditions. Under such conditions, non-equilibrium mechanisms may play a role in the transformation process. We will present experimental results and simulations which explore this possibility. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Security, LLC under Contract DE-AC52-07NA27344.

Surface induced selective deposition of Dysprosium Polyoxometalate on HOPG surface studied by STM and STS

NASA Astrophysics Data System (ADS)

Costa Milan, David; Pinilla Cienfuegos, Elena; Cardona Serra, Salvador; Coronado Miralles, Eugenio; Untiedt Lecuona, Carlos

2013-03-01

Scanning Tunneling Microscope (STM) and scanning Tunnelling spectroscopy (STS) techniques have been used to study the Preyssler type Polyoxometalate K12[DyP5W30O110] molecules deposited on Highly Oriented Pyrolytic Graphite surface (HOPG). Chainlike arrangements of clusters containing two or three molecules, as well as different cluster sizes are observed. As many structural artifacts are present on the graphite surface, like Moiré patterns, that could look like the molecular deposits, we have studied their STS and size to ensure the presence of the POM molecules on the surface. This article shows the possibility of addressing POMs on a flat surface to obtain their electronic properties through STS.

Reflection of Low Energy Positrons from the Surface of Highly Oriented Pyrolytic Graphite and Single Layer Graphene.

NASA Astrophysics Data System (ADS)

Imam, S. K.; Chirayath, V. A.; Chrysler, M. D.; Fairchild, A. J.; Gladen, R. W.; Koymen, A. R.; Weiss, A. H.; UT Arlington Positron Surface Laboratory Team

A time of flight positron annihilation induced Auger electron spectrometer (TOF-PAES) was utilized to measure the reflection of positrons as a function of incident positron energy (0 to 10 eV) from the surface of highly oriented pyrolytic graphite (HOPG) and from a single layer graphene (SLG) on a Cu foil. A NaI scintillation detector was used to measure the annihilation gamma from the reflected positrons as a function of incident positron kinetic energy. The annihilation of the positrons on HOPG and SLG were simultaneously measured using another NaI detector near the sample. The Auger electrons emitted as a result of the annihilation of positrons from the surface of the sample were also measured concurrently. As the positron kinetic energy was increased, the number of reflected positrons calculated from the intensity under the annihilation gamma peak showed a steady decrease. The positronium formation measured at the sample using the gamma spectrum showed a peak at 6 eV. The intensity of the carbon KVV Auger peak showed a dip at the same energy. The correlation of the three signals, intensity of reflected positrons, positrons annihilating at the sample and the Auger intensity are discussed for both samples. This work was supported by NSF Grant No. DMR 1508719 and DMR 1338130.

Magneto-transport properties of As-implanted highly oriented pyrolytic graphite

NASA Astrophysics Data System (ADS)

de Jesus, R. F.; Camargo, B. C.; da Silva, R. R.; Kopelevich, Y.; Behar, M.; Gusmão, M. A.; Pureur, P.

2016-11-01

We report on magneto-transport experiments in a high-quality sample of highly-oriented pyrolytic graphite (HOPG). Magneto-resistance and Hall resistivity measurements were carried out in magnetic inductions up to B = 9 T applied parallel to the c-axis at fixed temperatures between T=2 K and T=12 K. The sample was submitted to three subsequent irradiations with As ions. The implanted As contents were 2.5, 5 and 10 at% at the maximum of the distribution profile. Experiments were performed after each implantation stage. Shubnikov-de Haas (SdH) oscillations were observed in both the magneto-resistance and Hall-effect measurements. Analyses of these results with fast Fourier transform (FFT) lead to fundamental frequencies and effective masses for electrons and holes that are independent of the implantation fluences. The Hall resistivity at low temperatures shows a sign reversal as a function of the field in all implanted states. We interpret the obtained results with basis on a qualitative model that supposes the existence of an extrinsic hole density associated to the defect structure of our sample. We conclude that the As implantation does not produce a semiconductor-type doping in our HOPG sample. Instead, an increase in the extrinsic hole density is likely to occur as a consequence of disorder induced by implantation.

Graphene Nanobubbles Produced by Water Splitting.

PubMed

An, Hongjie; Tan, Beng Hau; Moo, James Guo Sheng; Liu, Sheng; Pumera, Martin; Ohl, Claus-Dieter

2017-05-10

Graphene nanobubbles are of significant interest due to their ability to trap mesoscopic volumes of gas for various applications in nanoscale engineering. However, conventional protocols to produce such bubbles are relatively elaborate and require specialized equipment to subject graphite samples to high temperatures or pressures. Here, we demonstrate the formation of graphene nanobubbles between layers of highly oriented pyrolytic graphite (HOPG) with electrolysis. Although this process can also lead to the formation of gaseous surface nanobubbles on top of the substrate, the two types of bubbles can easily be distinguished using atomic force microscopy. We estimated the Young's modulus, internal pressure, and the thickness of the top membrane of the graphene nanobubbles. The hydrogen storage capacity can reach ∼5 wt % for a graphene nanobubble with a membrane that is four layers thick. The simplicity of our protocol paves the way for such graphitic nanobubbles to be utilized for energy storage and industrial applications on a wide scale.

Aqueous alteration of VHTR fuels particles under simulated geological conditions

NASA Astrophysics Data System (ADS)

Ait Chaou, Abdelouahed; Abdelouas, Abdesselam; Karakurt, Gökhan; Grambow, Bernd

2014-05-01

Very High Temperature Reactor (VHTR) fuels consist of the bistructural-isotropic (BISO) or tristructural-isotropic (TRISO)-coated particles embedded in a graphite matrix. Management of the spent fuel generated during VHTR operation would most likely be through deep geological disposal. In this framework we investigated the alteration of BISO (with pyrolytic carbon) and TRISO (with SiC) particles under geological conditions simulated by temperatures of 50 and 90 °C and in the presence of synthetic groundwater. Solid state (scanning electron microscopy (SEM), micro-Raman spectroscopy, electron probe microanalyses (EPMA) and X-ray photoelectron spectroscopy (XPS)) and solution analyses (ICP-MS, ionique chromatography (IC)) showed oxidation of both pyrolytic carbon and SiC at 90 °C. Under air this led to the formation of SiO2 and a clay-like Mg-silicate, while under reducing conditions (H2/N2 atmosphere) SiC and pyrolytic carbon were highly stable after a few months of alteration. At 50 °C, in the presence and absence of air, the alteration of the coatings was minor. In conclusion, due to their high stability in reducing conditions, HTR fuel disposal in reducing deep geological environments may constitute a viable solution for their long-term management.

Magnetic Surfaces, Thin Films, and Multilayers

DTIC Science & Technology

1992-01-01

investigations %as the cleaved ((00)I) face of highly oriented pyrolytic graphite ( HOPG ). This surface is inert in air and is easily imaged with the STM[83-86...Parkin IBM Almaden Research Center, San Jose, California, U.S.A. Herbert Hopster University of California -Irvine, Irvine, California, U.S.A. Jean...magnetic fields (typically 10 to 100 kOe). For polycrystalline samples and at normal temperatures more modest increases, typically of a factor of 2 to 10

Finite Element and Molecular Dynamics Modeling and Simulation of Thermal Properties

DTIC Science & Technology

2007-06-01

dots represent the experimental results of the normalized conductivity data ke/kf (ke is κ of the composite, kf is κ of the fluid) CNT in oil ...individual Single Walled Nanotube to four centimeters in length. [4] 6 Carbon based materials, in-plane pyrolytic graphite and diamonds, have the...conductivity of nanocomposites has not yet been achieved. A 2001 experiment studied the thermal conductivity of oil with CNT in suspension. The results

Improving a high-efficiency, gated spectrometer for x-ray Thomson scattering experiments at the National Ignition Facility.

PubMed

Döppner, T; Kraus, D; Neumayer, P; Bachmann, B; Emig, J; Falcone, R W; Fletcher, L B; Hardy, M; Kalantar, D H; Kritcher, A L; Landen, O L; Ma, T; Saunders, A M; Wood, R D

2016-11-01

We are developing x-ray Thomson scattering for applications in implosion experiments at the National Ignition Facility. In particular we have designed and fielded MACS, a high-efficiency, gated x-ray spectrometer at 7.5-10 keV [T. Döppner et al., Rev. Sci. Instrum. 85, 11D617 (2014)]. Here we report on two new Bragg crystals based on Highly Oriented Pyrolytic Graphite (HOPG), a flat crystal and a dual-section cylindrically curved crystal. We have performed in situ calibration measurements using a brass foil target, and we used the flat HOPG crystal to measure Mo K-shell emission at 18 keV in 2nd order diffraction. Such high photon energy line emission will be required to penetrate and probe ultra-high-density plasmas or plasmas of mid-Z elements.

Impact of corrosion test container material in molten fluorides

DOE PAGES

Olson, Luke C.; Fuentes, Roderick E.; Martinez-Rodriguez, Michael J.; ...

2015-10-15

The effects of crucible material choice on alloy corrosion rates in immersion tests in molten LiF–NaF–KF (46.5–11.5-42 mol. %) salt held at 850 °C for 500 hrs are described. Four crucible materials were studied. Molten salt exposures of Incoloy-800H in graphite, Ni, Incoloy-800H, and pyrolytic boron nitride (PyBN) crucibles all led to weight-loss in the Incoloy-800H coupons. Alloy weight loss was ~30 times higher in the graphite and Ni crucibles in comparison to the Incoloy-800H and PyBN crucibles. It is hypothesized galvanic coupling between the alloy coupons and crucible materials contributed to the higher corrosion rates. Alloy salt immersion inmore » graphite and Ni crucibles had similar weight-loss hypothesized to occur due to the rate limiting out diffusion of Cr in the alloys to the surface where it reacts with and dissolves into the molten salt, followed by the reduction of Cr from solution at the molten salt and graphite/Ni interfaces. As a result, both the graphite and the Ni crucibles provided sinks for the Cr, in the formation of a Ni–Cr alloy in the case of the Ni crucible, and Cr carbide in the case of the graphite crucible.« less

A study of Kapton degradation under simulated shuttle environment

NASA Technical Reports Server (NTRS)

Eck, T. G.; Hoffman, R. W.

1986-01-01

A system was developed which employs a source of low energy oxygen ion to simulate the shuttle low Earth orbit environment. This source, together with diagnostic tools including surface analysis ans mass spectroscopic capability, was used to measure the dependence of ion energy of the oxygen induced CO signals from pyrolytic graphite and Kapton. For graphite the CO signal was examined at energies ranging form 4.5 to 465 eV and for Kapton from 4.5 to 188 eV. While the relative quantum yields inferred from the data are reasonably precise, there are large uncertainties in the absolute yields because of the assumptions necessary to covert the measured signal strengths to quantum yields. These assumptions are discussed in detail.

Stacked graphene nanofibers for electrochemical oxidation of DNA bases.

PubMed

Ambrosi, Adriano; Pumera, Martin

2010-08-21

In this article, we show that stacked graphene nanofibers (SGNFs) demonstrate superior electrochemical performance for oxidation of DNA bases over carbon nanotubes (CNTs). This is due to an exceptionally high number of accessible graphene sheet edges on the surface of the nanofibers when compared to carbon nanotubes, as shown by transmission electron microscopy and Raman spectroscopy. The oxidation signals of adenine, guanine, cytosine, and thymine exhibit two to four times higher currents than on CNT-based electrodes. SGNFs also exhibit higher sensitivity than do edge-plane pyrolytic graphite, glassy carbon, or graphite microparticle-based electrodes. We also demonstrate that influenza A(H1N1)-related strands can be sensitively oxidized on SGNF-based electrodes, which could therefore be applied to label-free DNA analysis.

Investigating the Co-Adsorption Behavior of Nucleic-Acid Base (Thymine and Cytosine) and Melamine at Liquid/Solid Interface

NASA Astrophysics Data System (ADS)

Zhao, Huiling; Li, Yinli; Chen, Dong; Liu, Bo

2016-12-01

The co-adsorption behavior of nucleic-acid base (thymine; cytosine) and melamine was investigated by scanning tunneling microscopy (STM) technique at liquid/solid (1-octanol/graphite) interface. STM characterization results indicate that phase separation happened after dropping the mixed solution of thymine-melamine onto highly oriented pyrolytic graphite (HOPG) surface, while the hetero-component cluster-like structure was observed when cytosine-melamine binary assembly system is used. From the viewpoints of non-covalent interactions calculated by using density functional theory (DFT) method, the formation mechanisms of these assembled structures were explored in detail. This work will supply a methodology to design the supramolecular assembled structures and the hetero-component materials composed by biological and chemical compound.

Fabrication of novel coated pyrolytic graphite electrodes for the selective nano-level monitoring of Cd²⁺ ions in biological and environmental samples using polymeric membrane of newly synthesized macrocycle.

PubMed

Sahani, Manoj Kumar; Singh, A K; Jain, A K; Upadhyay, Anjali; Kumar, Amit; Singh, Udai P; Narang, Shikha

2015-02-20

Novel 5-amino-1,3,4-thiadiazole-2-thiol unit based macrocyclic ionophore 5,11,17-trithia-1,3,7,9,13,15,19,20,21-nonaazatetracyclo[14.2.1.1(4,7).1(10,13)]henicosa-4(20),10(21),16(19)-triene-6,12,18-trithione (M1), was synthesized and characterized. Preliminary studies on M1 have showed that it has more the affinity toward Cd(2+) ion. Thus, the macrocyclic ionophore (M1) was used as electroactive material in the fabrication of PVC-membrane electrodes such as polymeric membrane electrode (PME), coated graphite electrode (CGE) and coated pyrolytic graphite electrode (CPGE) were prepared and its performance characteristic were compared with. The electroanalytical studies performed on PME, CGE and CPGE revealed that CPGE having membrane composition M1:PVC:1-CN:NaTPB in the ratio of 7:37:54:2 exhibits the best potentiometric characteristics in terms of detection limit of 7.58×10(-9) mol L(-1), Nernstian slope of 29.6 mV decade(-1) of activity. The sensor was found to be independent of pH in the range 2.5-8.5. The sensor showed a fast response time of 10s and could be used over a period of 4 months without any significant divergence in its potentiometric characteristics. The sensor has been employed for monitoring of the Cd(2+) ion in real samples and also used as an indicator electrode in the potentiometric titration of Cd(2+) ion with EDTA. Copyright © 2014. Published by Elsevier B.V.

Fullerenes, nanotubes, and graphite as matrices for collision mechanism in secondary ion mass spectrometry: determination of cyclodextrin.

PubMed

Stupavska, Monika; Jerigova, Monika; Michalka, Miroslav; Hasko, Daniel; Szoecs, Vojtech; Velic, Dusan

2011-12-01

A technique for improving the sensitivity of high mass molecular analysis is described. Three carbon species, fullerenes, single walled carbon nanotubes, and highly ordered pyrolytic graphite are introduced as matrices for the secondary ion mass spectrometry analysis of cyclodextrin (C(42)H(70)O(35), 1134 u). The fullerene and nanotubes are deposited as single deposition, and 10, 20, or 30 deposition films and cyclodextrin is deposited on top. The cyclodextrin parent-like ions and two fragments were analyzed. A 30 deposition fullerene film enhanced the intensity of cationized cyclodextrin with Na by a factor of 37. While the C(6)H(11)O(5) fragment, corresponding to one glucopyranose unit, increased by a factor of 16. Although fragmentation on fullerene is not suppressed, the intensity is twice as low as the parent-like ion. Deprotonated cyclodextrin increases by 100× and its C(8)H(7)O fragment by 10×. While the fullerene matrix enhances secondary ion emission, the nanotubes matrix film generates a basically constant yield. Graphite gives rise to lower intensity peaks than either fullerene or nanotubes. Scanning electron microscopy and atomic force microscopy provide images of the fullerene and nanotubes deposition films revealing flat and web structured surfaces, respectively. A "colliding ball" model is presented to provide a plausible physical mechanism of parent-like ion enhancement using the fullerene matrix. © American Society for Mass Spectrometry, 2011

Coupling Graphene Sheets with Magnetic Nanoparticles for Energy Storage and Microelectronics

DTIC Science & Technology

2015-08-13

sheets obtained from three different synthetic methods: (i) electrochemical exfoliation of highly oriented pyrolytic graphite ( HOPG ) [8], (ii...Figure 8d, the characteristic lattice fringes of ɤ-Fe2O3 nanoparticles in graphene sheet is shown. Typical X-ray diffraction ( XRD ) patterns of the HOPG ...pattern in honey comb crystal lattice, (c) TEM (d) HRTEM image of graphene- PyDop1-MNP hybrid, (e) XRD pattern of the HOPG , exfoliated graphene, PyDop1

Characterization of ultralow thermal conductivity in anisotropic pyrolytic carbon coating for thermal management applications

DOE PAGES

Wang, Yuzhou; Hurley, David H.; Luther, Erik Paul; ...

2017-12-11

Pyrolytic carbon (PyC) is an important material used in many applications including thermal management of electronic devices and structural stability of ceramic composites. Accurate measurement of physical properties of structures containing textured PyC layers with few-micrometer thickness poses new challenges. Here a laser-based thermoreflectance technique is used to measure thermal conductivity in a 30-μm-thick textured PyC layer deposited using chemical vapor deposition on the surface of spherical zirconia particles. Raman spectroscopy is used to confirm the graphitic nature and characterize microstructure of the deposited layer. Room temperature radial and circumferential thermal conductivities are found to be 0.28 W m –1more » K –1 and 11.5 W m –1 K –1, corresponding to cross-plane and in-plane conductivities of graphite. While the anisotropic ratio of the in-plane to cross-plane conductivities is smaller than previous results, the magnitude of the smallest conductivity is noticeably smaller than previously reported values for carbon materials and offers opportunities in thermal management applications. Very low in-plane and cross-plane thermal conductivities are attributed to strong grain boundary scattering, high defect concentration, and small inter-laminar porosity. Lastly, experimental results agree with the prediction of thermal transport model informed by the microstructure information revealed by Raman spectroscopy.« less

Characterization of ultralow thermal conductivity in anisotropic pyrolytic carbon coating for thermal management applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Yuzhou; Hurley, David H.; Luther, Erik Paul

Pyrolytic carbon (PyC) is an important material used in many applications including thermal management of electronic devices and structural stability of ceramic composites. Accurate measurement of physical properties of structures containing textured PyC layers with few-micrometer thickness poses new challenges. Here a laser-based thermoreflectance technique is used to measure thermal conductivity in a 30-μm-thick textured PyC layer deposited using chemical vapor deposition on the surface of spherical zirconia particles. Raman spectroscopy is used to confirm the graphitic nature and characterize microstructure of the deposited layer. Room temperature radial and circumferential thermal conductivities are found to be 0.28 W m –1more » K –1 and 11.5 W m –1 K –1, corresponding to cross-plane and in-plane conductivities of graphite. While the anisotropic ratio of the in-plane to cross-plane conductivities is smaller than previous results, the magnitude of the smallest conductivity is noticeably smaller than previously reported values for carbon materials and offers opportunities in thermal management applications. Very low in-plane and cross-plane thermal conductivities are attributed to strong grain boundary scattering, high defect concentration, and small inter-laminar porosity. Lastly, experimental results agree with the prediction of thermal transport model informed by the microstructure information revealed by Raman spectroscopy.« less

Time-resolved investigations of the non-thermal ablation process of graphite induced by femtosecond laser pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kalupka, C., E-mail: christian.kalupka@llt.rwth-aachen.de; Finger, J.; Reininghaus, M.

2016-04-21

We report on the in-situ analysis of the ablation dynamics of the, so-called, laser induced non-thermal ablation process of graphite. A highly oriented pyrolytic graphite is excited by femtosecond laser pulses with fluences below the classic thermal ablation threshold. The ablation dynamics are investigated by axial pump-probe reflection measurements, transversal pump-probe shadowgraphy, and time-resolved transversal emission photography. The combination of the applied analysis methods allows for a continuous and detailed time-resolved observation of the non-thermal ablation dynamics from several picoseconds up to 180 ns. Formation of large, μm-sized particles takes place within the first 3.5 ns after irradiation. The following propagation ofmore » ablation products and the shock wave front are tracked by transversal shadowgraphy up to 16 ns. The comparison of ablation dynamics of different fluences by emission photography reveals thermal ablation products even for non-thermal fluences.« less

Direct determination of Pb in raw milk by graphite furnace atomic absorption spectrometry (GF AAS) with electrothermal atomization sampling from slurries.

PubMed

de Oliveira, Tatiane Milão; Augusto Peres, Jayme; Lurdes Felsner, Maria; Cristiane Justi, Karin

2017-08-15

Milk is an important food in the human diet due to its physico-chemical composition; therefore, it is necessary to monitor contamination by toxic metals such as Pb. Milk sample slurries were prepared using Triton X-100 and nitric acid for direct analysis of Pb using graphite furnace atomic absorption spectrometry - GF AAS. After dilution of the slurries, 10.00µl were directly introduced into the pyrolytic graphite tube without use of a chemical modifier, which acts as an advantage considering this type of matrix. The limits of detection and quantification were 0.64 and 2.14µgl -1 , respectively. The figures of merit studied showed that the proposed methodology without pretreatment of the raw milk sample and using external standard calibration is suitable. The methodology was applied in milk samples from the Guarapuava region, in Paraná State (Brazil) and Pb concentrations ranged from 2.12 to 37.36µgl -1 . Copyright © 2017 Elsevier Ltd. All rights reserved.

Improving a high-efficiency, gated spectrometer for x-ray Thomson scattering experiments at the National Ignition Facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Döppner, T., E-mail: doeppner1@llnl.gov; Bachmann, B.; Emig, J.

We are developing x-ray Thomson scattering for applications in implosion experiments at the National Ignition Facility. In particular we have designed and fielded MACS, a high-efficiency, gated x-ray spectrometer at 7.5–10 keV [T. Döppner et al., Rev. Sci. Instrum. 85, 11D617 (2014)]. Here we report on two new Bragg crystals based on Highly Oriented Pyrolytic Graphite (HOPG), a flat crystal and a dual-section cylindrically curved crystal. We have performed in situ calibration measurements using a brass foil target, and we used the flat HOPG crystal to measure Mo K-shell emission at 18 keV in 2nd order diffraction. Such high photonmore » energy line emission will be required to penetrate and probe ultra-high-density plasmas or plasmas of mid-Z elements.« less

Moiré-Modulated Conductance of Hexagonal Boron Nitride Tunnel Barriers.

PubMed

Summerfield, Alex; Kozikov, Aleksey; Cheng, Tin S; Davies, Andrew; Cho, Yong-Jin; Khlobystov, Andrei N; Mellor, Christopher J; Foxon, C Thomas; Watanabe, Kenji; Taniguchi, Takashi; Eaves, Laurence; Novoselov, Kostya S; Novikov, Sergei V; Beton, Peter H

2018-06-27

Monolayer hexagonal boron nitride (hBN) tunnel barriers investigated using conductive atomic force microscopy reveal moiré patterns in the spatial maps of their tunnel conductance consistent with the formation of a moiré superlattice between the hBN and an underlying highly ordered pyrolytic graphite (HOPG) substrate. This variation is attributed to a periodc modulation of the local density of states and occurs for both exfoliated hBN barriers and epitaxially grown layers. The epitaxial barriers also exhibit enhanced conductance at localized subnanometer regions which are attributed to exposure of the substrate to a nitrogen plasma source during the high temperature growth process. Our results show clearly a spatial periodicity of tunnel current due to the formation of a moiré superlattice and we argue that this can provide a mechanism for elastic scattering of charge carriers for similar interfaces embedded in graphene/hBN resonant tunnel diodes.

Improving a high-efficiency, gated spectrometer for x-ray Thomson scattering experiments at the National Ignition Facility

DOE PAGES

Döppner, T.; Kraus, D.; Neumayer, P.; ...

2016-08-03

We are developing x-ray Thomson scattering for applications in implosion experiments at the National Ignition Facility. In particular we have designed and fielded MACS, a high-efficiency, gated x-ray spectrometer at 7.5-10 keV [T. Döppner et al., Rev. Sci. Instrum. 85, 11D617 (2014)]. Here in this paper we report on two new Bragg crystals based on Highly Oriented Pyrolytic Graphite (HOPG), a flat crystal and a dual-section cylindrically curved crystal. We have performed in situ calibration measurements using a brass foil target, and we used the flat HOPG crystal to measure Mo K-shell emission at 18 keV in 2nd order diffraction.more » Such high photon energy line emission will be required to penetrate and probe ultra-high-density plasmas or plasmas of mid-Z elements.« less

Recent results concerning the stability of viscoelastic shear deformable plates under compressive edge loading

NASA Technical Reports Server (NTRS)

Librescu, L.; Chandiramani, N. K.

1989-01-01

Some recent results obtained by the authors are summarized concerning the stability of transversely isotropic flat panels whose materials exhibit a viscoelastic behavior and whose edges are subjected to in-plane biaxial compressive loads. Two transversely isotropic type materials, largely used in advanced technology, are considered: (1) the pyrolytic-graphite type, used in the thermal protection of aerospace vehicles, and (2) the type corresponding to unidirectional fiber-reinforced composites. In the former case, the planes of isotropy are parallel at each point to the midplane of the plate. In the latter case, they are normal to the fiber directions. The micromechanical relations developed by Aboudi (1984, 1986, 1987) are considered in conjunction with the correspondence principle of linear viscoelastic theory in order to predict the macroscopic viscoelastic properties of a material composed of uniaxial elastic fibers embedded in a linear viscoelastic matrix.

The Physics and Chemistry of carbides, Nitrides and Borides. Volume 185

DTIC Science & Technology

1990-01-01

and C-B-C chains [15,17]. Clearly, the use of boron-rich solids as electronic materials will place new demands on the quality of materials. In this...first heated in a pyrolytic boron nitride (PBN) crucible ( Union Carbide Corp.) under high vacuum (< 50 mTorr) to 1900°C. This removed surface...contamination of the sample. The powders were loaded into a graphite die with a high-purity BN die liner ( Union Carbide Grade HBC) with inner diameter of 3/8

Local atomic order of a metallic glass made visible by scanning tunneling microscopy

NASA Astrophysics Data System (ADS)

Luo, Yuansu; Samwer, Konrad

2018-06-01

Exploring the atomic level structure in amorphous materials by STM becomes extremely difficult due to the localized electronic states. Here we carried out STM studies on a quasi-low-dimensional film of metallic glass Zr65Cu27.5Al7.5 which is ‘ultrathin’ compared with the localization length and/or the length scale of short range order. The local electronic structure must appear more inherent, having states at E f available for tip-sample tunneling current. To enhance imaging contrasts between long-range and short-range orders, the highly oriented pyrolytic graphite was chosen as substrate, so that the structural heterogeneity arising from competition between the glass former ability and the epitaxy can be ascertained. A chemical order predicted for this system was observed in atomic ordered regimes (1–2 monolayers), accompanied with a superstructure with the period Zr–Cu(Al)–Zr along three hexagonal axes. The result implies a chemical short range order in disordered regimes, where polyhedral clusters are dominant with the solute atom Cu(Al) in the center. An attempt for the structural modelling was made based on high resolution STM images, giving icosahedral order on the surface and different Voronoi clusters in 3D space.

Electron reflection and secondary emission characteristics of sputter-textured pyrolytic graphite surfaces

NASA Technical Reports Server (NTRS)

Wintucky, E. G.; Curren, A. N.; Sovey, J. S.

1981-01-01

Measurements are presented of secondary electron emission and reflected primary electron characteristics of sputter-textured pyrolitic graphite surfaces with microstructures of various sizes and densities, made with an Auger cylindrical mirror analyzer in a high-vacuum chamber at pressures below 1.33 x 10 to the -7th N/sq m (10 to the -9th torr). A dense, tall, thin, spire-like microstructure, obtained at ion energies of 1000 eV and ion current densities of 5 mA/sq cm, is the most effective. The secondary electron emission from such a surface is lower than that of soot, whose secondary emission is among the lowest of any material. At a primary electron energy of 1000 eV, the secondary electron emission yield of smooth CU is about 350% greater than the lowest value obtained for sputter-textured pyrolitic graphite. The reflected primary electron index of smooth Cu is a factor of 80 greater. If the secondary electron emission yield is reduced to 0.3, which is possible with sputter-textured pyrolitic graphite, the traveling wave tube collector efficiency could be improved by as much as 4% over that for smooth copper.

Preliminary Results of Field Emission Cathode Tests

NASA Technical Reports Server (NTRS)

Sovey, James S.; Kovaleski, Scott D.

2001-01-01

Preliminary screening tests of field emission cathodes such as chemical vapor deposited (CVD) diamond, textured pyrolytic graphite, and textured copper were conducted at background pressures typical of electric thruster test facilities to assess cathode performance and stability. Very low power electric thrusters which provide tens to hundreds micronewtons of thrust may need field emission neutralizers that have a capability of tens to hundreds of microamperes. From current voltage characteristics, it was found that the CVD diamond and textured metals cathodes clearly satisfied the Fowler-Nordheim emission relation. The CVD diamond and a textured copper cathode had average current densities of 270 and 380 mA/sq cm, respectively, at the beginning-of-life. After a few hours of operation the cathode emission currents degraded by 40 to 75% at background pressures in the 10(exp -5) Pa to 10(exp -4) Pa range. The textured pyrolytic graphite had a modest current density at beginning-of-life of 84 mA/sq cm, but this cathode was the most stable of all. Extended testing of the most promising cathodes is warranted to determine if current degradation is a burn-in effect or whether it is a long-term degradation process. Preliminary experiments with ferroelectric emission cathodes, which are ceramics with spontaneous electric polarization, were conducted. Peak current densities of 30 to 120 mA/sq cm were obtained for pulse durations of about 500 ns in the 10(exp -4) Pa pressure range.

Soft X-Ray Absorption Spectroscopy of High-Abrasion-Furnace Carbon Black

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muramatsu, Yasuji; Harada, Ryusuke; Gullikson, Eric M.

2007-02-02

The soft x-ray absorption spectra of high-abrasion-furnace carbon black were measured to obtain local-structure/chemical-states information of the primary particles and/or crystallites. The soft x-ray absorption spectral features of carbon black represent broader {pi}* and {sigma}* peak structures compared to highly oriented pyrolytic graphite (HOPG). The subtracted spectra between the carbon black and HOPG, (carbon black) - (HOPG), show double-peak structures on both sides of the {pi}* peak. The lower-energy peak, denoted as the 'pre-peak', in the subtracted spectra and the {pi}*/{sigma}* peak intensity ratio in the absorption spectra clearly depend on the specific surface area by nitrogen adsorption (NSA). Therefore,more » it is concluded that the pre-peak intensity and the {pi}*/{sigma}* ratio reflect the local graphitic structure of carbon black.« less

Internal and external atomic steps in graphite exhibit dramatically different physical and chemical properties.

PubMed

Lee, Hyunsoo; Lee, Han-Bo-Ram; Kwon, Sangku; Salmeron, Miquel; Park, Jeong Young

2015-04-28

We report on the physical and chemical properties of atomic steps on the surface of highly oriented pyrolytic graphite (HOPG) investigated using atomic force microscopy. Two types of step edges are identified: internal (formed during crystal growth) and external (formed by mechanical cleavage of bulk HOPG). The external steps exhibit higher friction than the internal steps due to the broken bonds of the exposed edge C atoms, while carbon atoms in the internal steps are not exposed. The reactivity of the atomic steps is manifested in a variety of ways, including the preferential attachment of Pt nanoparticles deposited on HOPG when using atomic layer deposition and KOH clusters formed during drop casting from aqueous solutions. These phenomena imply that only external atomic steps can be used for selective electrodeposition for nanoscale electronic devices.

From Graphite to Graphene via Scanning Tunneling Microscopy

NASA Astrophysics Data System (ADS)

Qi, Dejun

The primary objective of this dissertation is to study both graphene on graphite and pristine freestanding grapheme using scanning tunneling microscopy (STM) and density functional theory (DFT) simulation technique. In the experiment part, good quality tungsten metalic tips for experiment were fabricated using our newly developed tip making setup. Then a series of measurements using a technique called electrostatic-manipulation scanning tunneling microscopy (EM-STM) of our own development were performed on a highly oriented pyrolytic graphite (HOPG) surface. The electrostatic interaction between the STM tip and the sample can be tuned to produce both reversible and irreversible large-scale movement of the graphite surface. Under this influence, atomic-resolution STM images reveal that a continuous electronic transition between two distinct patterns can be systematically controlled. DFT calculations reveal that this transition can be related to vertical displacements of the top layer of graphite relative to the bulk. Evidence for horizontal shifts in the top layer of graphite is also presented. Excellent agreement is found between experimental STM images and those simulated using DFT. In addition, the EM-STM technique was also used to controllably and reversibly pull freestanding graphene membranes up to 35 nm from their equilibrium height. Atomic-scale corrugation amplitudes 20 times larger than the STM electronic corrugation for graphene on a substrate were observed. The freestanding graphene membrane responds to a local attractive force created at the STM tip as a highly conductive yet flexible grounding plane with an elastic restoring force.

SUMMARY OF THE SEVENTH MEETING OF THE REFRACTORY COMPOSITES WORKING GROUP

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gibeaut, W.A.; Ogden, H.R.

1963-05-30

Information on refractory composites for use above 2500 deg F is summarized. Reports are concerned with protective coatings, insulating ceramics, materials for rocket thrust chambers, dispersion strengthening of metals, joining of refractory materials, and testing techniques. The problem of accelerated failure of silicide coatings under conditions of very low air pressure at high temperatures is studied. Although the maximum temperature capability of most silicide coatings is reduced about 50 theta deg at low air pressures, several coatings can protect molybdenum for 1/2 hr at 2800 to 3000 deg F under these conditions. The tin-aluminum coating also is susceptible to earlymore » failure at reduced pressure. An evaluation of the mechanical properties of 6-mil foils of D- 36, B-68, and TZM coated with commercial coatings demonstrated that some coatings seriously degrade substrate mechanical properties. Research on thermal- protection systems for re-entry vehicles whose surface temperatures reach from 3300 to 5500 deg F has resulted in agreement upon oxide coatings and thick metal- reinforced oxide composites. Simple plasmaarc-sprayed oxide coatings have demonstrated adequate oxidation resistance, but their structural stability in cyclic thermal exposure is inferior to metal-reinforced oxide. Thin unreinforced oxide coatings tend to spall in tests involving cyclic heating. A metal- reinforced oxide composite (reinforcement welded to substrate) has survived cyclic tests such as five 3-minute exposures at 4500 deg F without failing. A new carbon material called glassy carbon has demonstrnted better oxidation resistance than pyrolytic graphite at very high temperatures. The erosion resistance of pyrolytic graphite coatings on regular graphite in rocket firing tests using solid propellants is encouraging. There is considerable interest in fabricating small radiation-cooled rocket thrust chambers by plasma arc spraying. The design concept of internal reinforcement of sprayed-metal rocket chambers with wrought ductile wife appears impractical because of poor bonding and porosity around the wire. (auth)« less

Nano-level monitoring of Mn(2+) ion by fabrication of coated pyrolytic graphite electrode based on isonicotinohydrazide derivatives.

PubMed

Sahani, Manoj Kumar; Singh, A K; Jain, A K

2015-05-01

The two ionophores N'(N',N‴E,N',N‴E)-N',N‴-((((oxybis(ethane-2,1-diyl))bis(oxy)) bis(2,1-phenylene))bis(methanylylidene))di(isonicotinohydrazide) (I1) and (N',N‴E,N',N‴E)-N',N‴-(((propane-1,3-diylbis(oxy))bis(2,1-phenylene))bis(methanylylidene))di(isonicotinohydrazide) (I2) were synthesised and investigated as neutral carrier in the fabrication of Mn(2+) ion selective sensor. Several membranes were prepared by incorporating different plasticizers and anionic excluders and their effect on potentiometric response was studied. The best analytical performance was obtained with the electrode having a membrane of composition of I2: PVC: o-NPOE: NaTPB in the ratio of 6:34:58:2 (w/w, mg). Comparative studies of coated graphite electrode (CGE) and coated pyrolytic graphite electrode (CPGE) based on I2 reveal the superiority of CPGE. The CPGE exhibits wide working concentration range of 1.23×10(-8)-1.0×10(-1) mol L(-1) and a detection limit down to 4.78×10(-9) mol L(-1) with a Nernstian slope of 29.5±0.4 mV decade(-1) of activity. The sensor performs satisfactorily over a wide pH range (3.5-9.0) and exhibited a quick response time (9s). The sensor can work satisfactorily in water-acetonitrile and water-methanol mixtures. It can tolerate 30% acetonitrile and 20% methanol content in the mixtures. The sensor could be used for a period of four months without any significant divergence in performance. The sensor reflects its utility in the quantification of Mn(2+) ion in real samples and has been successfully employed as an indicator electrode in the potentiometric titration of Mn(2+) ion with ethylenediaminetetraacetic acid (EDTA). Copyright © 2015 Elsevier B.V. All rights reserved.

Two-dimensional network stability of nucleobases and amino acids on graphite under ambient conditions: adenine, L-serine and L-tyrosine.

PubMed

Bald, Ilko; Weigelt, Sigrid; Ma, Xiaojing; Xie, Pengyang; Subramani, Ramesh; Dong, Mingdong; Wang, Chen; Mamdouh, Wael; Wang, Jianguo; Besenbacher, Flemming

2010-04-14

We have investigated the stability of two-dimensional self-assembled molecular networks formed upon co-adsorption of the DNA base, adenine, with each of the amino acids, L-serine and L-tyrosine, on a highly oriented pyrolytic graphite (HOPG) surface by drop-casting from a water solution. L-serine and L-tyrosine were chosen as model systems due to their different interaction with the solvent molecules and the graphite substrate, which is reflected in a high and low solubility in water, respectively, compared with adenine. Combined scanning tunneling microscopy (STM) measurements and density functional theory (DFT) calculations show that the self-assembly process is mainly driven by the formation of strong adenine-adenine hydrogen bonds. We find that pure adenine networks are energetically more stable than networks built up of either pure L-serine, pure L-tyrosine or combinations of adenine with L-serine or L-tyrosine, and that only pure adenine networks are stable enough to be observable by STM under ambient conditions.

HOPG/ZnO/HOPG pressure sensor

NASA Astrophysics Data System (ADS)

Jahangiri, Mojtaba; Yousefiazari, Ehsan; Ghalamboran, Milad

2017-12-01

Pressure sensor is one of the most commonly used sensors in the research laboratories and industries. These are generally categorized in three different classes of absolute pressure sensors, gauge pressure sensors, and differential pressure sensors. In this paper, we fabricate and assess the pressure sensitivity of the current vs. voltage diagrams in a graphite/ZnO/graphite structure. Zinc oxide layers are deposited on highly oriented pyrolytic graphite (HOPG) substrates by sputtering a zinc target under oxygen plasma. The top electrode is also a slice of HOPG which is placed on the ZnO layer and connected to the outside electronic circuits. By recording the I-V characteristics of the device under different forces applied to the top HOPG electrode, the pressure sensitivity is demonstrated; at the optimum biasing voltage, the device current changes 10 times upon changing the pressure level on the top electrode by 20 times. Repeatability and reproducibility of the observed effect is studied on the same and different samples. All the materials used for the fabrication of this pressure sensor are biocompatible, the fabricated device is anticipated to find potential applications in biomedical engineering.

Magnetotransport in Two Dimensional Electron Systems Under Microwave Excitation and in Highly Oriented Pyrolytic Graphite

DTIC Science & Technology

2012-01-01

Phys. Rev. Lett. 82, 2147 (1999). [89] Y. Zhang, Y. Tan, H. L. Stormer and P. Kim, Nature 438, 10 (2005). [90] J. W. McClure, Phys. Rev. 108, 612 (1957...Phys. 2, 595 (2006). [97] H. L. Stormer , J. P. Eisenstein, A. C. Gossard, W. Wiegmann, and K. Baldwin, Phys. Rev. Lett. 56, 85 (1985). [98] B. A...Sadowski, J. M. Schneider, and M. Potemski, J. Phys.: Cond. Matter 20, 454223 (2008). [108] W. Pan, J. S. Xia, H. L. Stormer , D. C. Tsui, C. L

Coupling Graphene Sheets with Iron Oxide Nanoparticles for Energy Storage and Microelectronics

DTIC Science & Technology

2015-08-13

of highly oriented pyrolytic graphite ( HOPG ) flake. Two electrode system containing platinum as counter electrode and HOPG as working electrode is... XRD ) patterns of the HOPG , exfoliated graphene, PyDop1-ɤ-Fe2O3 and PyDop1-ɤ-Fe2O3-graphene are given in Figure 1e. HOPG show a very sharp diffraction...atoms arranged in hexagonal pattern in honey comb crystal lattice, (c) TEM (d) HRTEM image of graphene- PyDop1-MNP hybrid, (e) XRD pattern of the HOPG

Spectroscopic and electrochemical behavior of the novel tetra-2-methyl-pyrazinoporphyrazines

NASA Astrophysics Data System (ADS)

Pişkin, Mehmet; Öztürk, Naciye; Durmuş, Mahmut

2017-12-01

This study presents the synthesis and characterization of novel metal-free (H2Pc) and metallo porphyrazines (magnesium(II) (MgPz), copper(II) (CuPz), iron(II) (FePz), manganese(II) (MnPz) and nickel(II) (NiPz)) substituted with four 2-methylpyrazine groups on the peripheral positions. The spectroscopic properties of newly synthesized porphyrazines were investigated. The electrochemical behaviors of these porphyrazines were also determined in DMSO solution by cyclic voltammetry (CV) and square wave voltammetry (SWV) methods on edge plane pyrolytic graphite electrode (EPPG) electrode.

Auto-assembly of nanometer thick, water soluble layers of plasmid DNA complexed with diamines and basic amino acids on graphite: Greatest DNA protection is obtained with arginine.

PubMed

Khalil, T T; Boulanouar, O; Heintz, O; Fromm, M

2017-02-01

We have investigated the ability of diamines as well as basic amino acids to condense DNA onto highly ordered pyrolytic graphite with minimum damage after re-dissolution in water. Based on a bibliographic survey we briefly summarize DNA binding properties with diamines as compared to basic amino acids. Thus, solutions of DNA complexed with these linkers were drop-cast in order to deposit ultra-thin layers on the surface of HOPG in the absence or presence of Tris buffer. Atomic Force Microscopy analyses showed that, at a fixed ligand-DNA mixing ratio of 16, the mean thickness of the layers can be statistically predicted to lie in the range 0-50nm with a maximum standard deviation ±6nm, using a simple linear law depending on the DNA concentration. The morphology of the layers appears to be ligand-dependent. While the layers containing diamines present holes, those formed in the presence of basic amino acids, except for lysine, are much more compact and dense. X-ray Photoelectron Spectroscopy measurements provide compositional information indicating that, compared to the maximum number of DNA sites to which the ligands may bind, the basic amino acids Arg and His are present in large excess. Conservation of the supercoiled topology of the DNA plasmids was studied after recovery of the complex layers in water. Remarkably, arginine has the best protection capabilities whether Tris was present or not in the initial solution. Copyright © 2016 Elsevier B.V. All rights reserved.

Effects of chemical states of carbon on deuterium retention in carbon-containing materials

NASA Astrophysics Data System (ADS)

Oyaidzu, Makoto; Kimura, Hiromi; Nakahata, Toshihiko; Nishikawa, Yusuke; Tokitani, Masayuki; Oya, Yasuhisa; Iwakiri, Hirotomo; Yoshida, Naoaki; Okuno, Kenji

2007-08-01

Deuterium retention behavior in highly oriented pyrolytic graphite (HOPG), poly-crystalline diamond, poly-crystalline SiC, sintered WC, and converted B 4C were investigated to reveal tritium behavior in re-deposition and co-deposition layers. Such layers would contain carbon, when the first wall and/or divertor were made of graphite or carbon-containing materials. Furthermore, the employment of other materials such as tungsten, and first wall conditioning such as boronization would complicate the layers. No different deuterium trapping sites due to carbon from those in HOPG were found in all the samples, where two deuterium trapping processes were observed: hot atom chemical trapping of energetic deuterium by a dangling bond of carbon and thermochemical trapping of thermalized deuterium in a constituent atom vacancy surrounded by carbons. Additionally, the latter reaction could be easily counteracted by or competed with the other deuterium trapping reactions by constituent atoms.

Nucleation processes of nanobubbles at a solid/water interface

NASA Astrophysics Data System (ADS)

Fang, Chung-Kai; Ko, Hsien-Chen; Yang, Chih-Wen; Lu, Yi-Hsien; Hwang, Ing-Shouh

2016-04-01

Experimental investigations of hydrophobic/water interfaces often return controversial results, possibly due to the unknown role of gas accumulation at the interfaces. Here, during advanced atomic force microscopy of the initial evolution of gas-containing structures at a highly ordered pyrolytic graphite/water interface, a fluid phase first appeared as a circular wetting layer ~0.3 nm in thickness and was later transformed into a cap-shaped nanostructure (an interfacial nanobubble). Two-dimensional ordered domains were nucleated and grew over time outside or at the perimeter of the fluid regions, eventually confining growth of the fluid regions to the vertical direction. We determined that interfacial nanobubbles and fluid layers have very similar mechanical properties, suggesting low interfacial tension with water and a liquid-like nature, explaining their high stability and their roles in boundary slip and bubble nucleation. These ordered domains may be the interfacial hydrophilic gas hydrates and/or the long-sought chemical surface heterogeneities responsible for contact line pinning and contact angle hysteresis. The gradual nucleation and growth of hydrophilic ordered domains renders the original homogeneous hydrophobic/water interface more heterogeneous over time, which would have great consequence for interfacial properties that affect diverse phenomena, including interactions in water, chemical reactions, and the self-assembly and function of biological molecules.

Femtosecond laser ablation of highly oriented pyrolytic graphite: a green route for large-scale production of porous graphene and graphene quantum dots.

PubMed

Russo, Paola; Hu, Anming; Compagnini, Giuseppe; Duley, Walter W; Zhou, Norman Y

2014-02-21

Porous graphene (PG) and graphene quantum dots (GQDs) are attracting attention due to their potential applications in photovoltaics, catalysis, and bio-related fields. We present a novel way for mass production of these promising materials. The femtosecond laser ablation of highly oriented pyrolytic graphite (HOPG) is employed for their synthesis. Porous graphene (PG) layers were found to float at the water-air interface, while graphene quantum dots (GQDs) were dispersed in the solution. The sheets consist of one to six stacked layers of spongy graphene, which form an irregular 3D porous structure that displays pores with an average size of 15-20 nm. Several characterization techniques have confirmed the porous nature of the collected layers. The analyses of the aqueous solution confirmed the presence of GQDs with dimensions of about 2-5 nm. It is found that the formation of both PG and GQDs depends on the fs-laser ablation energy. At laser fluences less than 12 J cm(-2), no evidence of either PG or GQDs is detected. However, polyynes with six and eight carbon atoms per chain are found in the solution. For laser energies in the 20-30 J cm(-2) range, these polyynes disappeared, while PG and GQDs were found at the water-air interface and in the solution, respectively. The origin of these materials can be explained based on the mechanisms for water breakdown and coal gasification. The absence of PG and GQDs, after the laser ablation of HOPG in liquid nitrogen, confirms the proposed mechanisms.

Determination of the Wetting Angle of Germanium and Germanium-Silicon Melts on Different Substrate Materials

NASA Technical Reports Server (NTRS)

Kaiser, Natalie; Croell, Arne; Szofran, F. R.; Cobb. S. D.; Dold, P.; Benz, K. W.

1999-01-01

During Bridgman growth of semiconductors detachment of the crystal and the melt meniscus has occasionally been observed, mainly under microgravity (microg) conditions. An important factor for detached growth is the wetting angle of the melt with the crucible material. High contact angles are more likely to result in detachment of the growing crystal from the ampoule wall. In order to achieve detached growth of germanium (Ge) and germanium-silicon (GeSi) crystals under 1g and microg conditions, sessile drop measurements were performed to determine the most suitable ampoule material as well as temperature dependence of the surface tension for GeSi. Sapphire, fused quartz, glassy carbon, graphite, SiC, pyrolytic Boron Nitride (pBN), AIN, and diamond were used as substrates. Furthermore, different cleaning procedures and surface treatments (etching, sandblasting, etc.) of the same substrate material and their effect on the wetting behavior were studied during these experiments. pBN and AIN substrates exhibited the highest contact angles with values around 170 deg.

Metastable nanobubbles at the solid-liquid interface due to contact angle hysteresis.

PubMed

Nishiyama, Takashi; Yamada, Yutaka; Ikuta, Tatsuya; Takahashi, Koji; Takata, Yasuyuki

2015-01-27

Nanobubbles exist at solid-liquid interfaces between pure water and hydrophobic surfaces with very high stability, lasting in certain cases up to several days. Not only semispherical but also other shapes, such as micropancakes, are known to exist at such interfaces. However, doubt has been raised as to whether or not the nanobubbles are gas-phase entities. In this study, surface nanobubbles at a pure water-highly ordered pyrolytic graphite (HOPG) interface were investigated by peak force quantitative nanomechanics (PF-QNM). Multiple isolated nanobubbles generated by the solvent-exchange method were present on the terraced areas, avoiding the steps of the HOPG surface. Adjacent nanobubbles coalesced and formed metastable nanobubbles. Coalescence was enhanced by the PF-QNM measurement. We determined that nanobubbles can exist for a long time because of nanoscale contact angle hysteresis at the water-HOPG interface. Moreover, the hydrophilic steps of HOPG were avoided during coalescence, providing evidence that the nanobubbles are truly gas phase.

Surface rearrangement of water-immersed hydrophobic solids by gaseous nanobubbles.

PubMed

Tarábková, Hana; Bastl, Zdeněk; Janda, Pavel

2014-12-09

Interactions of gaseous (ambient) nanobubbles (10-100 nm diameter) with different hydrophobic materials-Teflon, polystyrene, paraffin, and basal plane highly ordered pyrolytic graphite (HOPG)-are studied by AFM in situ and ex situ. Exactly identical surface locations are examined before and after exposure to ambient gas nanobubbles in deionized water and compared for nanomorphological changes. While freely flooded/immersed surfaces, regularly occupied by nanobubbles, do not exhibit resolvable alterations, significant surface rearrangement is found on whole flooded area after mild pressure drop (10 kPa) applied on the solid-liquid interface. Nanopattern and its characteristic dimension appear to be material specific and solely reflect surface-nanobubble interaction. Mild, nonswelling, noncorrosive conditions (20 °C, deionized water) prevent intervention of chemical reaction and high-energy-demanding processes. Experimental results, in accordance with the presented model, indicate that the mild pressure drop triggers expansion of pinned nanobubbles, imposing local tensile stress on the solid surface. Consequently, nanobubbles should be considered as large-area nanoscale patterning elements.

A priori calculations of the free energy of formation from solution of polymorphic self-assembled monolayers.

PubMed

Reimers, Jeffrey R; Panduwinata, Dwi; Visser, Johan; Chin, Yiing; Tang, Chunguang; Goerigk, Lars; Ford, Michael J; Sintic, Maxine; Sum, Tze-Jing; Coenen, Michiel J J; Hendriksen, Bas L M; Elemans, Johannes A A W; Hush, Noel S; Crossley, Maxwell J

2015-11-10

Modern quantum chemical electronic structure methods typically applied to localized chemical bonding are developed to predict atomic structures and free energies for meso-tetraalkylporphyrin self-assembled monolayer (SAM) polymorph formation from organic solution on highly ordered pyrolytic graphite surfaces. Large polymorph-dependent dispersion-induced substrate-molecule interactions (e.g., -100 kcal mol(-1) to -150 kcal mol(-1) for tetratrisdecylporphyrin) are found to drive SAM formation, opposed nearly completely by large polymorph-dependent dispersion-induced solvent interactions (70-110 kcal mol(-1)) and entropy effects (25-40 kcal mol(-1) at 298 K) favoring dissolution. Dielectric continuum models of the solvent are used, facilitating consideration of many possible SAM polymorphs, along with quantum mechanical/molecular mechanical and dispersion-corrected density functional theory calculations. These predict and interpret newly measured and existing high-resolution scanning tunnelling microscopy images of SAM structure, rationalizing polymorph formation conditions. A wide range of molecular condensed matter properties at room temperature now appear suitable for prediction and analysis using electronic structure calculations.

Monochromatic X-ray sources based on a mechanism of real and virtual photon diffraction in crystals

NASA Astrophysics Data System (ADS)

Wagner, A. R.; Kuznetsov, S. I.; Potylitsyn, A. P.; Razin, S. V.; Uglov, S. R.; Zabaev, V. N.

2008-09-01

A source of monochromatic X-ray radiation is wanted in industry, science, medicine and so on. Many ways of making such a source are known. The present work describes two mechanisms for the creation of a monochromatic X-ray beam, which are parametric X-ray radiation (PXR) and bremsstrahlung diffraction (DBS). Both the experiments were carried out using an electron beam at a microtron. During the first experiment, the DBS process was investigated as a scattering of the Bremsstrahlung (BS) beam on the crystallographic surfaces of tungsten and pyrolytic graphite crystals. The second experiment consisted in the registration of the PXR and DBS yield during the passage of the electrons through the same crystals as in the first experiment. The spectral and orientation radiation characteristics and simulation results obtained for the DBS and PXR processes are presented. It is shown that the usage of mosaic crystalline targets is rather useful in order to obtain a monochromatic X-ray source based on bremsstrahlung diffraction from moderately relativistic electrons.

Substrate Selection for Fundamental Studies of Electrocatalysts and Photoelectrodes: Inert Potential Windows in Acidic, Neutral, and Basic Electrolyte

PubMed Central

Gorlin, Yelena; Jaramillo, Thomas F.

2014-01-01

The selection of an appropriate substrate is an important initial step for many studies of electrochemically active materials. In order to help researchers with the substrate selection process, we employ a consistent experimental methodology to evaluate the electrochemical reactivity and stability of seven potential substrate materials for electrocatalyst and photoelectrode evaluation. Using cyclic voltammetry with a progressively increased scan range, we characterize three transparent conducting oxides (indium tin oxide, fluorine-doped tin oxide, and aluminum-doped zinc oxide) and four opaque conductors (gold, stainless steel 304, glassy carbon, and highly oriented pyrolytic graphite) in three different electrolytes (sulfuric acid, sodium acetate, and sodium hydroxide). We determine the inert potential window for each substrate/electrolyte combination and make recommendations about which materials may be most suitable for application under different experimental conditions. Furthermore, the testing methodology provides a framework for other researchers to evaluate and report the baseline activity of other substrates of interest to the broader community. PMID:25357131

Effect of thermal behavior of β-lactoglobulin on the oxidative stability of menhaden oil-in-water emulsions.

PubMed

Phoon, Pui Yeu; Narsimhan, Ganesan; San Martin-Gonzalez, Maria Fernanda

2013-02-27

This study reports how emulsion oxidative stability was affected by the interfacial structure of β-lactoglobulin due to different heat treatments. Four percent (v/v) menhaden oil-in-water emulsions, stabilized by 1% (w/v) β-lactoglobulin at pH 7, were prepared by homogenization under different thermal conditions. Oxidative stability was monitored by the ferric thiocyanate peroxide value assay. Higher oxidative stability was attained by β-lactoglobulin in the molten globule state than in the native or denatured state. From atomic force microscopy of β-lactoglobulin adsorbed onto highly ordered pyrolytic graphite in buffer, native β-lactoglobulin formed a relatively smooth interfacial layer of 1.2 GPa in Young's modulus, whereas additional aggregates of similar stiffness were found when β-lactoglobulin was preheated to the molten globule state. For denatured β-lactoglobulin, although aggregates were also observed, they were larger and softer (Young's modulus = 0.45 GPa), suggesting increased porosity and thus an offset in the advantage of increased layer coverage on oxidative stability.

A scanning tunneling microscope for a dilution refrigerator.

PubMed

Marz, M; Goll, G; Löhneysen, H v

2010-04-01

We present the main features of a home-built scanning tunneling microscope that has been attached to the mixing chamber of a dilution refrigerator. It allows scanning tunneling microscopy and spectroscopy measurements down to the base temperature of the cryostat, T approximately 30 mK, and in applied magnetic fields up to 13 T. The topography of both highly ordered pyrolytic graphite and the dichalcogenide superconductor NbSe(2) has been imaged with atomic resolution down to T approximately 50 mK as determined from a resistance thermometer adjacent to the sample. As a test for a successful operation in magnetic fields, the flux-line lattice of superconducting NbSe(2) in low magnetic fields has been studied. The lattice constant of the Abrikosov lattice shows the expected field dependence proportional to 1/square root of B and measurements in the scanning tunneling spectroscopy mode clearly show the superconductive density of states with Andreev bound states in the vortex core.

Substrate Selection for Fundamental Studies of Electrocatalysts and Photoelectrodes: Inert Potential Windows in Acidic, Neutral, and Basic Electrolyte

DOE PAGES

Benck, Jesse D.; Pinaud, Blaise A.; Gorlin, Yelena; ...

2014-10-30

The selection of an appropriate substrate is an important initial step for many studies of electrochemically active materials. In order to help researchers with the substrate selection process, we employ a consistent experimental methodology to evaluate the electrochemical reactivity and stability of seven potential substrate materials for electrocatalyst and photoelectrode evaluation. Using cyclic voltammetry with a progressively increased scan range, we characterize three transparent conducting oxides (indium tin oxide, fluorine-doped tin oxide, and aluminum-doped zinc oxide) and four opaque conductors (gold, stainless steel 304, glassy carbon, and highly oriented pyrolytic graphite) in three different electrolytes (sulfuric acid, sodium acetate, andmore » sodium hydroxide). Here, we determine the inert potential window for each substrate/electrolyte combination and make recommendations about which materials may be most suitable for application under different experimental conditions. Furthermore, the testing methodology provides a framework for other researchers to evaluate and report the baseline activity of other substrates of interest to the broader community.« less

High temperature blackbody BB2000/40 for calibration of radiation thermometers and thermocouple

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ogarev, S. A.; Khlevnoy, B. B.; Samoylov, M. L.

2013-09-11

The cavity-type high temperature blackbody (HTBB) models of BB3200/3500 series are the most spread among metrological institutes worldwide as sources for radiometry and radiation thermometry, due to their ultra high working temperatures, high emissivity and stability. The materials of radiating cavities are graphite, pyrolytic graphite (PG) and their combination. The paper describes BB2000/40 blackbody with graphite-tube cavity that was developed for calibration of radiation thermometers at SCEI (Singapore). The peculiarity of BB2000/40 is a possibility to use it, besides calibration of pyrometers, as an instrument for thermocouples calibration. Operating within the temperature range from 900 °C to 2000 °C, themore » blackbody has a wide cavity opening of 40 mm. Emissivity of the cavity, with PG heater rings replaced partly by graphite elements, was estimated as 0.998 ± 0.0015 in the spectral range from 350 nm to 2000 nm. The uniformity along the cavity axis, accounting for 10 °C, was measured using a B-type thermocouple at 1500 °C. The BB2000/40, if necessary, can be easily modified, by replacing the graphite radiator with a set of PG rings, to be able to reach temperatures as high as 3200 °C. The HTBB utilizes an optical feedback system which allows temperature stabilization within 0.1 °C. This rear-view feedback allows the whole HTBB aperture to be used for measurements.« less

Pyrolytic carbon-coated stainless steel felt as a high-performance anode for bioelectrochemical systems.

PubMed

Guo, Kun; Hidalgo, Diana; Tommasi, Tonia; Rabaey, Korneel

2016-07-01

Scale up of bioelectrochemical systems (BESs) requires highly conductive, biocompatible and stable electrodes. Here we present pyrolytic carbon-coated stainless steel felt (C-SS felt) as a high-performance and scalable anode. The electrode is created by generating a carbon layer on stainless steel felt (SS felt) via a multi-step deposition process involving α-d-glucose impregnation, caramelization, and pyrolysis. Physicochemical characterizations of the surface elucidate that a thin (20±5μm) and homogenous layer of polycrystalline graphitic carbon was obtained on SS felt surface after modification. The carbon coating significantly increases the biocompatibility, enabling robust electroactive biofilm formation. The C-SS felt electrodes reach current densities (jmax) of 3.65±0.14mA/cm(2) within 7days of operation, which is 11 times higher than plain SS felt electrodes (0.30±0.04mA/cm(2)). The excellent biocompatibility, high specific surface area, high conductivity, good mechanical strength, and low cost make C-SS felt a promising electrode for BESs. Copyright © 2016 Elsevier Ltd. All rights reserved.

MISSE 2 PEACE Polymers Experiment Atomic Oxygen Erosion Yield Error Analysis

NASA Technical Reports Server (NTRS)

McCarthy, Catherine E.; Banks, Bruce A.; deGroh, Kim, K.

2010-01-01

Atomic oxygen erosion of polymers in low Earth orbit (LEO) poses a serious threat to spacecraft performance and durability. To address this, 40 different polymer samples and a sample of pyrolytic graphite, collectively called the PEACE (Polymer Erosion and Contamination Experiment) Polymers, were exposed to the LEO space environment on the exterior of the International Space Station (ISS) for nearly 4 years as part of the Materials International Space Station Experiment 1 & 2 (MISSE 1 & 2). The purpose of the PEACE Polymers experiment was to obtain accurate mass loss measurements in space to combine with ground measurements in order to accurately calculate the atomic oxygen erosion yields of a wide variety of polymeric materials exposed to the LEO space environment for a long period of time. Error calculations were performed in order to determine the accuracy of the mass measurements and therefore of the erosion yield values. The standard deviation, or error, of each factor was incorporated into the fractional uncertainty of the erosion yield for each of three different situations, depending on the post-flight weighing procedure. The resulting error calculations showed the erosion yield values to be very accurate, with an average error of 3.30 percent.

Mechanisms of ultrafast laser-induced deep-subwavelength gratings on graphite and diamond

NASA Astrophysics Data System (ADS)

Huang, Min; Zhao, Fuli; Cheng, Ya; Xu, Ningsheg; Xu, Zhizhan

2009-03-01

Deep-subwavelength gratings with periodicities of 170, 120, and 70 nm can be observed on highly oriented pyrolytic graphite irradiated by a femtosecond (fs) laser at 800 nm. Under picosecond laser irradiation, such gratings likewise can be produced. Interestingly, the 170-nm grating is also observed on single-crystal diamond irradiated by the 800-nm fs laser. In our opinion, the optical properties of the high-excited state of material surface play a key role for the formation of the deep-subwavelength gratings. The numerical simulations of the graphite deep-subwavelength grating at normal and high-excited states confirm that in the groove the light intensity can be extraordinarily enhanced via cavity-mode excitation in the condition of transverse-magnetic wave irradiation with near-ablation-threshold fluences. This field enhancement of polarization sensitiveness in deep-subwavelength apertures acts as an important feedback mechanism for the growth and polarization dependence of the deep-subwavelength gratings. In addition, we suggest that surface plasmons are responsible for the formation of seed deep-subwavelength apertures with a particular periodicity and the initial polarization dependence. Finally, we propose that the nanoscale Coulomb explosion occurring in the groove is responsible for the ultrafast nonthermal ablation mechanism.

Effective regeneration of anode material recycled from scrapped Li-ion batteries

NASA Astrophysics Data System (ADS)

Zhang, Jin; Li, Xuelei; Song, Dawei; Miao, Yanli; Song, Jishun; Zhang, Lianqi

2018-06-01

Recycling high-valuable metal elements (such as Li, Ni, Co, Al and Cu elements) from scrapped lithium ion batteries can bring significant economic benefits. However, recycling and reusing anode material has not yet attracted wide attention up to now, due to the lower added-value than the above valuable metal materials and the difficulties in regenerating process. In this paper, a novel regeneration process with significant green advance is proposed to regenerate anode material recycled from scrapped Li-ion batteries for the first time. After regenerated, most acetylene black (AB) and all the styrene butadiene rubber (SBR), carboxymethylcellulose sodium (CMC) in recycled anode material are removed, and the surface of anode material is coated with pyrolytic carbon from phenolic resin again. Finally, the regenerated anode material (graphite with coating layer, residual AB and a little CMC pyrolysis product) is obtained. As expected, all the technical indexs of regenerated anode material exceed that of a midrange graphite with the same type, and partial technical indexs are even closed to that of the unused graphite. The results indicate the effective regeneration of anode material recycled from scrapped Li-ion batteries is really achieved.

Electronic structure of multi-walled carbon fullerenes

NASA Astrophysics Data System (ADS)

Doore, Keith; Cook, Matthew; Clausen, Eric; Lukashev, Pavel V.; Kidd, Tim E.; Stollenwerk, Andrew J.

2017-02-01

Despite an enormous amount of research on carbon based nanostructures, relatively little is known about the electronic structure of multi-walled carbon fullerenes, also known as carbon onions. In part, this is due to the very high computational expense involved in estimating electronic structure of large molecules. At the same time, experimentally, the exact crystal structure of the carbon onion is usually unknown, and therefore one relies on qualitative arguments only. In this work we present the results of a computational study on a series of multi-walled fullerenes and compare their electronic structures to experimental data. Experimentally, the carbon onions were fabricated using ultrasonic agitation of isopropanol alcohol and deposited onto the surface of highly ordered pyrolytic graphite using a drop cast method. Scanning tunneling microscopy images indicate that the carbon onions produced using this technique are ellipsoidal with dimensions on the order of 10 nm. The majority of differential tunneling spectra acquired on individual carbon onions are similar to that of graphite with the addition of molecular-like peaks, indicating that these particles span the transition between molecules and bulk crystals. A smaller, yet sizable number exhibited a semiconducting gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) levels. These results are compared with the electronic structure of different carbon onion configurations calculated using first-principles. Similar to the experimental results, the majority of these configurations are metallic with a minority behaving as semiconductors. Analysis of the configurations investigated here reveals that each carbon onion exhibiting an energy band gap consisted only of non-metallic fullerene layers, indicating that the interlayer interaction is not significant enough to affect the total density of states in these structures.

Analyzing the impact of reactive transport on the repository performance of TRISO fuel

NASA Astrophysics Data System (ADS)

Schmidt, Gregory

One of the largest determiners of the amount of electricity generated by current nuclear reactors is the efficiency of the thermodynamic cycle used for power generation. Current light water reactors (LWR) have an efficiency of 35% or less for the conversion of heat energy generated by the reactor to electrical energy. If this efficiency could be improved, more power could be generated from equivalent volumes of nuclear fuel. One method of improving this efficiency is to use a coolant flow that operates at a much higher temperature for electricity production. A reactor design that is currently proposed to take advantage of this efficiency is a graphite-moderated, helium-cooled reactor known as a High Temperature Gas Reactor (HTGR). There are significant differences between current LWR's and the proposed HTGR's but most especially in the composition of the nuclear fuel. For LWR's, the fuel elements consist of pellets of uranium dioxide or plutonium dioxide that are placed in long tubes made of zirconium metal alloys. For HTGR's, the fuel, known as TRISO (TRIstructural-ISOtropic) fuel, consists of an inner sphere of fissile material, a layer of dense pyrolytic carbon (PyC), a ceramic layer of silicon carbide (SiC) and a final dense outer layer of PyC. These TRISO particles are then compacted with graphite into fuel rods that are then placed in channels in graphite blocks. The blocks are then arranged in an annular fashion to form a reactor core. However, this new fuel form has unanswered questions on the environmental post-burn-up behavior. The key question for current once-through fuel operations is how these large irradiated graphite blocks with spent fuel inside will behave in a repository environment. Data in the literature to answer this question is lacking, but nevertheless this is an important question that must be answered before wide-spread adoption of HTGR's could be considered. This research has focused on answering the question of how the large quantity of graphite surrounding the spent HTGR fuel will impact the release of aqueous uranium from the TRISO fuel. In order to answer this question, the sorption and partitioning behavior of uranium to graphite under a variety of conditions was investigated. Key systematic variables that were analyzed include solution pH, dissolved carbonate concentration, uranium metal concentration and ionic strength. The kinetics and desorption characteristics of uranium/graphite partitioning were studied as well. The graphite used in these experiments was also characterized by a variety of techniques and conclusions are drawn about the relevant surface chemistry of graphite. This data was then used to generate a model for the reactive transport of uranium in a graphite matrix. This model was implemented with the software code CXTFIT and validated through the use of column studies mirroring the predicted system.

Time dependent wettability of graphite upon ambient exposure: The role of water adsorption

NASA Astrophysics Data System (ADS)

Amadei, Carlo A.; Lai, Chia-Yun; Heskes, Daan; Chiesa, Matteo

2014-08-01

We report the temporal evolution of the wettability of highly ordered pyrolytic graphite (HOPG) exposed to environmental conditions. Macroscopic wettability is investigated by static and dynamic contact angles (SCA and DCA) obtaining values comparable to the ones presented in the literature. SCA increases from ˜68° to ˜90° during the first hour of exposure after cleaving, whereas DCA is characterized by longer-scale (24 h) time evolution. We interpret these results in light of Fourier transform infrared spectroscopy, which indicates that the evolution of the HOPG wettability is due to adsorption of molecules from the surrounding atmosphere. This hypothesis is further confirmed by nanoscopic observations obtained by atomic force microscope (AFM)-based force spectroscopy, which monitor the evolution of surface properties with a spatial resolution superior to macroscopic experiments. Moreover, we observe that the results of macro- and nanoscale measurements evolve in similar fashion with time and we propose a quantitative correlation between SCA and AFM measurements. Our results suggest that the cause of the transition in the wettability of HOPG is due to the adsorption of hydrocarbon contaminations and water molecules from the environment. This is corroborated by annealing the HOPG is vacuum conditions at 150°, allowing the desorption of molecules on the surface, and thus re-establishing the initial macro and nano surface properties. Our findings can be used in the interpretation of the wettability of more complicated systems derived from HOPG (i.e., graphene).

Time dependent wettability of graphite upon ambient exposure: The role of water adsorption

DOE Office of Scientific and Technical Information (OSTI.GOV)

Amadei, Carlo A.; Lai, Chia-Yun; Heskes, Daan

We report the temporal evolution of the wettability of highly ordered pyrolytic graphite (HOPG) exposed to environmental conditions. Macroscopic wettability is investigated by static and dynamic contact angles (SCA and DCA) obtaining values comparable to the ones presented in the literature. SCA increases from ∼68° to ∼90° during the first hour of exposure after cleaving, whereas DCA is characterized by longer-scale (24 h) time evolution. We interpret these results in light of Fourier transform infrared spectroscopy, which indicates that the evolution of the HOPG wettability is due to adsorption of molecules from the surrounding atmosphere. This hypothesis is further confirmedmore » by nanoscopic observations obtained by atomic force microscope (AFM)-based force spectroscopy, which monitor the evolution of surface properties with a spatial resolution superior to macroscopic experiments. Moreover, we observe that the results of macro- and nanoscale measurements evolve in similar fashion with time and we propose a quantitative correlation between SCA and AFM measurements. Our results suggest that the cause of the transition in the wettability of HOPG is due to the adsorption of hydrocarbon contaminations and water molecules from the environment. This is corroborated by annealing the HOPG is vacuum conditions at 150°, allowing the desorption of molecules on the surface, and thus re-establishing the initial macro and nano surface properties. Our findings can be used in the interpretation of the wettability of more complicated systems derived from HOPG (i.e., graphene)« less

Quantized edge modes in atomic-scale point contacts in graphene

NASA Astrophysics Data System (ADS)

Kinikar, Amogh; Phanindra Sai, T.; Bhattacharyya, Semonti; Agarwala, Adhip; Biswas, Tathagata; Sarker, Sanjoy K.; Krishnamurthy, H. R.; Jain, Manish; Shenoy, Vijay B.; Ghosh, Arindam

2017-07-01

The zigzag edges of single- or few-layer graphene are perfect one-dimensional conductors owing to a set of gapless states that are topologically protected against backscattering. Direct experimental evidence of these states has been limited so far to their local thermodynamic and magnetic properties, determined by the competing effects of edge topology and electron-electron interaction. However, experimental signatures of edge-bound electrical conduction have remained elusive, primarily due to the lack of graphitic nanostructures with low structural and/or chemical edge disorder. Here, we report the experimental detection of edge-mode electrical transport in suspended atomic-scale constrictions of single and multilayer graphene created during nanomechanical exfoliation of highly oriented pyrolytic graphite. The edge-mode transport leads to the observed quantization of conductance close to multiples of G0 = 2e2/h. At the same time, conductance plateaux at G0/2 and a split zero-bias anomaly in non-equilibrium transport suggest conduction via spin-polarized states in the presence of an electron-electron interaction.

Scanning tunneling microscopy investigation of copper phthalocyanine and truxenone derivative binary superstructures on graphite.

PubMed

Liu, Jia; Wang, Dong; Wang, Jie-Yu; Pei, Jian; Wan, Li-Jun

2011-02-01

The binary self-assembly of copper phthalocyanine (CuPc) and 2,3,7,8,12,13-hexahexyloxy-truxenone (TrO23) at the solid/liquid interface of highly oriented pyrolytic graphite (HOPG) was investigated by using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Pseduohexagonal and linear patterned superstructures of CuPc are obtained by co-adsorbing with TrO23. High-resolution STM images reveal the structural details of the arrangement of TrO23 and CuPc in the binary assembly structures. The molecular ratio between CuPc and TrO23 in the adlayer can be modulated by the CuPc concentration in liquid phase. The electronic properties of CuPc and TrO23 in the co-adsorbed self-assembly are investigated by STS. The results presented here are helpful to the design and fabrication of multi-component functional molecular nanostructures. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

An equipment for Rayleigh scattering of Mössbauer radiation

NASA Astrophysics Data System (ADS)

Enescu, S. E.; Bibicu, I.; Zoran, V.; Kluger, A.; Stoica, A. D.; Tripadus, V.

1998-07-01

A personal computer driven equipment designed for Rayleigh scattering of Mössbauer radiation experiments at room temperature is described. The performances of the system were tested using like scatterers crystals with different mosaic divergences: lithium fluoride (LiF) and pyrolytic graphite (C). The equipment, suitable for any kind of Mössbauer scattering experiments, permits low and adjustable horizontal divergences of the incident beam. On décrit un équipement dédié aux mesures de diffusion Rayleigh de la radiation Mössbauer controlée par ordinateur. Les performances du système ont été testées sur des cristaux ayant des divergences de mosaïque différentes: le fluorure de lithium (LiF) et le graphite pyrolytique (C). L'équipement, qui peut être utilisé dans des différents types d'expérimentations basées sur la diffusion de la radiation Mössbauer, admet des divergences horizontales du faisceau incident faibles et réglables.

Quantized edge modes in atomic-scale point contacts in graphene.

PubMed

Kinikar, Amogh; Phanindra Sai, T; Bhattacharyya, Semonti; Agarwala, Adhip; Biswas, Tathagata; Sarker, Sanjoy K; Krishnamurthy, H R; Jain, Manish; Shenoy, Vijay B; Ghosh, Arindam

2017-07-01

The zigzag edges of single- or few-layer graphene are perfect one-dimensional conductors owing to a set of gapless states that are topologically protected against backscattering. Direct experimental evidence of these states has been limited so far to their local thermodynamic and magnetic properties, determined by the competing effects of edge topology and electron-electron interaction. However, experimental signatures of edge-bound electrical conduction have remained elusive, primarily due to the lack of graphitic nanostructures with low structural and/or chemical edge disorder. Here, we report the experimental detection of edge-mode electrical transport in suspended atomic-scale constrictions of single and multilayer graphene created during nanomechanical exfoliation of highly oriented pyrolytic graphite. The edge-mode transport leads to the observed quantization of conductance close to multiples of G 0  = 2e 2 /h. At the same time, conductance plateaux at G 0 /2 and a split zero-bias anomaly in non-equilibrium transport suggest conduction via spin-polarized states in the presence of an electron-electron interaction.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fedrigo, Anna, E-mail: anna.fedrigo@nbi.ku.dk; Istituto dei Sistemi Complessi, Consiglio Nazionale delle Ricerche, 50019 Sesto Fiorentino; European Spallation Source ESS AB, SE-221 00 Lund

VESPA, Vibrational Excitation Spectrometer with Pyrolytic-graphite Analysers, aims to probe molecular excitations via inelastic neutron scattering. It is a thermal high resolution inverted geometry time-of-flight instrument designed to maximise the use of the long pulse of the European Spallation Source. The wavelength frame multiplication technique was applied to provide simultaneously a broad dynamic range (about 0-500 meV) while a system of optical blind choppers allows to trade flux for energy resolution. Thanks to its high flux, VESPA will allow the investigation of dynamical and in situ experiments in physical chemistry. Here we describe the design parameters and the corresponding McStasmore » simulations.« less

Pulsed Laser Ablation Synthesis of Diamond Molecules in Supercritical Fluids

NASA Astrophysics Data System (ADS)

Nakahara, Sho; Stauss, Sven; Miyazoe, Hiroyuki; Shizuno, Tomoki; Suzuki, Minoru; Kataoka, Hiroshi; Sasaki, Takehiko; Terashima, Kazuo

2010-09-01

Nanocarbon materials have been synthesized by pulsed laser ablation (532 nm; 52 J/cm2; 7 ns; 10 Hz) of highly oriented pyrolytic graphite in adamantane-dissolved supercritical xenon at a temperature T = 290.2 K and pressure p = 5.86 MPa. Micro-Raman spectroscopy of the products revealed the presence of hydrocarbons possessing sp3 hybridized bonds also found in diamond structures. The synthesis of diamantane was confirmed by gas chromatography-mass spectrometry. The same measurements also indicate the possible synthesis of other diamondoids up to octamantane. Thus, laser ablation in supercritical fluids is proposed as one practical method of synthesizing diamondoids.

Bias-induced conformational switching of supramolecular networks of trimesic acid at the solid-liquid interface

NASA Astrophysics Data System (ADS)

Ubink, J.; Enache, M.; Stöhr, M.

2018-05-01

Using the tip of a scanning tunneling microscope, an electric field-induced reversible phase transition between two planar porous structures ("chickenwire" and "flower") of trimesic acid was accomplished at the nonanoic acid/highly oriented pyrolytic graphite interface. The chickenwire structure was exclusively observed for negative sample bias, while for positive sample bias only the more densely packed flower structure was found. We suggest that the slightly negatively charged carboxyl groups of the trimesic acid molecule are the determining factor for this observation: their adsorption behavior varies with the sample bias and is thus responsible for the switching behavior.

Sulfur redox reactions on nanostructured highly oriented pyrolytic graphite (HOPG) electrodes: Direct evidence for superior electrocatalytic performance on defect sites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Gongwei; Zheng, Dong; Liu, Dan

Fundamental research of sulfur redox reactions on well-defined controlled model electrode surfaces can provide new information to design high-performance lithium-sulfur batteries. In this paper, we study the electrochemical reduction and oxidation of sulfur on the nanostructured HOPG electrodes with pure basal planes, step plans, and pure edge planes. Finally, our results directly indicate that electrochemical reduction and oxidation of sulfur is significantly affected by the carbon surface structure, namely, the electrochemical reversibility of sulfur redox reaction is much better on edge plane, compared with basal plane and step plane.

Sulfur redox reactions on nanostructured highly oriented pyrolytic graphite (HOPG) electrodes: Direct evidence for superior electrocatalytic performance on defect sites

DOE PAGES

Wang, Gongwei; Zheng, Dong; Liu, Dan; ...

2017-04-28

Fundamental research of sulfur redox reactions on well-defined controlled model electrode surfaces can provide new information to design high-performance lithium-sulfur batteries. In this paper, we study the electrochemical reduction and oxidation of sulfur on the nanostructured HOPG electrodes with pure basal planes, step plans, and pure edge planes. Finally, our results directly indicate that electrochemical reduction and oxidation of sulfur is significantly affected by the carbon surface structure, namely, the electrochemical reversibility of sulfur redox reaction is much better on edge plane, compared with basal plane and step plane.

A priori calculations of the free energy of formation from solution of polymorphic self-assembled monolayers

PubMed Central

Reimers, Jeffrey R.; Panduwinata, Dwi; Visser, Johan; Chin, Yiing; Tang, Chunguang; Goerigk, Lars; Ford, Michael J.; Sintic, Maxine; Sum, Tze-Jing; Coenen, Michiel J. J.; Hendriksen, Bas L. M.; Elemans, Johannes A. A. W.; Hush, Noel S.; Crossley, Maxwell J.

2015-01-01

Modern quantum chemical electronic structure methods typically applied to localized chemical bonding are developed to predict atomic structures and free energies for meso-tetraalkylporphyrin self-assembled monolayer (SAM) polymorph formation from organic solution on highly ordered pyrolytic graphite surfaces. Large polymorph-dependent dispersion-induced substrate−molecule interactions (e.g., −100 kcal mol−1 to −150 kcal mol−1 for tetratrisdecylporphyrin) are found to drive SAM formation, opposed nearly completely by large polymorph-dependent dispersion-induced solvent interactions (70–110 kcal mol−1) and entropy effects (25–40 kcal mol−1 at 298 K) favoring dissolution. Dielectric continuum models of the solvent are used, facilitating consideration of many possible SAM polymorphs, along with quantum mechanical/molecular mechanical and dispersion-corrected density functional theory calculations. These predict and interpret newly measured and existing high-resolution scanning tunnelling microscopy images of SAM structure, rationalizing polymorph formation conditions. A wide range of molecular condensed matter properties at room temperature now appear suitable for prediction and analysis using electronic structure calculations. PMID:26512115

DOE Office of Scientific and Technical Information (OSTI.GOV)

Han, Yong; Lii-Rosales, A.; Zhou, Y.

Theory and stochastic lattice-gas modeling is developed for the formation of intercalated metal islands in the gallery between the top layer and the underlying layer at the surface of layered materials. Our model for this process involves deposition of atoms, some fraction of which then enter the gallery through well-separated pointlike defects in the top layer. Subsequently, these atoms diffuse within the subsurface gallery leading to nucleation and growth of intercalated islands nearby the defect point source. For the case of a single point defect, continuum diffusion equation analysis provides insight into the nucleation kinetics. However, complementary tailored lattice-gas modelingmore » produces a more comprehensive and quantitative characterization. We analyze the large spread in nucleation times and positions relative to the defect for the first nucleated island. We also consider the formation of subsequent islands and the evolution of island growth shapes. The shapes reflect in part our natural adoption of a hexagonal close-packed island structure. As a result, motivation and support for the model is provided by scanning tunneling microscopy observations of the formation of intercalated metal islands in highly-ordered pyrolytic graphite at higher temperatures.« less

Comprehensive Adsorption Studies of Doxycycline and Ciprofloxacin Antibiotics by Biochars Prepared at Different Temperatures

PubMed Central

Zeng, Zhi-wei; Tan, Xiao-fei; Liu, Yun-guo; Tian, Si-rong; Zeng, Guang-ming; Jiang, Lu-hua; Liu, Shao-bo; Li, Jiang; Liu, Ni; Yin, Zhi-hong

2018-01-01

This paper comparatively investigated the removal efficiency and mechanisms of rice straw biochars prepared under three pyrolytic temperatures for two kinds of tetracycline and quinolone antibiotics (doxycycline and ciprofloxacin). The influencing factors of antibiotic adsorption (including biochar dosage, pH, background electrolytes, humic acid, initial antibiotics concentration, contact time, and temperature) were comprehensively studied. The results suggest that biochars produced at high-temperature [i.e., 700°C (BC700)], have higher adsorption capacity for the two antibiotics than low-temperature (i.e., 300–500°C) biochars (BC300 and BC500). Higher surface area gives rise to greater volume of micropores and mesopores, and higher graphitic surfaces of the BC700 contributed to its higher functionality. The maximum adsorption capacity was found to be in the following order: DOX > CIP. The π-π EDA interaction and hydrogen bonding might be the predominant adsorption mechanisms. Findings in this study highlight the important roles of high-temperature biochars in controlling the contamination of tetracycline and quinolone antibiotics in the environment. PMID:29637067

Imaging nanoclusters in the constant height mode of the dynamic SFM.

PubMed

Barth, Clemens; Pakarinen, Olli H; Foster, Adam S; Henry, Claude R

2006-04-14

For the first time, high quality images of metal nanoclusters which were recorded in the constant height mode of a dynamic scanning force microscope (dynamic SFM) are shown. Surfaces of highly ordered pyrolytic graphite (HOPG) were used as a test substrate since metal nanoclusters with well defined and symmetric shapes can be created by epitaxial growth. We performed imaging of gold clusters with sizes between 5 and 15 nm in both scanning modes, constant Δf mode and constant height mode, and compared the image contrast. We notice that clusters in constant height images appear much sharper, and exhibit more reasonable lateral shapes and sizes in comparison to images recorded in the constant Δf mode. With the help of numerical simulations we show that only a microscopically small part of the tip apex (nanotip) is probably the main contributor for the image contrast formation. In principle, the constant height mode can be used for imaging surfaces of any material, e.g. ionic crystals, as shown for the system Au/NaCl(001).

Comprehensive adsorption studies of doxycycline and ciprofloxacin antibiotics by biochars prepared at different temperatures

NASA Astrophysics Data System (ADS)

Zeng, Zhi-wei; Tan, Xiao-fei; Liu, Yun-guo; Tian, Si-rong; Zeng, Guang-ming; Jiang, Lu-hua; Liu, Shao-bo; Li, Jiang; Liu, Ni; Yin, Zhi-hong

2018-03-01

This paper comparatively investigated the removal efficiency and mechanisms of rice straw biochars prepared under three pyrolytic temperatures for two kinds of tetracycline and quinolone antibiotics (doxycycline and ciprofloxacin). The influencing factors of antibiotic adsorption (including biochar dosage, pH, background electrolytes, humic acid, initial antibiotics concentration, contact time, and temperature) were comprehensively studied. The results suggest that biochars produced at high-temperature (i.e., 700°C (BC700)), have higher adsorption capacity for the two antibiotics than low-temperature (i.e., 300-500°C) biochars (BC300 and BC500). Higher surface area gives rise to greater volume of micropores and mesopores, and higher graphitic surfaces of the BC700 contributed to its higher functionality. The maximum adsorption capacity was found to be in the following order: DOX > CIP. The π-π EDA interaction and hydrogen bonding might be the predominant adsorption mechanisms. Findings in this study highlight the important roles of high-temperature biochars in controlling the contamination of tetracycline and quinolone antibiotics in the environment.

Transport of energy by ultraintense laser-generated electrons in nail-wire targets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ma, T.; Lawrence Livermore National Laboratory, Livermore, California 94550; Key, M. H.

2009-11-15

Nail-wire targets (20 {mu}m diameter copper wires with 80 {mu}m hemispherical head) were used to investigate energy transport by relativistic fast electrons generated in intense laser-plasma interactions. The targets were irradiated using the 300 J, 1 ps, and 2x10{sup 20} W{center_dot}cm{sup -2} Vulcan laser at the Rutherford Appleton Laboratory. A spherically bent crystal imager, a highly ordered pyrolytic graphite spectrometer, and single photon counting charge-coupled device gave absolute Cu K{alpha} measurements. Results show a concentration of energy deposition in the head and an approximately exponential fall-off along the wire with about 60 {mu}m 1/e decay length due to resistive inhibition.more » The coupling efficiency to the wire was 3.3{+-}1.7% with an average hot electron temperature of 620{+-}125 keV. Extreme ultraviolet images (68 and 256 eV) indicate additional heating of a thin surface layer of the wire. Modeling using the hybrid E-PLAS code has been compared with the experimental data, showing evidence of resistive heating, magnetic trapping, and surface transport.« less

Tellurium speciation analysis using hydride generation in situ trapping electrothermal atomic absorption spectrometry and ruthenium or palladium modified graphite tubes.

PubMed

Yildirim, Emrah; Akay, Pınar; Arslan, Yasin; Bakirdere, Sezgin; Ataman, O Yavuz

2012-12-15

Speciation of tellurium can be achieved by making use of different kinetic behaviors of Te(IV) and Te(VI) upon their reaction with sodium borohydride using hydride generation. While Te(IV) can form H(2)Te, Te(VI) will not form any volatile species during the course of hydride formation and measurement by atomic absorption spectrometry. Quantitative reduction of Te(VI) was achieved through application of a microwave assisted prereduction of Te(VI) in 6.0 mol/L HCl solution. Enhanced sensitivity was achieved by in situ trapping of the generated H(2)Te species in a previously heated graphite furnace whose surface was modified using Pd or Ru. Overall efficiency for in situ trapping in pyrolytically coated graphite tube surface was found to be 15% when volatile analyte species are trapped for 60s at 300°C. LOD and LOQ values were calculated as 0.086 ng/mL and 0.29 ng/mL, respectively. Efficiency was increased to 46% and 36% when Pd and Ru surface modifiers were used, respectively. With Ru modified graphite tube 173-fold enhancement was obtained over 180 s trapping period with respect to ETAAS; the tubes could be used for 250 cycles. LOD values were 0.0064 and 0.0022 ng/mL for Pd and Ru treated ETAAS systems, respectively, for 180 s collection of 9.6 mL sample solution. Copyright © 2012 Elsevier B.V. All rights reserved.

High heat flux Langmuir probe array for the DIII-D divertor platesa)

NASA Astrophysics Data System (ADS)

Watkins, J. G.; Taussig, D.; Boivin, R. L.; Mahdavi, M. A.; Nygren, R. E.

2008-10-01

Two modular arrays of Langmuir probes designed to handle a heat flux of up to 25 MW/m2 for 10 s exposures have been installed in the lower divertor target plates of the DIII-D tokamak. The 20 pyrolytic graphite probe tips have more than three times higher thermal conductivity and 16 times larger mass than the original DIII-D isotropic graphite probes. The probe tips have a fixed 12.5° surface angle to distribute the heat flux more uniformly than the previous 6 mm diameter domed collectors and a symmetric "rooftop" design to allow operation with reversed toroidal magnetic field. A large spring-loaded contact area improves heat conduction from each probe tip through a ceramic insulator into a cooled graphite divertor floor tile. The probe tips, brazed to molybdenum foil to ensure good electrical contact, are mounted in a ceramic tray for electrical isolation and reliable cable connections. The new probes are located 1.5 cm radially apart in a staggered arrangement near the entrance to the lower divertor pumping baffle and are linearly spaced 3 cm apart on the shelf above the in-vessel cryopump. Typical target plate profiles of Jsat, Te, and Vf with 4 mm spatial resolution are shown.

Epitaxial Growth of Aligned and Continuous Carbon Nanofibers from Carbon Nanotubes.

PubMed

Lin, Xiaoyang; Zhao, Wei; Zhou, Wenbin; Liu, Peng; Luo, Shu; Wei, Haoming; Yang, Guangzhi; Yang, Junhe; Cui, Jie; Yu, Richeng; Zhang, Lina; Wang, Jiaping; Li, Qunqing; Zhou, Weiya; Zhao, Weisheng; Fan, Shoushan; Jiang, Kaili

2017-02-28

Exploiting the superior properties of nanomaterials at macroscopic scale is a key issue of nanoscience. Different from the integration strategy, "additive synthesis" of macroscopic structures from nanomaterial templates may be a promising choice. In this paper, we report the epitaxial growth of aligned, continuous, and catalyst-free carbon nanofiber thin films from carbon nanotube films. The fabrication process includes thickening of continuous carbon nanotube films by gas-phase pyrolytic carbon deposition and further graphitization of the carbon layer by high-temperature treatment. As-fabricated nanofibers in the film have an "annual ring" cross-section, with a carbon nanotube core and a graphitic periphery, indicating the templated growth mechanism. The absence of a distinct interface between the carbon nanotube template and the graphitic periphery further implies the epitaxial growth mechanism of the fiber. The mechanically robust thin film with tunable fiber diameters from tens of nanometers to several micrometers possesses low density, high electrical conductivity, and high thermal conductivity. Further extension of this fabrication method to enhance carbon nanotube yarns is also demonstrated, resulting in yarns with ∼4-fold increased tensile strength and ∼10-fold increased Young's modulus. The aligned and continuous features of the films together with their outstanding physical and chemical properties would certainly promote the large-scale applications of carbon nanofibers.

Redox-dependent spatially resolved electrochemistry at graphene and graphite step edges.

PubMed

Güell, Aleix G; Cuharuc, Anatolii S; Kim, Yang-Rae; Zhang, Guohui; Tan, Sze-yin; Ebejer, Neil; Unwin, Patrick R

2015-04-28

The electrochemical (EC) behavior of mechanically exfoliated graphene and highly oriented pyrolytic graphite (HOPG) is studied at high spatial resolution in aqueous solutions using Ru(NH3)6(3+/2+) as a redox probe whose standard potential sits close to the intrinsic Fermi level of graphene and graphite. When scanning electrochemical cell microscopy (SECCM) data are coupled with that from complementary techniques (AFM, micro-Raman) applied to the same sample area, different time-dependent EC activity between the basal planes and step edges is revealed. In contrast, other redox couples (ferrocene derivatives) whose potential is further removed from the intrinsic Fermi level of graphene and graphite show uniform and high activity (close to diffusion-control). Macroscopic voltammetric measurements in different environments reveal that the time-dependent behavior after HOPG cleavage, peculiar to Ru(NH3)6(3+/2+), is not associated particularly with any surface contaminants but is reasonably attributed to the spontaneous delamination of the HOPG with time to create partially coupled graphene layers, further supported by conductive AFM measurements. This process has a major impact on the density of states of graphene and graphite edges, particularly at the intrinsic Fermi level to which Ru(NH3)6(3+/2+) is most sensitive. Through the use of an improved voltammetric mode of SECCM, we produce movies of potential-resolved and spatially resolved HOPG activity, revealing how enhanced activity at step edges is a subtle effect for Ru(NH3)6(3+/2+). These latter studies allow us to propose a microscopic model to interpret the EC response of graphene (basal plane and edges) and aged HOPG considering the nontrivial electronic band structure.

Analysis of the substrate influence on the ordering of epitaxial molecular layers: The special case of point-on-line coincidence

NASA Astrophysics Data System (ADS)

Mannsfeld, S. C.; Fritz, T.

2004-02-01

The physical structure of organic-inorganic heteroepitaxial thin films is usually governed by a fine balance between weak molecule-molecule interactions and a weakly laterally varying molecule-substrate interaction potential. Therefore, in order to investigate the energetics of such a layer system one has to consider large molecular domains. So far, layer potential calculations for large domains of organic thin films on crystalline substrates were difficult to perform concerning the computational effort which stems from the vast number of atoms which have to be included. Here, we present a technique which enables the calculation of the molecule-substrate interaction potential for large molecular domains by utilizing potential energy grid files. This technique allows the investigation of the substrate influence in systems prepared by organic molecular beam epitaxy (OMBE), like 3,4,9,10-perylenetetracarboxylicdianhydride on highly oriented pyrolytic graphite. For this system the so-called point-on-line coincidence was proposed, a growth mode which has been controversially discussed in literature. Furthermore, we are able to provide evidence for a general energetic advantage of such point-on-line coincident domain orientations over arbitrarily oriented domains which substantiates that energetically favorable lattice structures in OMBE systems are not restricted to commensurate unit cells or coincident super cells.

Marcus-Hush-Chidsey theory of electron transfer to and from species bound at a non-uniform electrode surface: Theory and experiment

NASA Astrophysics Data System (ADS)

Henstridge, Martin C.; Batchelor-McAuley, Christopher; Gusmão, Rui; Compton, Richard G.

2011-11-01

Two simple models of electrode surface inhomogeneity based on Marcus-Hush theory are considered; a distribution in formal potentials and a distribution in electron tunnelling distances. Cyclic voltammetry simulated using these models is compared with that simulated using Marcus-Hush theory for a flat, uniform and homogeneous electrode surface, with the two models of surface inhomogeneity yielding broadened peaks with decreased peak-currents. An edge-plane pyrolytic graphite electrode is covalently modified with ferrocene via 'click' chemistry and the resulting voltammetry compared with each of the three previously considered models. The distribution of formal potentials is seen to fit the experimental data most closely.

Atomic Oxygen Energy in Low Frequency Hyperthermal Plasma Ashers

NASA Technical Reports Server (NTRS)

Banks, Bruce A.; Miller, Sharon K R.; Kneubel, Christian A.

2014-01-01

Experimental and analytical analysis of the atomic oxygen erosion of pyrolytic graphite as well as Monte Carlo computational modeling of the erosion of Kapton H (DuPont, Wilmington, DE) polyimide was performed to determine the hyperthermal energy of low frequency (30 to 35 kHz) plasma ashers operating on air. It was concluded that hyperthermal energies in the range of 0.3 to 0.9 eV are produced in the low frequency air plasmas which results in texturing similar to that in low Earth orbit (LEO). Monte Carlo computational modeling also indicated that such low energy directed ions are fully capable of producing the experimentally observed textured surfaces in low frequency plasmas.

Influence of alkyl chain length and anion species on ionic liquid structure at the graphite interface as a function of applied potential

NASA Astrophysics Data System (ADS)

Li, Hua; Wood, Ross J.; Endres, Frank; Atkin, Rob

2014-07-01

Atomic force microscopy (AFM) force measurements elucidate the effect of cation alkyl chain length and the anion species on ionic liquid (IL) interfacial structure at highly ordered pyrolytic graphite (HOPG) surfaces as a function of potential. Three ILs are examined: 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([HMIM] FAP), 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([EMIM] FAP), and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM] TFSA). The step-wise force-distance profiles indicate the ILs adopt a multilayered morphology near the surface. When the surface is biased positively or negatively versus Pt quasireference electrode, both the number of steps, and the force required to rupture each step increase, indicating stronger interfacial structure. At all potentials, push-through forces for [HMIM] FAP are the highest, because the long alkyl chain results in strong cohesive interactions between cations, leading to well-formed layers that resist the AFM tip. The most layers are observed for [EMIM] FAP, because the C2 chains are relatively rigid and the dimensions of the cation and anion are similar, facilitating neat packing. [EMIM] TFSA has the smallest push-through forces and fewest layers, and thus the weakest interfacial structure. Surface-tip attractive forces are measured for all ILs. At the same potential, the attractions are the strongest for [EMIM] TFSA and the weakest for [HMIM] FAP because the interfacial layers are better formed for the longer alkyl chain cation. This means interfacial forces are stronger, which masks the weak attractive forces.

Atomic Oxygen Fluence Monitor

NASA Technical Reports Server (NTRS)

Banks, Bruce A.

2011-01-01

This innovation enables a means for actively measuring atomic oxygen fluence (accumulated atoms of atomic oxygen per area) that has impinged upon spacecraft surfaces. Telemetered data from the device provides spacecraft designers, researchers, and mission managers with real-time measurement of atomic oxygen fluence, which is useful for prediction of the durability of spacecraft materials and components. The innovation is a compact fluence measuring device that allows in-space measurement and transmittance of measured atomic oxygen fluence as a function of time based on atomic oxygen erosion yields (the erosion yield of a material is the volume of material that is oxidized per incident oxygen atom) of materials that have been measured in low Earth orbit. It has a linear electrical response to atomic oxygen fluence, and is capable of measuring high atomic oxygen fluences (up to >10(exp 22) atoms/sq cm), which are representative of multi-year low-Earth orbital missions (such as the International Space Station). The durability or remaining structural lifetime of solar arrays that consist of polymer blankets on which the solar cells are attached can be predicted if one knows the atomic oxygen fluence that the solar array blanket has been exposed to. In addition, numerous organizations that launch space experiments into low-Earth orbit want to know the accumulated atomic oxygen fluence that their materials or components have been exposed to. The device is based on the erosion yield of pyrolytic graphite. It uses two 12deg inclined wedges of graphite that are over a grit-blasted fused silica window covering a photodiode. As the wedges erode, a greater area of solar illumination reaches the photodiode. A reference photodiode is also used that receives unobstructed solar illumination and is oriented in the same direction as the pyrolytic graphite covered photodiode. The short-circuit current from the photodiodes is measured and either sent to an onboard data logger, or transmitted to a receiving station on Earth. By comparison of the short-circuit currents from the fluence-measuring photodiode and the reference photodiode, one can compute the accumulated atomic oxygen fluence arriving in the direction that the fluence monitor is pointing. The device produces a signal that is linear with atomic oxygen fluence using a material whose atomic oxygen erosion yield has been measured over a period of several years in low-Earth orbit.

One-Step Pyrolytic Synthesis of Multiwalled Carbon Nanotubes: The Role of Resupply of Carbon Species on the Quality Control.

PubMed

Rajavel, Krishnamoorthy; Saravanan, Padmanapan; Kumar, Ramasamy Thangavelu Rajendra

2018-05-01

An investigation on varying experimental parameters such as solution quantity (2.5, 5 and 7.5 mL) and reaction time (15, 30, 45 and 60 min) was carried out for the production of high-quality multiwalled carbon nanotubes (MWCNTs) in one step pyrolysis. Structural analysis revealed the uniform diameter distribution and the length of nanotubes in the range of 60-80 nm and 0.4-2 μm, respectively. Raman and X-ray diffraction analysis showed a remarkable reduction in defect density with increase in graphitization degree, upon increasing the solution volume and reaction time. MWCNTs prepared at higher solution quantity (7.5 mL) with higher reaction time (60 min) showed higher crystallinity (70% graphitization) and lower defect density (ID/IG: 0.56). The attainment in equilibrium of evaporation cum precipitation in formation of high quality nanotubes structure is evaluated. An effective resupplying of condensed precursors by re-evaporation leads for the achievement of low defect density nanotubes with higher product yield is achieved.

Metal dependent motif transition in a self-assembled monolayer of bipyridine derivatives via coordination: An STM study.

PubMed

Wang, Yi; Yuan, Qunhui; Xu, Hongbo; Zhu, Xuefeng; Gan, Wei

2016-07-21

Low-dimensional molecular motifs with diversity developed via the on-surface chemistry are attracting growing interest for their potential in advanced nanofabrication. In this work, scanning tunneling microscopy was employed to investigate the in situ and ex situ metal coordinations between 4,4'-ditetradecyl-2,2'-bipyridine (bpy) and Zn(ii) or Cu(ii) ions at a highly oriented pyrolytic graphite (HOPG)/1-phenyloctane interface under ambient conditions. The results demonstrate that the bpy adopts a flat-lying orientation with its substituted alkyl chains in a tail-to-tail arrangement in a bpy monolayer. For the in situ coordination, the bpy/Zn(ii) and bpy/Cu(ii) complexes are aligned in edge-on fashions, wherein the bpy stands vertically on the HOPG surface and interdigitates at the alkyl chains. In the two-dimensional arrays of ex situ coordinated complexes, metal dependent motifs have been observed with Zn(ii) and Cu(ii), wherein the bipyridine moieties are parallel to the graphite surface. These results suggest that the desired on-surface coordination architectures may be achieved by the intentional selection of the metal centers.

Sb-Te alloy nanostructures produced on a graphite surface by a simple annealing process

NASA Astrophysics Data System (ADS)

Kuwahara, Masashi; Uratsuji, Hideaki; Abe, Maho; Sone, Hayato; Hosaka, Sumio; Sakai, Joe; Uehara, Yoichi; Endo, Rie; Tsuruoka, Tohru

2015-08-01

We have produced Sb-Te alloy nanostructures from a thin Sb2Te3 layer deposited on a highly oriented pyrolytic graphite substrate using a simple rf-magnetron sputtering and annealing technique. The size, shape, and chemical composition of the structures were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy dispersive X-ray spectrometry (EDX), respectively. The shape of the nanostructures was found to depend on the annealing temperature; nanoparticles appear on the substrate by annealing at 200 °C, while nanoneedles are formed at higher temperatures. Chemical composition analysis has revealed that all the structures were in the composition of Sb:Te = 1:3, Te rich compared to the target composition Sb2Te3, probably due to the higher movability of Te atoms on the substrate compared with Sb. We also tried to observe the production process of nanostructures in situ using SEM. Unfortunately, this was not possible because of evaporation in vacuum, suggesting that the formation of nanostructures is highly sensitive to the ambient pressure.

Macrosegregation of GeSi Alloys Grown in a Static Magnetic Field

NASA Technical Reports Server (NTRS)

Ritter, T. M.; Volz, M. P.; Cobb, S. D.; Szofran, F. R.

1999-01-01

Axial and radial macrosegregation profiles have been determined for GeSi alloy crystals grown by the vertical Bridgman technique. An axial 5 Tesla magnetic field was applied to several samples during growth to decrease the melt velocities by means of the Lorentz force. Compositions were measured with either energy dispersive X-ray spectroscopy (EDS) on a scanning electron microscope (SEM) or by wavelength dispersive X-ray spectroscopy (WDS) on a microprobe. The crystals were processed in graphite, hot-pressed boron nitride (BN), and pyrolytic boron nitride (PBN) ampoules, which produced various solid-liquid interface shapes during solidification. Those samples grown in a graphite ampoule exhibited radial profiles consistent with a highly concave interface and axial profiles indicative of complete mixing in the melt. The samples grown in BN and PBN ampoules had less radial variation. Axial macrosegregation profiles of these samples fell between the predictions for a completely mixed melt and one where solute transport is dominated by diffusion. Possible explanations for the apparent insufficiency of the magnetic field to achieve diffusion controlled growth conditions are discussed.

The electrochemical performance of graphene modified electrodes: an analytical perspective.

PubMed

Brownson, Dale A C; Foster, Christopher W; Banks, Craig E

2012-04-21

We explore the use of graphene modified electrodes towards the electroanalytical sensing of various analytes, namely dopamine hydrochloride, uric acid, acetaminophen and p-benzoquinone via cyclic voltammetry. In line with literature methodologies and to investigate the full-implications of employing graphene in this electrochemical context, we modify electrode substrates that exhibit either fast or slow electron transfer kinetics (edge- or basal- plane pyrolytic graphite electrodes respectively) with well characterised commercially available graphene that has not been chemically treated, is free from surfactants and as a result of its fabrication has an extremely low oxygen content, allowing the true electroanalytical applicability of graphene to be properly de-convoluted and determined. In comparison to the unmodified underlying electrode substrates (constructed from graphite), we find that graphene exhibits a reduced analytical performance in terms of sensitivity, linearity and observed detection limits towards each of the various analytes studied within. Owing to graphene's structural composition, low proportion of edge plane sites and consequent slow heterogeneous electron transfer rates, there appears to be no advantages, for the analytes studied here, of employing graphene in this electroanalytical context.

Ultra-facile fabrication of phosphorus doped egg-like hierarchic porous carbon with superior supercapacitance performance by microwave irradiation combining with self-activation strategy

NASA Astrophysics Data System (ADS)

Zhang, Deyi; Han, Mei; Li, Yubing; He, Jingjing; Wang, Bing; Wang, Kunjie; Feng, Huixia

2017-12-01

Herein, we report an ultra-facile fabrication method for a phosphorus doped egg-like hierarchic porous carbon by microwave irradiation combining with self-activation strategy under air atmosphere. Comparing with the traditional pyrolytic carbonization method, the reported method exhibits incomparable merits, such as high energy efficiency, ultra-fast and inert atmosphere protection absent fabrication process. Similar morphology and graphitization degree with the sample fabricated by the traditional pyrolytic carbonization method under inert atmosphere protection for 2 h can be easily achieved by the reported microwave irradiation method just for 3 min under ambient atmosphere. The samples fabricated by the reported method display a unique phosphorus doped egg-like hierarchic porous structure, high specific surface area (1642 m2 g-1) and large pore volume (2.04 cm3 g-1). Specific capacitance of the samples fabricated by the reported method reaches up to 209 F g-1, and over 96.2% of initial capacitance remains as current density increasing from 0.5 to 20 A g-1, indicating the superior capacitance performance of the fabricated samples. The hierarchic porous structure, opened microporosity, additional pseudocapacitance, high electrolyte-accessible surface area and good conductivity make essential contribution to its superior capacitance performance.

Nucleation, aggregative growth and detachment of metal nanoparticles during electrodeposition at electrode surfaces.

PubMed

Lai, Stanley C S; Lazenby, Robert A; Kirkman, Paul M; Unwin, Patrick R

2015-02-01

The nucleation and growth of metal nanoparticles (NPs) on surfaces is of considerable interest with regard to creating functional interfaces with myriad applications. Yet, key features of these processes remain elusive and are undergoing revision. Here, the mechanism of the electrodeposition of silver on basal plane highly oriented pyrolytic graphite (HOPG) is investigated as a model system at a wide range of length scales, spanning electrochemical measurements from the macroscale to the nanoscale using scanning electrochemical cell microscopy (SECCM), a pipette-based approach. The macroscale measurements show that the nucleation process cannot be modelled as either truly instantaneous or progressive, and that step edge sites of HOPG do not play a dominant role in nucleation events compared to the HOPG basal plane, as has been widely proposed. Moreover, nucleation numbers extracted from electrochemical analysis do not match those determined by atomic force microscopy (AFM). The high time and spatial resolution of the nanoscale pipette set-up reveals individual nucleation and growth events at the graphite basal surface that are resolved and analysed in detail. Based on these results, corroborated with complementary microscopy measurements, we propose that a nucleation-aggregative growth-detachment mechanism is an important feature of the electrodeposition of silver NPs on HOPG. These findings have major implications for NP electrodeposition and for understanding electrochemical processes at graphitic materials generally.

Performance and Vibration of 30 cm Pyrolytic Ion Thruster Optics

NASA Technical Reports Server (NTRS)

Haag, Thomas; Soulas, George C.

2004-01-01

Carbon has a sputter erosion rate about an order of magnitude less than that of molybdenum, over the voltages typically used in ion thruster applications. To explore its design potential, 30 cm pyrolytic carbon ion thruster optics have been fabricated geometrically similar to the molybdenum ion optics used on NSTAR. They were then installed on an NSTAR Engineering Model thruster, and experimentally evaluated over much of the original operating envelope. Ion beam currents ranged from 0.51 to 1.76 Angstroms, at total voltages up to 1280 V. The perveance, electron back-streaming limit, and screen-grid transparency were plotted for these operating points, and compared with previous data obtained with molybdenum. While thruster performance with pyrolytic carbon was quite similar to that with molybdenum, behavior variations can reasonably be explained by slight geometric differences. Following all performance measurements, the pyrolytic carbon ion optics assembly was subjected to an abbreviated vibration test. The thruster endured 9.2 g(sub rms) of random vibration along the thrust axis, similar to DS 1 acceptance levels. Despite significant grid clashing, there was no observable damage to the ion optics assembly.

High viscosity environments: an unexpected route to obtain true atomic resolution with atomic force microscopy.

PubMed

Weber, Stefan A L; Kilpatrick, Jason I; Brosnan, Timothy M; Jarvis, Suzanne P; Rodriguez, Brian J

2014-05-02

Atomic force microscopy (AFM) is widely used in liquid environments, where true atomic resolution at the solid-liquid interface can now be routinely achieved. It is generally expected that AFM operation in more viscous environments results in an increased noise contribution from the thermal motion of the cantilever, thereby reducing the signal-to-noise ratio (SNR). Thus, viscous fluids such as ionic and organic liquids have been generally avoided for high-resolution AFM studies despite their relevance to, e.g. energy applications. Here, we investigate the thermal noise limitations of dynamic AFM operation in both low and high viscosity environments theoretically, deriving expressions for the amplitude, phase and frequency noise resulting from the thermal motion of the cantilever, thereby defining the performance limits of amplitude modulation, phase modulation and frequency modulation AFM. We show that the assumption of a reduced SNR in viscous environments is not inherent to the technique and demonstrate that SNR values comparable to ultra-high vacuum systems can be obtained in high viscosity environments under certain conditions. Finally, we have obtained true atomic resolution images of highly ordered pyrolytic graphite and mica surfaces, thus revealing the potential of high-resolution imaging in high viscosity environments.

Development of Passive Fuel Cell Thermal Management Technology

NASA Technical Reports Server (NTRS)

Burke, Kenneth A.; Jakupca, Ian; Colozza, Anthony

2011-01-01

The NASA Glenn Research Center is developing advanced passive thermal management technology to reduce the mass and improve the reliability of space fuel cell systems for the NASA exploration program. The passive thermal management system relies on heat conduction within the cooling plate to move the heat from the central portion of the cell stack out to the edges of the fuel cell stack rather than using a pumped loop cooling system to convectively remove the heat. Using the passive approach eliminates the need for a coolant pump and other cooling loop components which reduces fuel cell system mass and improves overall system reliability. Previous analysis had identified that low density, ultra-high thermal conductivity materials would be needed for the cooling plates in order to achieve the desired reductions in mass and the highly uniform thermal heat sink for each cell within a fuel cell stack. A pyrolytic graphite material was identified and fabricated into a thin plate using different methods. Also a development project with Thermacore, Inc. resulted in a planar heat pipe. Thermal conductivity tests were done using these materials. The results indicated that lightweight passive fuel cell cooling is feasible.

Field-assisted nanopatterning of metals, metal oxides and metal salts

NASA Astrophysics Data System (ADS)

Liu, Jun-Fu; Miller, Glen P.

2009-02-01

The tip-based nanofabrication method called field-assisted nanopatterning or FAN has now been extended to the transfer of metals, metal oxides and metal salts onto various receiving substrates including highly ordered pyrolytic graphite, passivated gold and indium-tin oxide. Standard atomic force microscope tips were first dip-coated using suspensions of inorganic compounds in solvent. The films prepared in this manner were non-uniform and contained inorganic nanoparticles. Tip-based nanopatterning on chosen substrates was conducted under high electric field conditions. The same tip was used for both nanofabrication and imaging. Arbitrary patterns were formed with dimensions that ranged from tens of microns to sub-20 nm and were controlled by tuning the tip bias during fabrication. Most tip-based nanopatterning techniques are limited in terms of the type of species that can be deposited and the type of substrates onto which the deposition occurs. With the successful deposition of inorganic species reported here, FAN is demonstrated to be a truly versatile tip-based nanofabrication technique that is useful for the deposition of a wide variety of both organic and inorganic species including small molecules, large molecules and polymers.

High viscosity environments: an unexpected route to obtain true atomic resolution with atomic force microscopy

NASA Astrophysics Data System (ADS)

Weber, Stefan A. L.; Kilpatrick, Jason I.; Brosnan, Timothy M.; Jarvis, Suzanne P.; Rodriguez, Brian J.

2014-05-01

Atomic force microscopy (AFM) is widely used in liquid environments, where true atomic resolution at the solid-liquid interface can now be routinely achieved. It is generally expected that AFM operation in more viscous environments results in an increased noise contribution from the thermal motion of the cantilever, thereby reducing the signal-to-noise ratio (SNR). Thus, viscous fluids such as ionic and organic liquids have been generally avoided for high-resolution AFM studies despite their relevance to, e.g. energy applications. Here, we investigate the thermal noise limitations of dynamic AFM operation in both low and high viscosity environments theoretically, deriving expressions for the amplitude, phase and frequency noise resulting from the thermal motion of the cantilever, thereby defining the performance limits of amplitude modulation, phase modulation and frequency modulation AFM. We show that the assumption of a reduced SNR in viscous environments is not inherent to the technique and demonstrate that SNR values comparable to ultra-high vacuum systems can be obtained in high viscosity environments under certain conditions. Finally, we have obtained true atomic resolution images of highly ordered pyrolytic graphite and mica surfaces, thus revealing the potential of high-resolution imaging in high viscosity environments.

Pectin-Lipid Self-Assembly: Influence on the Formation of Polyhydroxy Fatty Acids Nanoparticles

PubMed Central

Guzman-Puyol, Susana; Benítez, José Jesús; Domínguez, Eva; Bayer, Ilker Sefik; Cingolani, Roberto; Athanassiou, Athanassia; Heredia, Antonio; Heredia-Guerrero, José Alejandro

2015-01-01

Nanoparticles, named cutinsomes, have been prepared from aleuritic (9,10,16-trihidroxipalmitic) acid and tomato fruit cutin monomers (a mixture of mainly 9(10),16-dihydroxypalmitic acid (85%, w/w) and 16-hydroxyhexadecanoic acid (7.5%, w/w)) with pectin in aqueous solution. The process of formation of the nanoparticles of aleuritic acid plus pectin has been monitored by UV-Vis spectrophotometry, while their chemical and morphological characterization was analyzed by ATR-FTIR, TEM, and non-contact AFM. The structure of these nanoparticles can be described as a lipid core with a pectin shell. Pectin facilitated the formation of nanoparticles, by inducing their aggregation in branched chains and favoring the condensation between lipid monomers. Also, pectin determined the self-assembly of cutinsomes on highly ordered pyrolytic graphite (HOPG) surfaces, causing their opening and forming interconnected structures. In the case of cutin monomers, the nanoparticles are fused, and the condensation of the hydroxy fatty acids is strongly affected by the presence of the polysaccharide. The interaction of pectin with polyhydroxylated fatty acids could be related to an initial step in the formation of the plant biopolyester cutin. PMID:25915490

Nucleation and growth kinetics for intercalated islands during deposition on layered materials with isolated pointlike surface defects

DOE PAGES

Han, Yong; Lii-Rosales, A.; Zhou, Y.; ...

2017-10-13

Theory and stochastic lattice-gas modeling is developed for the formation of intercalated metal islands in the gallery between the top layer and the underlying layer at the surface of layered materials. Our model for this process involves deposition of atoms, some fraction of which then enter the gallery through well-separated pointlike defects in the top layer. Subsequently, these atoms diffuse within the subsurface gallery leading to nucleation and growth of intercalated islands nearby the defect point source. For the case of a single point defect, continuum diffusion equation analysis provides insight into the nucleation kinetics. However, complementary tailored lattice-gas modelingmore » produces a more comprehensive and quantitative characterization. We analyze the large spread in nucleation times and positions relative to the defect for the first nucleated island. We also consider the formation of subsequent islands and the evolution of island growth shapes. The shapes reflect in part our natural adoption of a hexagonal close-packed island structure. As a result, motivation and support for the model is provided by scanning tunneling microscopy observations of the formation of intercalated metal islands in highly-ordered pyrolytic graphite at higher temperatures.« less

P(VDF/TrFE) morphologies and crystalline lamellae orientations dependence on substrates characterized by scanning probe microscopy

NASA Astrophysics Data System (ADS)

Lakbita, Imane; El-Hami, Khalil

2018-02-01

Ultra-thin films of the polyvinylidene fluoride and trifluoroethylene (P(VDF/TrFE)) copolymer were elaborated on various different substrates by the spin coating method. The purpose of this paper is to study the P(VDF/TrFE) morphologies and crystalline lamellae orientation dependence on substrates. We chose the potassium chloride (KCl), Sodium Chloride (NaCl) and Potassium Bromide (KBr) with the [110] direction and the highly ordered pyrolytic graphite (HOPG) substrates because they present different crystallographic structures. The atomic force microscopy is used for imaging P(VDF/TrFE) morphologies with nanometer resolution and determining the surface roughness. The analysis of the AFM topography images revealed that the P(VDF/TrFE) film has, almost, the same texture on KCl, NaCl or on KBr substrates and their crystalline lamellae had grown in two preferred orientations. Unlike the HOPG substrate, their crystalline lamellae were entangled, randomly oriented and positioned adjacent to each other. The growth texture of the P(VDF/TrFE) copolymer showed experimentally a strong dependence on substrate types. Since the P(VDF/TrFE) is ferroelectric, piezoelectric and pyroelectric, this finding may lead to potential applications.

Deducing 2D crystal structure at the liquid/solid interface with atomic resolution: a combined STM and SFG study.

PubMed

McClelland, Arthur A; Ahn, Seokhoon; Matzger, Adam J; Chen, Zhan

2009-11-17

Sum frequency generation vibrational spectroscopy (SFG) has been applied to study two-dimensional (2D) crystals formed by an isophthalic acid diester on the surface of highly oriented pyrolytic graphite, providing complementary measurements to scanning tunneling microscopy (STM) and computational modeling. SFG results indicate that both aromatic and C=O groups in the 2D crystal tilt from the surface. This study demonstrates that a combination of SFG and STM techniques can be used to gain a more complete picture of 2D crystal structure, and it is necessary to consider solvent-2D crystal interactions and dynamics in the computer models to achieve an accurate representation of interfacial structure.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoenig, M.; Elsen, Y.V.; Cauter, R.V.

The progressive degradation of the pyrolytic graphite surface of atomizers provides variable and misleading results of molybdenum peak-height measurements. The changes in the peak shapes produce no analytical problems during the lifetime of the atomizer (approx.300 firings) when integrated absorbance (A.s signals) is considered and the possible base-line drifts are controlled. This was demonstrated on plant samples mineralized by simple digestion with a mixture of HNO/sub 3/ and H/sub 2/O/sub 2/. The value of this method was assessed by comparison with a standard dry oxidation method and by molybdenum determination in National Bureau of Standards reference plant samples. The relativemore » standard deviations (n = 5) of the full analytical procedure do not exceed 7%. 13 references, 3 figures, 3 tables.« less

Chiral symmetry breaking during the self-assembly of monolayers from achiral purine molecules.

PubMed

Sowerby, S J; Heckl, W M; Petersen, G B

1996-11-01

Scanning tunneling microscopy was used to investigate the structure of the two-dimensional adsorbate formed by molecular self-assembly of the purine base, adenine, on the surfaces of the naturally occurring mineral molybdenite and the synthetic crystal highly oriented pyrolytic graphite. Although formed from adenine, which is achiral, the observed adsorbate surface structures were enantiomorphic on molybdenite. This phenomenon suggests a mechanism for the introduction of a localized chiral symmetry break by the spontaneous crystallization of these prebiotically available molecules on inorganic surfaces and may have some role in the origin of biomolecular optical asymmetry. The possibility that purine-pyrimidine arrays assembled on naturally occurring mineral surfaces might act as possible templates for biomolecular assembly is discussed.

Nanoscale multiple gaseous layers on a hydrophobic surface.

PubMed

Zhang, Lijuan; Zhang, Xuehua; Fan, Chunhai; Zhang, Yi; Hu, Jun

2009-08-18

The nanoscale gas state at the interfaces of liquids (water, acid, and salt solutions) and highly oriented pyrolytic graphite (HOPG) was investigated via tapping-mode atomic force microscopy (AFM). For the first time, we report that the interfacial gases could form bilayers and trilayers, i.e., on the top of a flat gas layer, there are one or two more gas layers. The formation of these gas layers could be induced by a local supersaturation of gases, which can be achieved by (1) temperature difference between the liquids and the HOPG substrates or (2) exchange ethanol with water. Furthermore, we found that the gas layers were less stable than spherical bubbles. They could transform to bubbles with time or under the perturbation of the AFM tip.

A two-dimensional polymer synthesized at the air/water interface.

PubMed

Schlüter, A Dieter; Müller, Vivian; Hinaut, Antoine; Moradi, Mina; Baljozovic, Milos; Jung, Thomas; Shahgaldian, Patrick; Möhwald, Helmuth; Hofer, Gregor; Kröger, Martin; King, Benjamin; Meyer, Ernst; Glatzel, Thilo

2018-06-11

A trifunctional, partially fluorinated anthracene-substituted triptycene monomer is spread at the air/water interface into a monolayer, which is transformed into a long-range ordered 2D polymer by irradiation with a standard ultraviolet lamp using 365 nm light. The polymer is analyzed by Brewster angle microscopy directly at this interface and by scanning tunneling microscopy measurements and non-contact atomic force microscopy (nc-AFM), both after transfer from below the interface onto highly oriented pyrolytic graphite and then into ultra-high vacuum. Both methods confirm a network structure, the lattice parameters of which are virtually identical to a structural model network based on X-ray diffractometry of a closely related 2D polymer unequivocally established in a single crystal. The nc-AFM images are obtained with unprecedentedly high resolution and prove long-range order over areas of at least 300 × 300 nm2. As required for a 2D polymer, the pore sizes are monodisperse, except for the regions, where the network is somewhat stretched because it spans over protrusions. Together with a previous report on the nature of the cross-links in this network, the structural information provided here leaves no doubt that a 2D polymer has been synthesized under ambient conditions at an air/water interface. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Study of Copper and Purine-Copper Complexes on Modified Carbon Electrodes by Cyclic and Elimination Voltammetry

PubMed Central

Trnkova, Libuse; Zerzankova, Lenka; Dycka, Filip; Mikelova, Radka; Jelen, Frantisek

2008-01-01

Using a paraffin impregnated graphite electrode (PIGE) and mercury-modified pyrolytic graphite electrode with basal orientation (Hg-PGEb) copper(II) and Cu(II)-DNA purine base solutions have been studied by cyclic (CV) and linear sweep voltammetry (LSV) in connection with elimination voltammetry with linear scan (EVLS). In chloride and bromide solutions (pH 6), the redox process of Cu(II) proceeded on PIGE with two cathodic and two anodic potentially separated signals. According to the elimination function E4, the first cathodic peak corresponds to the reduction Cu(II) + e- → Cu(I) with the possibility of fast disproportionation 2Cu(I) → Cu(II)+ Cu(0). The E4 of the second cathodic peak signalized an electrode process controlled by a surface reaction. The electrode system of Cu(II) on Hg-PGEb in borate buffer (pH 9.2) was characterized by one cathodic and one anodic peak. Anodic stripping voltammetry (ASV) on PIGE and cathodic stripping voltammetry (CSV) on Hg-PGEb were carried out at potentials where the reduction of copper ions took place and Cu(I)-purine complexes were formed. By using ASV and CSV in combination with EVLS, the sensitivity of Cu(I)-purine complex detection was enhanced relative to either ASV or CSV alone, resulting in higher peak currents of more than one order of magnitude. The statistical treatment of CE data was used to determine the reproducibility of measurements. Our results show that EVLS in connection with the stripping procedure is useful for both qualitative and quantitative microanalysis of purine derivatives and can also reveal details of studied electrode processes. PMID:27879715

Ultralight anisotropic foams from layered aligned carbon nanotube sheets

NASA Astrophysics Data System (ADS)

Faraji, Shaghayegh; L. Stano, Kelly; Yildiz, Ozkan; Li, Ang; Zhu, Yuntian; Bradford, Philip D.

2015-10-01

In this work, we present large scale, ultralight aligned carbon nanotube (CNT) structures which have densities an order of magnitude lower than CNT arrays, have tunable properties and exhibit resiliency after compression. By stacking aligned sheets of carbon nanotubes and then infiltrating with a pyrolytic carbon (PyC), resilient foam-like materials were produced that exhibited complete recovery from 90% compressive strain. With density as low as 3.8 mg cm-3, the foam structure is over 500 times less dense than bulk graphite. Microscopy revealed that PyC coated the junctions among CNTs, and also increased CNT surface roughness. These changes in the morphology explain the transition from inelastic behavior to foam-like recovery of the layered CNT sheet structure. Mechanical and thermal properties of the foams were tuned for different applications through variation of PyC deposition duration while dynamic mechanical analysis showed no change in mechanical properties over a large temperature range. Observation of a large and linear electrical resistance change during compression of the aligned CNT/carbon (ACNT/C) foams makes strain/pressure sensors a relevant application. The foams have high oil absorption capacities, up to 275 times their own weight, which suggests they may be useful in water treatment and oil spill cleanup. Finally, the ACNT/C foam's high porosity, surface area and stability allow for demonstration of the foams as catalyst support structures.In this work, we present large scale, ultralight aligned carbon nanotube (CNT) structures which have densities an order of magnitude lower than CNT arrays, have tunable properties and exhibit resiliency after compression. By stacking aligned sheets of carbon nanotubes and then infiltrating with a pyrolytic carbon (PyC), resilient foam-like materials were produced that exhibited complete recovery from 90% compressive strain. With density as low as 3.8 mg cm-3, the foam structure is over 500 times less dense than bulk graphite. Microscopy revealed that PyC coated the junctions among CNTs, and also increased CNT surface roughness. These changes in the morphology explain the transition from inelastic behavior to foam-like recovery of the layered CNT sheet structure. Mechanical and thermal properties of the foams were tuned for different applications through variation of PyC deposition duration while dynamic mechanical analysis showed no change in mechanical properties over a large temperature range. Observation of a large and linear electrical resistance change during compression of the aligned CNT/carbon (ACNT/C) foams makes strain/pressure sensors a relevant application. The foams have high oil absorption capacities, up to 275 times their own weight, which suggests they may be useful in water treatment and oil spill cleanup. Finally, the ACNT/C foam's high porosity, surface area and stability allow for demonstration of the foams as catalyst support structures. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr03899e

The effects of temperature and catalysts on the pyrolysis of industrial wastes (herb residue).

PubMed

Wang, Pan; Zhan, Sihui; Yu, Hongbing; Xue, Xufang; Hong, Nan

2010-05-01

Pyrolysis of herb residue was investigated in a fixed-bed to determine the effects of pyrolysis temperature and catalysts (ZSM-5, Al-SBA-15 and alumina) on the products yields and the qualities of bio-oils. The results indicated that the maximum bio-oil yield of 34.26% was obtained at 450 degrees Celsius with 10 wt.% alumina catalyst loaded. The pyrolytic oils were examined by ultimate analysis and calorific values determination, and the results indicated that the presence of all catalysts decreased the oxygen content of bio-oils and increased the calorific values. The order of the catalytic effect for upgrading the pyrolytic oil was Al(2)O(3)>Al-SBA-15>ZSM-5. The bio-oil with the lowest oxygen content (26.71%) and the highest calorific value (25.94 MJ kg(-1)) was obtained with 20 wt.% alumina catalyst loaded. Furthermore, the gas chromatography/mass spectrometry (GC/MS) was used in order to investigate the components of obtained pyrolytic oils. It was found that the alumina catalyst could clearly enhance the formation of aliphatics and aromatics. Crown Copyright 2009. Published by Elsevier Ltd. All rights reserved.

Vaporization thermodynamics of K2S and K2SO3

NASA Technical Reports Server (NTRS)

Bennet, J. E.

1982-01-01

The vaporization reactions, vapor pressures, and thermodynamics of potassium sulfide and potassium sulfite were studied for purposes of providing fundamental data for the seed cycle in magnetohydrodynamic electric power generation. Rate of effusion studies, supported by tube furnace experiments, X-ray powder diffraction, mass spectrometry and appropriate chemical analyses and tests, revealed that potassium sulfite disproportionates at high temperatures to form potassium sulfide and potassium sulfate. Potassium sulfide was observed to vaporize incongruently, the initial vapors beng predominantly potassium atoms, with minor species being S2 and various K-S molecules. The ratio of K/S2 in the vapor is very large initially and decreases steadily with prolonged heating. Several materials were evaluated for purposes of containing K2S/K2SO3 at temperatures or = 800 C: Pt, Mo, W, quartz, machinable glass, BN, high density graphite, pyrolytic coated graphite, and alumina. Of these, only alumina was observed to be chemically inert to both K2S but reacted with K2SO3. The other materials were not suitable for either substance. Thermodynamic calculations based on measured vapor pressures and approximate free energy functions are described. Results from isothermal total mass loss experiments and from thermogravimetric experiments are also included.

Comparison of VVV Auger electron spectra from single and multilayer graphene and graphite.

NASA Astrophysics Data System (ADS)

Chirayath, V. A.; Callewaert, V.; Fairchild, A. J.; Chrysler, M. D.; Gladen, R. W.; Imam, S. K.; Koymen, A. R.; Saniz, R.; Barbiellini, B.; Rajeshwar, K.; Partoens, B.; Weiss, A. H.

A direct observation of a low energy electron peak in the positron annihilation induced Auger electron spectra (PAES) from a single layer of graphene was made recently. A low energy positron beam (<1.25 eV) was used to deposit the positron on single layer graphene on a Cu substrate and the low energy peak was designated as VVV following the X-ray notation. The PAES signal is almost entirely from the top graphene layer due to the trapping of positrons in the image potential well on the surface of graphene. We utilize this monolayer sensitivity of PAES to compare the shape of the VVV Auger peak from the single layer graphene to the shapes of the VVV Auger peak obtained from multilayer graphene on Cu and from highly oriented pyrolytic graphite (HOPG). The VVV Auger peak from multilayer graphene on Cu and HOPG shows a systematic shift towards lower energies relative to the VVV Auger peak from the single layer graphene. The influence of the hole-hole interaction in distorting and shifting the VVV Auger spectra are discussed in relation to this observed shift. NSF Grant No. DMR 1508719 and DMR 1338130.

Facilitation of NADH Electrooxidation at Treated Carbon Nanotubes

PubMed Central

Wooten, Marilyn; Gorski, Waldemar

2010-01-01

The relationship between the state of the surface of carbon nanotubes (CNT) and their electrochemical activity was investigated using the enzyme cofactor dihydronicotinamide adenine dinucleotide (NADH) as a redox probe. The boiling of CNT in water, while nondestructive, activated them toward the oxidation of NADH as indicated by a shift in the anodic peak potential of NADH (ENADH) from 0.4 to 0.0 V. The shift in ENADH was due to the redox mediation of NADH oxidation by traces of quinone species that were formed on the surface of treated CNT. The harsher treatment that comprised of microwaving of CNT in concentrated nitric acid had a similar effect on the ENADH and, additionally, it increased the anodic peak current of NADH. The latter correlated with the formation of defects on the surface of acid-microwaved CNT as indicated by their Raman spectra. The increase in current was discussed considering a role of surface mediators on the buckled graphene sheets of acid-microwaved CNT. The other carbon allotropes including the edge plane pyrolytic graphite, graphite powder, and glassy carbon did not display a comparable activation toward the oxidation of NADH. PMID:20088562

Development of a Scanning Microscale Fast Neutron Irradiation Platform for Examining the Correlation Between Local Neutron Damage and Graphite Microstructure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pinhero, Patrick; Windes, William

2015-03-10

The fast particle radiation damage effect of graphite, a main material in current and future nuclear reactors, has significant influence on the utilization of this material in fission and fusion plants. Atoms on graphite crystals can be easily replaced or dislocated by fast protons and result in interstitials and vacancies. The currently accepted model indicates that after most of the interstitials recombine with vacancies, surviving interstitials form clusters and furthermore gather to create loops with each other between layers. Meanwhile, surviving vacancies and interstitials form dislocation loops on the layers. The growth of these inserted layers cause the dimensional increase,more » i.e. swelling, of graphite. Interstitial and vacancy dislocation loops have been reported and they can easily been observed by electron microscope. However, observation of the intermediate atom clusters becomes is paramount in helping prove this model. We utilize fast protons generated from the University of Missouri Research Reactor (MURR) cyclotron to irradiate highly- oriented pyrolytic graphite (HOPG) as target for this research. Post-irradiation examination (PIE) of dosed targets with high-resolution transmission electron microscopy (HRTEM) has permit observation and analysis of clusters and dislocation loops to support the proposed theory. Another part of the research is to validate M.I. Heggie’s Ruck and Tuck model, which introduced graphite layers may fold under fast particle irradiation. Again, we employed microscopy to image irradiated specimens to determine how the extent of Ruck and Tuck by calculating the number of folds as a function of dose. Our most significant accomplishment is the invention of a novel class of high-intensity pure beta-emitters for long-term lightweight batteries. We have filed four invention disclosure records based on the research conducted in this project. These batteries are lightweight because they consist of carbon and tritium and can be fabricated to conform to many geometric shapes. In addition, we have published eight peer-reviewed American Nuclear Society (ANS) transactions, and presented our findings at ANS National Meetings, and several universities.« less

NANOWIRE CATHODE MATERIAL FOR LITHIUM-ION BATTERIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

John Olson, PhD

2004-07-21

This project involved the synthesis of nanowire ã-MnO2 and characterization as cathode material for high-power lithium-ion batteries for EV and HEV applications. The nanowire synthesis involved the edge site decoration nanowire synthesis developed by Dr. Reginald Penner at UC Irvine (a key collaborator in this project). Figure 1 is an SEM image showing ã-MnO2 nanowires electrodeposited on highly oriented pyrolytic graphite (HOPG) electrodes. This technique is unique to other nanowire template synthesis techniques in that it produces long (>500 um) nanowires which could reduce or eliminate the need for conductive additives due to intertwining of fibers. Nanowire cathode for lithium-ionmore » batteries with surface areas 100 times greater than conventional materials can enable higher power batteries for electric vehicles (EVs) and hybrid electric vehicles (HEVs). The synthesis of the ã-MnO2 nanowires was successfully achieved. However, it was not found possible to co-intercalate lithium directly in the nanowire synthesis. Based on input from proposal reviewers, the scope of the project was altered to attempt the conversion into spinel LiMn2O4 nanowire cathode material by solid state reaction of the ã-MnO2 nanowires with LiNO3 at elevated temperatures. Attempts to perform the conversion on the graphite template were unsuccessful due to degradation of the graphite apparently caused by oxidative attack by LiNO3. Emphasis then shifted to quantitative removal of the nanowires from the graphite, followed by the solid state reaction. Attempts to quantitatively remove the nanowires by several techniques were unsatisfactory due to co-removal of excess graphite or poor harvesting of nanowires. Intercalation of lithium into ã-MnO2 electrodeposited onto graphite was demonstrated, showing a partial demonstration of the ã-MnO2 material as a lithium-ion battery cathode material. Assuming the issues of nanowires removal can be solved, the technique does offer potential for creating high-power lithium-ion battery cathode needed for advanced EV and HEVs. Several technical advancements will still be required to meet this goal, and are likely topics for future SBIR feasibility studies.« less

Reexamination of Basal Plane Thermal Conductivity of Suspended Graphene Samples Measured by Electro-Thermal Micro-Bridge Methods

DOE PAGES

Jo, Insun; Pettes, Michael; Lindsay, Lucas R.; ...

2015-05-18

Thermal transport in suspended graphene samples has been measured in prior works and this work with the use of a suspended electro-thermal micro-bridge method. These measurement results are analyzed here to evaluate and eliminate the errors caused by the extrinsic thermal contact resistance. It is noted that the thermal resistance measured in a recent work increases linearly with the suspended length of the single-layer graphene samples synthesized by chemical vapor deposition (CVD), and that such a feature does not reveal the failure of Fourier s law despite the increase in the apparent thermal conductivity with length. The re-analyzed thermal conductivitymore » of a single-layer CVD graphene sample reaches about ( 1680 180 )Wm-1K-1 at room temperature, which is close to the highest value reported for highly oriented pyrolytic graphite. In comparison, the thermal conductivity values measured for two suspended exfoliated bi-layer graphene samples are about ( 880 60 ) and ( 730 60 ) Wm-1K-1 at room temperature, and approach that of the natural graphite source above room temperature. However, the low-temperature thermal conductivities of these suspended graphene samples are still considerably lower than the graphite values, with the peak thermal conductivities shifted to much higher temperatures. Analysis of the thermal conductivity data reveals that the low temperature behavior is dominated by phonon scattering by polymer residue instead of by the lateral boundary.« less

Effect of molecular mass on supramolecular organisation of poly(4,4''-dioctyl-2,2':5',2''-terthiophene).

PubMed

Jaroch, Tomasz; Knor, Marek; Nowakowski, Robert; Zagórska, Małgorzata; Proń, Adam

2008-10-28

The effect of the chain length on the type and extent of the 2D supramolecular organization in poly(4,4''-dioctyl-2,2':5',2''-terthiophene) (PDOTT) monomolecular layers deposited on highly oriented pyrolytic graphite (HOPG) is studied by scanning tunneling microscopy (STM) and analyzed in terms of molecular modeling. The strictly monodispersed fractions of increasing molecular mass used in this study were obtained by chromatographic fractionation of the crude product of 4,4''-dioctyl-2,2':5',2''-terthiophene oxidative polymerization. STM investigations of PDOTT layers, deposited on HOPG from poly- and monodispersed fractions, show that polydispersity can be considered as a key factor seriously limiting supramolecular ordering. This is a consequence of significant differences in the type of supramolecular order observed for molecules of different chain length. It has been demonstrated that shorter molecules (consisting of 6 and 9 thiophene units) form well-defined two-dimensional islands, while the interactions between longer molecules (consisting of 12 and 15 thiophene units) become anisotropic. Consequently, for higher molecular mass fractions, the supramolecular organization is one-dimensional and consists of more or less separated rows of ordered macromolecules. In this case an increase of the chain length leads to amplification of the intermolecular interactions proceeding via interdigitation of the alkyl substituents of adjacent molecules. Polydispersed fractions show much less ordered organization because of the incompatibility of the supramolecular structures of molecules of different molecular masses. This finding is of crucial importance for the application of polythiophene derivatives in organic and molecular electronics since ordered supramolecular organization constitutes the condition sine qua non of good electrical transport properties.

Pyrolytic synthesis and characterization of N-doped carbon nanoflakes for electrochemical applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Savilov, S.V., E-mail: savilov@chem.msu.ru; N.S. Kurnakov Institute of General and Inorganic Chemistry Of Russian Academy of Sciences, Leninsky avenue, 31, Moscow 119991; Arkhipova, E.A.

2015-09-15

Highlights: • Carbon nanoflakes doped with nitrogen were produced by a pyrolytic technique. • Quarternary, pyrrolic and pyridinic types of nitrogen are confirmed by XPS. • Nitrogen content depends on precursor used and temperature processed. • Specific surface area values decrease with increasing of synthesis duration. • N-doped carbon nanoflakes may be suitable for electrochemical applications. - Abstract: Nitrogen doped carbon nanoflakes, which are very important for many electrochemical applications, were synthesized by pyrolysis of nitrogen containing organic compounds over metal oxide template. Acetonitrile, pyridine and butylamine, which are of different volatility were tested as N-containing precursors. Morphology, structure andmore » chemical composition of the as-synthesized materials were investigated by scanning electron microscopy (SEM), high resolution transmission electron microscopy (TEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). It was found that materials are highly defective and consist of a few malformed graphene layers. X-ray photoelectron spectra reflect the dominant graphitic and pyridinic N-bonding configuration. It was also noted that specific surface area depends on the duration and temperature of the reaction. Increase in duration and temperature led to decrease of the specific surface area from 1000 to 160 m{sup 2}/g, 1170 to 210 m{sup 2}/g and 1180 to 480 m{sup 2}/g for acetonitrile, butylamine and pyridine precursors, respectively.« less

Atomic force microscope characterization of self-assembly behaviors of cyclo[8] pyrrole on solid substrates

NASA Astrophysics Data System (ADS)

Xu, Hai; Zhao, Siqi; Xiong, Xiang; Jiang, Jinzhi; Xu, Wei; Zhu, Daoben; Zhang, Yi; Liang, Wenjie; Cai, Jianfeng

2017-04-01

Cyclo [8] pyrrole (CP) is a porphyrin analogue containing eight α-conjugated pyrrole units which are arranged in a nearly coplanar conformation. The π-π interactions between CP molecules lead to regular aggregations through a solution casting process. Using tapping mode atomic force microscope (AFM), we investigated the morphology of self-assembled aggregates formed by deposition of different CP solutions on different substrates. We found that in the n-butanol solution, nanofibrous structures could be formed on the silicon or mica surface. Interestingly, on the highly oriented pyrolytic graphite (HOPG) surface, or silicon and mica surface with a toluene solution, only irregular spherical structures were identified. The difference in the nanomorphology may be attributed to distinct interactions between molecule-molecule, molecule-solvent and molecule-substrate.

Highly sensitive protein detection by biospecific AFM-based fishing with pulsed electrical stimulation.

PubMed

Pleshakova, Tatyana O; Malsagova, Kristina A; Kaysheva, Anna L; Kopylov, Arthur T; Tatur, Vadim Yu; Ziborov, Vadim S; Kanashenko, Sergey L; Galiullin, Rafael A; Ivanov, Yuri D

2017-08-01

We report here the highly sensitive detection of protein in solution at concentrations from 10 -15 to 10 -18 m using the combination of atomic force microscopy (AFM) and mass spectrometry. Biospecific detection of biotinylated bovine serum albumin was carried out by fishing out the protein onto the surface of AFM chips with immobilized avidin, which determined the specificity of the analysis. Electrical stimulation was applied to enhance the fishing efficiency. A high sensitivity of detection was achieved by application of nanosecond electric pulses to highly oriented pyrolytic graphite placed under the AFM chip. A peristaltic pump-based flow system, which is widely used in routine bioanalytical assays, was employed throughout the analysis. These results hold promise for the development of highly sensitive protein detection methods using nanosensor devices.

Femtosecond laser ablation of highly oriented pyrolytic graphite: a green route for large-scale production of porous graphene and graphene quantum dots

NASA Astrophysics Data System (ADS)

Russo, Paola; Hu, Anming; Compagnini, Giuseppe; Duley, Walter W.; Zhou, Norman Y.

2014-01-01

Porous graphene (PG) and graphene quantum dots (GQDs) are attracting attention due to their potential applications in photovoltaics, catalysis, and bio-related fields. We present a novel way for mass production of these promising materials. The femtosecond laser ablation of highly oriented pyrolytic graphite (HOPG) is employed for their synthesis. Porous graphene (PG) layers were found to float at the water-air interface, while graphene quantum dots (GQDs) were dispersed in the solution. The sheets consist of one to six stacked layers of spongy graphene, which form an irregular 3D porous structure that displays pores with an average size of 15-20 nm. Several characterization techniques have confirmed the porous nature of the collected layers. The analyses of the aqueous solution confirmed the presence of GQDs with dimensions of about 2-5 nm. It is found that the formation of both PG and GQDs depends on the fs-laser ablation energy. At laser fluences less than 12 J cm-2, no evidence of either PG or GQDs is detected. However, polyynes with six and eight carbon atoms per chain are found in the solution. For laser energies in the 20-30 J cm-2 range, these polyynes disappeared, while PG and GQDs were found at the water-air interface and in the solution, respectively. The origin of these materials can be explained based on the mechanisms for water breakdown and coal gasification. The absence of PG and GQDs, after the laser ablation of HOPG in liquid nitrogen, confirms the proposed mechanisms.Porous graphene (PG) and graphene quantum dots (GQDs) are attracting attention due to their potential applications in photovoltaics, catalysis, and bio-related fields. We present a novel way for mass production of these promising materials. The femtosecond laser ablation of highly oriented pyrolytic graphite (HOPG) is employed for their synthesis. Porous graphene (PG) layers were found to float at the water-air interface, while graphene quantum dots (GQDs) were dispersed in the solution. The sheets consist of one to six stacked layers of spongy graphene, which form an irregular 3D porous structure that displays pores with an average size of 15-20 nm. Several characterization techniques have confirmed the porous nature of the collected layers. The analyses of the aqueous solution confirmed the presence of GQDs with dimensions of about 2-5 nm. It is found that the formation of both PG and GQDs depends on the fs-laser ablation energy. At laser fluences less than 12 J cm-2, no evidence of either PG or GQDs is detected. However, polyynes with six and eight carbon atoms per chain are found in the solution. For laser energies in the 20-30 J cm-2 range, these polyynes disappeared, while PG and GQDs were found at the water-air interface and in the solution, respectively. The origin of these materials can be explained based on the mechanisms for water breakdown and coal gasification. The absence of PG and GQDs, after the laser ablation of HOPG in liquid nitrogen, confirms the proposed mechanisms. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr05572h

X-ray photoelectron spectroscopic and morphologic studies of Ru nanoparticles deposited onto highly oriented pyrolytic graphite

NASA Astrophysics Data System (ADS)

Bavand, R.; Yelon, A.; Sacher, E.

2015-11-01

Ruthenium nanoparticles (Ru NPs) function as effective catalysts in specific reactions, such as methanation and Fischer-Tropsch syntheses. It is our purpose to physicochemically characterize their surfaces, at which catalysis occurs, by surface-sensitive X-ray photoelectron spectroscopy (XPS), using the symmetric peak component anaylsis technique developed in our laboratory to reveal previously hidden components. Ru NPs were deposited by evaporation (0.25-1.5 nm nominal deposition range) onto highly oriented pyrolytic graphite (HOPG). In addition to their surfaces being characterized by XPS, an indication of morphology was obtained from transmission electron microscopy (TEM). Our use of symmetric peak component XPS analysis has revealed detailed information on a previously unidentified surface oxide initially formed, as well as on the valence electronic structure and its variation with NP size, information that is of potential importance in the use of these NPs in catalysis. Each of the several Ru core XPS spectra characterized (3d, 3p and 3s) was found to be composed of three symmetric components. Together with two metal oxide O1s components, these give evidence of a rather complex, previously unidentified oxide that is initially formed. The Ru valence band (4d and 5s) spectra clearly demonstrate a loss of metallicity, a simultaneous increase of the Kubo gap, and an abrupt transfer in valence electron density from the 4d to the 5s orbitals (known as electron spill-over), as the NP size decreases below 0.5 nm. TEM photomicrographs, as a function of deposition rate, show that, at a rate that gives insufficient time for the NP condensation energy to dissipate, the initially well-separated NPs are capable of diffusing laterally and aggregating. This indicates weak NP bonding to the HOPG substrate. Carbide is formed, at both high and low deposition rates, at Ru deposition thicknesses greater than 0.25 nm, its formation explained by Ru NPs reacting with residual hydrocarbon vapor, under the influence of the heat of condensation released on Ru deposition, and not by Ru reacting with the HOPG substrate.

Interfacial gas nanobubbles or oil nanodroplets?

PubMed

Wang, Xingya; Zhao, Binyu; Hu, Jun; Wang, Shuo; Tai, Renzhong; Gao, Xingyu; Zhang, Lijuan

2017-01-04

The existence of nanobubbles at a solid-liquid interface with high stability has been confirmed by myriad experimental studies, and their gaseous nature has also been extensively verified. However, nanodroplets of polydimethylsiloxane (PDMS) recently observed in the atomic force microscopy (AFM) measurement of nanobubbles plague the nanobubble community. It may easily lead to wrong interpretations of the AFM results and thus hinders further application of the already widely used AFM in nanobubble studies. Therefore, finding a direct experimental solution to distinguish nanobubbles from nanodroplets in AFM measurements is a matter of great urgency. Herein, we first developed an effective and reproducible method to produce PDMS nanodroplets at the highly ordered pyrolytic graphite (HOPG)/water interface. From their size, contact angle, and stiffness, the formed PDMS nanodroplets are not distinguishable from nanobubbles. However, the force curves on these two objects are strikingly different from each other, i.e., a peculiar plateau in both the approach and retraction curves was found on nanobubbles whereas they changed linearly between the jump-in and jump-off point on PDMS nanodroplets. Thus, the present study not only provided a simple and effective procedure to generate PDMS nanodroplets but also paved a simple practical and in situ way to discriminate nanobubbles from the PDMS nanodroplets by direct AFM force measurements.

The effect of thermal reduction on the photoluminescence and electronic structures of graphene oxides.

PubMed

Chuang, C-H; Wang, Y-F; Shao, Y-C; Yeh, Y-C; Wang, D-Y; Chen, C-W; Chiou, J W; Ray, Sekhar C; Pong, W F; Zhang, L; Zhu, J F; Guo, J H

2014-04-10

Electronic structures of graphene oxide (GO) and hydro-thermally reduced graphene oxides (rGOs) processed at low temperatures (120-180°C) were studied using X-ray absorption near-edge structure (XANES), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS). C K-edge XANES spectra of rGOs reveal that thermal reduction restores C = C sp(2) bonds and removes some of the oxygen and hydroxyl groups of GO, which initiates the evolution of carbonaceous species. The combination of C K-edge XANES and Kα XES spectra shows that the overlapping π and π* orbitals in rGOs and GO are similar to that of highly ordered pyrolytic graphite (HOPG), which has no band-gap. C Kα RIXS spectra provide evidence that thermal reduction changes the density of states (DOSs) that is generated in the π-region and/or in the gap between the π and π* levels of the GO and rGOs. Two-dimensional C Kα RIXS mapping of the heavy reduction of rGOs further confirms that the residual oxygen and/or oxygen-containing functional groups modify the π and σ features, which are dispersed by the photon excitation energy. The dispersion behavior near the K point is approximately linear and differs from the parabolic-like dispersion observed in HOPG.

Coherent anti-Stokes Raman scattering enhancement of thymine adsorbed on graphene oxide

PubMed Central

2014-01-01

Coherent anti-Stokes Raman scattering (CARS) of carbon nanostructures, namely, highly oriented pyrolytic graphite, graphene nanoplatelets, graphene oxide, and multiwall carbon nanotubes as well CARS spectra of thymine (Thy) molecules adsorbed on graphene oxide were studied. The spectra of the samples were compared with spontaneous Raman scattering (RS) spectra. The CARS spectra of Thy adsorbed on graphene oxide are characterized by shifts of the main bands in comparison with RS. The CARS spectra of the initial nanocarbons are definitely different: for all investigated materials, there is a redistribution of D- and G-mode intensities, significant shift of their frequencies (more than 20 cm-1), and appearance of new modes about 1,400 and 1,500 cm-1. The D band in CARS spectra is less changed than the G band; there is an absence of 2D-mode at 2,600 cm-1 for graphene and appearance of intensive modes of the second order between 2,400 and 3,000 cm-1. Multiphonon processes in graphene under many photon excitations seem to be responsible for the features of the CARS spectra. We found an enhancement of the CARS signal from thymine adsorbed on graphene oxide with maximum enhancement factor about 105. The probable mechanism of CARS enhancement is discussed. PMID:24948887

Pyrolytic product characteristics of biosludge from the wastewater treatment plant of a petrochemical industry.

PubMed

Lin, Kuo-Hsiung; Hsu, Hui-Tsung; Ko, Ya-Wen; Shieh, Zhu-Xin; Chiang, Hung-Lung

2009-11-15

Biosludge was produced from the wastewater treatment plant of a petrochemical industry. The element compositions of pyrolytic residues, CO, CO(2), NOx, SOx, total hydrocarbons and detailed volatile organic compounds of pyrolytic gas, and C, H, N, S content and compositions in biofuel were determined in this study. Generally, 75-80% water content in sludge cakes and about 65-70% weight of water vapor and volatile compounds were volatilized during the drying process. Propene, propane, 1-butene, n-butane, isobutene, toluene and benzene were the major volatile organic compounds (VOCs) of the pyrolytic gas, and the concentrations for most of the top 20 VOC species were greater than 5 ppm. C(5)-C(9) compounds contributed 60% by weight of biofuel; 4-hydroxy-4-methyl-2-pentanone was the highest species, accounting for 28-53% of biofuel at various pyrolytic temperatures. Based on the dried residues, there was 8.5-13% weight in pyrolytic residues, 62-82% weight in liquid products (water and crude oil) and 5.8-30% weight in the gas phase after pyrolytic processing at 500-800 degrees C. Finally, 1.5-2.5 wt% liquid fuel was produced after the distillation process. The pyrolytic residues could be reused, the pyrolytic liquid product could be used as a fuel after distillation, and the pyrolytic gas could be recycled in the pyrolytic process to achieve non-toxic discharge and reduce the cost of sludge disposal.

Production of hydrocarbon fuels from pyrolysis of soybean oils using a basic catalyst.

PubMed

Xu, Junming; Jiang, Jianchun; Sun, Yunjuan; Chen, Jie

2010-12-01

Triglycerides obtained from animals and plants have attracted great attention from researchers for developing an environmental friendly and high-quality fuel, free of nitrogen and sulfur. In the present work, the production of biofuel by catalytic cracking of soybean oil over a basic catalyst in a continuous pyrolysis reactor at atmospheric pressure has been studied. Experiments were designed to study the effect of different types of catalysts on the yield and acid value of the diesel and gasoline fractions from the pyrolytic oil. It was found that basic catalyst gave a product with relatively low acid number. These pyrolytic oils were also further reacted with alcohol in order to decrease their acid value. After esterification, the physico-chemical properties of these biofuels were characterized, and compared with Chinese specifications for conventional diesel fuels. The results showed that esterification of pyrolytic oil from triglycerides represents an alternative technique for producing biofuels from soybean oils with characteristics similar to those of petroleum fuels. Published by Elsevier Ltd.

Design and evaluation of precise current integrator for scanning probe microscopy

NASA Astrophysics Data System (ADS)

Raczkowski, Kamil; Piasecki, Tomasz; Rudek, Maciej; Gotszalk, Teodor

2017-03-01

Several of the scanning probe microscopy (SPM) techniques, such as the scanning tunnelling microscopy (STM) or conductive atomic force microscopy (C-AFM), rely on precise measurements of current flowing between the investigated sample and the conductive nanoprobe. The parameters of current-to-voltage converter (CVC), which should detect current in the picompere range, are of utmost importance to those systems as they determine the microscopes’ measuring capabilities. That was the motivation for research on the precise current integrator (PCI), described in this paper, which could be used as the CVC in the C-AFM systems. The main design goal of the PCI was to provide a small and versatile device with the sub-picoampere level resolution with high dynamic range in the order of nanoamperes. The PCI was based on the integrating amplifier (Texas Instruments DDC112) paired with a STM32F4 microcontroller unit (MCU).The gain and bandwidth of the PCI might be easily changed by varying the integration time and the feedback capacitance. Depending on these parameters it was possible to obtain for example the 2.15 pA resolution at 688 nA range with 1 kHz bandwidth or 7.4 fA resolution at 0.98 nA range with 10 Hz bandwidth. The measurement of sinusoidal current with 28 fA amplitude was also presented. The PCI was integrated with the C-AFM system and used in the highly ordered pyrolytic graphite (HOPG) and graphene samples imaging.

Role of iron modifier on boron atomization process using graphite furnace-atomic absorption spectrometry based on speciation of iron using X-ray absorption fine structure

NASA Astrophysics Data System (ADS)

Yamamoto, Yuhei; Tagami, Azusa; Shiarasaki, Toshihiro; Yonetani, Akira; Yamamoto, Takashi; Imai, Shoji

2018-04-01

The role of an Fe modifier on boron atomization process using graphite furnace-atomic absorbance spectrometry was investigated using a spectroscopic approach. The initial state of the Fe modifier in a pyrolytic graphite (PG) furnace was trivalent. With an increase in pyrolysis temperature, the Fe modifier was reduced in a stepwise manner. Fe2O3 and Fe3O4 were dominant at pyrolysis temperatures below 1300 K. From 1300 to 1500 K, FeO was dominant. At temperatures higher than 1700 K, Fe metal was dominant. After a drying step, 17.7% of the initial B remained in the PG furnace. After the pyrolysis step at 773 K, the residual fraction of B was similar to that after the drying step. After the pyrolysis step at a temperature of 1073 K, the residual fraction was 11.7%. At pyrolysis temperatures > 1738 K, the residual fraction was <3.3% (

Electrothermal atomic absorption spectrometric determination of arsenic in essential lavender and rose oils.

PubMed

Karadjova, Irina B; Lampugnani, Leonardo; Tsalev, Dimiter L

2005-02-28

Analytical procedures for electrothermal atomic absorption spectrometric (ETAAS) determination of arsenic in essential oils from lavender (Lavendula angustifolia) and rose (Rosa damascena) are described. For direct ETAAS analysis, oil samples are diluted with ethanol or i-propanol for lavender and rose oil, respectively. Leveling off responses of four different arsenic species (arsenite, arsenate, monomethylarsonate and dimethylarsinate) is achieved by using a composite chemical modifier: l-cysteine (0.05gl(-1)) in combination with palladium (2.5mug) and citric acid (100mug). Transverse-heated graphite atomizer (THGA) with longitudinal Zeeman-effect background correction and 'end-capped' graphite tubes with integrated pyrolytic graphite platforms, pre-treated with Zr-Ir for permanent modification are employed as most appropriate atomizer. Calibration with solvent-matched standard solutions of As(III) is used for four- and five-fold diluted samples of lavender and rose oil, respectively. Lower dilution factors required standard addition calibration by using aqueous (for lavender oil) or i-propanol (for rose oil) solutions of As(III). The limits of detection (LOD) for the whole analytical procedure are 4.4 and 4.7ngg(-1) As in levender and rose oil, respectively. The relative standard deviation (R.S.D.) for As at 6-30ngg(-1) levels is between 8 and 17% for both oils. As an alternative, procedure based on low temperature plasma ashing in oxygen with ETAAS, providing LODs of 2.5 and 2.7ngg(-1) As in levender and rose oil, respectively, and R.S.D. within 8-12% for both oils has been elaborated. Results obtained by both procedures are in good agreement.

Spring Constants for Stacks of Curved Leaves of Pyrolytic Boron Nitride

NASA Technical Reports Server (NTRS)

Kaforey, M. L.; Deeb, C. W.; Matthiesen, D. H.

1999-01-01

Stacks of curved leaves of pyrolytic boron nitride (PBN) were deflected and the force versus deflection data was recorded. From this data, the spring constant for a given spring geometry (radius of curvature of a leaf, width of a leaf, thickness of a leaf, and number of leaves in the stack) was determined. These experiments were performed at room temperature, 500 C and 1000 C. However, temperature was not found to affect the spring constant. The measured values were generally within one order of magnitude of predictions made using a previously derived equation for a simply supported cylindrical section with a line force at the center.

Deposition of an Ultraflat Graphene Oxide Nanosheet on Atomically Flat Substrates

NASA Astrophysics Data System (ADS)

Khan, M. Z. H.; Shahed, S. M. F.; Yuta, N.; Komeda, T.

2017-07-01

In this study, graphene oxide (GO) sheets produced in the form of stable aqueous dispersions were deposited on Au (111), freshly cleaved mica, and highly oriented pyrolytic graphite (HOPG) substrates. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to study the presence and distinct contact of GO sheets on the substrates. It was revealed from the topography images that high-quality ultraflat GO monolayer sheets formed on the substrates without distinct cracking/wrinkling or folding. GO sheets with apparent height variation observed by microscopy also indicate ultraflat deposition with clear underlying steps. It was observed that ultrasonication and centrifuge steps prior to deposition were very effective for getting oxidation debris (OD)-free ultraflat single monolayer GO nanosheets onto substrates and that the process depends on the concentration of supplied GO solutions.

Investigations by Protein Film Electrochemistry of Alternative Reactions of Nickel-Containing Carbon Monoxide Dehydrogenase.

PubMed

Wang, Vincent C-C; Islam, Shams T A; Can, Mehmet; Ragsdale, Stephen W; Armstrong, Fraser A

2015-10-29

Protein film electrochemistry has been used to investigate reactions of highly active nickel-containing carbon monoxide dehydrogenases (CODHs). When attached to a pyrolytic graphite electrode, these enzymes behave as reversible electrocatalysts, displaying CO2 reduction or CO oxidation at minimal overpotential. The O2 sensitivity of CODH is suppressed by adding cyanide, a reversible inhibitor of CO oxidation, or by raising the electrode potential. Reduction of N2O, isoelectronic with CO2, is catalyzed by CODH, but the reaction is sluggish, despite a large overpotential, and results in inactivation. Production of H2 and formate under highly reducing conditions is consistent with calculations predicting that a nickel-hydrido species might be formed, but the very low rates suggest that such a species is not on the main catalytic pathway.

Calibration and characterization of a highly efficient spectrometer in von Hamos geometry for 7-10 keV x-rays

DOE PAGES

Jarrott, L. C.; Wei, M. S.; McGuffey, C.; ...

2017-04-27

Here, we have built an absolutely calibrated, highly efficient, Bragg crystal spectrometer in von Hamos geometry. This zinc von Hamos spectrometer uses a crystal made from highly oriented pyrolytic graphite that is cylindrically bent along the non-dispersive axis. It is tuned to measure x-ray spectra in the 7–10 keV range and has been designed to be used on a Ten Inch Manipulator for the Omega and OmegaEP target chambers at the Laboratory for Laser Energetics in Rochester, USA. Significant shielding strategies and fluorescence mitigation have been implemented in addition to an imaging plate detector making it well suited for experimentsmore » in high-intensity environments. Here we present the design and absolute calibration as well as mosaicity and integrated reflectivity measurements.« less

Imaging of subunit complexes of thermophilic bacterium H(+)-ATPase with scanning tunneling microscopy.

PubMed

Masai, J; Shibata, T; Kagawa, Y; Kondo, S

1992-07-01

Using a scanning tunneling microscope (STM), we observed reconstructed subunit complexes of H(+)-ATPase of a thermophilic bacterium. The measurement was carried out in air without conductive coating on the samples deposited on a highly oriented pyrolytic graphite (HOPG). The F1 subunit complex of the H(+)-ATPase, and an H(+)-ATPase whose F0 portion was embedded into liposomes prepared from soybean lecithin were imaged. Overall structural images of the subunit complex F1 were obtained: the structural dimensions of the STM images are in agreement with those deduced from conventional methods such as an transmission electron microscopy (TEM) and small-angle X-ray scattering (SAX) experimentation. Regarding the STM imaging of these samples, we discuss the advantages and disadvantages of the STM over those of conventional methods such as a TEM and SAX.

Characterization of submonolayer film composed of soft-landed copper nanoclusters on HOPG

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mondal, Shyamal, E-mail: shyamal.mondal@saha.ac.in; Das, Pabitra; Chowdhury, Debasree

Preformed Copper nanoclusters are deposited on highly oriented pyrolytic graphite (HOPG) at very low energy. For the study of chemical composition X-ray Photoelectron Spectroscopy (XPS) is performed for a wide range of binding energy without exposing the sample in the ambient. Morphological aspects of the supported clusters are characterized employing high resolution scanning electron microscope (SEM). Different types of morphology are observed depending on the nature of the substrate surface. Big fractal islands are formed on terraces while at the step edges small islands are found to form. Ex-situ cathodoluminescence (CL) measurement shows peak at 558 nm wavelength which corresponds tomore » the band gap of 2.22 eV which is due to Cu{sub 2}O nanocrystals formed due to oxidation of the deposited film in ambient.« less

High resolution x-ray Thomson scattering measurements from cryogenic hydrogen jets using the linac coherent light source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fletcher, L. B., E-mail: lbfletch@slac.stanford.edu; Galtier, E.; Gamboa, E. J.

2016-11-15

We present the first spectrally resolved measurements of x-rays scattered from cryogenic hydrogen jets in the single photon counting limit. The 120 Hz capabilities of the LCLS, together with a novel hydrogen jet design [J. B. Kim et al., Rev. Sci. Instrum. (these proceedings)], allow for the ability to record a near background free spectrum. Such high-dynamic-range x-ray scattering measurements enable a platform to study ultra-fast, laser-driven, heating dynamics of hydrogen plasmas. This measurement has been achieved using two highly annealed pyrolytic graphite crystal spectrometers to spectrally resolve 5.5 keV x-rays elastically and inelastically scattered from cryogenic hydrogen and focusedmore » on Cornell-SLAC pixel array detectors [S. Herrmann et al., Nucl. Instrum. Methods Phys. Res., Sect. A 718, 550 (2013)].« less

Molecular and electronic structure of thin films of protoporphyrin(IX)Fe(III)Cl

NASA Astrophysics Data System (ADS)

Snyder, Shelly R.; White, Henry S.

1991-11-01

Electrochemical, scanning tunneling microscopy (STM), and tunneling spectroscopy studies of the molecular and electronic properties of thin films of protoporphyrin(IX)Fe(III)Cl (abbreviated as PP(IX)Fe(III)Cl) on highly oriented pyrolytic graphite (HOPG) electrodes are reported. PP(IX)Fe(III)Cl films are prepared by two different methods: (1) adsorption, yielding an electrochemically-active film, and (2) irreversible electrooxidative polymerization, yielding an electrochemically-inactive film. STM images, in conjunction with electro-chemical results, indicate that adsorption of PP(IX)Fe(III)Cl from aqueous solutions onto freshly cleaved HOPG results in a film comprised of molecular aggregates. In contrast, films prepared by irreversible electrooxidative polymerization of PP(IX)Fe(III)Cl have a denser, highly structured morphology, including what appear to be small pinholes (approx. 50A diameter) in an otherwise continuous film.

A study to improve the mechanical properties of silicon carbide ribbon fibers

NASA Technical Reports Server (NTRS)

Debolt, H. E.; Robey, R. J.

1976-01-01

Preliminary deposition studies of SiC ribbon on a carbon ribbon substrate showed that the dominant strength limiting flaws were at the substrate surface. Procedures for making the carbon ribbon substrate from polyimide film were improved, providing lengths up to 450 meters (1,500 ft.) of flat carbon ribbon substrate 1,900 microns (75 mils) wide by 25 microns (1 mil) thick. The flaws on the carbon ribbon were smaller and less frequent than on carbon ribbon used earlier. SiC ribbon made using the improved substrate, including a layer of pyrolytic graphite to reduce further the severity of substrate surface flaws, showed strength levels up to the 2,068 MPa (300 Ksi) target of the program, with average strength levels over 1,700 MPa (250 Ksi) with coefficient of variation as low as 10% for some runs.

Formation of Amorphous Carbon Nanoparticles by the Laser Electrodispersion Method

NASA Astrophysics Data System (ADS)

Gurevich, S. A.; Gorokhov, M. V.; Kozhevin, V. M.; Kukushkin, M. V.; Levitskii, V. S.; Markov, L. K.; Yavsin, D. A.

2018-03-01

Experimental results on the laser ablation of the highly oriented pyrolytic graphite by using light pulses of an Nd:YAG laser (pulse width 25 ns, pulse energy 220 mJ) are presented. Analysis of the surface profile of the carbon target shows that the target material melts in the course of the laser ablation. As a result of ablation, a coating consisting of carbon nanoparticles about 10 nm in size is formed on the substrate placed at a distance of 4 cm from the target. It is assumed that such particles are formed as a result of the electrodispersion of carbon droplets detached from the target surface and charged to an unstable state in the laser plasma plume. Raman spectra of the coatings indicate that the carbon nanoparticles being formed have an amorphous structure.

Orientation-dependent energy level alignment and film growth of 2,7-diocty[1]benzothieno[3,2-b]benzothiophene (C8-BTBT) on HOPG

NASA Astrophysics Data System (ADS)

Lyu, Lu; Niu, Dongmei; Xie, Haipeng; Cao, Ningtong; Zhang, Hong; Zhang, Yuhe; Liu, Peng; Gao, Yongli

2016-01-01

Combining ultraviolet photoemission spectroscopy, X-ray photoemission spectroscopy, atomic force microscopy, and X-ray diffraction measurements, we performed a systematic investigation on the correlation of energy level alignment, film growth, and molecular orientation of 2,7-diocty[1]benzothieno[3,2-b]benzothiophene (C8-BTBT) on highly oriented pyrolytic graphite. The molecules lie down in the first layer and then stand up from the second layer. The ionization potential shows a sharp decrease from the lying down region to the standing up region. When C8-BTBT molecules start standing up, unconventional energy level band-bending-like shifts are observed as the film thickness increases. These shifts are ascribed to gradual decreasing of the molecular tilt angle about the substrate normal with the increasing film thickness.

Orientation-dependent energy level alignment and film growth of 2,7-diocty[1]benzothieno[3,2-b]benzothiophene (C8-BTBT) on HOPG.

PubMed

Lyu, Lu; Niu, Dongmei; Xie, Haipeng; Cao, Ningtong; Zhang, Hong; Zhang, Yuhe; Liu, Peng; Gao, Yongli

2016-01-21

Combining ultraviolet photoemission spectroscopy, X-ray photoemission spectroscopy, atomic force microscopy, and X-ray diffraction measurements, we performed a systematic investigation on the correlation of energy level alignment, film growth, and molecular orientation of 2,7-diocty[1]benzothieno[3,2-b]benzothiophene (C8-BTBT) on highly oriented pyrolytic graphite. The molecules lie down in the first layer and then stand up from the second layer. The ionization potential shows a sharp decrease from the lying down region to the standing up region. When C8-BTBT molecules start standing up, unconventional energy level band-bending-like shifts are observed as the film thickness increases. These shifts are ascribed to gradual decreasing of the molecular tilt angle about the substrate normal with the increasing film thickness.

Nanospectroscopy of thiacyanine dye molecules adsorbed on silver nanoparticle clusters

NASA Astrophysics Data System (ADS)

Ralević, Uroš; Isić, Goran; Anicijević, Dragana Vasić; Laban, Bojana; Bogdanović, Una; Lazović, Vladimir M.; Vodnik, Vesna; Gajić, Radoš

2018-03-01

The adsorption of thiacyanine dye molecules on citrate-stabilized silver nanoparticle clusters drop-cast onto freshly cleaved mica or highly oriented pyrolytic graphite surfaces is examined using colocalized surface-enhanced Raman spectroscopy and atomic force microscopy. The incidence of dye Raman signatures in photoluminescence hotspots identified around nanoparticle clusters is considered for both citrate- and borate-capped silver nanoparticles and found to be substantially lower in the former case, suggesting that the citrate anions impede the efficient dye adsorption. Rigorous numerical simulations of light scattering on random nanoparticle clusters are used for estimating the electromagnetic enhancement and elucidating the hotspot formation mechanism. The majority of the enhanced Raman signal, estimated to be more than 90%, is found to originate from the nanogaps between adjacent nanoparticles in the cluster, regardless of the cluster size and geometry.

Main principles of passive devices based on graphene and carbon films in microwave-THz frequency range

NASA Astrophysics Data System (ADS)

Kuzhir, Polina P.; Paddubskaya, Alesia G.; Volynets, Nadezhda I.; Batrakov, Konstantin G.; Kaplas, Tommi; Lamberti, Patrizia; Kotsilkova, Rumiana; Lambin, Philippe

2017-07-01

The ability of thin conductive films, including graphene, pyrolytic carbon (PyC), graphitic PyC (GrPyC), graphene with graphitic islands (GrI), glassy carbon (GC), and sandwich structures made of all these materials separated by polymer slabs to absorb electromagnetic radiation in microwave-THz frequency range, is discussed. The main physical principles making a basis for high absorption ability of these heterostructures are explained both in the language of electromagnetic theory and using representation of equivalent electrical circuits. The idea of using carbonaceous thin films as the main working elements of passive radiofrequency (RF) devices, such as shields, filters, polarizers, collimators, is proposed theoretically and proved experimentally. The important advantage of PyC, GrI, GrPyC, and GC is that, in contrast to graphene, they either can be easily deposited onto a dielectric substrate or are strong enough to allow their transfer from the catalytic substrate without a shuttle polymer layer. This opens a new avenue toward the development of a scalable protocol for cost-efficient production of ultralight electromagnetic shields that can be transferred to commercial applications. A robust design via finite-element method and design of experiment for RF devices based on carbon/graphene films and sandwiches is also discussed in the context of virtual prototyping.

Suspended-Bed Reactor preliminary design, /sup 233/U--/sup 232/Th cycle. Final report (revised)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karam, R.A.; Alapour, A.; Lee, C.C.

1977-11-01

The preliminary design Suspended-Bed Reactor is described. Coated particles about 2 mm in diameter are used as the fuel. The coatings consist of three layers: (1) low density pyrolytic graphite, 70 ..mu.. thick, (2) silicon carbide pressure vessel, 30 ..mu.. thick, and (3) ZrC layer, 50 ..mu.. thick, to protect the pressure vessel from moisture and oxygen. The fuel kernel can be either uranium-thorium dicarbide or metal. The coated particles are suspended by helium gas (coolant) in a cluster of pressurized tubes. The upward flow of helium fluidizes the coated particles. As the flow rate increases, the bed of particlesmore » is lifted upward to the core section. The particles are restrained at the upper end of the core by a suitable screen. The overall particle density in the core is just enough for criticality condition. Should the helium flow cease, the bed in the core section will collapse, and the particles will flow downward into the section where the increased physical spacings among the tubes brings about a safe shutdown. By immersing this section of the tubes in a large graphite block to serve as a heat sink, dissipation of decay heat becomes manageable. This eliminates the need for emergency core cooling systems.« less

Trace element content and magnetic properties of commercial HOPG samples studied by ion beam microscopy and SQUID magnetometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spemann, D., E-mail: spemann@uni-leipzig.de; Esquinazi, P., E-mail: esquin@physik.uni-leipzig.de; Setzer, A.

In this study, the impurity concentration and magnetic response of nine highly oriented pyrolytic graphite (HOPG) samples with different grades and from different providers were determined using ion beam microscopy and SQUID magnetometry. Apart from sideface contaminations in the as-received state, bulk contamination of the samples in most cases consists of disk-shaped micron-sized particles made of Ti and V with an additional Fe contamination around the grain perimeter. The saturation magnetization typically increases with Fe concentration, however, there is no simple correlation between Fe content and magnetic moment. The saturation magnetization of one, respectively six, out of nine samples clearlymore » exceeds the maximum contribution from pure Fe or Fe{sub 3}C. For most samples the temperature dependence of the remanence decreases linearly with T – a dependence found previously for defect-induced magnetism (DIM) in HOPG. We conclude that apart from magnetic impurities, additional contribution to the ferromagnetic magnetization exists in pristine HOPG in agreement with previous studies. A comparative study between the results of ion beam microscopy and the commonly used EDX analysis shows clearly that EDX is not a reliable method for quantitative trace elemental analysis in graphite, clarifying weaknesses and discrepancies in the element concentrations given in the recent literature.« less

Reactive Capture of Gold Nanoparticles by Strongly Physisorbed Monolayers on Graphite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wei, Xiaoliang; Tong, Wenjun; Fidler, Vlastimil

2012-12-01

Anthracene Diels Alder adducts (DAa) bearing two long side chains (H-(CH2)22O(CH2)6OCH2-) at the 1- and 5-positions form self-assembled monolayers (SAMs) at the phenyloctane - highly oriented pyrolytic graphite (HOPG) interface. The long DAa side chains promote strong physisorption of the monolayer to HOPG and maintain the monolayer morphology upon rinsing or incubation in ethanol and air-drying of the substrate. Incorporating a carboxylic acid group on the DAa core enables capture of 1 - 4 nm diameter gold nanoparticles (AuNP) provided (i) the monolayer containing DAa-carboxylic acids is treated with Cu2+ ions and (ii) the organic coating on the AuNP containsmore » carboxylic acids (11-mercaptoundecanoic acid, MUA-AuNP). AuNP capture by the monolayer proceeds with formation of Cu2+ - carboxylate coordination complexes. The captured AuNP appear as mono- and multi-layered clusters at high coverage on HOPG. The surface density of the captured AuNPs can be adjusted from AuNP multi-layers to isolated AuNPs by varying incubation times, MUA-AuNP concentration, the number density of carboxylic acids in the monolayer, the number of MUA per AuNP, and the post-incubation treatments.« less

Magnetically Orchestrated Formation of Diamond at Lower Temperatures and Pressures

NASA Astrophysics Data System (ADS)

Little, Reginald B.; Lochner, Eric; Goddard, Robert

2005-01-01

Man's curiosity and fascination with diamonds date back to ancient times. The knowledge of the many properties of diamond is recorded during Biblical times. Antoine Lavoisier determined the composition of diamond by burning in O2 to form CO2. With the then existing awareness of graphite as carbon, the race began to convert graphite to diamond. The selective chemical synthesis of diamond has been pursued by Cagniard, Hannay, Moisson and Parson. On the basis of the thermodynamically predicted equilibrium line of diamond and graphite, P W Bridgman attempted extraordinary conditions of high temperature (>2200°C) and pressure (>100,000 atm) for the allotropic conversion of graphite to diamond. H T Hall was the first to successfully form bulk diamond by realizing the kinetic restrictions to Bridgman's (thermodynamic) high pressure high temperature direct allotropic conversion. Moreover, Hall identified catalysts for the faster kinetics of diamond formation. H M Strong determined the import of the liquid catalyst during Hall's catalytic synthesis. W G Eversole discovered the slow metastable low pressure diamond formation by pyrolytic chemical vapor deposition with the molecular hydrogen etching of the rapidly forming stable graphitic carbon. J C Angus determined the import of atomic hydrogen for faster etching for faster diamond growth at low pressure. S Matsumoto has developed plasma and hot filament technology for faster hydrogen and carbon radical generations at low pressure for faster diamond formation. However the metastable low pressure chemical vapor depositions by plasma and hot filament are prone to polycrystalline films. From Bridgman to Hall to Eversole, Angus and Matsumoto, much knowledge has developed of the importance of pressure, temperature, transition metal catalyst, liquid state of metal (metal radicals atoms) and the carbon radical intermediates for diamond synthesis. Here we advance this understanding of diamond formation by demonstrating the external magnetic organization of carbon, metal and hydrogen radicals for lower temperature and pressure synthesis. Here we show that strong static external magnetic field (>15 T) enhances the formation of single crystal diamond at lower pressure and even atmospheric pressure with implications for much better, faster high quality diamond formation by magnetization of current high pressure and temperature technology.

Friction and transfer behavior of pyrolytic boron nitride in contact with various metals

NASA Technical Reports Server (NTRS)

Buckley, D. H.

1976-01-01

Sliding friction experiments were conducted with pyrolytic boron nitride in sliding contact with itself and various metals. Auger emission spectroscopy was used to monitor transfer of pyrolytic boron nitride to metals and metals to pyrolytic boron nitride. Results indicate that the friction coefficient for pyrolytic boron nitride in contact with metals can be related to the chemical activity of the metals and more particularly to the d valence bond character of the metal. Transfer was found to occur to all metals except silver and gold and the amount of transfer was less in the presence than in the absence of metal oxide. Friction was less for pyrolytic boron nitride in contact with a metal in air than in vacuum.

Structural disorder of graphite and implications for graphite thermometry

NASA Astrophysics Data System (ADS)

Kirilova, Martina; Toy, Virginia; Rooney, Jeremy S.; Giorgetti, Carolina; Gordon, Keith C.; Collettini, Cristiano; Takeshita, Toru

2018-02-01

Graphitization, or the progressive maturation of carbonaceous material, is considered an irreversible process. Thus, the degree of graphite crystallinity, or its structural order, has been calibrated as an indicator of the peak metamorphic temperatures experienced by the host rocks. However, discrepancies between temperatures indicated by graphite crystallinity versus other thermometers have been documented in deformed rocks. To examine the possibility of mechanical modifications of graphite structure and the potential impacts on graphite thermometry, we performed laboratory deformation experiments. We sheared highly crystalline graphite powder at normal stresses of 5 and 25 megapascal (MPa) and aseismic velocities of 1, 10 and 100 µm s-1. The degree of structural order both in the starting and resulting materials was analyzed by Raman microspectroscopy. Our results demonstrate structural disorder of graphite, manifested as changes in the Raman spectra. Microstructural observations show that brittle processes caused the documented mechanical modifications of the aggregate graphite crystallinity. We conclude that the calibrated graphite thermometer is ambiguous in active tectonic settings.

METHOD OF FABRICATING A GRAPHITE MODERATED REACTOR

DOEpatents

Kratz, H.R.

1963-05-01

S>A nuclear reactor formed of spaced bodies of uranium and graphite blocks is improved by diffusing helium through the graphite blocks in order to replace the air in the pores of the graphite with helium. The helium-impregnated graphite conducts heat better, and absorbs neutrons less, than the original air- impregnated graphite. (AEC)

Influence of carbonization conditions on the pyrolytic carbon deposition in acacia and eucalyptus wood chars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, M.; Gupta, R.C.

1997-04-01

The amount of deposited pyrolytic carbon (resulting from the cracking of volatile matter) was found to depend on wood species and carbonization conditions, such as temperature and heating rate. Maximum pyrolytic carbon deposition in both the acacia and eucalyptus wood chars has been observed at a carbonization temperature of 800 C. Rapid carbonization (higher heating rate) of wood significantly reduces the amount of deposited pyrolytic carbon in resulting chars. Results also indicate that the amount of deposited pyrolytic carbon in acacia wood char is less than that in eucalyptus wood char.

Carbon treated commercial aluminium alloys as anodes for aluminium-air batteries in sodium chloride electrolyte

NASA Astrophysics Data System (ADS)

Pino, M.; Herranz, D.; Chacón, J.; Fatás, E.; Ocón, P.

2016-09-01

An easy treatment based in carbon layer deposition into aluminium alloys is presented to enhance the performance of Al-air primary batteries with neutral pH electrolyte. The jellification of aluminate in the anode surface is described and avoided by the carbon covering. Treated commercial Al alloys namely Al1085 and Al7475 are tested as anodes achieving specific capacities above 1.2 Ah g-1vs 0.5 Ah g-1 without carbon covering. The influence of the binder proportion in the treatment as well as different carbonaceous materials, Carbon Black, Graphene and Pyrolytic Graphite are evaluated as candidates for the covering. Current densities of 1-10 mA cm-2 are measured and the influence of the alloy explored. A final battery design of 4 cells in series is presented for discharges with a voltage plateau of 2 V and 1 Wh g-1 energy density.

Low-noise humidity controller for imaging water mediated processes in atomic force microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gaponenko, I., E-mail: iaroslav.gaponenko@unige.ch; Gamperle, L.; Herberg, K.

2016-06-15

We demonstrate the construction of a novel low-noise continuous flow humidity controller and its integration with a commercial variable-temperature atomic force microscope fluid cell, allowing precise control of humidity and temperature at the sample during nanoscale measurements. Based on wet and dry gas mixing, the design allows a high mechanical stability to be achieved by means of an ultrasonic atomiser for the generation of water-saturated gas, improving upon previous bubbler-based architectures. Water content in the flow is measured both at the inflow and outflow of the fluid cell, enabling the monitoring of water condensation and icing, and allowing controlled variationmore » of the sample temperature independently of the humidity. To benchmark the performance of the controller, the results of detailed noise studies and time-based imaging of the formation of ice layers on highly oriented pyrolytic graphite are shown.« less

High resolution x-ray Thomson scattering measurements from cryogenic hydrogen jets using the linac coherent light source

DOE PAGES

Fletcher, L. B.; Zastrau, U.; Galtier, E.; ...

2016-08-15

Here, we present the first spectrally resolved measurements of x-rays scattered from cryogenic hydrogen jets in the single photon counting limit. The 120 Hz capabilities of the LCLS, together with a novel hydrogen jet design [J. B. Kim et al., Rev. Sci. Instrum. (these proceedings)], allow for the ability to record a near background free spectrum. Such high-dynamic-range x-ray scattering measurements enable a platform to study ultra-fast, laser-driven, heating dynamics of hydrogen plasmas. This measurement has been achieved using two highly annealed pyrolytic graphite crystal spectrometers to spectrally resolve 5.5 keV x-rays elastically and inelastically scattered from cryogenic hydrogen andmore » focused on Cornell-SLAC pixel array detectors [S. Herrmann et al., Nucl. Instrum. Methods Phys. Res., Sect. A 718, 550 (2013)].« less

Comparison of Hyperthermal Ground Laboratory Atomic Oxygen Erosion Yields With Those in Low Earth Orbit

NASA Technical Reports Server (NTRS)

Banks, Bruce A.; Dill, Grace C.; Loftus, Ryan J.; deGroh, Kim K.; Miller, Sharon K.

2013-01-01

The atomic oxygen erosion yields of 26 materials (all polymers except for pyrolytic graphite) were measured in two directed hyperthermal radio frequency (RF) plasma ashers operating at 30 or 35 kHz with air. The hyperthermal asher results were compared with thermal energy asher results and low Earth orbital (LEO) results from the Materials International Space Station Experiment 2 and 7 (MISSE 2 and 7) flight experiments. The hyperthermal testing was conducted to a significant portion of the atomic oxygen fluence similar polymers were exposed to during the MISSE 2 and 7 missions. Comparison of the hyperthermal asher prediction of LEO erosion yields with thermal energy asher erosion yields indicates that except for the fluorocarbon polymers of PTFE and FEP, the hyperthermal energy ashers are a much more reliable predictor of LEO erosion yield than thermal energy asher testing, by a factor of four.

Orientation-dependent energy level alignment and film growth of 2,7-diocty[1]benzothieno[3,2-b]benzothiophene (C8-BTBT) on HOPG

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lyu, Lu; Niu, Dongmei, E-mail: mayee@csu.edu.cnmailto; Xie, Haipeng

Combining ultraviolet photoemission spectroscopy, X-ray photoemission spectroscopy, atomic force microscopy, and X-ray diffraction measurements, we performed a systematic investigation on the correlation of energy level alignment, film growth, and molecular orientation of 2,7-diocty[1]benzothieno[3,2-b]benzothiophene (C8-BTBT) on highly oriented pyrolytic graphite. The molecules lie down in the first layer and then stand up from the second layer. The ionization potential shows a sharp decrease from the lying down region to the standing up region. When C8-BTBT molecules start standing up, unconventional energy level band-bending-like shifts are observed as the film thickness increases. These shifts are ascribed to gradual decreasing of the molecularmore » tilt angle about the substrate normal with the increasing film thickness.« less

Intrinsic stress modulation in diamond like carbon films with incorporation of gold nanoparticles by PLA

NASA Astrophysics Data System (ADS)

Panda, Madhusmita; Krishnan, R.; Krishna, Nanda Gopala; Madapu, Kishore K.; Kamruddin, M.

2018-04-01

Intrinsic stress modulation in the diamond-like carbon (DLC) coatings with incorporation of gold nanoparticles was studied qualitatively from Raman shift. The films were deposited on Si (1 0 0) substrates by using Pulsed laser ablation (PLA) of pure pyrolytic graphite target and with a gold foil on it. Films compositional and chemical behavior was studied by X-ray photoelectron spectroscopy (XPS) and Visible Raman spectroscopy, respectively. The sp3 content obtained from XPS shows dramatic variation in DLC, DLC-Au(100), DLC-Au(200) and DLC-Au(300) as 39%, 41%, 47% and 66% with various gold contentsas 0%, 12%, 7.3% and 4.7%, respectively. The Raman spectra of DLC/Au films showed G-peak shift towards lower wavenumber indicating the reduction of intrinsic stress (internal compressive stress). The sp2, sp3 fraction in the films are also determined from FWHM (G-Peak).

Method of making carbon-carbon composites

DOEpatents

Engle, Glen B.

1993-01-01

A process for making 2D and 3D carbon-carbon composites having a combined high crystallinity, high strength, high modulus and high thermal and electrical conductivity. High-modulus/high-strength mesophase derived carbon fibers are woven into a suitable cloth. Layers of this easily graphitizible woven cloth are infiltrated with carbon material to form green composites. The carbonized composite is then impregnated several times with pitch by covering the composite with hot pitch under pressure. The composites are given a heat treatment between each impregnant step to crack up the infiltrated carbon and allow additional pitch to enter the microstructure during the next impregnation cycle. The impregnated composites are then given a final heat treatment in the range 2500.degree. to 3100.degree. C. to fully graphitize the fibers and the matrix carbon. The composites are then infiltrated with pyrolytic carbon by chemical vapor deposition in the range 1000.degree. C. to 1300.degree. C. at a reduced. pressure.

Optically transparent cathode for Co(III/II) mediated dye-sensitized solar cells based on graphene oxide.

PubMed

Kavan, Ladislav; Yum, Jun-Ho; Graetzel, Michael

2012-12-01

Thin semitransparent films were fabricated on F-doped SnO(2) (FTO) from single-layer graphene oxide (GO) either pure or in a composite with graphene nanoplatelets. Electrocatalytic activity of prepared films was tested for the Co(bpy)(3)(3+/2+) redox couple in acetonitrile electrolyte solution. Pristine GO showed almost no activity, resembling the properties of basal plane pyrolytic graphite. However, electrochemical performance of graphene oxide improved dramatically upon chemical reduction with hydrazine and/or heat treatment. All GO-containing films were firmly bonded to FTO, which contrasted with the poor adhesion of sole graphene nanoplatelets to this support. The activity loss during long-term aging was considerably improved, too. Enhanced stability of GO-containing films together with high electrocatalytic activity is beneficial for application in a new generation of dye-sensitized solar cells employing Co(bpy)(3)(3+/2+) as the redox shuttle.

Electrochemical studies on polysorbate-20 (Tween 20)-entrapped haemoglobin and its application in a hydrogen peroxide biosensor.

PubMed

Ma, Xiang; Chen, Ting; Liu, Lifang; Li, Genxi

2005-06-01

Haemoglobin (Hb) was entrapped in polysorbate 20 and then modified on a pyrolytic graphite electrode. Electrochemical studies revealed that a pair of stable and well-defined redox peaks attributed to the direct redox reaction of Hb could be observed in a phosphate buffer solution (pH 6.0). The anodic and cathodic peaks were located at -236 and -316 mV (versus a saturated calomel reference electrode) separately. The formal potential, E0', was linearly varied with pH in the range from 3.0 to 10.0 with a slope of -48.0 mV.pH-1. Moreover, the protein was capable of catalysing the reduction of H2O2. Accordingly, an unmediated biosensor for H2O2 was prepared with a linear range from 8.0x10(-7) to 1.0x10(-3) M. This biosensor exhibited good stability, sensitivity and reproducibility.

Preparation of iron oxide-impregnated spherical granular activated carbon-carbon composite and its photocatalytic removal of methylene blue in the presence of oxalic acid.

PubMed

Kadirova, Zukhra C; Hojamberdiev, Mirabbos; Katsumata, Ken-Ichi; Isobe, Toshihiro; Matsushita, Nobuhiro; Nakajima, Akira; Sharipov, Khasan; Okada, Kiyoshi

2014-01-01

The spherical granular activated carbon-carbon composites (GAC-Fe) with different iron oxide contents (Fe mass% = 0.6-10) were prepared by a pore volume impregnation method. The X-ray diffraction (XRD), scanning electron microscopy (SEM), and N2-adsorption results confirm the presence of amorphous iron oxide, pyrolytic carbon, and graphitized globular carbon nanoparticles covered with amorphous carbon in the CAG-Fe. The rate of photodegradation of methylene blue (MB) in aqueous solution under UV light in the presence of oxalic acid correlates with porosity of the prepared materials. The total MB removal includes the combination of adsorption and photodegradation without the addition of H2O2. The results of total organic carbon (TOC) analysis reveal that the decolorization of MB in aqueous solution containing oxalic acid corresponds to the decomposition of organic compounds to CO2 and H2O.

A low-temperature scanning tunneling microscope capable of microscopy and spectroscopy in a Bitter magnet at up to 34 T.

PubMed

Tao, W; Singh, S; Rossi, L; Gerritsen, J W; Hendriksen, B L M; Khajetoorians, A A; Christianen, P C M; Maan, J C; Zeitler, U; Bryant, B

2017-09-01

We present the design and performance of a cryogenic scanning tunneling microscope (STM) which operates inside a water-cooled Bitter magnet, which can attain a magnetic field of up to 38 T. Due to the high vibration environment generated by the magnet cooling water, a uniquely designed STM and a vibration damping system are required. The STM scan head is designed to be as compact and rigid as possible, to minimize the effect of vibrational noise as well as fit the size constraints of the Bitter magnet. The STM uses a differential screw mechanism for coarse tip-sample approach, and operates in helium exchange gas at cryogenic temperatures. The reliability and performance of the STM are demonstrated through topographic imaging and scanning tunneling spectroscopy on highly oriented pyrolytic graphite at T = 4.2 K and in magnetic fields up to 34 T.

Production and characterization of pyrolytic oils by pyrolysis of waste machinery oil.

PubMed

Sinağ, Ali; Gülbay, Selen; Uskan, Burçin; Uçar, Suat; Ozgürler, Sara Bilge

2010-01-15

The main objective of this work is to propose an alternative method for evaluation of the waste machinery oil which is an environmental problem in Turkey. For this purpose, pyrolysis of waste machinery oil was conducted in a tubular reactor. Effect of the experimental conditions (various temperatures, catalyst type) on the formation of pyrolytic oil, gas, and char was investigated. Nickel supported on silica and zeolite (HZSM-5) were used as catalysts. Properties of the pyrolytic oils were characterized by gas chromatograph equipped with a mass selective detector (GC-MS), gas chromatography with flame ionization detector (GC-FID for boiling point range distribution), nuclear magnetic resonance ((1)H NMR) spectroscopy, higher heating value measurement, and elemental analysis. The behavior of the metals in the waste machinery oil and the pyrolytic oil samples was also quantitatively detected by inductively coupled plasma (ICP) analysis. As, Cd and Cr contents of the all pyrolytic oils were found as <0.05 ppm, while Cu content of the pyrolytic oils varied between 0.3 ppm and 0.61 ppm. Only Vanadium contents of the pyrolytic oils obtained at 800 degrees C (0.342 ppm) and in the presence of HZSM5 (0.57 ppm) increased compared to that obtained by waste machinery oil (0.1 ppm). Lower metal contents of the pyrolytic oils reveal that pyrolysis of the waste machinery oils leads to the formation of environmental friendly pyrolytic oils with higher heating values.

Nucleation, growth, and repair of a cobalt-based oxygen evolving catalyst.

PubMed

Surendranath, Yogesh; Lutterman, Daniel A; Liu, Yi; Nocera, Daniel G

2012-04-11

The mechanism of nucleation, steady-state growth, and repair is investigated for an oxygen evolving catalyst prepared by electrodeposition from Co(2+) solutions in weakly basic electrolytes (Co-OEC). Potential step chronoamperometry and atomic force microscopy reveal that nucleation of Co-OEC is progressive and reaches a saturation surface coverage of ca. 70% on highly oriented pyrolytic graphite substrates. Steady-state electrodeposition of Co-OEC exhibits a Tafel slope approximately equal to 2.3 × RT/F. The electrochemical rate law exhibits a first order dependence on Co(2+) and inverse orders on proton (third order) and proton acceptor, methylphosphonate (first order for 1.8 mM ≤ [MeP(i)] ≤ 18 mM and second order dependence for 32 mM ≤ [MeP(i)] ≤ 180 mM). These electrokinetic studies, combined with recent XAS studies of catalyst structure, suggest a mechanism for steady state growth at intermediate MeP(i) concentration (1.8-18 mM) involving a rapid solution equilibrium between aquo Co(II) and Co(III) hydroxo species accompanied with a rapid surface equilibrium involving electrolyte dissociation and deprotonation of surface bound water. These equilibria are followed by a chemical rate-limiting step for incorporation of Co(III) into the growing cobaltate clusters comprising Co-OEC. At higher concentrations of MeP(i) ([MeP(i)] ≥ 32 mM), MePO(3)(2-) equilibrium binding to Co(II) in solution is suggested by the kinetic data. Consistent with the disparate pH profiles for oxygen evolution electrocatalysis and catalyst formation, NMR-based quantification of catalyst dissolution as a function of pH demonstrates functional stability and repair at pH values >6 whereas catalyst corrosion prevails at lower pH values. These kinetic insights provide a basis for developing and operating functional water oxidation (photo)anodes under benign pH conditions. © 2012 American Chemical Society

Ultralight anisotropic foams from layered aligned carbon nanotube sheets.

PubMed

Faraji, Shaghayegh; Stano, Kelly L; Yildiz, Ozkan; Li, Ang; Zhu, Yuntian; Bradford, Philip D

2015-10-28

In this work, we present large scale, ultralight aligned carbon nanotube (CNT) structures which have densities an order of magnitude lower than CNT arrays, have tunable properties and exhibit resiliency after compression. By stacking aligned sheets of carbon nanotubes and then infiltrating with a pyrolytic carbon (PyC), resilient foam-like materials were produced that exhibited complete recovery from 90% compressive strain. With density as low as 3.8 mg cm(-3), the foam structure is over 500 times less dense than bulk graphite. Microscopy revealed that PyC coated the junctions among CNTs, and also increased CNT surface roughness. These changes in the morphology explain the transition from inelastic behavior to foam-like recovery of the layered CNT sheet structure. Mechanical and thermal properties of the foams were tuned for different applications through variation of PyC deposition duration while dynamic mechanical analysis showed no change in mechanical properties over a large temperature range. Observation of a large and linear electrical resistance change during compression of the aligned CNT/carbon (ACNT/C) foams makes strain/pressure sensors a relevant application. The foams have high oil absorption capacities, up to 275 times their own weight, which suggests they may be useful in water treatment and oil spill cleanup. Finally, the ACNT/C foam's high porosity, surface area and stability allow for demonstration of the foams as catalyst support structures.

The Effect of Thermal Reduction on the Photoluminescence and Electronic Structures of Graphene Oxides

PubMed Central

Chuang, C.-H.; Wang, Y.-F.; Shao, Y.-C.; Yeh, Y.-C.; Wang, D.-Y.; Chen, C.-W.; Chiou, J. W.; Ray, Sekhar C.; Pong, W. F.; Zhang, L.; Zhu, J. F.; Guo, J. H.

2014-01-01

Electronic structures of graphene oxide (GO) and hydro-thermally reduced graphene oxides (rGOs) processed at low temperatures (120–180°C) were studied using X-ray absorption near-edge structure (XANES), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS). C K-edge XANES spectra of rGOs reveal that thermal reduction restores C = C sp2 bonds and removes some of the oxygen and hydroxyl groups of GO, which initiates the evolution of carbonaceous species. The combination of C K-edge XANES and Kα XES spectra shows that the overlapping π and π* orbitals in rGOs and GO are similar to that of highly ordered pyrolytic graphite (HOPG), which has no band-gap. C Kα RIXS spectra provide evidence that thermal reduction changes the density of states (DOSs) that is generated in the π-region and/or in the gap between the π and π* levels of the GO and rGOs. Two-dimensional C Kα RIXS mapping of the heavy reduction of rGOs further confirms that the residual oxygen and/or oxygen-containing functional groups modify the π and σ features, which are dispersed by the photon excitation energy. The dispersion behavior near the K point is approximately linear and differs from the parabolic-like dispersion observed in HOPG. PMID:24717290

Porous graphitic carbon nanosheets derived from cornstalk biomass for advanced supercapacitors.

PubMed

Wang, Lei; Mu, Guang; Tian, Chungui; Sun, Li; Zhou, Wei; Yu, Peng; Yin, Jie; Fu, Honggang

2013-05-01

Porous graphitic carbon nanosheets (PGCS) are synthesized by an in situ self-generating template strategy based on the carburized effect of iron with cornstalks. Cornstalks firstly coordinate with [Fe(CN)(6)](4-) ions to form the cornstalk-[Fe(CN)(6)](4-) precursor. After carbonization and removal of the catalyst, PGCS are obtained. Series experiments indicate that PGCS can only be formed when using an iron-based catalyst that can generate a carburized phase during the pyrolytic process. The unique structures of PGCS exhibit excellent capacitive performance. The PGCS-1-1100 sample (synthesized from 0.1 M [Fe(CN)(6)](4-) with a carbonization temperature of 1100 °C), which shows excellent electrochemical capacitance (up to 213 F g(-1) at 1 A g(-1)), cycling stability, and rate performance in 6 M KOH electrolyte. In the two-electrode symmetric supercapacitors, the maximum energy densities that can be achieved are as high as 9.4 and 61.3 Wh kg(-1) in aqueous and organic electrolytes, respectively. Moreover, high energy densities of 8.3 and 40.6 Wh kg(-1) are achieved at the high power density of 10.5 kW kg(-1) in aqueous and organic electrolytes, respectively. This strategy holds great promise for preparing PGCS from natural resources, including cornstalks, as advanced electrodes in supercapacitors. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Influence of Applied Thermal Gradients and a Static Magnetic Field on Bridgman-Grown GeSi Alloys

NASA Technical Reports Server (NTRS)

Volz, M. P.; Szofran, F. R.; Cobb, S. D.; Ritter, T. M.

1999-01-01

The effect of applied axial and radial thermal gradients and an axial static magnetic field on the macrosegregation profiles of Bridgman-grown GeSi alloy crystals has been assessed. The axial thermal gradients were adjusted by changing the control setpoints of a seven-zone vertical Bridgman furnace. The radial thermal gradients were affected by growing samples in ampoules with different thermal conductivities, namely graphite, hot-pressed boron nitride (BN), and pyrolytic boron nitride (PBN). Those samples grown in a graphite ampoule exhibited radial profiles consistent with a highly concave interface and axial profiles indicative of complete mixing in the melt. The samples grown in BN and PBN ampoules had less radial variation. Axial macrosegregation profiles of these samples fell between the predictions for a completely mixed melt and one where solute transport is dominated by diffusion. All of the samples were grown on Ge seeds. This resulted in a period of free growth until the Si concentration in the solid was in equilibrium with the Si concentration in the liquid. The length of crystal grown during this period was inversely proportional to the applied axial thermal gradient. Several samples were grown in an axial 5 Tesla magnetic field. Measured macroscopic segregation profiles on these samples indicate that the magnetic field did not, in general, reduce the melt flow velocities to below the growth velocities.

Physical vapor deposition of one-dimensional nanoparticle arrays on graphite: seeding the electrodeposition of gold nanowires.

PubMed

Cross, C E; Hemminger, J C; Penner, R M

2007-09-25

One-dimensional (1D) ensembles of 2-15 nm diameter gold nanoparticles were prepared using physical vapor deposition (PVD) on highly oriented pyrolytic graphite (HOPG) basal plane surfaces. These 1D Au nanoparticle ensembles (NPEs) were prepared by depositing gold (0.2-0.6 nm/s) at an equivalent thickness of 3-4 nm onto HOPG surfaces at 670-690 K. Under these conditions, vapor-deposited gold nucleated selectively at the linear step edge defects present on these HOPG surfaces with virtually no nucleation of gold particles on terraces. The number density of 2-15 nm diameter gold particles at step edges was 30-40 microm-1. These 1D NPEs were up to a millimeter in length and organized into parallel arrays on the HOPG surface, following the organization of step edges. Surprisingly, the deposition of more gold by PVD did not lead to the formation of continuous gold nanowires at step edges under the range of sample temperature or deposition flux we have investigated. Instead, these 1D Au NPEs were used as nucleation templates for the preparation by electrodeposition of gold nanowires. The electrodeposition of gold occurred selectively on PVD gold nanoparticles over the potential range from 700-640 mV vs SCE, and after optimization of the electrodeposition parameters continuous gold nanowires as small as 80-90 nm in diameter and several micrometers in length were obtained.

Ion irradiation induced surface modification studies of polymers using SPM

NASA Astrophysics Data System (ADS)

Tripathi, A.; Kumar, Amit; Singh, F.; Kabiraj, D.; Avasthi, D. K.; Pivin, J. C.

2005-07-01

Various types of scanning probe microscopy (SPM) techniques: atomic force microscopy (AFM) (contact and tapping in height and amplitude mode), scanning tunnelling microscopy (STM) and conducting atomic force microscopy (C-AFM) are used for studying ion beam induced surface modifications, nanostructure/cluster formation and disintegration in polymers and similar soft carbon based materials. In the present study, the results of studies on four materials, namely, (A) methyltriethoxysilane/phenyltriethoxysilane (MTES/PTES) based gel, (B) triethoxisilane (TH) based gel, (C) highly oriented pyrolytic graphite (HOPG) bulk and (D) fullerene (C60) thin films are discussed. In the case of Si based gels prepared from pre-cursors containing organic groups (MTES/PTES), hillocks are observed at the surface and their size decreases from 70 to 25 nm with increasing fluence, whereas, in the case of a gel with a stoichiometry SiO1.25H1, prepared from TH, an increases in the size of hillocks is observed. Hillocks are also formed at the surface of HOPG irradiated with 120 MeV Au beam at a low fluence, whereas, formation of craters and a re-organisation of surface features is observed at a higher fluence. In the case of C60 films, 120 MeV Au ion irradiation induces the formation of conducting ion tracks, which is attributed to the transformation from insulating C60 to conducting graphite like carbon.

Method for fabricating thin films of pyrolytic carbon

DOEpatents

Brassell, G.W.; Lewis, J. Jr.; Weber, G.W.

1980-03-13

The present invention relates to a method for fabricating ultrathin films of pyrolytic carbon. Pyrolytic carbon is vapor deposited onto a concave surface of a heated substrate to a total uniform thickness in the range of about 0.1 to 1.0 micrometer. The carbon film on the substrate is provided with a layer of adherent polymeric resin. The resulting composite film of pyrolytic carbon and polymeric resin is then easily separated from the substrate by shrinking the 10 polymeric resin coating with thermally induced forces.

Method for fabricating thin films of pyrolytic carbon

DOEpatents

Brassell, Gilbert W.; Lewis, Jr., John; Weber, Gary W.

1982-01-01

The present invention relates to a method for fabricating ultra-thin films of pyrolytic carbon. Pyrolytic carbon is vapor deposited onto a concave surface of a heated substrate to a total uniform thickness in the range of about 0.1 to 1.0 micrometer. The carbon film on the substrate is provided with a layer of adherent polymeric resin. The resulting composite film of pyrolytic carbon and polymeric resin is then easily separated from the substrate by shrinking the polymeric resin coating with thermally induced forces.

Synthesis of polymer nanostructures via the use of surfactant surface aggregates as templates

NASA Astrophysics Data System (ADS)

Marquez, Maricel

The subject of this work is the synthesis of polymer nanostructures via the use of surfactant surface aggregates as templates, also termed Template Assisted Admicellar Polymerization (TAAP). The first chapter reviews some of the most current nanopatterning techniques (including both top-down and bottom-up approaches), with particular emphasis on the fabrication of organic and inorganic patterned nanostructures via particle lithography. In chapter 2, highly ordered hexagonal arrays of latex spheres were prepared on highly ordered pyrolytic graphite (HOPG) from a variation of the Langmuir Blodgett technique, using an anionic surfactant (SDS), and a low molecular weight (ca. 10000) polyacrylamide as spreading agents. When a nonionic polyethoxylated (EO = 9) surfactant was used as the spreading agent, no ordered arrays were observed. Based on the correlation found between the surface tension in the presence of the latex particles and the critical concentration at which hexagonal arrangements of latex spheres occurs; a model was proposed to explain the role of the spreading agent in forming stable monolayers at the air/liquid interface, which in turn are necessary for the formation of well-ordered monolayers on a solid substrate from the LB technique. According to this model, solid-like regions of small numbers of latex spheres form at the liquid-air interface, which are then transferred to the substrate. These ordered regions then act as nuclei for the formation of 2D arrays of latex spheres on the surface upon water evaporation. The role of other factors such as relative humidity, substrate and solvent choice, and pulling vs. compression speed were also found to affect the quality of the monolayers formed. Finally, a simple, easy to automate, yet effective surface tension method was proposed to predict the optimal conditions for the formation of ordered monolayers using a variation of the LB deposition method from any monodisperse set of spheres. In chapter 3, a novel method for the formation of nanometer-scale polymer structures on solid surfaces via template assisted admicellar polymerization (TAAP) is described. Admicellar polymerization uses a surfactant layer adsorbed on a surface to localize monomer to the surface prior to polymerization of the monomer. TAAP refers to nanostructures that form by restricting adsorption to the uncovered sites of an already-templated surface. In this case, the interstitial sites between adsorbed latex spheres were used as the template. Unlike most other process that form polymer nanostructures, polymer dimensions can be significantly smaller than the interstitial size because of sphere-surfactant-monomer interactions. As a proof of concept, nanostructures formed via TAAP were compared to structures prepared by others via adsorption of three different proteins (Bovine serum albumin, fibrinogen, and anti-mouse IgG) in the interstitial sites of colloidal monolayers. The size and shape of the nanostructures formed (honeycomb vs. pillars) was dependent upon the size of the spheres utilized and the method of polymer deposition (i.e. admicellar polymerization vs. polymer adsorption). Thinner honeycomb walls, and larger separation distances between the template and the nanostructures were consistently found for TAAP. In chapter 4, an in-depth study of the factors affecting TAAP is presented for three different monomers: aniline, pyrrole and methyl methacrylate; and three different surfaces: highly ordered pyrolytic graphite (HOPG), gold, and SiO2. Among the parameters discussed are the effect of monomer and surfactant concentration, surfactant chain length, polymerization time and temperature, solution ionic strength, substrate choice and surface treatment. Control over these parameters allowed the synthesis of polymer nanopillars, nanorings, honeycombs, and "honeytubes." Experimental results showed that the nanostructures' morphology can be effectively modified by changing the length of the hydrophobic chain of the surfactant. Nanostructures with fewer defects were found for surfactants with the longest hydrophobic tails (i.e. 12 carbon atoms). The hydrophobic nature of the monomer also seemed to affect the morphology of the nanostructure; poly(methyl methacrylate) (PMMA) honeycombs showed thicker walls compared to polyaniline (PANI) and polypyrrole (Ppy). In general, HOPG seems to be a better choice of substrate for TAAP compared to gold-coated glass and SiO2 wafers. Preliminary results on the formation of layered polymer nanostructures via multiple TAAP sequences were also presented.

Nanocarbon: Defect Architectures and Properties

NASA Astrophysics Data System (ADS)

Vuong, Amanda

The allotropes of carbon make its solid phases amongst the most diverse of any element. It can occur naturally as graphite and diamond, which have very different properties that make them suitable for a wide range of technological and commercial purposes. Recent developments in synthetic carbon include Highly Oriented Pyrolytic Graphite (HOPG) and nano-carbons, such as fullerenes, nanotubes and graphene. The main industrial application of bulk graphite is as an electrode material in steel production, but in purified nuclear graphite form, it is also used as a moderator in Advanced Gas-cooled Reactors across the United Kingdom. Both graphene and graphite are damaged over time when subjected to bombardment by electrons, neutrons or ions, and these have a wide range of effects on their physical and electrical properties, depending on the radiation flux and temperature. This research focuses on intrinsic defects in graphene and dimensional change in nuclear graphite. The method used here is computational chemistry, which complements physical experiments. Techniques used comprise of density functional theory (DFT) and molecular dynamics (MD), which are discussed in chapter 2 and chapter 3, respectively. The succeeding chapters describe the results of simulations performed to model defects in graphene and graphite. Chapter 4 presents the results of ab initio DFT calculations performed to investigate vacancy complexes that are formed in AA stacked bilayer graphene. In AB stacking, carbon atoms surrounding the lattice vacancies can form interlayer structures with sp2 bonding that are lower in energy compared to in-plane reconstructions. From the investigation of AA stacking, sp2 interlayer bonding of adjacent multivacancy defects in registry creates a type of stable sp2 bonded wormhole between the layers. Also, a new class of mezzanine structure characterised by sp3 interlayer bonding, resembling a prismatic vacancy loop has also been identified. The mezzanine, which is a V6 hexavacancy variant, where six sp3 carbon atoms sit midway between two carbon layers and bond to both, is substantially more stable than any other vacancy aggregate in AA stacked layers. Chapter 5 presents the results of ab initio DFT calculations performed to investigate the wormhole and mezzanine defect that were identified in chapter 4 and the ramp defect discovered by Trevethan et al.. DFT calculations were performed on these defects in twisted bilayer graphene. From the investigation of vacancy complexes in twisted bilayer graphene, it is found that vacancy complexes are unstable in the twisted region and are more favourable in formation energy when the stacking arrangement is close to AA or AB stacking. It has also been discovered that the ramp defect is more stable in the twisted bilayer graphene compared to the mezzanine defect. Chapter 6 presents the results of ab initio DFT calculations performed to investigate a form of extending defect, prismatic edge dislocation. Suarez-Martinez et al.'s research suggest the armchair core is disconnected from any other layer, whilst the zigzag core is connected. In the investigation here, the curvature of the mezzanine defect allows it to swing between the armchair, zigzag and Klein in the AA stacking. For the AB stacking configuration, the armchair and zigzag core are connected from any other layer. Chapter 7 present results of MD simulations using the adaptive intermolecular reactive empirical bond order (AIREBO) potential to investigate the dimensional change of graphite due to the formation of vacancies present in a single crystal. It has been identified that there is an expansion along the c-axis, whilst a contraction along the a- and b- axes due to the coalescence of vacancy forming in-plane and between the layers. The results here are in good agreement with experimental studies of low temperature irradiation. The final chapter gives conclusions to this work.

Fundamental studies of graphene/graphite and graphene-based Schottky photovoltaic devices

NASA Astrophysics Data System (ADS)

Miao, Xiaochang

In the carbon allotropes family, graphene is one of the most versatile members and has been extensively studied since 2004. The goal of this dissertation is not only to investigate the novel fundamental science of graphene and its three-dimensional sibling, graphite, but also to explore graphene's promising potential in modern electronic and optoelectronic devices. The first two chapters provide a concise introduction to the fundamental solid state physics of graphene (as well as graphite) and the physics at the metal/semiconductor interfaces. In the third chapter, we demonstrate the formation of Schottky junctions at the interfaces of graphene (semimetal) and various inorganic semiconductors that play dominating roles in today's semiconductor technology, such as Si, SiC, GaAs and GaN. As shown from their current-voltage (I -V) and capacitance-voltage (C-V) characteristics, the interface physics can be well described within the framework of the Schottky-Mott model. The results are also well consist with that from our previous studies on graphite based Schottky diodes. In the fourth chapter, as an extension of graphene based Schottky work, we investigate the photovoltaic (PV) effect of graphene/Si junctions after chemically doped with an organic polymer (TFSA). The power conversion efficiency of the solar cell improves from 1.9% to 8.6% after TFSA doping, which is the record in all graphene based PVs. The I -V, C-V and external quantum efficiency measurements suggest 12 that such a significant enhancement in the device performance can be attributed to a doping-induced decrease in the series resistance and a simultaneous increase in the built-in potential. In the fifth chapter, we investigate for the first time the effect of uniaxial strains on magneto-transport properties of graphene. We find that low-temperature weak localization effect in monolayer graphene is gradually suppressed under increasing strains, which is due to a strain-induced decreased intervalley-scattering rate. In chapter 6, we study the high vacuum thermal annealing effect on an unconventional ferromagnetism (FM) in highly oriented pyrolytic graphite (HOPG). The FM diminishes and eventually disappears in annealed samples accompanied by improved electrical transport properties and crystallinity. Our results indicate that the FM is mainly coming from the lattice imperfections.

Structure and radical scavenging activity relationships of pyrolytic lignins

USDA-ARS?s Scientific Manuscript database

This work deals with antioxidant properties of pyrolytic lignins against two free radicals, the 1,1-diphenyl-2-picrylhydrazyl and the 2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid). Pyrolytic lignins produced by the thermal pyrolysis of the Etek lignin were extracted from the liquid pyrolysi...

Spin-density wave state in simple hexagonal graphite

NASA Astrophysics Data System (ADS)

Mosoyan, K. S.; Rozhkov, A. V.; Sboychakov, A. O.; Rakhmanov, A. L.

2018-02-01

Simple hexagonal graphite, also known as AA graphite, is a metastable configuration of graphite. Using tight-binding approximation, it is easy to show that AA graphite is a metal with well-defined Fermi surface. The Fermi surface consists of two sheets, each shaped like a rugby ball. One sheet corresponds to electron states, another corresponds to hole states. The Fermi surface demonstrates good nesting: a suitable translation in the reciprocal space superposes one sheet onto another. In the presence of the electron-electron repulsion, a nested Fermi surface is unstable with respect to spin-density-wave ordering. This instability is studied using the mean-field theory at zero temperature, and the spin-density-wave order parameter is evaluated.

78 FR 56864 - Small Diameter Graphite Electrodes From the People's Republic of China: Affirmative Final...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-09-16

... DEPARTMENT OF COMMERCE International Trade Administration [A-570-929] Small Diameter Graphite... (Department) determines that imports from the People's Republic of China (PRC) of graphite electrodes... Act of 1930, as amended (the Act).\\1\\ \\1\\ See Antidumping Duty Order: Small Diameter Graphite...

Linearization of calibration curves by aerosol carrier effect of CCl 4 vapor in electrothermal vaporization inductively coupled plasma mass spectrometry

NASA Astrophysics Data System (ADS)

Kántor, Tibor; de Loos-Vollebregt, Margaretha T. C.

2005-03-01

Carbon tetrachloride vapor as gaseous phase modifier in a graphite furnace electrothermal vaporizer (GFETV) converts heavy volatile analyte forms to volatile and medium volatile chlorides and produces aerosol carrier effect, the latter being a less generally recognized benefit. However, the possible increase of polyatomic interferences in inductively coupled plasma mass spectrometry (GFETV-ICP-MS) by chlorine and carbon containing species due to CCl 4 vapor introduction has been discouraging with the use of low resolution, quadrupole type MS equipment. Being aware of this possible handicap, it was aimed at to investigate the feasibility of the use of this halogenating agent in ICP-MS with regard of possible hazards to the instrument, and also to explore the advantages under these specific conditions. With sample gas flow (inner gas flow) rate not higher than 900 ml min -1 Ar in the torch and 3 ml min -1 CCl 4 vapor flow rate in the furnace, the long-term stability of the instrument was ensured and the following benefits by the halocarbon were observed. The non-linearity error (defined in the text) of the calibration curves (signal versus mass functions) with matrix-free solution standards was 30-70% without, and 1-5% with CCl 4 vapor introduction, respectively, at 1 ng mass of Cu, Fe, Mn and Pb analytes. The sensitivity for these elements increased by 2-4-fold with chlorination, while the relative standard deviation (RSD) was essentially the same (2-5%) for the two cases in comparison. A vaporization temperature of 2650 °C was required for Cr in Ar atmosphere, while 2200 °C was sufficient in Ar + CCl 4 atmosphere to attain complete vaporization. Improvements in linear response and sensitivity were the highest for this least volatile element. The pyrolytic graphite layer inside the graphite tube was protected by the halocarbon, and tube life time was further increased by using traces of hydrocarbon vapor in the external sheath gas of the graphite furnace. Details of the modification of the gas supply for HGA-600MS furnace and the design of the volatilization device are described.

Removal of copper by oxygenated pyrolytic tire char: kinetics and mechanistic insights.

PubMed

Quek, Augustine; Balasubramanian, Rajashekhar

2011-04-01

The kinetics of copper ion (Cu(II)) removal from aqueous solution by pyrolytic tire char was modeled using five different conventional models. A modification to these models was also developed through a modified equation that accounts for precipitation. Conventional first- and second-order reaction models did not fit the copper sorption kinetics well, indicating a lack of simple rate-order dependency on solute concentration. Instead, a reversible first-order rate reaction showed the best fit to the data, indicating a dependence on surface functional groups. Due to the varying solution pH during the sorption process, modified external and internal mass transfer models were employed. Results showed that the sorption of copper onto oxygenated chars was limited by external mass transfer and internal resistance with and without the modification. However, the modification of the sorption process produced very different results for unoxygenated chars, which showed neither internal nor external limitation to sorption. Instead, its slow sorption rate indicates a lack of surface functional groups. The sorption of Cu(II) by oxygenated and unoxygenated chars was also found to occur via three and two distinct stages, respectively. Copyright © 2010 Elsevier Inc. All rights reserved.

Damage to the microbial cell membrane during pyrolytic sugar utilization and strategies for increasing resistance.

PubMed

Jin, Tao; Rover, Marjorie R; Petersen, Elspeth M; Chi, Zhanyou; Smith, Ryan G; Brown, Robert C; Wen, Zhiyou; Jarboe, Laura R

2017-09-01

Lignocellulosic biomass is an appealing feedstock for the production of biorenewable fuels and chemicals, and thermochemical processing is a promising method for depolymerizing it into sugars. However, trace compounds in this pyrolytic sugar syrup are inhibitory to microbial biocatalysts. This study demonstrates that hydrophobic inhibitors damage the cell membrane of ethanologenic Escherichia coli KO11+lgk. Adaptive evolution was employed to identify design strategies for improving pyrolytic sugar tolerance and utilization. Characterization of the resulting evolved strain indicates that increased resistance to the membrane-damaging effects of the pyrolytic sugars can be attributed to a glutamine to leucine mutation at position 29 of carbon storage regulator CsrA. This single amino acid change is sufficient for decreasing EPS protein production and increasing membrane integrity when exposed to pyrolytic sugars.

76 FR 36092 - Small Diameter Graphite Electrodes From the People's Republic of China: Extension of Time Limit...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-06-21

... DEPARTMENT OF COMMERCE International Trade Administration [A-570-929] Small Diameter Graphite... antidumping duty order on small diameter graphite electrodes from the People's Republic of China (``PRC'') for... preliminary results of this review were published on March 7, 2011. See Small Diameter Graphite Electrodes...

77 FR 6060 - Small Diameter Graphite Electrodes from the People's Republic of China: Extension of Time Limit...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-07

... DEPARTMENT OF COMMERCE International Trade Administration [A-570-929] Small Diameter Graphite... Department) initiated an administrative review of the antidumping duty order on small diameter graphite... preliminary results of this review by 95 days until February 3, 2012. See Small Diameter Graphite Electrodes...

Study of high resistance inorganic coatings on graphite fibers. [for graphite-epoxy composite materials

NASA Technical Reports Server (NTRS)

Galasso, F. S.; Veltri, R. D.; Scola, D. A.

1979-01-01

Coatings made of boron, silicon carbide, silica, and silica-like materials were studied to determine their ability to increase resistance of graphite fibers. The most promising results were attained by chemical vapor depositing silicon carbide on graphite fiber followed by oxidation, and drawing graphite fiber through ethyl silicate followed by appropriate heat treatments. In the silicon carbide coating studies, no degradation of the graphite fibers was observed and resistance values as high as three orders of magnitude higher than that of the uncoated fiber was attained. The strength of a composite fabricated from the coated fiber had a strength which compared favorably with those of composites prepared from uncoated fiber. For the silica-like coated fiber prepared by drawing the graphite fiber through an ethyl silicate solution followed by heating, coated fiber resistances about an order of magnitude greater than that of the uncoated fiber were attained. Composites prepared using these fibers had flexural strengths comparable with those prepared using uncoated fibers, but the shear strengths were lower.

Destruction Chemistry of Mustard Simulants

DTIC Science & Technology

2008-07-04

organosulfur compounds under both pyrolytic and oxidative conditions. We focus on the destruction of alkyl sulfides that are surrogates for chemical...destruction chemistry of organosulfur compounds under both pyrolytic and oxidative conditions. We focus on the destruction of alkyl sulfides that are...ACCOMPLISHMENTS ABSTRACT This study investigates the destruction chemistry of organosulfur compounds under both pyrolytic and oxidative conditions. We

Deducing 2D Crystal Structure at the Solid/Liquid Interface with Atomic Resolution by Combined STM and SFG Study

NASA Astrophysics Data System (ADS)

McClelland, Arthur; Ahn, Seokhoon; Matzger, Adam J.; Chen, Zhan

2009-03-01

Supplemented by computed models, Scanning Tunneling Microscopy (STM) can provide detailed structure of 2D crystals formed at the liquid/solid interface with atomic resolution. However, some structural information such as functional group orientations in such 2D crystals needs to be tested experimentally to ensure the accuracy of the deduced structures. Due to the limited sensitivity, many other experimental techniques such as Raman and infrared spectroscopy have not been allowed to provide such structural information of 2D crystals. Here we showed that Sum Frequency Generation Vibrational Spectroscopy (SFG) can measure average orientation of functional groups in such 2D crystals, or physisorbed monolayers, providing key experimental data to aid in the modeling and interpretation of the STM images. The usefulness of combining these two techniques is demonstrated with a phthalate diesters monolayer formed at the 1-phenyloctane/ highly oriented pyrolytic graphite (HOPG) interface. The spatial orientation of the ester C=O of the monolayer was successfully determined using SFG.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liscio, A.; CNISM and Dipartimento di Fisica, Universita di Roma Tre, Via Vasca Navale 84, 00146 Roma; Ruocco, A.

This paper deals with the mechanism of grazing incidence (e,2e) events from surfaces. Two different approaches are considered. In both cases, elastic scattering with the crystal lattice assists the inelastic collision; these two steps are coupled either coherently or incoherently. Experimental evidence is given that the 'coherent' approach reproduces better the cross section dependence on momentum transfer in the specific case of asymmetric kinematics at moderate electron energies. This model has allowed us to map out the band dispersion of the outermost valence states of highly oriented pyrolytic graphite and to measure the momentum distribution of {pi}-electron states without invokingmore » the contribution of reciprocal lattice vectors in the momentum conservation. Agreement between theory and experiment is satisfactory, though the presence of events where crystal momentum is reconstructed cannot be ruled out. These results, obtained with a significant reduction of the experiment duration by an implemented apparatus, show that reflection (e,2e) can be used to build up a momentum spectroscopy with high surface sensitivity.« less

Addressing individual metal ion centers in supramolecules by STS

NASA Astrophysics Data System (ADS)

Alam, M. S.; Ako, A. M.; Ruben, M.; Thompson, L. K.; Lehn, J.-M.

2005-03-01

As the information of STM measurements arises from electronic structure, separating information on the topography is not straightforward for complex molecules. Scanning tunneling spectroscopy (STS) measurements give information about the molecular energy levels, which are next to the molecules Fermi level. Using a home built STM working under ambient conditions, we succeeded to combine high resolution topography mapping with simultaneous current-voltage characteristics (STS) measurements on single molecules deposited on highly oriented pyrolytic graphite surfaces. We present our recent results on grid-type molecules [Co4L4] (L=4,6-bis(2',2''-bipyridyl-6-yl)pyrimidine) and [Mn9L6] (L=2POAP-2H) as well as on ring-shaped Fe ion chains [Fe6Cl6L6] (L=1-Ecosyliminodiethanol). Small, regular molecule clusters as well as separated single molecules were observed. We found a rather large contrast at the expected location of the metal centers in our molecules, i.e. the location of the individual metal ions in their organic matrix is directly addressable by STS.

Space processing of composite materials

NASA Technical Reports Server (NTRS)

Steurer, W. H.; Kaye, S.

1975-01-01

Materials and processes for the testing of aluminum-base fiber and particle composites, and of metal foams under extended-time low-g conditions were investigated. A wetting and dispersion technique was developed, based on the theory that under the absence of a gas phase all solids are wetted by liquids. The process is characterized by a high vacuum environment and a high temperature cycle. Successful wetting and dispersion experiments were carried out with sapphire fibers, whiskers and particles, and with fibers of silicon carbide, pyrolytic graphite and tungsten. The developed process and facilities permit the preparation of a precomposite which serves as sample material for flight experiments. Low-g processing consists then merely in the uniform redistribution of the reinforcements during a melting cycle. For the preparation of metal foams, gas generation by means of a thermally decomposing compound was found most adaptable to flight experiments. For flight experiments, the use of compacted mixture of the component materials limits low-g processing to a simple melt cycle.

Direct determination of the local Hamaker constant of inorganic surfaces based on scanning force microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krajina, Brad A.; Kocherlakota, Lakshmi S.; Overney, René M., E-mail: roverney@u.washington.edu

The energetics involved in the bonding fluctuations between nanometer-sized silicon dioxide (SiO{sub 2}) probes and highly oriented pyrolytic graphite (HOPG) and molybdenum disulfide (MoS{sub 2}) could be quantified directly and locally on the submicron scale via a time-temperature superposition analysis of the lateral forces between scanning force microscopy silicon dioxide probes and inorganic sample surfaces. The so-called “intrinsic friction analysis” (IFA) provided direct access to the Hamaker constants for HOPG and MoS{sub 2}, as well as the control sample, calcium fluoride (CaF{sub 2}). The use of scanning probe enables nanoscopic analysis of bonding fluctuations, thereby overcoming challenges associated with largermore » scale inhomogeneity and surface roughness common to conventional techniques used to determine surface free energies and dielectric properties. A complementary numerical analysis based on optical and electron energy loss spectroscopy and the Lifshitz quantum electrodynamic theory of van der Waals interactions is provided and confirms quantitatively the IFA results.« less

Septipyridines as conformationally controlled substitutes for inaccessible bis(terpyridine)-derived oligopyridines in two-dimensional self-assembly

PubMed Central

Caterbow, Daniel; Künzel, Daniela; Mavros, Michael G; Groß, Axel; Landfester, Katharina

2011-01-01

Summary The position of the peripheral nitrogen atoms in bis(terpyridine)-derived oligopyridines (BTPs) has a strong impact on their self-assembly behavior at the liquid/HOPG (highly oriented pyrolytic graphite) interface. The intermolecular hydrogen bonding interactions in these peripheral pyridine units show specific 2D structures for each BTP isomer. From nine possible constitutional isomers only four have been described in the literature. The synthesis and self-assembling behavior of an additional isomer is presented here, but the remaining four members of the series are synthetically inaccessible. The self-assembling properties of three of the missing four BTP isomers can be mimicked by making use of the energetically preferred N–C–C–N transoid conformation between 2,2'-bipyridine subunits in a new class of so-called septipyridines. The structures are investigated by scanning tunneling microscopy (STM) and a combination of force-field and first-principles electronic structure calculations. PMID:22003448

Diffraction based method to reconstruct the spectrum of the Thomson scattering x-ray source

NASA Astrophysics Data System (ADS)

Chi, Zhijun; Yan, Lixin; Zhang, Zhen; Zhou, Zheng; Zheng, Lianmin; Wang, Dong; Tian, Qili; Wang, Wei; Nie, Zan; Zhang, Jie; Du, Yingchao; Hua, Jianfei; Shi, Jiaru; Pai, Chihao; Lu, Wei; Huang, Wenhui; Chen, Huaibi; Tang, Chuanxiang

2017-04-01

As Thomson scattering x-ray sources based on the collision of intense laser and relativistic electrons have drawn much attention in various scientific fields, there is an increasing demand for the effective methods to reconstruct the spectrum information of the ultra-short and high-intensity x-ray pulses. In this paper, a precise spectrum measurement method for the Thomson scattering x-ray sources was proposed with the diffraction of a Highly Oriented Pyrolytic Graphite (HOPG) crystal and was demonstrated at the Tsinghua Thomson scattering X-ray source. The x-ray pulse is diffracted by a 15 mm (L) ×15 mm (H)× 1 mm (D) HOPG crystal with 1° mosaic spread. By analyzing the diffraction pattern, both x-ray peak energies and energy spectral bandwidths at different polar angles can be reconstructed, which agree well with the theoretical value and simulation. The higher integral reflectivity of the HOPG crystal makes this method possible for single-shot measurement.

Diffraction based method to reconstruct the spectrum of the Thomson scattering x-ray source.

PubMed

Chi, Zhijun; Yan, Lixin; Zhang, Zhen; Zhou, Zheng; Zheng, Lianmin; Wang, Dong; Tian, Qili; Wang, Wei; Nie, Zan; Zhang, Jie; Du, Yingchao; Hua, Jianfei; Shi, Jiaru; Pai, Chihao; Lu, Wei; Huang, Wenhui; Chen, Huaibi; Tang, Chuanxiang

2017-04-01

As Thomson scattering x-ray sources based on the collision of intense laser and relativistic electrons have drawn much attention in various scientific fields, there is an increasing demand for the effective methods to reconstruct the spectrum information of the ultra-short and high-intensity x-ray pulses. In this paper, a precise spectrum measurement method for the Thomson scattering x-ray sources was proposed with the diffraction of a Highly Oriented Pyrolytic Graphite (HOPG) crystal and was demonstrated at the Tsinghua Thomson scattering X-ray source. The x-ray pulse is diffracted by a 15 mm (L) ×15 mm (H)× 1 mm (D) HOPG crystal with 1° mosaic spread. By analyzing the diffraction pattern, both x-ray peak energies and energy spectral bandwidths at different polar angles can be reconstructed, which agree well with the theoretical value and simulation. The higher integral reflectivity of the HOPG crystal makes this method possible for single-shot measurement.

Electrodeposition of Si from an Ionic Liquid Bath at Room Temperature in the Presence of Water.

PubMed

Shah, Nisarg K; Pati, Ranjan Kumar; Ray, Abhijit; Mukhopadhyay, Indrajit

2017-02-21

The electrochemical deposition of Si has been carried out in an ionic liquid medium in the presence of water in a limited dry nitrogen environment on highly oriented pyrolytic graphite (HOPG) at room temperature. It has been found that the presence of water in ionic liquids does not affect the available effective potential window to a large extent. Silicon has been successfully deposited electrochemically in the overpotential regime in two different ionic liquids, namely, BMImTf 2 N and BMImPF 6 , in the presence of water. Although a Si thin film has been obtained from BMImTf 2 N; only distinguished Si crystals protected in ionic liquid droplets have been observed from BMImPF 6 . The most important observation of the present investigation is that the Si precursor, SiCl 4 , instead of undergoing hydrolysis, even in the presence of water, coexisted with ionic liquids, and elemental Si has been successfully electrodeposited.

Simultaneous voltammetric determination of prednisone and prednisolone in human body fluids.

PubMed

Goyal, Rajendra N; Bishnoi, Sunita

2009-08-15

A sensitive, rapid and reliable electrochemical method based on voltammetry at single wall carbon nanotube (SWNT) modified edge plane pyrolytic graphite electrode (EPPGE) is proposed for the simultaneous determination of prednisolone and prednisone in human body fluids and pharmaceutical preparations. The electrochemical response of both the drugs was evaluated by osteryoung square wave voltammetry (OSWV) in phosphate buffer medium of pH 7.2. The modified electrode exhibited good electrocatalytic properties towards prednisone and prednisolone reduction with a peak potential of approximately -1230 and approximately -1332 mV respectively. The concentration versus peak current plots were linear for both the analytes in the range 0.01-100 microM and the detection limit (3 sigma/slope) observed for prednisone and prednisolone were 0.45 x 10(-8), 0.90 x 10(-8)M, respectively. The results of the quantitative estimation of prednisone and prednisolone in biological fluids were also compared with HPLC and the results were in good agreement.

Study of Drug Metabolism by Xanthine Oxidase

PubMed Central

Zhao, Jing; He, Xiaolin; Yang, Nana; Sun, Lizhou; Li, Genxi

2012-01-01

In this work, we report the studies of drug metabolism by xanthine oxidase (XOD) with electrochemical techniques. Firstly, a pair of stable, well-defined and quasi-reversible oxidation/reduction peaks is obtained with the formal potential at −413.1 mV (vs. SCE) after embedding XOD in salmon sperm DNA membrane on the surface of pyrolytic graphite electrode. Then, a new steady peak can be observed at −730 mV (vs. SCE) upon the addition of 6-mercaptopurine (6-MP) to the electrochemical system, indicating the metabolism of 6-MP by XOD. Furthermore, the chronoamperometric response shows that the current of the catalytic peak located at −730 mV increases with addition of 6-MP in a concentration-dependent manner, and the increase of the chronoamperometric current can be inhibited by an XOD inhibitor, quercetin. Therefore, our results prove that XOD/DNA modified electrode can be efficiently used to study the metabolism of 6-MP, which may provide a convenient approach for in vitro studies on enzyme-catalyzed drug metabolism. PMID:22606015

Enzyme electrokinetics: hydrogen evolution and oxidation by Allochromatium vinosum [NiFe]-hydrogenase.

PubMed

Léger, Christophe; Jones, Anne K; Roseboom, Winfried; Albracht, Simon P J; Armstrong, Fraser A

2002-12-31

The mechanism of catalytic hydrogen evolution and oxidation by Allochromatium vinosum [NiFe]-hydrogenase has been studied by protein film voltammetry (PFV) with the enzyme adsorbed at a pyrolytic graphite edge electrode. By analyzing the entire shapes of catalytic voltammograms, the energetics of the catalytic cycles (reduction potentials and acidity constants of the active states), including the detailed profiles of activity against pH and the sequences of proton and electron transfers, have been determined, and these are discussed with respect to the mechanism. PFV, which probes rates as a continuous function of the electrochemical potential (i.e., in the "potential domain"), is proven to be an invaluable tool for determining the redox properties of an active site in the presence of its substrate, at room temperature, and during turnover. This is especially relevant in the case of the active states of hydrogenase, since one of its substrates (the proton) is always present at significant levels in the titration medium at physiological pH values.

Size-dependent electrocatalytic activity of gold nanoparticles on HOPG and highly boron-doped diamond surfaces.

PubMed

Brülle, Tine; Ju, Wenbo; Niedermayr, Philipp; Denisenko, Andrej; Paschos, Odysseas; Schneider, Oliver; Stimming, Ulrich

2011-12-06

Gold nanoparticles were prepared by electrochemical deposition on highly oriented pyrolytic graphite (HOPG) and boron-doped, epitaxial 100-oriented diamond layers. Using a potentiostatic double pulse technique, the average particle size was varied in the range from 5 nm to 30 nm in the case of HOPG as a support and between < 1 nm and 15 nm on diamond surfaces, while keeping the particle density constant. The distribution of particle sizes was very narrow, with standard deviations of around 20% on HOPG and around 30% on diamond. The electrocatalytic activity towards hydrogen evolution and oxygen reduction of these carbon supported gold nanoparticles in dependence of the particle sizes was investigated using cyclic voltammetry. For oxygen reduction the current density normalized to the gold surface (specific current density) increased for decreasing particle size. In contrast, the specific current density of hydrogen evolution showed no dependence on particle size. For both reactions, no effect of the different carbon supports on electrocatalytic activity was observed.

Absorber for wakefield interference management at the entrance of the wiggler of a free electron laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marchlik, Matthew; Biallas, George Herman

A method for managing the broad band microwave and TeraHertz (THz) radiation in a free electron laser (FEL) having a wiggler producing power in the electromagnetic spectrum. The method includes placement of broadband microwave and TeraHertz (THz) radiation absorbers on the upstream end of the wiggler. The absorbers dampen the bounced back, broad band microwave and THz radiation returning from the surfaces outside the nose of the cookie-cutter and thus preventing broadening of the electron beam pulse's narrow longitudinal energy distribution. Broadening diminishes the ultimate laser power from the wiggler. The broadband microwave and THz radiation absorbers are placed onmore » either side of the slot in the cookie-cutter that shapes the wake field wave of the electron pulse to the slot shape of the wiggler chamber aperture. The broad band microwave and THz radiation absorber is preferably a non-porous pyrolytic grade of graphite with small grain size.« less

Fabrication of bi-layer graphene and theoretical simulation for its possible application in thin film solar cell.

PubMed

Behura, Sanjay K; Mahala, Pramila; Nayak, Sasmita; Yang, Qiaoqin; Mukhopadhyay, Indrajit; Janil, Omkar

2014-04-01

High quality graphene film is fabricated using mechanical exfoliation of highly-oriented pyrolytic graphite. The graphene films on glass substrates are characterized using field-emission scanning electron microscopy, atomic force microscopy, Raman spectroscopy, UV-vis spectroscopy and Fourier transform infrared spectroscopy. A very high intensity ratio of 2D to G-band (to approximately 1.67) and narrow 2D-band full-width at half maximum (to approximately 40 cm(-1)) correspond to the bi-layer graphene formation. The bi-layer graphene/p-GaN/n-InGaN/n-GaN/GaN/sAl2O3 system is studied theoretically using TCAD Silvaco software, in which the properties of exfoliated bi-layer graphene are used as transparent and conductive film, and the device exhibits an efficiency of 15.24% compared to 13.63% for ITO/p-GaN/n-InGaN/n-GaN/GaN/Al2O3 system.

Production of sp3 hybridization by swift heavy ion irradiation of HOPG

NASA Astrophysics Data System (ADS)

Zeng, J.; Zhai, P. F.; Liu, J.; Yao, H. J.; Duan, J. L.; Hou, M. D.; Sun, Y. M.; Li, G. P.

2013-07-01

Highly oriented pyrolytic graphite (HOPG) samples were irradiated by swift heavy ions (86Kr, 209Bi and 238U) with the fluence of 1011-1013 ions/cm2 at room temperature. The production of sp3 hybridization by the irradiation process has been confirmed directly by X-ray photoelectron spectroscopy (XPS). In this work, both irradiated and pristine HOPG samples were investigated by XPS and Raman spectroscopy. The existence of sp3 component is confirmed on the surface of the irradiated HOPG samples. XPS result shows that the acreage ratio Isp3/Isp2 increases with the ion fluence and saturates at a higher value of irradiation. It is found that the amount of hybridization (Isp3/Isp2) strongly depends on the electronic energy loss in the sample. Raman spectra of the irradiated samples show the increasing of acreage ratio ID/IG with the ion fluence, which indicates the change of the atomic structure and the phase transition from sp2 to sp3.

Interfacial assembly structures and nanotribological properties of saccharic acids.

PubMed

Shi, Hongyu; Liu, Yuhong; Zeng, Qingdao; Yang, Yanlian; Wang, Chen; Lu, Xinchun

2017-01-04

Saccharides have been recognized as potential bio-lubricants because of their good hydration ability. However, the interfacial structures of saccharides and their derivatives are rarely studied and the molecular details of interaction mechanisms have not been well understood. In this paper, the supramolecular assembly structures of saccharic acids (including galactaric acid and lactobionic acid), mediated by hydrogen bonds O-HN and O-HO, were successfully constructed on a highly oriented pyrolytic graphite (HOPG) surface by introducing pyridine modulators and were explicitly revealed by using scanning tunneling microscopy (STM). Furthermore, friction forces were measured in the saccharic acid/pyridine co-assembled system by atomic force microscopy (AFM), revealing a larger value than a pristine saccharic acid system, which could be attributed to the stronger tip-assembled molecule interactions that lead to the higher potential energy barrier needed to overcome. The effort on saccharide-related supramolecular self-assembly and nanotribological behavior could provide a novel and promising pathway to explore the interaction mechanisms underlying friction and reveal the structure-property relationship at the molecular level.

Poly(ethylene oxide) surfactant polymers.

PubMed

Vacheethasanee, Katanchalee; Wang, Shuwu; Qiu, Yongxing; Marchant, Roger E

2004-01-01

We report on a series of structurally well-defined surfactant polymers that undergo surface-induced self-assembly on hydrophobic biomaterial surfaces. The surfactant polymers consist of a poly(vinyl amine) backbone with poly(ethylene oxide) and hexanal pendant groups. The poly(vinyl amine) (PVAm) was synthesized by hydrolysis of poly(N-vinyl formamide) following free radical polymerization of N-vinyl formamide. Hexanal and aldehyde-terminated poly(ethylene oxide) (PEO) were simultaneously attached to PVAm via reductive amination. Surfactant polymers with different PEO:hexanal ratios and hydrophilic/hydrophobic balances were prepared, and characterized by FT-IR, 1H-NMR and XPS spectroscopies. Surface active properties at the air/water interface were determined by surface tension measurements. Surface activity at a solid surface/water interface was demonstrated by atomic force microscopy, showing epitaxially molecular alignment for surfactant polymers adsorbed on highly oriented pyrolytic graphite. The surfactant polymers described in this report can be adapted for simple non-covalent surface modification of biomaterials and hydrophobic surfaces to provide highly hydrated interfaces.

Cluster formation in laser-induced ablation and evaporation of solids observed by laser ionization time-of-flight mass spectrometry and scanning tunneling microscopy

NASA Astrophysics Data System (ADS)

Tench, R. J.; Balooch, M.; Bernardez, L.; Allen, Mike J.; Siekhaus, W. J.; Olander, D. R.; Wang, W.

1990-04-01

Laser ionization time-of-flight mass analysis (LIMA) used pulses (5ns) of a frequency-quadrupled Nd-YAG laser (266 nm) focused onto spots of 4 to 100 microns diameter to ablate material, and a reflectron time of flight tube to mass-analyze the plume. The observed mass spectra for Si, Pt, SiC, and UO 2 varied in the distribution of ablation products among atoms, molecules and clusters, depending on laser power density and target material. Cleaved surfaces of highly oriented pyrolytic graphite (HOPG) positioned at room temperature either 10 cm away from materials ablated at 10(exp -5) Torr by 1 to 3 excimer laser (308 nm) pulses of 20 ns duration or 1 m away from materials vaporized at 10(exp -8) Torr by 10 Nd-Glass laser pulses of 1 ms duration were analyzed by Scanning Tunneling Microscopy (STM) in air with angstrom resolution. Clusters up to 30 A in diameter were observed.

Direct determination of the local Hamaker constant of inorganic surfaces based on scanning force microscopy

NASA Astrophysics Data System (ADS)

Krajina, Brad A.; Kocherlakota, Lakshmi S.; Overney, René M.

2014-10-01

The energetics involved in the bonding fluctuations between nanometer-sized silicon dioxide (SiO2) probes and highly oriented pyrolytic graphite (HOPG) and molybdenum disulfide (MoS2) could be quantified directly and locally on the submicron scale via a time-temperature superposition analysis of the lateral forces between scanning force microscopy silicon dioxide probes and inorganic sample surfaces. The so-called "intrinsic friction analysis" (IFA) provided direct access to the Hamaker constants for HOPG and MoS2, as well as the control sample, calcium fluoride (CaF2). The use of scanning probe enables nanoscopic analysis of bonding fluctuations, thereby overcoming challenges associated with larger scale inhomogeneity and surface roughness common to conventional techniques used to determine surface free energies and dielectric properties. A complementary numerical analysis based on optical and electron energy loss spectroscopy and the Lifshitz quantum electrodynamic theory of van der Waals interactions is provided and confirms quantitatively the IFA results.

Direct determination of the local Hamaker constant of inorganic surfaces based on scanning force microscopy.

PubMed

Krajina, Brad A; Kocherlakota, Lakshmi S; Overney, René M

2014-10-28

The energetics involved in the bonding fluctuations between nanometer-sized silicon dioxide (SiO2) probes and highly oriented pyrolytic graphite (HOPG) and molybdenum disulfide (MoS2) could be quantified directly and locally on the submicron scale via a time-temperature superposition analysis of the lateral forces between scanning force microscopy silicon dioxide probes and inorganic sample surfaces. The so-called "intrinsic friction analysis" (IFA) provided direct access to the Hamaker constants for HOPG and MoS2, as well as the control sample, calcium fluoride (CaF2). The use of scanning probe enables nanoscopic analysis of bonding fluctuations, thereby overcoming challenges associated with larger scale inhomogeneity and surface roughness common to conventional techniques used to determine surface free energies and dielectric properties. A complementary numerical analysis based on optical and electron energy loss spectroscopy and the Lifshitz quantum electrodynamic theory of van der Waals interactions is provided and confirms quantitatively the IFA results.

Bent crystal spectrometer for both frequency and wavenumber resolved x-ray scattering at a seeded free-electron laser.

PubMed

Zastrau, Ulf; Fletcher, Luke B; Förster, Eckhart; Galtier, Eric Ch; Gamboa, Eliseo; Glenzer, Siegfried H; Heimann, Philipp; Marschner, Heike; Nagler, Bob; Schropp, Andreas; Wehrhan, Ortrud; Lee, Hae Ja

2014-09-01

We present a cylindrically curved GaAs x-ray spectrometer with energy resolution ΔE/E = 1.1 × 10(-4) and wave-number resolution of Δk/k = 3 × 10(-3), allowing plasmon scattering at the resolution limits of the Linac Coherent Light Source (LCLS) x-ray free-electron laser. It spans scattering wavenumbers of 3.6 to 5.2/Å in 100 separate bins, with only 0.34% wavenumber blurring. The dispersion of 0.418 eV/13.5 μm agrees with predictions within 1.3%. The reflection homogeneity over the entire wavenumber range was measured and used to normalize the amplitude of scattering spectra. The proposed spectrometer is superior to a mosaic highly annealed pyrolytic graphite spectrometer when the energy resolution needs to be comparable to the LCLS seeded bandwidth of 1 eV and a significant range of wavenumbers must be covered in one exposure.

High translational energy release in H2 (D2) associative desorption from H (D) chemisorbed on C(0001).

PubMed

Baouche, S; Gamborg, G; Petrunin, V V; Luntz, A C; Baurichter, A; Hornekaer, L

2006-08-28

Highly energetic translational energy distributions are reported for hydrogen and deuterium molecules desorbing associatively from the atomic chemisorption states on highly oriented pyrolytic graphite (HOPG). Laser assisted associative desorption is used to measure the time of flight of molecules desorbing from a hydrogen (deuterium) saturated HOPG surface produced by atomic exposure from a thermal atom source at around 2100 K. The translational energy distributions normal to the surface are very broad, from approximately 0.5 to approximately 3 eV, with a peak at approximately 1.3 eV. The highest translational energy measured is close to the theoretically predicted barrier height. The angular distribution of the desorbing molecules is sharply peaked along the surface normal and is consistent with thermal broadening contributing to energy release parallel to the surface. All results are in qualitative agreement with recent density functional theory calculations suggesting a lowest energy para-type dimer recombination path.

Self-assembly of (perfluoroalkyl)alkanes on a substrate surface from solutions in supercritical carbon dioxide.

PubMed

Gallyamov, Marat O; Mourran, Ahmed; Tartsch, Bernd; Vinokur, Rostislav A; Nikitin, Lev N; Khokhlov, Alexei R; Schaumburg, Kjeld; Möller, Martin

2006-06-14

Toroidal self-assembled structures of perfluorododecylnonadecane and perfluorotetradecyloctadecane have been deposited on mica and highly oriented pyrolytic graphite surfaces by exposure of the substrates to solutions of the (pefluoroalkyl)alkanes in supercritical carbon dioxide. Scanning force microscopy (SFM) images have displayed a high degree of regularity of these self-assembled nanoobjects regarding size, shape, and packing in a monolayer. Analysis of SFM images allowed us to estimate that each toroidal domain has an outer diameter of about 50 nm and consists of several thousands of molecules. We propose a simple model explaining the clustering of the molecules to objects with a finite size. The model based on the close-packing principles predicts formation of toroids, whose size is determined by the molecular geometry. Here, we consider the amphiphilic nature of the (perfluoroalkyl)alkane molecules in combination with incommensurable packing parameters of the alkyl- and the perfluoralkyl-segments to be a key factor for such a self-assembly.

Waste-to-Energy Systems

DTIC Science & Technology

2009-04-01

at hospitals, at schools,” or wherever there are people creating masses of trash.5 Pyrolytic Gasification Pyrolytic gasification is not a new...prevalent with both. Gasification is . . . the chemical reaction and molecular breakdown or degradation of materials. The first pyrolytic gasification...dealing with about 2 tons of mixed solid waste per day, will destroy wood, paper card, food, plastics, and sanitary, clinical, and oil waste and

High vacuum tip-enhanced Raman spectroscope based on a scanning tunneling microscope.

PubMed

Fang, Yurui; Zhang, Zhenglong; Sun, Mengtao

2016-03-01

In this paper, we present the construction of a high-vacuum tip-enhanced Raman spectroscopy (HV-TERS) system that allows in situ sample preparation and measurement. A detailed description of the prototype instrument is presented with experimental validation of its use and novel ex situ experimental results using the HV-TERS system. The HV-TERS system includes three chambers held under a 10(-7) Pa vacuum. The three chambers are an analysis chamber, a sample preparation chamber, and a fast loading chamber. The analysis chamber is the core chamber and contains a scanning tunneling microscope (STM) and a Raman detector coupled with a 50 × 0.5 numerical aperture objective. The sample preparation chamber is used to produce single-crystalline metal and sub-monolayer molecular films by molecular beam epitaxy. The fast loading chamber allows ex situ preparation of samples for HV-TERS analysis. Atomic resolution can be achieved by the STM on highly ordered pyrolytic graphite. We demonstrate the measurement of localized temperature using the Stokes and anti-Stokes TERS signals from a monolayer of 1,2-benzenedithiol on a gold film using a gold tip. Additionally, plasmonic catalysis can be monitored label-free at the nanoscale using our device. Moreover, the HV-TERS experiments show simultaneously activated infrared and Raman vibrational modes, Fermi resonance, and some other non-linear effects that are not observed in atmospheric TERS experiments. The high spatial and spectral resolution and pure environment of high vacuum are beneficial for basic surface studies.

Voltammetric studies of Azathioprine on the surface of graphite electrode modified with graphene nanosheets decorated with Ag nanoparticles.

PubMed

Asadian, Elham; Iraji Zad, Azam; Shahrokhian, Saeed

2016-01-01

By using graphene nanosheets decorated with Ag nanoparticles (AgNPs-G) as an effective approach for the surface modification of pyrolytic graphite electrode (PGE), a sensing platform was fabricated for the sensitive voltammetric determination of Azathioprine (Aza). The prepared AgNPs-G nanosheets were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-vis and Raman spectroscopy techniques. The electrochemical behavior of Aza was investigated by means of cyclic voltammetry. Comparing to the bare PGE, a remarkable enhancement was observed in the response characteristics of Aza on the surface of the modified electrode (AgNPs-G/PGE) as well as a noticeable decrease in its reduction overpotential. These results can be attributed to the incredible enlargement in the microscopic surface area of the electrode due to the presence of graphene nanosheets together with strong adsorption of Aza on its surface. The effect of experimental parameters such as accumulation time, the amount of modifier suspension and pH of the supporting electrolyte were also optimized toward obtaining the maximum sensitivity. Under the optimum conditions, the calibration curve studies demonstrated that the peak current increased linearly with Aza concentrations in the range of 7 × 10(-7) to 1 × 10(-4)mol L(-1) with the detection limit of 68 nM. Further experiments revealed that the modified electrode can be successfully applied for the accurate determination of Aza in pharmaceutical preparations. Copyright © 2015 Elsevier B.V. All rights reserved.

Detailed line shape analysis of the C KVV Auger peak of two carbon allotropes measured using a time of flight positron annihilation induced Auger electron spectrometer

NASA Astrophysics Data System (ADS)

Fairchild, A. J.; Chirayath, V. A.; Chrysler, M. D.; Gladen, R. W.; Imam, S. K.; Koymen, A. R.; Weiss, A. H.

We report a detailed line shape analysis of the positron induced C KVV Auger line shape from highly oriented pyrolytic graphite (HOPG) and a single layer of graphene grown on polycrystalline Cu. A model consisting of the self-fold of the one-electron density of states including terms for hole-hole interactions, charge screening effects, and intrinsic loss mechanisms is compared to experimental C KVV line shapes measured using a positron induced Auger electron spectrometer (PAES). In traditional Auger spectroscopies which use an electron or photon to initiate the Auger process, extracting the relatively small Auger signal from the large secondary background can be quite difficult. Using a very low energy positron beam to create the core hole through an anti-matter matter annihilation entirely eliminates this background. Additionally, PAES has sensitivity to the top most atomic layer since the positron becomes trapped in an image potential well at the surface before annihilation. Therefore, the PAES signal from a single layer of graphene on polycrystalline Cu is primarily from the graphene overlayer with small contributions from the Cu substrate while the PAES signal from HOPG can be viewed as a single graphene layer with a graphite substrate. The influence of these two substrates on C KVV line shape is discussed. This work was supported by NSF Grant No. DMR 1508719 and DMR 1338130.

Ion irradiation used as surrogate of neutron irradiation in graphite: Consequences on 14C and 36Cl behavior and structural evolution

NASA Astrophysics Data System (ADS)

Galy, N.; Toulhoat, N.; Moncoffre, N.; Pipon, Y.; Bérerd, N.; Ammar, M. R.; Simon, P.; Deldicque, D.; Sainsot, P.

2018-04-01

Graphite has been widely used as neutron moderator, reflector or fuel matrix in different types of reactors such as gas cooled nuclear reactors (UNGG, Magnox, AGR), RBMK reactors or high temperature gas cooled reactors. Their operation produces a great quantity of irradiated graphite or other carbonaceous waste (around 250,000 tons worldwide) that requires a special management strategy. In the case of disposal, which is a current management strategy, two main radionuclides, 14C and 36Cl might be dose determining at the outlet. Particular attention is paid to 14C due to its long half-life (T∼5730 years) [1] and as major contributor to the radioactive dose. 14C has two main production routes, i) transmutation of nitrogen (14N(n,p)14C) where nitrogen is mainly adsorbed at the surfaces of the irradiated graphite; ii) activation of carbon from the matrix (13C(n,γ)14C). According to leaching tests, it was shown that even if the quantity of 14C released in the solution is low (less than 1% of the initial inventory), around 30% is in the organic form that would be mobile in repository conditions [2,3]. 36Cl is mainly produced through the activation of 35Cl (35Cl(n,γ)36Cl) which is an impurity in nuclear graphite. Its activity is low but it might be highly mobile in clay host rocks. Thus, in order to make informed decisions about the best management process and to anticipate potential radionuclide dissemination during dismantling and in the repository, it is necessary to collect information on 14C and 36Cl location and speciation in graphite, after reactor closure. The goal of the present paper is therefore to use ion irradiation to simulate neutron irradiation and to evaluate the irradiation effects on the behavior of 36Cl and 14C as well as on the induced graphite structure modifications. For that, to understand and model the underlying mechanisms, we used an indirect approach based on 13C or 37Cl implantation to simulate the respective presence of 14C or 36Cl. These isotopes were implanted into Highly Oriented Pyrolytic Graphite (HOPG) samples used as a model material system representative of the nuclear graphite coke grains which form around 80% of nuclear graphite. Nuclear graphite is manufactured from petroleum coke grains (filler) blended with coal tar pitch acting as a binder. Shaped blocks are formed by extrusion of the blend. They are heat-treated up to about 2800 °C (graphitisation treatment) and polycrystalline graphite is obtained. Blocks, intended for the moderator or reflector, may be further impregnated with pitch, re-baked and regraphitised in order to increase the density. Virgin nuclear graphites have initial densities in the range 1.6-1.8 g cm-3. The difference with graphite crystal (density = 2.265 g cm-3) is due to internal porosity. As a result of mixing of several carbon compounds, this material is structurally heterogeneous at a local scale. Nuclear graphite presents a complex multiscale organisation. It can be locally more or less anisotropic and not completely graphitised. Nuclear graphite has a polycrystalline structure and contains micrometer sized grains. The grains are formed by several more or less oriented crystallites with a size of a few hundreds nanometers. Each crystallite is formed by a triperiodical stacking of graphene planes. Nuclear graphite contains also small amounts of impurities like oxygen, hydrogen, metals and halogens, among them chlorine [4]. Ion beam irradiation was used as a surrogate for neutrons because it may produce cascades (due to ballistic interactions) that could be similar to those created by neutrons in the nuclear reactor. Ion beam (or electron beam) irradiation has been used for many years to simulate neutron irradiation. It has advantages such as for example the possibility to vary the irradiation conditions and sometimes to carry out in situ observations. Moreover, depending on the ion nature and energy, it allows covering a broad range of the neutron recoil spectrum and the rate at which atoms are displaced can be increased in comparison to reactor conditions. Dose rates can thus be much higher than under neutron irradiation allowing for higher amounts of displacements per atoms (dpa) to be reached within some days instead of months or years. Moreover, because there is no sample activation, the samples are not radioactive [5-11]. During neutron irradiation, the neutrons interact with the matter both by collision with the atom nuclei (i.e. ballistic damage) and by nuclear reactions. The first atoms hit by neutrons are caused to move, thus starting a cascade of atomic collisions leading to electronic excitation as they go through the matter and on the path of the atoms they displace (recoil atoms). The ballistic damage can be evaluated using the nuclear stopping power and can be denoted by the number of displacements per atom (dpa). The effect of electronic excitation can be quantified using the electronic stopping power. The experimental simulation of neutron irradiation in a reactor can be done by irradiation of the graphite samples with different ions of different energies. The choice of these parameters enables the study of the damage effects with or without electron excitation or ballistic damage. Thus, knowing that the impinging neutrons induce mainly ballistic damage into the graphite matrix but that part of the recoil carbon energy is also transferred through electronic excitation, it is interesting to use ion irradiation because both ballistic damage and electronic excitation effects can be studied coupled or decoupled according to the nature of the ion, its energy and the fluence. It is possible to cover a wide range of electronic and nuclear stopping powers by working with different particle accelerators. Thus, we simulated the effects of these different irradiation regimes using ion irradiation by varying the Sn(nuclear)/Se(electronic) stopping power ratio as well as the irradiation temperature (from room temperature up to 1000 °C). Indeed, during reactor operation, neutron irradiation leads to changes in the graphite lattice parameters depending on irradiation conditions such as flux and fluence but also temperature [12]. Finally, Secondary Ion Mass Spectrometry (SIMS) analysis was used to determine 13C and 37Cl distribution profiles and allowed us to follow the implanted isotopes behavior. The structural modifications were followed by High Resolution Transmission Electron Microscopy (HRTEM) and Raman microspectrometry.

Surfactant-assisted Nanocasting Route for Synthesis of Highly Ordered Mesoporous Graphitic Carbon and Its Application in CO2 Adsorption

NASA Astrophysics Data System (ADS)

Wang, Yangang; Bai, Xia; Wang, Fei; Qin, Hengfei; Yin, Chaochuang; Kang, Shifei; Li, Xi; Zuo, Yuanhui; Cui, Lifeng

2016-05-01

Highly ordered mesoporous graphitic carbon was synthesized from a simple surfactant-assisted nanocasting route, in which ordered mesoporous silica SBA-15 maintaining its triblock copolymer surfactant was used as a hard template and natural soybean oil (SBO) as a carbon precursor. The hydrophobic domain of the surfactant assisted SBO in infiltration into the template’s mesoporous channels. After the silica template was carbonized and removed, a higher yield of highly-ordered graphitic mesoporous carbon with rod-like morphology was obtained. Because of the improved structural ordering, the mesoporous carbon after amine modification could adsorb more CO2 compared with the amine-functionalized carbon prepared without the assistance of surfactant.

BUNDLE: A Novel Furnace for Performing Controlled Directional Solidification Experiments in a Microgravity Environment

NASA Technical Reports Server (NTRS)

Carrasquillo, Edgar J.; Griffin, Mark R.; Hammond, Monica S.; Johnson, Martin L.; Grugel, R. N.

2000-01-01

NASA Marshall Space Flight Center has developed a novel directional solidification furnace prototype for processing metals and alloys experiments in a microgravity environment. The BUNDLE (Bridgman Unidirectional Dendrite in Liquid Experiment) furnace is intended to accommodate the science requirements of Flight Definition Principle Investigators studying cellular/dendritic growth in aluminum and lead alloys at processing temperatures up to 1200 C. The furnace implements a number of innovative features to achieve high thermal gradients and quench rates in a low-power, light-weight design. These include a pyrolytic boron nitride/graphite composite heating element surrounded by layers of self-supporting refractory metal shielding, and a graphite fiber enhanced cold zone allowing high levels of heat extraction from the sample crucible. Novel to the BUNDLE design is an in-situ helium gas quench capability that ensures rapid freezing of the solidifying region (mushy zone) of the metal sample within the furnace without sample disturbance prior to quenching; this is a stringent requirement for subsequent analysis and understanding of microstructural development. The experiment hardware concept features multiple furnaces that may be "bundled" together so many samples, currently up to eight, can be processed at one time. The design of BUNDLE is flexible enough to be implemented on the Shuttle and Space Station in a number of locations (SpaceHab, Express Rack, MPESS, ISPR, etc). BUNDLE prototype furnaces have directionally solidified and quenched 1cm diameter lead - 5.8 weight percent antimony and aluminum - 4 weight percent copper alloys. Quenching of the mushy zone, as recorded by in-situ thermocouples, occurred on the order of 0.5 seconds or less, a rate within the PI's requirements. Subsequent metallographic examination revealed the solidified microstructure to be, as expected, unidirectional. Both the dendrite tips and the eutectic reaction were planar in nature indicating uniform axial heat flow. Delineation between the growing dendrites and eutectic structure with the "quenched-in" liquid was sharp, attesting to the efficacy of the helium quench. BUNDLE's conception, development, capability, and adaptability are presented (in view of Flight PI's needs and science requirements) through viewgraphs depicting actual hardware, generated thermal analysis, and micrographs prepared from BUNDLE processed, flight-like samples.

BUNDLE - A Novel Furnace for Performing Controlled Directional Solidification Experiments in a Microgravity Environment

NASA Technical Reports Server (NTRS)

Carrasquillo, Edgar J.; Griffin, Mark R.; Hammond, Monica S.; Johnson, Martin L.; Grugel, R. N.

2001-01-01

NASA Marshall Space Flight Center has developed a novel directional solidification furnace prototype for processing metals and alloys experiments in a microgravity environment. The BUNDLE (Bridgman Unidirectional Dendrite in Liquid Experiment) furnace is intended to accommodate the science requirements of Flight Definition Principle Investigators studying cellular/dendritic growth in aluminum and lead alloys at processing temperatures up to 1200 C. The furnace implements a number of innovative features to achieve high thermal gradients and quench rates in a low-power, light-weight design. These include a pyrolytic boron nitride/graphite composite heating element surrounded by layers of self-supporting refractory metal shielding, and a graphite fiber enhanced cold zone allowing high levels of heat extraction from the sample crucible. Novel to the BUNDLE design is an in-situ helium gas quench capability that ensures rapid freezing of the solidifying region (mushy zone) of the metal sample within the furnace without sample disturbance prior to quenching; this is a stringent requirement for subsequent analysis and understanding of microstructural development. The experiment hardware concept features multiple furnaces that may be "bundled" together so many samples, currently up to eight, can be processed at one time. The design of BUNDLE is flexible enough to be implemented on the Shuttle and Space Station in a number of locations (SpaceHab, Express Rack, MPESS, ISPR, etc). BUNDLE prototype furnaces have directionally solidified and quenched 1cm diameter lead - 5.8 weight percent antimony and aluminum - 4 weight percent copper alloys. Quenching of the mushy zone, as recorded by in-situ thermocouples, occurred on the order of 0.5 seconds or less, a rate within the PI's requirements. Subsequent metallographic examination revealed the solidified microstructure to be, as expected, unidirectional. Both the dendrite tips and the eutectic reaction were planar in nature indicating uniform axial heat flow. Delineation between the growing dendrites and eutectic structure with the "quenched-in" liquid was sharp, attesting to the efficacy of the helium quench. BUNDLE's conception, development, capability, and adaptability are presented (in view of Flight PI's needs and science requirements) through viewgraphs depicting actual hardware, generated thermal analysis, and micrographs prepared from BUNDLE processed, flight-like samples.

RESEARCH ON PHYSICAL AND CHEMICAL PRINCIPLES AFFECTING HIGH TEMPERATURE MATERIALS FOR ROCKET NOZZLES. Quarterly Progress Report, April 1, 1963-June 30, 1963

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lowrie, R.

1963-10-31

The development and properties of refractory materials are described. Corrosion of zirconium carbide, niobium carbide, and niobium carbide-zirconium carbide systems by carbon dioxide and hydrochloric acid at 2250 deg C is reported. Corrosion of silver-tungsten alloys by carbon dioxide and oxygen at 2150 to 2440 deg K is summarized. Measurements of pyrolytic and ZTA graphite corrosion by carbon dioxide and oxygen at 2100 to 2800 deg K are shown. At 2300 deg C the rate of formation of methane from graphite and hydrogen is greatly reduced by the addition of helium, at constant hydrogen pressure. Up to 2000 deg Cmore » the effect of helium is small. The pyrolysis of methane on graphite at 2000 deg C is tabulated. Oxidation of tungsten to form WO/sub 2/ and WO/sub 3/ is reported. Vaporization of hafnium borides at 2297 to 2538 deg K is analyzed. The lattice parameters of ZrB/sub 2/ at of TiN/sub 0.6/ and TiN/sub 0.75/ are discussed. Powder metallurgical techniques are used to prepare TiB/sub 2/, ZrB/sub 2/, HfB/ sub 2/, NbB/sub 2/, a nd TaB/sub 2/ for detailed x-ray characterization. The electric conductivity of NbC-ZrC systems is reported. General descriptions are given of analytical techniques for free carbon in carbides and spectrographic methods for metallic impurities in carbides and borides. Preliminary roomtemperature measurements are reported of the elastic properties of polycrystalline ZrB/sub 2/. Titanium carbide is brazed to tungsten with a platinum-boron system. A largegrained polycrystalline specimen of ZrC is plastically deformed in creep at 2134 deg C. Metallographic and x-ray examinations of polycrystalline TiC specimens deformed in creep reveal an increasing development with deformation of subgrains having preferred orientation. (N.W.R.)« less

Nucleation, aggregative growth and detachment of metal nanoparticles during electrodeposition at electrode surfaces† †Electronic supplementary information (ESI) available: S1 Scharifker–Hills model, S2 tapping mode-atomic force microscopy (TM-AFM) image of AM grade HOPG, after exposure to a droplet of 50 mM KNO3, S3 distribution of induction times, S4 results of the modified Cottrell fits at different potentials, S5 FE-SEM images of HOPG after control tip breaking, S6 extended current–time trace. See DOI: 10.1039/c4sc02792b Click here for additional data file.

PubMed Central

Lazenby, Robert A.; Kirkman, Paul M.

2015-01-01

The nucleation and growth of metal nanoparticles (NPs) on surfaces is of considerable interest with regard to creating functional interfaces with myriad applications. Yet, key features of these processes remain elusive and are undergoing revision. Here, the mechanism of the electrodeposition of silver on basal plane highly oriented pyrolytic graphite (HOPG) is investigated as a model system at a wide range of length scales, spanning electrochemical measurements from the macroscale to the nanoscale using scanning electrochemical cell microscopy (SECCM), a pipette-based approach. The macroscale measurements show that the nucleation process cannot be modelled as either truly instantaneous or progressive, and that step edge sites of HOPG do not play a dominant role in nucleation events compared to the HOPG basal plane, as has been widely proposed. Moreover, nucleation numbers extracted from electrochemical analysis do not match those determined by atomic force microscopy (AFM). The high time and spatial resolution of the nanoscale pipette set-up reveals individual nucleation and growth events at the graphite basal surface that are resolved and analysed in detail. Based on these results, corroborated with complementary microscopy measurements, we propose that a nucleation-aggregative growth-detachment mechanism is an important feature of the electrodeposition of silver NPs on HOPG. These findings have major implications for NP electrodeposition and for understanding electrochemical processes at graphitic materials generally. PMID:29560200

Thermal and catalytic slow pyrolysis of Calophyllum inophyllum fruit shell.

PubMed

Alagu, R M; Sundaram, E Ganapathy; Natarajan, E

2015-10-01

Pyrolysis of Calophyllum inophyllum shell was performed in a fixed bed pyrolyser to produce pyrolytic oil. Both thermal (without catalysts) and catalytic pyrolysis process were conducted to investigate the effect of catalysts on pyrolysis yield and pyrolysis oil characteristics. The yield of pyrolytic oil through thermal pyrolysis was maximum (41% wt) at 425 °C for particle size of 1.18 mm and heating rate of 40 °C/min. In catalytic pyrolysis the pyrolytic oil yield was maximum (45% wt) with both zeolite and kaolin catalysts followed by Al2O3 catalyst (44% wt). The functional groups and chemical components present in the pyrolytic oil are identified by Fourier Transform Infrared Spectroscopy (FT-IR) and Gas Chromatography-Mass Spectrometry (GC-MS) techniques. This study found that C. inophyllum shell is a potential new green energy source and that the catalytic pyrolysis process using zeolite catalyst improves the calorific value and acidity of the pyrolytic oil. Copyright © 2015 Elsevier Ltd. All rights reserved.

A comparison of thermal behaviors of raw biomass, pyrolytic biochar and their blends with lignite.

PubMed

Liu, Zhengang; Balasubramanian, Rajasekhar

2013-10-01

In this study, thermal characteristics of raw biomass, corresponding pyrolytic biochars and their blends with lignite were investigated. The results showed that pyrolytic biochars had better fuel qualities than their parent biomass. In comparison to raw biomass, the combustion of the biochars shifted towards higher temperature and occurred at continuous temperature zones. The biochar addition in lignite increased the reactivities of the blends. Obvious interactions were observed between biomass/biochar and lignite and resulted in increased total burnout, shortened combustion time and increased maximum weight loss rate, indicating increased combustion efficiencies than that of lignite combustion alone. Regarding ash-related problems, the tendency to form slagging and fouling increased, when pyrolytic biochars were co-combusted with coal. This present study demonstrated that the pyrolytic biochars were more suitable than raw biomass to be co-combusted with lignite for energy generation in existing coal-fired power plants. Copyright © 2013 Elsevier Ltd. All rights reserved.

Polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds (VOCs) mitigation in the pyrolysis process of waste tires using CO₂ as a reaction medium.

PubMed

Kwon, Eilhann E; Oh, Jeong-Ik; Kim, Ki-Hyun

2015-09-01

Our work reported the CO2-assisted mitigation of PAHs and VOCs in the thermo-chemical process (i.e., pyrolysis). To investigate the pyrolysis of used tires to recover energy and chemical products, the experiments were conducted using a laboratory-scale batch-type reactor. In particular, to examine the influence of the CO2 in pyrolysis of a tire, the pyrolytic products including C1-5-hydrocarbons (HCs), volatile organic carbons (VOCs), and polycyclic aromatic hydrocarbons (PAHs) were evaluated qualitatively by gas chromatography (GC) with mass spectroscopy (MS) as well as with a thermal conductivity detector (TCD). The mass balance of the pyrolytic products under various pyrolytic conditions was established on the basis of their weight fractions of the pyrolytic products. Our experimental work experimentally validated that the amount of gaseous pyrolytic products increased when using CO2 as a pyrolysis medium, while substantially altering the production of pyrolytic oil in absolute content (7.3-17.2%) and in relative composition (including PAHs and VOCs). Thus, the co-feeding of CO2 in the pyrolysis process can be considered an environmentally benign and energy efficient process. Copyright © 2015 Elsevier Ltd. All rights reserved.

Beyond the classical kinetic model for chronic graphite oxidation by moisture in high temperature gas-cooled reactors

DOE PAGES

Contescu, Cristian I.; Mee, Robert W.; Lee, Yoonjo; ...

2017-11-03

Four grades of nuclear graphite with various microstructures were subjected to accelerated oxidation tests in helium with traces of moisture and hydrogen in order to evaluate the effects of chronic oxidation on graphite components in high temperature gas cooled reactors. Kinetic analysis showed that the Langmuir-Hinshelwood (LH) model cannot consistently reproduce all results. In particular, at high temperatures and water partial pressures oxidation was always faster than the LH model predicts, with stronger deviations for superfine grain graphite than for medium grain grades. It was also found empirically that the apparent reaction order for water has a sigmoid-type variation withmore » temperature which follows the integral Boltzmann distribution function. This suggests that the apparent activation with temperature of graphite reactive sites that causes deviations from the LH model is rooted in specific structural and electronic properties of surface sites on graphite. A semi-global kinetic model was proposed, whereby the classical LH model was modified with a temperature-dependent reaction order for water. The new Boltzmann-enhanced model (BLH) was shown to consistently predict experimental oxidation rates over large ranges of temperature (800-1100 oC) and partial pressures of water (3-1200 Pa) and hydrogen (0-300 Pa), not only for the four grades of graphite but also for the historic grade H-451. The BLH model offers as more reliable input for modeling the chemical environment effects during the life-time operation of new grades of graphite in advanced nuclear reactors operating at high and very high temperatures.« less

Beyond the classical kinetic model for chronic graphite oxidation by moisture in high temperature gas-cooled reactors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Contescu, Cristian I.; Mee, Robert W.; Lee, Yoonjo

Four grades of nuclear graphite with various microstructures were subjected to accelerated oxidation tests in helium with traces of moisture and hydrogen in order to evaluate the effects of chronic oxidation on graphite components in high temperature gas cooled reactors. Kinetic analysis showed that the Langmuir-Hinshelwood (LH) model cannot consistently reproduce all results. In particular, at high temperatures and water partial pressures oxidation was always faster than the LH model predicts, with stronger deviations for superfine grain graphite than for medium grain grades. It was also found empirically that the apparent reaction order for water has a sigmoid-type variation withmore » temperature which follows the integral Boltzmann distribution function. This suggests that the apparent activation with temperature of graphite reactive sites that causes deviations from the LH model is rooted in specific structural and electronic properties of surface sites on graphite. A semi-global kinetic model was proposed, whereby the classical LH model was modified with a temperature-dependent reaction order for water. The new Boltzmann-enhanced model (BLH) was shown to consistently predict experimental oxidation rates over large ranges of temperature (800-1100 oC) and partial pressures of water (3-1200 Pa) and hydrogen (0-300 Pa), not only for the four grades of graphite but also for the historic grade H-451. The BLH model offers as more reliable input for modeling the chemical environment effects during the life-time operation of new grades of graphite in advanced nuclear reactors operating at high and very high temperatures.« less

Advanced Heat Exchangers for Dry Cooling Systems, Phase II

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fortini, Arthur J.; Horwath, Joseph

Dry cooling systems are an option for industrial and utility power plants that cannot obtain permits for cooling water or where cooling water is unavailable. Currently available dry cooling systems are more expensive and less efficient than wet cooling systems, so significant improvements in efficiency are needed to make them economically viable. Previous attempts at using foams as cooling fin materials for power generating systems have focused on high thermal conductivity graphite foams made via the Oak Ridge process. Because these materials have high flow restrictions and hence low permeability with respect to air flow, their internal volume and surfacemore » area were not effectively used. Consequently, they performed poorly and offered no advantage over aluminum fins. A foam with a more open structure would provide increased permeability, enable greater airflow through the bulk material, increase the rate of heat transfer, and enable the material to outperform traditional fin structures. In this project, Ultramet designed, fabricated, and tested low flow restriction, high-efficiency foam-based heat exchangers. Calculations based on existing thermal and hydraulic data for Ultramet’s high-performance open-cell foams indicated that 65-ppi (pores per linear inch) pyrolytic graphite foam with a relative density of 15 vol%, produced by chemical vapor infiltration (CVI), would have an effectiveness significantly greater than that of a state-of-the-art Hamon/Balcke-Durr aluminum fin system and greater than that of the POCO graphite foams previously tested for the DOE National Energy Technology Laboratory. Using the same chevron design, test setup, and run conditions as were used with the Hamon/Balcke-Durr fin system and the POCO foams, Ultramet tested graphite foams with air flow velocities of 0.07–3.2 m/sec and pressure drops of 0.03–9.7 inH2O. The best-performing graphite foam architectures had air velocities in excess of 2.5 m/sec when the pressure drop was 1 inH2O. Because a foam-based system is more efficient than a fin-based system, a smaller heat exchanger installation can be used, significantly reducing the installation cost. Furthermore, because the foam-based system is physically smaller with no increase in flow restriction, less electrical power is needed to run the fans to drive the air through the condenser. The result is a decrease in both the installation and operating costs, which in turn will decrease the overall life cycle cost of the system.« less

Thermodynamic evidence of first-order melting of Xe on graphite

NASA Astrophysics Data System (ADS)

Jin, A. J.; Bjurstrom, M. R.; Chan, M. H. W.

1989-03-01

Precision heat-capacity and vapor-pressure isotherm measurements indicate that the melting of monolayer Xe on graphite is always first order. This conclusion is consistent with the results of simulation studies but in sharp contrast with the claim advanced in a series of x-ray studies of a crossover from first-order to continuous Kosterlitz-Thouless-Halperin-Nelson-Young melting.

Pyrolysis of de-oiled seed cake of Jatropha Curcas and catalytic steam reforming of pyrolytic bio-oil to hydrogen.

PubMed

Renny, Andrew; Santhosh, Viswanathan; Somkuwar, Nitin; Gokak, D T; Sharma, Pankaj; Bhargava, Sanjay

2016-11-01

The aim of this work was to study the pyrolysis of de-oiled seed cake of Jatropha Curcas and catalytic steam reforming of pyrolytic bio-oil to hydrogen. As per literature, presence of heavy nitrogenous and oxygenated compounds leads to catalyst deactivation. Here, an attempt has been made to tune pyrolytic reactions to optimize the N and O content of the pyrolytic bio-oil. Bio-oil conversion and hydrogen yield decreased as reaction progressed, which attributes to temporary loss of catalytic activity by blockage of catalyst pores by carbon deposition. Further, retention of steam reforming activity after repetitive steam activation suggests long-term catalyst usage. Copyright © 2016 Elsevier Ltd. All rights reserved.

Graphite Sheet Coating for Improved Thermal Oxidative Stability of Carbon Fiber Reinforced/PMR-15 Composites

NASA Technical Reports Server (NTRS)

Campbell, Sandi; Papadopoulos, Demetrios; Heimann, Paula; Inghram, Linda; McCorkle, Linda

2005-01-01

Expanded graphite was compressed into graphite sheets and used as a coating for carbon fiber reinforced PMR-15 composites. BET analysis of the graphite indicated an increase in graphite pore size on compression, however the material was proven to be an effective barrier to oxygen when prepegged with PMR-15 resin. Oxygen permeability of the PMR-15/graphite was an order of magnitude lower than the compressed graphite sheet. By providing a barrier to oxygen permeation, the rate of oxidative degradation of PMR-15 was decreased. As a result, the composite thermo-oxidative stability increased by up to 25%. The addition of a graphite sheet as a top ply on the composites yielded little change in the material's flexural strength or interlaminar shear strength.

Method of fabricating graphite for use as a skeletal prosthesis and product thereof

DOEpatents

Eatherly, Walter P.; Robbins, J. M.; Rosson, Sr., David E.

1978-01-01

A method for producing porous graphite for use as bone replacement with a structure for osteon penetration. Graphite is produced with ordered circular pores of 100 to 1000 microns in diameter covering at least 25% of the exposed surfaces. A cylindrical fiber is coated with a carbon flour-pitch mix and is then wound on a bobbin in a predetermined manner. The product of winding is dried, pressed, carbonized, and then graphitized. The fibers are removed either chemically or by volatilization during carbonization or graphitization.

CH4 Hydrate Formation between Silica and Graphite Surfaces: Insights from Microsecond Molecular Dynamics Simulations.

PubMed

He, Zhongjin; Linga, Praveen; Jiang, Jianwen

2017-10-31

Microsecond simulations have been performed to investigate CH 4 hydrate formation from gas/water two-phase systems between silica and graphite surfaces, respectively. The hydrophilic silica and hydrophobic graphite surfaces exhibit substantially different effects on CH 4 hydrate formation. The graphite surface adsorbs CH 4 molecules to form a nanobubble with a flat or negative curvature, resulting in a low aqueous CH 4 concentration, and hydrate nucleation does not occur during 2.5 μs simulation. Moreover, an ordered interfacial water bilayer forms between the nanobubble and graphite surface thus preventing their direct contact. In contrast, the hydroxylated-silica surface prefers to be hydrated by water, with a cylindrical nanobubble formed in the solution, leading to a high aqueous CH 4 concentration and hydrate nucleation in the bulk region; during hydrate growth, the nanobubble is gradually covered by hydrate solid and separated from the water phase, hence slowing growth. The silanol groups on the silica surface can form strong hydrogen bonds with water, and hydrate cages need to match the arrangements of silanols to form more hydrogen bonds. At the end of the simulation, the hydrate solid is separated from the silica surface by liquid water, with only several cages forming hydrogen bonds with the silica surface, mainly due to the low CH 4 aqueous concentrations near the surface. To further explore hydrate formation between graphite surfaces, CH 4 /water homogeneous solution systems are also simulated. CH 4 molecules in the solution are adsorbed onto graphite and hydrate nucleation occurs in the bulk region. During hydrate growth, the adsorbed CH 4 molecules are gradually converted into hydrate solid. It is found that the hydrate-like ordering of interfacial water induced by graphite promotes the contact between hydrate solid and graphite. We reveal that the ability of silanol groups on silica to form strong hydrogen bonds to stabilize incipient hydrate solid, as well as the ability of graphite to adsorb CH 4 molecules and induce hydrate-like ordering of the interfacial water, are the key factors to affect CH 4 hydrate formation between silica and graphite surfaces.

Effect of graphite target power density on tribological properties of graphite-like carbon films

NASA Astrophysics Data System (ADS)

Dong, Dan; Jiang, Bailing; Li, Hongtao; Du, Yuzhou; Yang, Chao

2018-05-01

In order to improve the tribological performance, a series of graphite-like carbon (GLC) films with different graphite target power densities were prepared by magnetron sputtering. The valence bond and microstructure of films were characterized by AFM, TEM, XPS and Raman spectra. The variation of mechanical and tribological properties with graphite target power density was analyzed. The results showed that with the increase of graphite target power density, the deposition rate and the ratio of sp2 bond increased obviously. The hardness firstly increased and then decreased with the increase of graphite target power density, whilst the friction coefficient and the specific wear rate increased slightly after a decrease with the increasing graphite target power density. The friction coefficient and the specific wear rate were the lowest when the graphite target power density was 23.3 W/cm2.

Tribological properties of graphite-fiber-reinforced, partially fluorinated polyimide composites

NASA Technical Reports Server (NTRS)

Fusaro, R. L.; Hady, W. F.

1985-01-01

Graphite-fiber-reinforced polyimide (GFRPI) composites were formulated from three new partially fluorinated polyimides and three types of graphite fiber. Nine composites were molded into pins and evaluated in a pin-on-disk tribometer. Friction coefficients, wear rates, pin wear surface morphology, and transfer film formation were assessed at 25 and 300 C. Also assessed was the effect of sliding speed on friction. Wear was up to two orders of magnitude lower at 25 C and up to one order of magnitude lower at 300 C than with previously formulated NASA GFRPI composites.

Design and fabrication of a fixed-bed batch type pyrolysis reactor for pilot scale pyrolytic oil production in Bangladesh

NASA Astrophysics Data System (ADS)

Aziz, Mohammad Abdul; Al-khulaidi, Rami Ali; Rashid, MM; Islam, M. R.; Rashid, MAN

2017-03-01

In this research, a development and performance test of a fixed-bed batch type pyrolysis reactor for pilot scale pyrolysis oil production was successfully completed. The characteristics of the pyrolysis oil were compared to other experimental results. A solid horizontal condenser, a burner for furnace heating and a reactor shield were designed. Due to the pilot scale pyrolytic oil production encountered numerous problems during the plant’s operation. This fixed-bed batch type pyrolysis reactor method will demonstrate the energy saving concept of solid waste tire by creating energy stability. From this experiment, product yields (wt. %) for liquid or pyrolytic oil were 49%, char 38.3 % and pyrolytic gas 12.7% with an operation running time of 185 minutes.

75 FR 64250 - Small Diameter Graphite Electrodes From the People's Republic of China: Extension of Time Limit...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-10-19

... DEPARTMENT OF COMMERCE International Trade Administration [A-570-929] Small Diameter Graphite Electrodes From the People's Republic of China: Extension of Time Limit for the Preliminary Results of the... review of the antidumping duty order on small diameter graphite electrodes from the People's Republic of...

Selective removal of polycyclic aromatic hydrocarbons (PAHs) from soil washing effluents using biochars produced at different pyrolytic temperatures.

PubMed

Li, Helian; Qu, Ronghui; Li, Chao; Guo, Weilin; Han, Xuemei; He, Fang; Ma, Yibing; Xing, Baoshan

2014-07-01

Wheat straw biochars produced at 400, 600 and 800°C (BC400, BC600 and BC800) were used to selectively adsorb PAHs from soil washing effluents. For soil washing effluents contained Phenanthrene (PHE), Fluoranthene (FLU), Pyrene (PYR) and Triton X-100 (TX100), biochars at 2 (for BC800) or 6 g L(-1) (for BC400 and BC600) can remove 71.8-98.6% of PAHs while recover more than 87% of TX100. PAH removals increase with increasing biochar dose. However, excess biochar is detrimental to the recovery of surfactant. For a specific biochar dose, PAH removal and TX100 loss increase with increasing pyrolytic temperature. For BC400 and BC600, PAH removal follows the order of PHE>FLU>PYR, while the order is reversed with PYR>FLU>PHE for BC800. Biochars have much higher sorption affinity for PAHs than for TX100. It is therefore suggested that biochar is a good alternative for selective adsorption of PAHs and recovery of TX100 in soil washing process. Copyright © 2014 Elsevier Ltd. All rights reserved.

Effects of Prior Aging at Elevated Temperature in Air and in Argon Environments on Creep Response of PMR-15 Neat Resin at 288 deg C

DTIC Science & Technology

2007-03-01

either inert gases or air to distinguish between the pyrolytic and oxidative degradation mechanisms. This exposure is commonly called “aging” of...and performance under use conditions. 4 This thesis explores the effects of both pyrolytic and thermal oxidative degradation on the mechanical...fatigue. A third assumption is that the mechanical properties of the pyrolytically aged samples will approximate the mechanical properties of the inner

Fluorination of “brick and mortar” soft-templated graphitic ordered mesoporous carbons for high power lithium-ion battery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fulvio, Pasquale F.; Veith, Gabriel M.; Adcock, Jamie L.

2013-03-18

We prepared ordered mesoporous carbon graphitic carbon composites by the brick and mortar fluorinated methodusing F 2 and investigated as cathodes for primary lithium batteries. Our resulting materials have a rich array of C F species, asmeasured by XPS, which influence conduction and voltage profiles.

Secondary-electron-emission losses in multistage depressed collectors and traveling-wave-tube efficiency improvements with carbon collector electrode surfaces

NASA Technical Reports Server (NTRS)

Ramins, P.; Ebihara, B. T.

1986-01-01

Secondary-electron-emission losses in multistage depressed collectors (MDC's) and their effects on overall traveling-wave-tube (TWT) efficiency were investigated. Two representative TWT's and several computer-modeled MDC's were used. The experimental techniques provide the measurement of both the TWT overall and the collector efficiencies. The TWT-MDC performance was optimized and measured over a wide range of operating conditions, with geometrically identical collectors, which utilized different electrode surface materials. Comparisons of the performance of copper electrodes to that of various forms of carbon, including pyrolytic and iisotropic graphites, were stressed. The results indicate that: (1) a significant improvement in the TWT overall efficiency was obtained in all cases by the use of carbon, rather than copper electrodes, and (2) that the extent of this efficiency enhancement depended on the characteristics of the TWT, the TWT operating point, the MDC design, and collector voltages. Ion textured graphite was found to be particularly effective in minimizing the secondary-electron-emission losses. Experimental and analytical results, however, indicate that it is at least as important to provide a maximum amount of electrostatic suppression of secondary electrons by proper MDC design. Such suppression, which is obtained by ensuring that a substantial suppressing electric field exists over the regions of the electrodes where most of the current is incident, was found to be very effective. Experimental results indicate that, with proper MDC design and the use of electrode surfaces with low secondary-electron yield, degradation of the collector efficiency can be limited to a few percent.

Salt melt synthesis of curved nitrogen-doped carbon nanostructures: ORR kinetics boost

NASA Astrophysics Data System (ADS)

Rybarczyk, Maria K.; Gontarek, Emilia; Lieder, Marek; Titirici, Maria-Magdalena

2018-03-01

Implementing metal-free electrocatalysts for the oxygen reduction reaction (ORR) and revealing crucial chemical or topographical parameters driving their activity are vital for the development of power cells. The carbon-based catalysts are very often synthesized through carbonization of biopolymers, in particular, those one containing nitrogen groups such as chitosan. Unfortunately, the resulting carbonaceous materials usually lack specific porosity and exhibit low catalytic activity. Here, we demonstrate that pyrolysis of chitosan in a ZnCl2 melt assisted by the presence of LiCl results not only in a highly porous activated carbon material with a specific surface area of 1317.97 m2/g and the total nitrogen content of 6.5%, but also induces unexpected curvature in the grown graphitic layers. This is the first work that shows curved graphene layers obtained from a biopolymer precursor by its pyrolytic decomposition in the melted salt media. On the other hand, a carbonaceous material obtained from chitosan but without the salts has very low specific surface area of 7.8 m2/g, possesses no specific structural features, and contains 4.7% of nitrogen. The electrochemical studies show, that the former material is highly active towards four-electron pathway of the ORR in terms of an onset potential (0.89 V vs RHE) and the turnover frequency (TOFmax = 0.095 e site-1 s-1). We attribute this high catalytic performance to the presence of the pyridinic and pyrrolic sites in the structure. The ORR kinetics is probably further promoted by curvature in the graphitic layers.

Thermometry of the system “heat-resistant sample - incident plasma stream”

NASA Astrophysics Data System (ADS)

Sargsyan, M. A.; Chinnov, V. F.; Kavyrshin, D. I.; Gadzhiev, M. Kh; Khromov, M. A.; Chistolinov, A. V.; Senchenko, V. N.

2017-11-01

To study the interacting system “heat-resistant sample - an incident plasma stream” a setup of synchronized measurement equipment was developed and tested that recorded the main parameters of such interaction. Heat resistance tests were carried out on the samples of MPG-6 grade isotropic graphite, and samples of pyrolytic graphite that were subjected to a long (60 … 100 s) exposure to nitrogen, argon and air plasma streams at atmospheric pressure. As plasma generators a series of plasma torches with a vortex stabilization of the stream and an expanding anode channels was used. The temperature and composition of the plasma in the jet and near the sample were determined using two AvaSpec2048 and AvaSpec3648 scanning optical spectrometers and the MS5402i spectrograph with the Andor matrix at its outlet. The surface temperature of the sample was determined in real time using three independent ways: two pyrometric systems - a high-speed micro-pyrometer FMP1001 and a two-position visualization of the heated sample by high-speed Motion Pro X3 and VS-FAST cameras, and the spectral analysis of the wide-range thermal radiation of the samples. The main method for determining the rate of material loss during the action of a plasma jet on it was to analyze a two-position synchronous visualization of the “jet-sample” system. When a crater was formed on the surface of the sample under the “dagger” effect of a plasma jet, a video recording system of the crater zone was used, backlit using the “laser knife” method.

Nanobubbles do not sit alone at the solid-liquid interface.

PubMed

Peng, Hong; Hampton, Marc A; Nguyen, Anh V

2013-05-21

The unexpected stability and anomalous contact angle of gaseous nanobubbles at the hydrophobic solid-liquid interface has been an issue of debate for almost two decades. In this work silicon-nitride tipped AFM cantilevers are used to probe the highly ordered pyrolytic graphite (HOPG)-water interface with and without solvent-exchange (a common nanobubble production method). Without solvent-exchange the force obtained by the single force and force mapping techniques is consistent over the HOPG atomic layers and described by DLVO theory (strong EDL repulsion). With solvent-exchange the force is non-DLVO (no EDL repulsion) and the range of the attractive jump-in (>10 nm) over the surface is grouped into circular areas of longer range, consistent with nanobubbles, and the area of shorter range. The non-DLVO nature of the area between nanobubbles suggests that the interaction is no longer between a silicon-nitride tip and HOPG. Interfacial gas enrichment (IGE) covering the entire area between nanobubbles is suggested to be responsible for the non-DLVO forces. The absence of EDL repulsion suggests that both IGE and nanobubbles are not charged. The coexistence of nanobubbles and IGE provides further evidence of nanobubble stability by dynamic equilibrium. The IGE cannot be removed by contact mode scanning of a cantilever tip in pure water, but in a surfactant (SDS) solution the mechanical action of the tip and the chemical action of the surfactant molecules can successfully remove the enrichment. Strong EDL repulsion between the tip and nanobubbles/IGE in surfactant solutions is due to the polar heads of the adsorbed surfactant molecules.

Nanoscale pinning effect evaluated from deformed nanobubbles.

PubMed

Teshima, Hideaki; Nishiyama, Takashi; Takahashi, Koji

2017-01-07

Classical thermodynamics theory predicts that nanosized bubbles should disappear in a few hundred microseconds. The surprisingly long lifetime and stability of nanobubbles are therefore interesting research subjects. It has been proposed that the stability of nanobubbles arises through pinning of the three-phase contact line, which results from intrinsic nanoscale geometrical and chemical heterogeneities of the substrate. However, a definitive explanation of nanobubble stability is still lacking. In this work, we examined the stability mechanism by introducing a "pinning force." We investigated nanobubbles at a highly ordered pyrolytic graphite/pure water interface by peak force quantitative nano-mechanical mapping and estimated the pinning force and determined its maximum value. We then observed the shape of shrinking nanobubbles. Because the diameter of the shrinking nanobubbles was pinned, the height decreased and the contact angle increased. This phenomenon implies that the stability results from the pinning force, which flattens the bubble through the pinned three-phase contact line and prevents the Laplace pressure from increasing. The pinning force can also explain the metastability of coalesced nanobubbles, which have two semispherical parts that are joined to form a dumbbell-like shape. The pinning force of the semispherical parts was stronger than that of the joint region. This result demonstrates that the contact line of the semispherical parts is pinned strongly to keep the dumbbell-like shape. Furthermore, we proposed a nanobubble generation mechanism for the solvent-exchange method and explained why the pinning force of large nanobubbles was not initially at its maximum value, as it was for small nanobubbles.

Nanoscale pinning effect evaluated from deformed nanobubbles

NASA Astrophysics Data System (ADS)

Teshima, Hideaki; Nishiyama, Takashi; Takahashi, Koji

2017-01-01

Classical thermodynamics theory predicts that nanosized bubbles should disappear in a few hundred microseconds. The surprisingly long lifetime and stability of nanobubbles are therefore interesting research subjects. It has been proposed that the stability of nanobubbles arises through pinning of the three-phase contact line, which results from intrinsic nanoscale geometrical and chemical heterogeneities of the substrate. However, a definitive explanation of nanobubble stability is still lacking. In this work, we examined the stability mechanism by introducing a "pinning force." We investigated nanobubbles at a highly ordered pyrolytic graphite/pure water interface by peak force quantitative nano-mechanical mapping and estimated the pinning force and determined its maximum value. We then observed the shape of shrinking nanobubbles. Because the diameter of the shrinking nanobubbles was pinned, the height decreased and the contact angle increased. This phenomenon implies that the stability results from the pinning force, which flattens the bubble through the pinned three-phase contact line and prevents the Laplace pressure from increasing. The pinning force can also explain the metastability of coalesced nanobubbles, which have two semispherical parts that are joined to form a dumbbell-like shape. The pinning force of the semispherical parts was stronger than that of the joint region. This result demonstrates that the contact line of the semispherical parts is pinned strongly to keep the dumbbell-like shape. Furthermore, we proposed a nanobubble generation mechanism for the solvent-exchange method and explained why the pinning force of large nanobubbles was not initially at its maximum value, as it was for small nanobubbles.

Electrical conductivity in Langmuir-Blodgett films of n-alkyl cyanobiphenyls using current sensing atomic force microscope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gayathri, H. N.; Suresh, K. A., E-mail: suresh@cnsms.res.in

2015-06-28

We report our studies on the nanoscale electrical conductivity in monolayers of n-alkyl cyanobiphenyl materials deposited on solid surface. Initially, the 8CB, 9CB, and 10CB monolayer films were prepared by the Langmuir technique at air-water interface and characterized by surface manometry and Brewster angle microscopy. The monolayer films were transferred on to solid substrates by the Langmuir-Blodgett (L-B) technique. The 8CB, 9CB, and 10CB monolayer L-B films were deposited on freshly cleaved mica and studied by atomic force microscope (AFM), thereby measuring the film thickness as ∼1.5 nm. The electrical conductivity measurements were carried out on 9CB and 10CB monolayer L-Bmore » films deposited onto highly ordered pyrolytic graphite using current sensing AFM. The nanoscale current-voltage (I-V) measurements show a non-linear variation. The nature of the curve indicates electron tunneling to be the mechanism for electrical conduction. Furthermore, analysis of the I-V curve reveals a transition in the electron conduction mechanism from direct tunneling to injection tunneling. From the transition voltage, we have estimated the values of barrier height for 9CB and 10CB to be 0.71 eV and 0.37 eV, respectively. For both 9CB and 10CB, the effective mass of electron was calculated to be 0.021 m{sub e} and 0.065 m{sub e}, respectively. These parameters are important in the design of molecular electronic devices.« less

High vacuum tip-enhanced Raman spectroscope based on a scanning tunneling microscope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fang, Yurui; Bionanophotonics, Department of Applied Physics, Chalmers University of Technology, Göteborg, SE 41296; Zhang, Zhenglong

2016-03-15

In this paper, we present the construction of a high-vacuum tip-enhanced Raman spectroscopy (HV-TERS) system that allows in situ sample preparation and measurement. A detailed description of the prototype instrument is presented with experimental validation of its use and novel ex situ experimental results using the HV-TERS system. The HV-TERS system includes three chambers held under a 10{sup −7} Pa vacuum. The three chambers are an analysis chamber, a sample preparation chamber, and a fast loading chamber. The analysis chamber is the core chamber and contains a scanning tunneling microscope (STM) and a Raman detector coupled with a 50 ×more » 0.5 numerical aperture objective. The sample preparation chamber is used to produce single-crystalline metal and sub-monolayer molecular films by molecular beam epitaxy. The fast loading chamber allows ex situ preparation of samples for HV-TERS analysis. Atomic resolution can be achieved by the STM on highly ordered pyrolytic graphite. We demonstrate the measurement of localized temperature using the Stokes and anti-Stokes TERS signals from a monolayer of 1,2-benzenedithiol on a gold film using a gold tip. Additionally, plasmonic catalysis can be monitored label-free at the nanoscale using our device. Moreover, the HV-TERS experiments show simultaneously activated infrared and Raman vibrational modes, Fermi resonance, and some other non-linear effects that are not observed in atmospheric TERS experiments. The high spatial and spectral resolution and pure environment of high vacuum are beneficial for basic surface studies.« less

An investigation into graphene exfoliation and potential graphene application in MEMS devices

NASA Astrophysics Data System (ADS)

Fercana, George; Kletetschka, Gunther; Mikula, Vilem; Li, Mary

2011-02-01

The design of microelectromecanical systems (MEMS) and micro-opto-electromechanical systems (MOEMS) are often materials-limited with respect to the efficiency and capability of the material. Graphene, a one atom thick honeycomb lattice of carbon, is a highly desired material for MEMS applications. Relevant properties of graphene include the material's optical transparency, mechanical strength, energy efficiency, and electrical and thermal conductivity due to its electron mobility. Aforementioned properties make graphene a strong candidate to supplant existing transparent electrode technology and replace the conventionally used material, indium-tin oxide. In this paper we present preliminary results on work toward integration of graphene with MEMS structures. We are studying mechanical exfoliation of highly ordered pyrolytic graphite (HOPG) crystals by repeatedly applying and separating adhesive materials from the HOPG surface. The resulting graphene sheets are then transferred to silicon oxide substrate using the previously applied adhesive material. We explored different adhesive options, particularly the use of Kapton tape, to improve the yield of graphene isolation along with chemical cross-linking agents which operate on a mechanism of photoinsertion of disassociated nitrene groups. These perfluorophenyl nitrenes participate in C=C addition reactions with graphene monolayers creating a covalent binding between the substrate and graphene. We are focusing on maximizing the size of isolated graphene sheets and comparing to conventional exfoliation. Preliminary results allow isolation of few layer graphene (FLG) sheets (n<3) of approximately 10μm x 44μm. Photolithography could possibly be utilized to tailor designs for microshutter technology to be used in future deep space telescopes.

Negative differential resistance in nickel octabutoxy phthalocyanine and nickel octabutoxy phthalocyanine/graphene oxide ultrathin films

NASA Astrophysics Data System (ADS)

Sarkar, Arup; Suresh, K. A.

2018-04-01

We find negative differential resistance (NDR) at room temperature in ultrathin films of nickel (II) 1,4,8,11,15,18,22,25-octabutoxy-29H,31H-phthalocyanine [NiPc(OBu)8] deposited on highly ordered pyrolytic graphite (HOPG) substrate [NiPc(OBu)8/HOPG] and NiPc(OBu)8 on graphene oxide (GO) deposited on HOPG [NiPc(OBu)8/GO/HOPG]. For the NiPc(OBu)8/HOPG system, NiPc(OBu)8 was transferred four times onto HOPG by the Langmuir-Blodgett (LB) technique. We have prepared a stable Langmuir monolayer of amphiphilic GO at the air-water interface and transferred it onto HOPG by the LB technique. Further, the monolayer of NiPc(OBu)8 was transferred four times for good coverage on GO to obtain the NiPc(OBu)8/GO/HOPG system. The current-voltage characteristics were carried out using a current sensing atomic force microscope (CSAFM) with a platinum (Pt) tip that forms Pt/NiPc(OBu)8/HOPG and Pt/NiPc(OBu)8/GO/HOPG junctions. The CSAFM, UV-visible spectroscopy, and cyclic voltammetry studies show that the NDR effect occurs due to molecular resonant tunneling. In the Pt/NiPc(OBu)8/GO/HOPG junction, we find that due to the presence of GO, the features of NDR become more prominent. Also, GO causes a shift in NDR voltage towards a lower value in the negative bias direction. We attribute this behavior to the role of GO in injecting holes into the NiPc(OBu)8 film.

Status of Chronic Oxidation Studies of Graphite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Contescu, Cristian I.; Mee, Robert W.

Graphite will undergo extremely slow, but continuous oxidation by traces of moisture that will be present, albeit at very low levels, in the helium coolant of HTGR. This chronic oxidation may cause degradation of mechanical strength and thermal properties of graphite components if a porous oxidation layer penetrates deep enough in the bulk of graphite components during the lifetime of the reactor. The current research on graphite chronic oxidation is motivated by the acute need to understand the behavior of each graphite grade during prolonged exposure to high temperature chemical attack by moisture. The goal is to provide the elementsmore » needed to develop predictive models for long-time oxidation behavior of graphite components in the cooling helium of HTGR. The tasks derived from this goal are: (1) Oxidation rate measurements in order to determine and validate a comprehensive kinetic model suitable for prediction of intrinsic oxidation rates as a function of temperature and oxidant gas composition; (2) Characterization of effective diffusivity of water vapor in the graphite pore system in order to account for the in-pore transport of moisture; and (3) Development and validation of a predictive model for the penetration depth of the oxidized layer, in order to assess the risk of oxidation caused damage of particular graphite grades after prolonged exposure to the environment of helium coolant in HTGR. The most important and most time consuming of these tasks is the measurement of oxidation rates in accelerated oxidation tests (but still under kinetic control) and the development of a reliable kinetic model. This report summarizes the status of chronic oxidation studies on graphite, and then focuses on model development activities, progress of kinetic measurements, validation of results, and improvement of the kinetic models. Analysis of current and past results obtained with three grades of showed that the classical Langmuir-Hinshelwood model cannot reproduce all data collected so far. Starting from here we propose a modification of the LH model to include temperature activation of graphite surface as a Boltzmann activation function. The enhanced Boltzmann-Langmuir-Hinshelwood model (BLH) was tested successfully on three grades of graphite. The model is a robust, comprehensive mathematical function that allows better fitting of experimental results spanning a wide range of temperature and partial pressures of water vapor and hydrogen. However, the model did not fit satisfactorily the data extracted from the old report on graphite H-451 oxidation by water.« less

Ionic liquids at the surface of graphite: Wettability and structure

NASA Astrophysics Data System (ADS)

Bordes, Emilie; Douce, Laurent; Quitevis, Edward L.; Pádua, Agílio A. H.; Costa Gomes, Margarida

2018-05-01

The aim of this work is to provide a better understanding of the interface between graphite and different molecular and ionic liquids. Experimental measurements of the liquid surface tension and of the graphite-liquid contact angle for sixteen ionic liquids and three molecular liquids are reported. These experimental values allowed the calculation of the solid/liquid interfacial energy that varies, for the ionic liquids studied, between 14.5 mN m-1 for 1-ethyl-3-methylimidazolium dicyanamide and 37.8 mN m-1 for 3-dodecyl-1-(naphthalen-1-yl)-1H-imidazol-3-ium tetrafluoroborate. Imidazolium-based ionic liquids with large alkyl side-chains or functionalized with benzyl groups seem to interact more favourably with freshly peeled graphite surfaces. Even if the interfacial energy seems a good descriptor to assess the affinity of a liquid for a carbon-based solid material, we conclude that both the surface tension of the liquid and the contact angle between the liquid and the solid can be significant. Molecular dynamics simulations were used to investigate the ordering of the ions near the graphite surface. We conclude that the presence of large alkyl side-chains in the cations increases the ordering of ions at the graphite surface. Benzyl functional groups in the cations lead to a large affinity towards the graphite surface.

Role of oxygen-containing functional groups in forest fire-generated and pyrolytic chars for immobilization of copper and nickel.

PubMed

Esfandbod, Maryam; Merritt, Christopher R; Rashti, Mehran Rezaei; Singh, Balwant; Boyd, Sue E; Srivastava, Prashant; Brown, Christopher L; Butler, Orpheus M; Kookana, Rai S; Chen, Chengrong

2017-01-01

Char as a carbon-rich material, can be produced under pyrolytic conditions, wildfires or prescribed burn offs for fire management. The objective of this study was to elucidate mechanistic interactions of copper (Cu 2+ ) and nickel (Ni 2+ ) with different chars produced by pyrolysis (green waste, GW; blue-Mallee, BM) and forest fires (fresh-burnt by prescribed fire, FC; aged char produced by wild fire, AC). The pyrolytic chars were more effective sorbents of Cu 2+ (∼11 times) and Ni 2+ (∼5 times) compared with the forest fire chars. Both cross-polarization (CPMAS-NMR) and Bloch decay (BDMAS-NMR) 13 C NMR spectroscopies showed that forest fire chars have higher woody components (aromatic functional groups) and lower polar groups (e.g. O-alkyl C) compared with the pyrolytic chars. The polarity index was greater in the pyrolytic chars (0.99-1.34) than in the fire-generated chars (0.98-1.15), while aromaticity was lower in the former than in the latter. Fourier transform infrared (FTIR) and Raman spectroscopies indicated the binding of carbonate and phosphate with both Cu 2+ and Ni 2+ in all chars, but with a greater extent in pyrolytic than forest fire-generated chars. These findings have demonstrated the key role of char's oxygen-containing functional groups in determining their sorption capacity for the Cu 2+ and Ni 2+ in contaminated lands. Copyright © 2016 Elsevier Ltd. All rights reserved.

Enhanced performance of graphite anode materials by AlF3 coating for lithium-ion batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ding, Fei; Xu, Wu; Choi, Daiwon

2012-04-27

In order to form the stable surface film and to further enhance the long-term cycling stability of the graphite anodes of lithium-ion batteries, the surface of graphite powders has been modified by AlF3 coating through chemical precipitation method. The AlF3-coated graphite shows no evident changes in the bulk structure and a thin AlF3-coating layer of about 2 nm thick is found to uniformly cover the graphite particles with 2 wt% AlF3 content. However, it delivers a higher initial discharge capacity and largely improved rate performances compared to the pristine graphite. Remarkably, AlF3 coated graphite demonstrated a much better cycle life.more » After 300 cycles, AlF3 coated graphite and uncoated graphite show capacity retention of 92% and 81%, respectively. XPS measurement shows that a more conductive solid electrode interface (SEI) layer was formed on AlF3 coated graphite as compared to uncoated graphite. SEM monograph also reveals that the AlF3-coated graphite particles have a much more stable surface morphology after long-term cycling. Therefore, the improved electrochemical performance of AlF3 coated graphite can be attributed to a more stable and conductive SEI formed on coated graphite anode during cycling process.« less

2D nanosheet molybdenum disulphide (MoS2) modified electrodes explored towards the hydrogen evolution reaction

NASA Astrophysics Data System (ADS)

Rowley-Neale, Samuel J.; Brownson, Dale A. C.; Smith, Graham C.; Sawtell, David A. G.; Kelly, Peter J.; Banks, Craig E.

2015-10-01

We explore the use of two-dimensional (2D) MoS2 nanosheets as an electrocatalyst for the Hydrogen Evolution Reaction (HER). Using four commonly employed commercially available carbon based electrode support materials, namely edge plane pyrolytic graphite (EPPG), glassy carbon (GC), boron-doped diamond (BDD) and screen-printed graphite electrodes (SPE), we critically evaluate the reported electrocatalytic performance of unmodified and MoS2 modified electrodes towards the HER. Surprisingly, current literature focuses almost exclusively on the use of GC as an underlying support electrode upon which HER materials are immobilised. 2D MoS2 nanosheet modified electrodes are found to exhibit a coverage dependant electrocatalytic effect towards the HER. Modification of the supporting electrode surface with an optimal mass of 2D MoS2 nanosheets results in a lowering of the HER onset potential by ca. 0.33, 0.57, 0.29 and 0.31 V at EPPG, GC, SPE and BDD electrodes compared to their unmodified counterparts respectively. The lowering of the HER onset potential is associated with each supporting electrode's individual electron transfer kinetics/properties and is thus distinct. The effect of MoS2 coverage is also explored. We reveal that its ability to catalyse the HER is dependent on the mass deposited until a critical mass of 2D MoS2 nanosheets is achieved, after which its electrocatalytic benefits and/or surface stability curtail. The active surface site density and turn over frequency for the 2D MoS2 nanosheets is determined, characterised and found to be dependent on both the coverage of 2D MoS2 nanosheets and the underlying/supporting substrate. This work is essential for those designing, fabricating and consequently electrochemically testing 2D nanosheet materials for the HER.We explore the use of two-dimensional (2D) MoS2 nanosheets as an electrocatalyst for the Hydrogen Evolution Reaction (HER). Using four commonly employed commercially available carbon based electrode support materials, namely edge plane pyrolytic graphite (EPPG), glassy carbon (GC), boron-doped diamond (BDD) and screen-printed graphite electrodes (SPE), we critically evaluate the reported electrocatalytic performance of unmodified and MoS2 modified electrodes towards the HER. Surprisingly, current literature focuses almost exclusively on the use of GC as an underlying support electrode upon which HER materials are immobilised. 2D MoS2 nanosheet modified electrodes are found to exhibit a coverage dependant electrocatalytic effect towards the HER. Modification of the supporting electrode surface with an optimal mass of 2D MoS2 nanosheets results in a lowering of the HER onset potential by ca. 0.33, 0.57, 0.29 and 0.31 V at EPPG, GC, SPE and BDD electrodes compared to their unmodified counterparts respectively. The lowering of the HER onset potential is associated with each supporting electrode's individual electron transfer kinetics/properties and is thus distinct. The effect of MoS2 coverage is also explored. We reveal that its ability to catalyse the HER is dependent on the mass deposited until a critical mass of 2D MoS2 nanosheets is achieved, after which its electrocatalytic benefits and/or surface stability curtail. The active surface site density and turn over frequency for the 2D MoS2 nanosheets is determined, characterised and found to be dependent on both the coverage of 2D MoS2 nanosheets and the underlying/supporting substrate. This work is essential for those designing, fabricating and consequently electrochemically testing 2D nanosheet materials for the HER. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05164a|ART

The defect level and ideal thermal conductivity of graphene uncovered by residual thermal reffusivity at the 0 K limit

NASA Astrophysics Data System (ADS)

Xie, Yangsu; Xu, Zaoli; Xu, Shen; Cheng, Zhe; Hashemi, Nastaran; Deng, Cheng; Wang, Xinwei

2015-05-01

Due to its intriguing thermal and electrical properties, graphene has been widely studied for potential applications in sensor and energy devices. However, the reported value for its thermal conductivity spans from dozens to thousands of W m-1 K-1 due to different levels of alternations and defects in graphene samples. In this work, the thermal diffusivity of suspended four-layered graphene foam (GF) is characterized from room temperature (RT) down to 17 K. For the first time, we identify the defect level in graphene by evaluating the inverse of thermal diffusivity (termed ``thermal reffusivity'': Θ) at the 0 K limit. By using the Debye model of Θ = Θ0 + C × e-θ/2T and fitting the Θ-T curve to the point of T = 0 K, we identify the defect level (Θ0) and determine the Debye temperature of graphene. Θ0 is found to be 1878 s m-2 for the studied GF and 43-112 s m-2 for three highly crystalline graphite materials. This uncovers a 16-43-fold higher defect level in GF than that in pyrolytic graphite. In GF, the phonon mean free path solely induced by defects and boundary scattering is determined as 166 nm. The Debye temperature of graphene is determined to be 1813 K, which is very close to the average theoretical Debye temperature (1911 K) of the three acoustic phonon modes in graphene. By subtracting the defect effect, we report the ideal thermal diffusivity and conductivity (κideal) of graphene presented in the 3D foam structure in the range of 33-299 K. Detailed physics based on chemical composition and structure analysis are given to explain the κideal-T profile by comparing with those reported for suspended graphene.Due to its intriguing thermal and electrical properties, graphene has been widely studied for potential applications in sensor and energy devices. However, the reported value for its thermal conductivity spans from dozens to thousands of W m-1 K-1 due to different levels of alternations and defects in graphene samples. In this work, the thermal diffusivity of suspended four-layered graphene foam (GF) is characterized from room temperature (RT) down to 17 K. For the first time, we identify the defect level in graphene by evaluating the inverse of thermal diffusivity (termed ``thermal reffusivity'': Θ) at the 0 K limit. By using the Debye model of Θ = Θ0 + C × e-θ/2T and fitting the Θ-T curve to the point of T = 0 K, we identify the defect level (Θ0) and determine the Debye temperature of graphene. Θ0 is found to be 1878 s m-2 for the studied GF and 43-112 s m-2 for three highly crystalline graphite materials. This uncovers a 16-43-fold higher defect level in GF than that in pyrolytic graphite. In GF, the phonon mean free path solely induced by defects and boundary scattering is determined as 166 nm. The Debye temperature of graphene is determined to be 1813 K, which is very close to the average theoretical Debye temperature (1911 K) of the three acoustic phonon modes in graphene. By subtracting the defect effect, we report the ideal thermal diffusivity and conductivity (κideal) of graphene presented in the 3D foam structure in the range of 33-299 K. Detailed physics based on chemical composition and structure analysis are given to explain the κideal-T profile by comparing with those reported for suspended graphene. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr02012c

Covering surface nanobubbles with a NaCl nanoblanket.

PubMed

Berkelaar, Robin P; Zandvliet, Harold J W; Lohse, Detlef

2013-09-10

By letting a NaCl aqueous solution of low (0.01 M) concentration evaporate on a highly oriented pyrolytic graphite (HOPG) surface, it is possible to form a thin film of salt. However, pre-existing surface nanobubbles prevent the homogeneous coverage of the surface with the salt, keeping the footprint areas on the substrate pristine. Comparing the surface nanobubbles in the salt solution with their associated footprint after drying, provides information on the shrinkage of nanobubbles during the hours-long process of drying the liquid film. At a slightly higher NaCl concentration and thus salt layer thickness, the nanobubbles are covered with a thin blanket of salt. Once the liquid film has evaporated until a water film remains that is smaller than the height of the nanobubbles, the blanket of salt cracks and unfolds into a flower-like pattern of salt flakes that is located at the rim of the nanobubble footprint. The formation of a blanket of salt covering the nanobubbles is likely to considerably or even completely block the gas out-flux from the nanobubble, partially stabilizing the nanobubbles against dissolution.

Evolution of elastic x-ray scattering in laser-shocked warm dense lithium.

PubMed

Kugland, N L; Gregori, G; Bandyopadhyay, S; Brenner, C M; Brown, C R D; Constantin, C; Glenzer, S H; Khattak, F Y; Kritcher, A L; Niemann, C; Otten, A; Pasley, J; Pelka, A; Roth, M; Spindloe, C; Riley, D

2009-12-01

We have studied the dynamics of warm dense Li with near-elastic x-ray scattering. Li foils were heated and compressed using shock waves driven by 4-ns-long laser pulses. Separate 1-ns-long laser pulses were used to generate a bright source of 2.96 keV Cl Ly- alpha photons for x-ray scattering, and the spectrum of scattered photons was recorded at a scattering angle of 120 degrees using a highly oriented pyrolytic graphite crystal operated in the von Hamos geometry. A variable delay between the heater and backlighter laser beams measured the scattering time evolution. Comparison with radiation-hydrodynamics simulations shows that the plasma is highly coupled during the first several nanoseconds, then relaxes to a moderate coupling state at later times. Near-elastic scattering amplitudes have been successfully simulated using the screened one-component plasma model. Our main finding is that the near-elastic scattering amplitudes are quite sensitive to the mean ionization state Z[over ] and by extension to the choice of ionization model in the radiation-hydrodynamics simulations used to predict plasma properties within the shocked Li.

Voltammetric pH sensing using carbon electrodes: glassy carbon behaves similarly to EPPG.

PubMed

Lu, Min; Compton, Richard G

2014-09-21

Developing and building on recent work based on a simple sensor for pH determination using unmodified edge plane pyrolytic graphite (EPPG) electrodes, we present a voltammetric method for pH determination using a bare unmodified glassy carbon (GC) electrode. By exploiting the pH sensitive nature of quinones present on carbon edge-plane like sites within the GC, we show how GC electrodes can be used to measure pH. The electro-reduction of surface quinone groups on the glassy carbon electrode was characterised using cyclic voltammetry (CV) and optimised with square-wave voltammetry (SWV) at 298 K and 310 K. At both temperatures, a linear correlation was observed, corresponding to a 2 electron, 2 proton Nernstian response over the aqueous pH range 1.0 to 13.1. As such, unmodified glassy carbon electrodes are seen to be pH dependent, and the Nernstian response suggests its facile use for pH sensing. Given the widespread use of glassy carbon electrodes in electroanalysis, the approach offers a method for the near-simultaneous measurement and monitoring of pH during such analyses.

Thrombin-Binding Aptamer Quadruplex Formation: AFM and Voltammetric Characterization

PubMed Central

Diculescu, Victor Constantin; Chiorcea-Paquim, Ana-Maria; Eritja, Ramon; Oliveira-Brett, Ana Maria

2010-01-01

The adsorption and the redox behaviour of thrombin-binding aptamer (TBA) and extended TBA (eTBA) were studied using atomic force microscopy and voltammetry at highly oriented pyrolytic graphite and glassy carbon. The different adsorption patterns and degree of surface coverage were correlated with the sequence base composition, presence/absence of K+, and voltammetric behaviour of TBA and eTBA. In the presence of K+, only a few single-stranded sequences present adsorption, while the majority of the molecules forms stable and rigid quadruplexes with no adsorption. Both TBA and eTBA are oxidized and the only anodic peak corresponds to guanine oxidation. Upon addition of K+ ions, TBA and eTBA fold into a quadruplex, causing the decrease of guanine oxidation peak and occurrence of a new peak at a higher potential due to the oxidation of G-quartets. The higher oxidation potential of G-quartets is due to the greater difficulty of electron transfer from the inside of the quadruplex to the electrode surface than electron transfer from the more flexible single strands. PMID:20798847

Enzyme-linked electrochemical DNA ligation assay using magnetic beads.

PubMed

Stejskalová, Eva; Horáková, Petra; Vacek, Jan; Bowater, Richard P; Fojta, Miroslav

2014-07-01

DNA ligases are essential enzymes in all cells and have been proposed as targets for novel antibiotics. Efficient DNA ligase activity assays are thus required for applications in biomedical research. Here we present an enzyme-linked electrochemical assay based on two terminally tagged probes forming a nicked junction upon hybridization with a template DNA. Nicked DNA bearing a 5' biotin tag is immobilized on the surface of streptavidin-coated magnetic beads, and ligated product is detected via a 3' digoxigenin tag recognized by monoclonal antibody-alkaline phosphatase conjugate. Enzymatic conversion of napht-1-yl phosphate to napht-1-ol enables sensitive detection of the voltammetric signal on a pyrolytic graphite electrode. The technique was tested under optimal conditions and various situations limiting or precluding the ligation reaction (such as DNA substrates lacking 5'-phosphate or containing a base mismatch at the nick junction, or application of incompatible cofactor), and utilized for the analysis of the nick-joining activity of a range of recombinant Escherichia coli DNA ligase constructs. The novel technique provides a fast, versatile, specific, and sensitive electrochemical assay of DNA ligase activity.

Effect of intermolecular dipole-dipole interactions on interfacial supramolecular structures of C3-symmetric hexa-peri-hexabenzocoronene derivatives.

PubMed

Mu, Zhongcheng; Shao, Qi; Ye, Jun; Zeng, Zebing; Zhao, Yang; Hng, Huey Hoon; Boey, Freddy Yin Chiang; Wu, Jishan; Chen, Xiaodong

2011-02-15

Two-dimensional (2D) supramolecular assemblies of a series of novel C(3)-symmetric hexa-peri-hexabenzocoronene (HBC) derivatives bearing different substituents adsorbed on highly oriented pyrolytic graphite were studied by using scanning tunneling microscopy at a solid-liquid interface. It was found that the intermolecular dipole-dipole interactions play a critical role in controlling the interfacial supramolecular assembly of these C(3)-symmetric HBC derivatives at the solid-liquid interface. The HBC molecule bearing three -CF(3) groups could form 2D honeycomb structures because of antiparallel dipole-dipole interactions, whereas HBC molecules bearing three -CN or -NO(2) groups could form hexagonal superstructures because of a special trimeric arrangement induced by dipole-dipole interactions and weak hydrogen bonding interactions ([C-H···NC-] or [C-H···O(2)N-]). Molecular mechanics and dynamics simulations were performed to reveal the physics behind the 2D structures as well as detailed functional group interactions. This work provides an example of how intermolecular dipole-dipole interactions could enable fine control over the self-assembly of disklike π-conjugated molecules.

Kinetics of solvent supported tubule formation of Lotus (Nelumbo nucifera) wax on highly oriented pyrolytic graphite (HOPG) investigated by atomic force microscopy

PubMed Central

Koch, Kerstin; Barthlott, Wilhelm; Wandelt, Klaus

2018-01-01

The time dependence of the formation of lotus wax tubules after recrystallization from various chloroform-based solutions on an HOPG surface at room temperature was studied by atomic force microscopy (magnetic AC mode) taking series of consecutive images of the formation process. The growth of the tubules oriented in an upright fashion follows a sequential rodlet→ring→tubule behavior. The influence of a number of factors, e.g., different wax concentration in chloroform, the additional presence of water, or salts [(NH4)2SO4, NH4NO3] or a mixture of salt/water in the solution on the growth rate and orientation of the tubules is also investigated. Different wax concentrations were found to have no effect on the growth rate or the orientation of tubules in none of the solutions. The presence of water, however, considerably increased the growth rate of tubule formation, while the presence of salt was again found to have no effect on growth rate or orientation of tubules. PMID:29515959

The HB-2D Polarized Neutron Development Beamline at the High Flux Isotope Reactor

NASA Astrophysics Data System (ADS)

Crow, Lowell; Hamilton, WA; Zhao, JK; Robertson, JL

2016-09-01

The Polarized Neutron Development beamline, recently commissioned at the HB-2D position on the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory, provides a tool for development and testing of polarizers, polarized neutron devices, and prototyping of polarized neutron techniques. With available monochromators including pyrolytic graphite and polarizing enriched Fe-57 (Si), the instrument has operated at 4.25 and 2.6 Å wavelengths, using crystal, supermirror, or He-3 polarizers and analyzers in various configurations. The Neutron Optics and Development Team has used the beamline for testing of He-3 polarizers for use at other HFIR and Spallation Neutron Source (SNS) instruments, as well as a variety of flipper devices. Recently, we have acquired new supermirror polarizers which have improved the instrument performance. The team and collaborators also have continuing demonstration experiments of spin-echo focusing techniques, and plans to conduct polarized diffraction measurements. The beamline is also used to support a growing use of polarization techniques at present and future instruments at SNS and HFIR.

Direct electrochemistry of nitrate reductase from the fungus Neurospora crassa.

PubMed

Kalimuthu, Palraj; Ringel, Phillip; Kruse, Tobias; Bernhardt, Paul V

2016-09-01

We report the first direct (unmediated) catalytic electrochemistry of a eukaryotic nitrate reductase (NR). NR from the filamentous fungus Neurospora crassa, is a member of the mononuclear molybdenum enzyme family and contains a Mo, heme and FAD cofactor which are involved in electron transfer from NAD(P)H to the (Mo) active site where reduction of nitrate to nitrite takes place. NR was adsorbed on an edge plane pyrolytic graphite (EPG) working electrode. Non-turnover redox responses were observed in the absence of nitrate from holo NR and three variants lacking the FAD, heme or Mo cofactor. The FAD response is due to dissociated cofactor in all cases. In the presence of nitrate, NR shows a pronounced cathodic catalytic wave with an apparent Michaelis constant (KM) of 39μM (pH7). The catalytic cathodic current increases with temperature from 5 to 35°C and an activation enthalpy of 26kJmol(-1) was determined. In spite of dissociation of the FAD cofactor, catalytically activity is maintained. Copyright © 2016. Published by Elsevier B.V.

Effect of fluroine content, atmosphere, and burnishing technique on the lubricating properties of graphite fluoride

NASA Technical Reports Server (NTRS)

Fusaro, R. L.

1974-01-01

Eight different graphite fluoride compounds with fluorine to carbon ratios varying from x = 0.25 to 1.1 were evaluated as burnished films in order to determine the effect of fluorine content on the solid lubricant properties of graphite fluoride. For comparison, similar experiments were conducted on graphite burnished films. It was found that even a small amount of fluorine in graphite fluoride (CF0.25)n improved the lubricating properties of graphite. However, such factors as burnishing atmosphere, burnishing technique, test atmosphere, and specimen temperature affected the results as much as varying the fluorine to carbon ratio of the compound. Best life was found for films that were machined burnished in moist air and tested in moist air.

Graphite fluoride lubrication: The effect of fluorine content, atmosphere, and burnishing technique

NASA Technical Reports Server (NTRS)

Fusaro, R. L.

1975-01-01

Eight different graphite fluoride compounds with fluorine to carbon ratios varying from x = 0.25 to 1.1 were evaluated as burnished films in order to determine the effect of fluorine content on the solid lubricant properties of graphite fluoride. For comparison, similar experiments were conducted on graphite burnished films. It was found that even a small amount of fluorine in graphite fluoride (CF sub 0.25) sub n improved the lubricating properties of graphite. Such factors as burnishing atmosphere, burnishing technique, test atmosphere, and specimen temperature affected the results as much as varying the fluorine to carbon ratio of the compound. Best life was found for films that were machine-burnished in moist air and tested in moist air.

Void forming pyrolytic carbon coating process

DOEpatents

Beatty, Ronald L.; Cook, Jackie L.

2000-01-01

A pyrolytic carbon coated nuclear fuel particle and method of making it. The fuel particle has a core composed of a refractory compound of an actinide metal. The pyrolytic carbon coating surrounds the core so as to provide a void volume therebetween. The coating has an initial density of no greater than 1.45 grams/cm.sup.3 and an anisotropy factor than 3.0 and a final density upon heat treatment above about 2000.degree. C. of greater than 1.7 grams/cm.sup.3 and an anisotropy factor greater than 5.

Pyrolytic Characteristics and Kinetics of Phragmites australis

PubMed Central

Zhao, Hui; Yan, Huaxiao; Zhang, Congwang; Liu, Xiaodong; Xue, Yanhui; Qiao, Yingyun; Tian, Yuanyu; Qin, Song

2011-01-01

The pyrolytic kinetics of Phragmites australis was investigated using thermogravimetric analysis (TGA) method with linear temperature programming process under an inert atmosphere. Kinetic expressions for the degradation rate in devolatilization and combustion steps have been obtained for P. australis with Dollimore method. The values of apparent activation energy, the most probable mechanism functions, and the corresponding preexponential factor were determined. The results show that the model agrees well with the experimental data and provide useful information for the design of pyrolytic processing system using P. australis as feedstock to produce biofuel. PMID:22007256

Pyrolysis characteristics of integrated circuit boards at various particle sizes and temperatures.

PubMed

Chiang, Hung-Lung; Lin, Kuo-Hsiung; Lai, Mei-Hsiu; Chen, Ting-Chien; Ma, Sen-Yi

2007-10-01

A pyrolysis method was employed to recycle the metals and brominated compounds blended into printed circuit boards. This research investigated the effect of particle size and process temperature on the element composition of IC boards and pyrolytic residues, liquid products, and water-soluble ionic species in the exhaust, with the overall goal being to identify the pyrolysis conditions that will have the least impact on the environment. Integrated circuit (IC) boards were crushed into 5-40 mesh (0.71-4.4mm), and the crushed particles were pyrolyzed at temperatures ranging from 200 to 500 degrees C. The thermal decomposition kinetics were measured by a thermogravimetric (TG) analyzer. The composition of pyrolytic residues was analyzed by Energy Dispersive X-ray Spectrometer (EDS), Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). In addition, the element compositions of liquid products were analyzed by ICP-AES and ICP-MS. Pyrolytic exhaust was collected by a water-absorption system in an ice-bath cooler, and IC analysis showed that the absorbed solution comprised 11 ionic species. Based on the pyrolytic kinetic parameters of TG analysis and pyrolytic residues at various temperatures for 30 min, the effect of particle size was insignificant in this study, and temperature was the key factor for the IC board pyrolysis. Two stages of decomposition were found for IC board pyrolysis under nitrogen atmosphere. The activation energy was 38-47 kcal/mol for the first-stage reaction and 5.2-9.4 kcal/mol for the second-stage reaction. Metal content was low in the liquid by-product of the IC board pyrolysis process, which is an advantage in that the liquid product could be used as a fuel. Brominate and ammonium were the main water-soluble ionic species of the pyrolytic exhaust. A plan for their safe and effective disposal must be developed if the pyrolytic recycling process is to be applied to IC boards.

A First Look at Graphite Grains from Orgueil: Morphology, Carbon, Nitrogen and Neon Isotopic Compositions of Individual, Chemically Separated Grains

NASA Technical Reports Server (NTRS)

Pravdivtseva, O.; Zinner, E.; Meshik, A. P.; Hohenberg, C. M.; Walker, R. W.

2004-01-01

Presolar graphite in Murchison has been extensively studied. It is characterized by a unique Ne isotopic composition, known as the Ne-E(L) component. According to studies by Huss and Lewis, the concentration of Ne-E(L) in Orgueil is about one order of magnitude higher than in Murchison, when normalized to the matrix. This could be due to a higher presolar graphite abundance in Orgueil, or due to a higher Ne-E concentrations per grain. The Ne isotopic compositions in individual presolar graphite grains from Murchison have been measured before. It was shown, that a third of the grains have detectable excesses in 22Ne, characteristic of the Ne-E(L) component. One grain in a hundred had a Ne-22 concentration two orders of magnitude higher than blank.

High-resolution transmission electron microscopy studies of graphite materials prepared by high-temperature treatment of unburned carbon concentrates from combustion fly ashes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miguel Cabielles; Jean-Nol Rouzaud; Ana B. Garcia

2009-01-15

High-resolution transmission electron microscopy (HRTEM) has been used in this work to study the microstructural (structure and microtexture) changes occurring during the high-temperature treatment of the unburned carbon concentrates from coal combustion fly ashes. Emphasis was placed on two aspects: (i) the development of graphitic carbon structures and (ii) the disordered carbon forms remaining in the graphitized samples. In addition, by coupling HRTEM with energy-dispersive spectroscopy, the transformations with the temperature of the inorganic matter (mainly iron- and silicon-based phases) of the unburned carbon concentrates were evidenced. The HRTEM results were compared to the averaged structural order of the materialsmore » as evaluated by X-ray diffraction (XRD) and Raman spectroscopy. As indicated by XRD and Raman parameters, more-ordered materials were obtained from the unburned carbon concentrates with higher mineral/inorganic matter, thus inferring the catalytic effect of some of their components. However, the average character of the information provided by these instrumental techniques seems to be inconclusive in discriminating between carbon structures with different degrees of order (stricto sensu graphite, graphitic, turbostratic, etc.) in a given graphitized unburned carbon. Unlike XRD and Raman, HRTEM is a useful tool for imaging directly the profile of the polyaromatic layers (graphene planes), thus allowing the sample heterogeneity to be looked at, specifically the presence of disordered carbon phases. 49 refs., 9 figs., 3 tabs.« less

Preparation, quantitative surface analysis, intercalation characteristics and industrial implications of low temperature expandable graphite

NASA Astrophysics Data System (ADS)

Peng, Tiefeng; Liu, Bin; Gao, Xuechao; Luo, Liqun; Sun, Hongjuan

2018-06-01

Expandable graphite is widely used as a new functional carbon material, especially as fire-retardant; however, its practical application is limited due to the high expansion temperature. In this work, preparation process of low temperature and highly expandable graphite was studied, using natural flake graphite as raw material and KMnO4/HClO4/NH4NO3 as oxidative intercalations. The structure, morphology, functional groups and thermal properties were characterized during expanding process by Fourier transform infrared spectroscopy (FTIR), Raman spectra, thermo-gravimetry differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), and scanning electron microscope (SEM). The analysis showed that by oxidation intercalation, some oxygen-containing groups were grafted on the edge and within the graphite layer. The intercalation reagent entered the graphite layer to increase the interlayer spacing. After expansion, the original flaky expandable graphite was completely transformed into worm-like expanded graphite. The order of graphite intercalation compounds (GICs) was proposed and determined to be 3 for the prepared expandable graphite, based on quantitative XRD peak analysis. Meanwhile, the detailed intercalation mechanisms were also proposed. The comprehensive investigation paved a benchmark for the industrial application of such sulfur-free expanded graphite.

Ion irradiation to simulate neutron irradiation in model graphites: Consequences for nuclear graphite

NASA Astrophysics Data System (ADS)

Galy, N.; Toulhoat, N.; Moncoffre, N.; Pipon, Y.; Bérerd, N.; Ammar, M. R.; Simon, P.; Deldicque, D.; Sainsot, P.

2017-10-01

Due to its excellent moderator and reflector qualities, graphite was used in CO2-cooled nuclear reactors such as UNGG (Uranium Naturel-Graphite-Gaz). Neutron irradiation of graphite resulted in the production of 14C which is a key issue radionuclide for the management of the irradiated graphite waste. In order to elucidate the impact of neutron irradiation on 14C behavior, we carried out a systematic investigation of irradiation and its synergistic effects with temperature in Highly Oriented Pyrolitic Graphite (HOPG) model graphite used to simulate the coke grains of nuclear graphite. We used 13C implantation in order to simulate 14C displaced from its original structural site through recoil. The collision of the impinging neutrons with the graphite matrix carbon atoms induces mainly ballistic damage. However, a part of the recoil carbon atom energy is also transferred to the graphite lattice through electronic excitation. The effects of the different irradiation regimes in synergy with temperature were simulated using ion irradiation by varying Sn(nuclear)/Se(electronic) stopping power. Thus, the samples were irradiated with different ions of different energies. The structure modifications were followed by High Resolution Transmission Electron Microscopy (HRTEM) and Raman microspectrometry. The results show that temperature generally counteracts the disordering effects of irradiation but the achieved reordering level strongly depends on the initial structural state of the graphite matrix. Thus, extrapolating to reactor conditions, for an initially highly disordered structure, irradiation at reactor temperatures (200 - 500 °C) should induce almost no change of the initial structure. On the contrary, when the structure is initially less disordered, there should be a "zoning" of the reordering: In "cold" high flux irradiated zones where the ballistic damage is important, the structure should be poorly reordered; In "hot" low flux irradiated zones where the ballistic impact is lower and can therefore be counteracted by temperature, a better reordering of the structure should be achieved. Concerning 14C, except when located close to open pores where it can be removed through radiolytic corrosion, it tends to stabilize in the graphite matrix into sp2 or sp3 structures with variable proportions depending on the irradiation conditions.

Characterization of the Nonlinear Elastic Properties of Graphite/Epoxy Composites Using Ultrasound

NASA Technical Reports Server (NTRS)

Prosser, William H.; Green, Robert E., Jr.

1990-01-01

The normalized change in ultrasonic "natural" velocity as a function of stress and temperature was measured in a unidirectional laminate of T300/5208 graphite/epoxy composite using a pulsed phase locked loop ultrasonic interferometer. These measurements were used together with the linear (second order) elastic moduli to calculate some of the nonlinear (third order) moduli of this material.

Kinetic analyses and pyrolytic behavior of Para grass (Urochloa mutica) for its bioenergy potential.

PubMed

Ahmad, Muhammad Sajjad; Mehmood, Muhammad Aamer; Al Ayed, Omar S; Ye, Guangbin; Luo, Huibo; Ibrahim, Muhammad; Rashid, Umer; Arbi Nehdi, Imededdine; Qadir, Ghulam

2017-01-01

The biomass of Urochloa mutica was subjected to thermal degradation analyses to understand its pyrolytic behavior for bioenergy production. Thermal degradation experiments were performed at three different heating rates, 10, 30 and 50°Cmin -1 using simultaneous thermogravimetric-differential scanning calorimetric analyzer, under an inert environment. The kinetic analyses were performed using isoconversional models of Kissenger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO). The high heating value was calculated as 15.04MJmol -1 . The activation energy (E) values were shown to be ranging from 103 through 233 kJmol -1 . Pre-exponential factors (A) indicated the reaction to follow first order kinetics. Gibbs free energy (ΔG) was measured to be ranging from 169 to 173kJmol -1 and 168 to 172kJmol -1 , calculated by KAS and FWO methods, respectively. We have shown that Para grass biomass has considerable bioenergy potential comparable to established bioenergy crops such as switchgrass and miscanthus. Copyright © 2016 Elsevier Ltd. All rights reserved.

Effect of Ar{sup +} ion irradiation on the microstructure of pyrolytic carbon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feng, Shanglei; Zhang, Dongsheng; Yang, Xinmei

2015-03-21

Pyrolytic carbon (PyC) coatings prepared by chemical vapor deposition were irradiated by 300 keV Ar{sup +} ions. Then, atomic force microscopy, synchrotron-based grazing incidence X-ray diffraction, Raman spectroscopy, X-ray photoemission spectroscopy, and transmission electron microscopy were employed to study how Ar{sup +} irradiation affects the microstructure of PyC, including the microstructural damage mechanisms and physics driving these phenomena. The 300 keV Ar{sup +} ion irradiation deteriorated the structure along the c-axis, which increased the interlayer spacing between graphene layers. With increasing irradiation dose, the density of defect states on the surface of PyC coating increases, and the basal planes gradually loses theirmore » initial ordering resulting in breaks in the lattice and turbulence at the peak damage dose reaches 1.58 displacement per atom (dpa). Surprisingly, the PyC becomes more textured as it becomes richer in structural defects with increasing irradiation dose.« less

Internal graphite moderator forces study, C and K Reactors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cooley, D.E.

1963-10-28

The purpose of this study was to determine the maximum forces that can be imposed by the graphite moderator on prospective VSR channel sleeves. In order to do this, both the origins and modes of transmission of the forces were determined. Forces in the moderator stack that are capable of acting on a block or group of blocks may originate from any of the following primary effects: Contraction of graphite due to irradiation; thermal expansion of graphite; frictional resistance to motion; resistance from keys; gravity; and other.

Oxidation of hydrocarbons over ordered arrays of heteropolyacids and polyoxoanions on graphite

DOEpatents

Shaikh, S.N.; Ellis, P.E. Jr.; Lyons, J.E.

1994-08-02

Alkanes are catalytically oxidized using heteropolyacids or polyoxoanions deposited on a graphite surface. The heteropolyacids and polyoxoanions are framework-substituted with a different metal in place of a metal-oxygen unit.

Effect of friction on oxidative graphite intercalation and high-quality graphene formation.

PubMed

Seiler, Steffen; Halbig, Christian E; Grote, Fabian; Rietsch, Philipp; Börrnert, Felix; Kaiser, Ute; Meyer, Bernd; Eigler, Siegfried

2018-02-26

Oxidative wet-chemical delamination of graphene from graphite is expected to become a scalable production method. However, the formation process of the intermediate stage-1 graphite sulfate by sulfuric acid intercalation and its subsequent oxidation are poorly understood and lattice defect formation must be avoided. Here, we demonstrate film formation of micrometer-sized graphene flakes with lattice defects down to 0.02% and visualize the carbon lattice by transmission electron microscopy at atomic resolution. Interestingly, we find that only well-ordered, highly crystalline graphite delaminates into oxo-functionalized graphene, whereas other graphite grades do not form a proper stage-1 intercalate and revert back to graphite upon hydrolysis. Ab initio molecular dynamics simulations show that ideal stacking and electronic oxidation of the graphite layers significantly reduce the friction of the moving sulfuric acid molecules, thereby facilitating intercalation. Furthermore, the evaluation of the stability of oxo-species in graphite sulfate supports an oxidation mechanism that obviates intercalation of the oxidant.

Adsorption behavior of bisphenol A on CTAB-modified graphite

NASA Astrophysics Data System (ADS)

Wang, Li-Cong; Ni, Xin-jiong; Cao, Yu-Hua; Cao, Guang-qun

2018-01-01

In this work, the adsorption behavior of BPA on CTAB-modified graphite was investigated thoroughly to develop a novel absorbent material. Atomic force microscopy revealed that conical admicelles formed on the surface of graphite. The surface area of graphite decreased significantly from 1.46 to 0.95 m2 g-1, which confirmed the formation of the larger size admicelle instead of the original smaller particle on the surface. CTAB concentration and incubation time affected the progress of admicelle formation on the surface of graphite. Adsolubilization is key in BPA adsorption by CTAB-modified graphite. An extraordinary cation-π electron interaction between CTAB and BPA, revealed by a red-shift in the ultraviolet spectrum, as well as a hydrophobic interaction contribute substantially to BPA adsolubilization. The equilibrium adsorption capacity of the modified graphite for BPA was 125.01 mg g-1. The adsorption kinetic curves of BPA on modified graphite were shown to follow a pseudosecond-order rate. The adsorption process was observed to be both spontaneous and exothermic complied with the Freundlich model.

Quantifying microstructural dynamics and electrochemical activity of graphite and silicon-graphite lithium ion battery anodes

NASA Astrophysics Data System (ADS)

Pietsch, Patrick; Westhoff, Daniel; Feinauer, Julian; Eller, Jens; Marone, Federica; Stampanoni, Marco; Schmidt, Volker; Wood, Vanessa

2016-09-01

Despite numerous studies presenting advances in tomographic imaging and analysis of lithium ion batteries, graphite-based anodes have received little attention. Weak X-ray attenuation of graphite and, as a result, poor contrast between graphite and the other carbon-based components in an electrode pore space renders data analysis challenging. Here we demonstrate operando tomography of weakly attenuating electrodes during electrochemical (de)lithiation. We use propagation-based phase contrast tomography to facilitate the differentiation between weakly attenuating materials and apply digital volume correlation to capture the dynamics of the electrodes during operation. After validating that we can quantify the local electrochemical activity and microstructural changes throughout graphite electrodes, we apply our technique to graphite-silicon composite electrodes. We show that microstructural changes that occur during (de)lithiation of a pure graphite electrode are of the same order of magnitude as spatial inhomogeneities within it, while strain in composite electrodes is locally pronounced and introduces significant microstructural changes.

Oxidation of hydrocarbons over ordered arrays of heteropolyacids and polyoxoanions on graphite

DOEpatents

Shaikh, Shahid N.; Ellis, Jr., Paul E.; Lyons, James E.

1994-01-01

Alkanes are catalytically oxidized using heteropolyacids (HPAs) or polyoxoanions (POAs) deposited on a graphite surface. The HPAs and POAs are framework-substituted with a different metal in place of a metal-oxygen unit.

Adsorption of dysprosium on the graphite (0001) surface: Nucleation and growth at 300 K

DOE PAGES

Kwolek, Emma J.; Lei, Huaping; Lii-Rosales, Ann; ...

2016-06-13

We have studied nucleation and growth of Dy islands on the basal plane of graphite at 300 K using scanning tunneling microscopy, density functional theory (DFT) in a form that includes van der Waals interactions, and analytic theory. The interaction of atomic Dy with graphite is strong, while the diffusion barrier is small. Experiment shows that at 300 K, the density of nucleated islands is close to the value predicted for homogeneous nucleation, using critical nucleus size of 1 and the DFT-derived diffusion barrier. Homogeneous nucleation is also supported by the monomodal shape of the island size distributions. Comparison withmore » the published island density of Dy on graphene shows that the value is about two orders of magnitude smaller on graphite, which can be attributed to more effective charge screening in graphite. The base of each island is 3 atomic layers high and atomically ordered, forming a coincidence lattice with the graphite. Islands resist coalescence, probably due to multiple rotational orientations associated with the coincidence lattice. Upper levels grow as discernible single-atom layers. Analysis of the level populations reveals significant downward interlayer transport, which facilitates growth of the base. As a result, this island shape is metastable, since more compact three-dimensional islands form at elevated growth temperature.« less

Adsorption of dysprosium on the graphite (0001) surface: Nucleation and growth at 300 K

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kwolek, Emma J.; Lii-Rosales, Ann; Department of Chemistry, Iowa State University, Ames, Iowa 50011

2016-12-07

We have studied nucleation and growth of Dy islands on the basal plane of graphite at 300 K using scanning tunneling microscopy, density functional theory (DFT) in a form that includes van der Waals interactions, and analytic theory. The interaction of atomic Dy with graphite is strong, while the diffusion barrier is small. Experiment shows that at 300 K, the density of nucleated islands is close to the value predicted for homogeneous nucleation, using critical nucleus size of 1 and the DFT-derived diffusion barrier. Homogeneous nucleation is also supported by the monomodal shape of the island size distributions. Comparison withmore » the published island density of Dy on graphene shows that the value is about two orders of magnitude smaller on graphite, which can be attributed to more effective charge screening in graphite. The base of each island is 3 atomic layers high and atomically ordered, forming a coincidence lattice with the graphite. Islands resist coalescence, probably due to multiple rotational orientations associated with the coincidence lattice. Upper levels grow as discernible single-atom layers. Analysis of the level populations reveals significant downward interlayer transport, which facilitates growth of the base. This island shape is metastable, since more compact three-dimensional islands form at elevated growth temperature.« less

The defect level and ideal thermal conductivity of graphene uncovered by residual thermal reffusivity at the 0 K limit.

PubMed

Xie, Yangsu; Xu, Zaoli; Xu, Shen; Cheng, Zhe; Hashemi, Nastaran; Deng, Cheng; Wang, Xinwei

2015-06-14

Due to its intriguing thermal and electrical properties, graphene has been widely studied for potential applications in sensor and energy devices. However, the reported value for its thermal conductivity spans from dozens to thousands of W m(-1) K(-1) due to different levels of alternations and defects in graphene samples. In this work, the thermal diffusivity of suspended four-layered graphene foam (GF) is characterized from room temperature (RT) down to 17 K. For the first time, we identify the defect level in graphene by evaluating the inverse of thermal diffusivity (termed "thermal reffusivity": Θ) at the 0 K limit. By using the Debye model of Θ = Θ0 + C× e(-θ/2T) and fitting the Θ-T curve to the point of T = 0 K, we identify the defect level (Θ0) and determine the Debye temperature of graphene. Θ0 is found to be 1878 s m(-2) for the studied GF and 43-112 s m(-2) for three highly crystalline graphite materials. This uncovers a 16-43-fold higher defect level in GF than that in pyrolytic graphite. In GF, the phonon mean free path solely induced by defects and boundary scattering is determined as 166 nm. The Debye temperature of graphene is determined to be 1813 K, which is very close to the average theoretical Debye temperature (1911 K) of the three acoustic phonon modes in graphene. By subtracting the defect effect, we report the ideal thermal diffusivity and conductivity (κideal) of graphene presented in the 3D foam structure in the range of 33-299 K. Detailed physics based on chemical composition and structure analysis are given to explain the κideal-T profile by comparing with those reported for suspended graphene.

Determination of cadmium in coal using solid sampling graphite furnace high-resolution continuum source atomic absorption spectrometry.

PubMed

da Silva, Alessandra Furtado; Borges, Daniel L G; Lepri, Fábio Grandis; Welz, Bernhard; Curtius, Adilson J; Heitmann, Uwe

2005-08-01

This work describes the development of a method to determine cadmium in coal, in which iridium is used as a permanent chemical modifier and calibration is performed against aqueous standards by high-resolution continuum source atomic absorption spectrometry (HR-CS AAS). This new instrumental concept makes the whole spectral environment in the vicinity of the analytical line accessible, providing a lot more data than just the change in absorbance over time available from conventional instruments. The application of Ir (400 microg) as a permanent chemical modifier, thermally deposited on the pyrolytic graphite platform surface, allowed pyrolysis temperatures of 700 degrees C to be used, which was sufficiently high to significantly reduce the continuous background that occurred before the analyte signal at pyrolysis temperatures <700 degrees C. Structured background absorption also occurred after the analyte signal when atomization temperatures of >1600 degrees C were used, which arose from the electron-excitation spectrum (with rotational fine structure) of a diatomic molecule. Under optimized conditions (pyrolysis at 700 degrees C and atomization at 1500 degrees C), interference-free determination of cadmium in seven certified coal reference materials and two real samples was achieved by direct solid sampling and calibrating against aqueous standards, resulting in good agreement with the certified values (where available) at the 95% confidence level. A characteristic mass of 0.4 pg and a detection limit of 2 ng g(-1), calculated for a sample mass of 1.0 mg coal, was obtained. A precision (expressed as the relative standard deviation, RSD) of <10% was typically obtained when coal samples in the mass range 0.6-1.2 mg were analyzed.

2D nanosheet molybdenum disulphide (MoS2) modified electrodes explored towards the hydrogen evolution reaction.

PubMed

Rowley-Neale, Samuel J; Brownson, Dale A C; Smith, Graham C; Sawtell, David A G; Kelly, Peter J; Banks, Craig E

2015-11-21

We explore the use of two-dimensional (2D) MoS2 nanosheets as an electrocatalyst for the Hydrogen Evolution Reaction (HER). Using four commonly employed commercially available carbon based electrode support materials, namely edge plane pyrolytic graphite (EPPG), glassy carbon (GC), boron-doped diamond (BDD) and screen-printed graphite electrodes (SPE), we critically evaluate the reported electrocatalytic performance of unmodified and MoS2 modified electrodes towards the HER. Surprisingly, current literature focuses almost exclusively on the use of GC as an underlying support electrode upon which HER materials are immobilised. 2D MoS2 nanosheet modified electrodes are found to exhibit a coverage dependant electrocatalytic effect towards the HER. Modification of the supporting electrode surface with an optimal mass of 2D MoS2 nanosheets results in a lowering of the HER onset potential by ca. 0.33, 0.57, 0.29 and 0.31 V at EPPG, GC, SPE and BDD electrodes compared to their unmodified counterparts respectively. The lowering of the HER onset potential is associated with each supporting electrode's individual electron transfer kinetics/properties and is thus distinct. The effect of MoS2 coverage is also explored. We reveal that its ability to catalyse the HER is dependent on the mass deposited until a critical mass of 2D MoS2 nanosheets is achieved, after which its electrocatalytic benefits and/or surface stability curtail. The active surface site density and turn over frequency for the 2D MoS2 nanosheets is determined, characterised and found to be dependent on both the coverage of 2D MoS2 nanosheets and the underlying/supporting substrate. This work is essential for those designing, fabricating and consequently electrochemically testing 2D nanosheet materials for the HER.

Aromatics extraction from pyrolytic sugars using ionic liquid to enhance sugar fermentability.

PubMed

Li, Xiaohua; Luque-Moreno, Luis C; Oudenhoven, Stijn R G; Rehmann, Lars; Kersten, Sascha R A; Schuur, Boelo

2016-09-01

Fermentative bioethanol production from pyrolytic sugars was improved via aromatics removal by liquid-liquid extraction. As solvents, the ionic liquid (IL) trihexyltetradecylphosphonium dicyanamide (P666,14[N(CN)2]) and ethyl acetate (EA) were compared. Two pyrolytic sugar solutions were created from acid-leached and untreated pinewood, with levoglucosan contents (most abundant sugar) of 29.0% and 8.3% (w/w), respectively. In a single stage extraction, 70% of the aromatics were effectively removed by P666,14[N(CN)2] and 50% by EA, while no levoglucosan was extracted. The IL was regenerated by vacuum evaporation (100mbar) at 220°C, followed by extraction of aromatics from fresh pyrolytic sugar solutions. Regenerated IL extracted aromatics with similar extraction efficiency as the fresh IL, and the purified sugar fraction from pretreated pinewood was hydrolyzed to glucose and fermented to ethanol, yielding 0.46g ethanol/(g glucose), close to the theoretical maximum yield. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

Interface structure between tetraglyme and graphite

NASA Astrophysics Data System (ADS)

Minato, Taketoshi; Araki, Yuki; Umeda, Kenichi; Yamanaka, Toshiro; Okazaki, Ken-ichi; Onishi, Hiroshi; Abe, Takeshi; Ogumi, Zempachi

2017-09-01

Clarification of the details of the interface structure between liquids and solids is crucial for understanding the fundamental processes of physical functions. Herein, we investigate the structure of the interface between tetraglyme and graphite and propose a model for the interface structure based on the observation of frequency-modulation atomic force microscopy in liquids. The ordering and distorted adsorption of tetraglyme on graphite were observed. It is found that tetraglyme stably adsorbs on graphite. Density functional theory calculations supported the adsorption structure. In the liquid phase, there is a layered structure of the molecular distribution with an average distance of 0.60 nm between layers.

Program for the development of high temperature electrical materials and components

NASA Technical Reports Server (NTRS)

Neff, W. S.; Lowry, L. R.

1972-01-01

Evaluation of high temperature, space-vacuum performance of selected electrical materials and components, high temperature capacitor development, and evaluation, construction, and endurance testing of compression sealed pyrolytic boron nitride slot insulation are described. The first subject above covered the aging evaluation of electrical devices constructed from selected electrical materials. Individual materials performances were also evaluated and reported. The second subject included study of methods of improving electrical performance of pyrolytic boron nitride capacitors. The third portion was conducted to evaluate the thermal and electrical performance of pyrolytic boron nitride as stator slot liner material under varied temperature and compressive loading. Conclusions and recommendations are presented.

Graphitic and oxidised high pressure high temperature (HPHT) nanodiamonds induce differential biological responses in breast cancer cell lines.

PubMed

Woodhams, Benjamin; Ansel-Bollepalli, Laura; Surmacki, Jakub; Knowles, Helena; Maggini, Laura; de Volder, Michael; Atatüre, Mete; Bohndiek, Sarah

2018-06-19

Nanodiamonds have demonstrated potential as powerful sensors in biomedicine, however, their translation into routine use requires a comprehensive understanding of their effect on the biological system being interrogated. Under normal fabrication processes, nanodiamonds are produced with a graphitic carbon shell, but are often oxidized in order to modify their surface chemistry for targeting to specific cellular compartments. Here, we assessed the biological impact of this purification process, considering cellular proliferation, uptake, and oxidative stress for graphitic and oxidized nanodiamond surfaces. We show for the first time that oxidized nanodiamonds possess improved biocompatibility compared to graphitic nanodiamonds in breast cancer cell lines, with graphitic nanodiamonds inducing higher levels of oxidative stress despite lower uptake.

77 FR 33405 - Small Diameter Graphite Electrodes From the People's Republic of China: Affirmative Preliminary...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-06-06

...The Department of Commerce (``Department'') preliminarily determines that certain small diameter graphite electrodes (``SDGE'') are being exported from the United Kingdom (``U.K.'') to the United States by UK Carbon and Graphite Co., Ltd. (``UKCG'') in circumvention of the antidumping duty order on SDGE from the People's Republic of China (``PRC''),\\1\\ as provided in section 781(b) of the Tariff Act of 1930, as amended (``the Act''). ---------------------------------------------------------------------------

Effects of sequential treatment with fluorine and bromine on graphite fibers

NASA Technical Reports Server (NTRS)

Hung, Ching-Cheh; Stahl, Mark; Maciag, Carolyn; Slabe, Melissa

1987-01-01

Three pitch based graphite fibers with different degrees of graphitization and one polyacryonitrile (PAN) based carbon fiber from Amoco Corporation were treated with 1 atm, room temperature fluorine gas for 90 hrs. Fluorination resulted in higher electrical conductivity for all pitch fibers. Further bromination after ambient condition defluorination resulted in further increases in electrical defluorination conductivity for less graphitized, less structurally ordered pitch fibers (P-55) which contain about 3% fluorine by weight before bromination. This product can be stable in 200 C air, or 100% humidity at 60 C. Due to its low cost, this less graphitized fiber may be useful for industrial application, such as airfoil deicer materials. The same bromination process, however, resulted in conductivity decreases for fluorine rich, more graphitized, structurally oriented pitch fibers (P-100 and P-75). Such decreases in electrical conductivity were partially reversed by heating the fibers at 185 C in air. Differential scanning calorimetric (DSC) data indicated that the more graphitized fibers (P-100) contained BrF3, whereas the less graphitized fibers (P-55) did not.

Catalytic pyrolysis of car tire waste using expanded perlite.

PubMed

Kar, Y

2011-08-01

In this study, the non-catalytic and catalytic pyrolysis experiments were conducted on the sample of tire waste using expanded perlite as an additive material to determine especially the effect of temperature and catalyst-to-tire ratio on the products yields and the compositions and qualities of pyrolytic oils (NCPO and CPO). Non-catalytic studies, which were carried out under the certain conditions (a nitrogen flow of 100mL/min and a heating rate of 10°C/min), showed that the highest yield of pyrolytic oil (NCPO) was 60.02wt.% at 425°C. Then, the catalytic pyrolysis studies were carried out at catalyst-to-tire ratio range of 0.05-0.25 and the highest catalytic pyrolytic oil (CPO) yield was 65.11wt.% at the ratio of 0.10 with the yield increase of 8.48wt.% compared with the non-catalytic pyrolysis. Lastly, the pyrolytic oils were characterized with applying a various techniques such as elemental analyses and various chromatographic and spectroscopic techniques (GC-MS, (1)H NMR, FT-IR, etc.). The characterization results revealed that the pyrolytic oils which were complex mixtures of C(5)-C(15) organic compounds (predominantly aromatic compounds) and also the CPO compared to the NCPO was more similar to conventional fuels in view of the certain fuel properties. Copyright © 2011 Elsevier Ltd. All rights reserved.

Graphite/Cyanate Ester Face Sheets for Adaptive Optics

NASA Technical Reports Server (NTRS)

Bennett, Harold; Shaffer, Joseph; Romeo, Robert

2008-01-01

It has been proposed that thin face sheets of wide-aperture deformable mirrors in adaptive-optics systems be made from a composite material consisting of cyanate ester filled with graphite. This composite material appears to offer an attractive alternative to low-thermal-expansion glasses that are used in some conventional optics and have been considered for adaptive-optics face sheets. Adaptive-optics face sheets are required to have maximum linear dimensions of the order of meters or even tens of meters for some astronomical applications. If the face sheets were to be made from low-thermal-expansion glasses, then they would also be required to have thicknesses of the order of a millimeter so as to obtain the optimum compromise between the stiffness needed for support and the flexibility needed to enable deformation to controlled shapes by use of actuators. It is difficult to make large glass sheets having thicknesses less than 3 mm, and 3-mm-thick glass sheets are too stiff to be deformable to the shapes typically required for correction of wavefronts of light that has traversed the terrestrial atmosphere. Moreover, the primary commercially produced candidate low-thermal-expansion glass is easily fractured when in the form of thin face sheets. Graphite-filled cyanate ester has relevant properties similar to those of the low-expansion glasses. These properties include a coefficient of thermal expansion (CTE) of the order of a hundredth of the CTEs of other typical mirror materials. The Young s modulus (which quantifies stiffness in tension and compression) of graphite-filled cyanate ester is also similar to the Young's moduli of low-thermal-expansion glasses. However, the fracture toughness of graphite-filled cyanate ester is much greater than that of the primary candidate low-thermal-expansion glass. Therefore, graphite-filled cyanate ester could be made into nearly unbreakable face sheets, having maximum linear dimensions greater than a meter and thicknesses of the order of a millimeter, that would satisfy the requirements for use in adaptive optics.

Kelvin Probe Force Microscopy in liquid using Electrochemical Force Microscopy

DOE PAGES

Collins, Liam; Jesse, Stephen; Kilpatrick, J.; ...

2015-01-19

Conventional closed loop-Kelvin probe force microscopy (KPFM) has emerged as a powerful technique for probing electric and transport phenomena at the solid-gas interface. The extension of KPFM capabilities to probe electrostatic and electrochemical phenomena at the solid–liquid interface is of interest for a broad range of applications from energy storage to biological systems. However, the operation of KPFM implicitly relies on the presence of a linear lossless dielectric in the probe-sample gap, a condition which is violated for ionically-active liquids (e.g., when diffuse charge dynamics are present). Here, electrostatic and electrochemical measurements are demonstrated in ionically-active (polar isopropanol, milli-Q watermore » and aqueous NaCl) and ionically-inactive (non-polar decane) liquids by electrochemical force microscopy (EcFM), a multidimensional (i.e., bias- and time-resolved) spectroscopy method. In the absence of mobile charges (ambient and non-polar liquids), KPFM and EcFM are both feasible, yielding comparable contact potential difference (CPD) values. In ionically-active liquids, KPFM is not possible and EcFM can be used to measure the dynamic CPD and a rich spectrum of information pertaining to charge screening, ion diffusion, and electrochemical processes (e.g., Faradaic reactions). EcFM measurements conducted in isopropanol and milli-Q water over Au and highly ordered pyrolytic graphite electrodes demonstrate both sample- and solvent-dependent features. Finally, the feasibility of using EcFM as a local force-based mapping technique of material-dependent electrostatic and electrochemical response is investigated. The resultant high dimensional dataset is visualized using a purely statistical approach that does not require a priori physical models, allowing for qualitative mapping of electrostatic and electrochemical material properties at the solid–liquid interface.« less

Boundary layer friction of solvate ionic liquids as a function of potential.

PubMed

Li, Hua; Rutland, Mark W; Watanabe, Masayoshi; Atkin, Rob

2017-07-01

Atomic force microscopy (AFM) has been used to investigate the potential dependent boundary layer friction at solvate ionic liquid (SIL)-highly ordered pyrolytic graphite (HOPG) and SIL-Au(111) interfaces. Friction trace and retrace loops of lithium tetraglyme bis(trifluoromethylsulfonyl)amide (Li(G4) TFSI) at HOPG present clearer stick-slip events at negative potentials than at positive potentials, indicating that a Li + cation layer adsorbed to the HOPG lattice at negative potentials which enhances stick-slip events. The boundary layer friction data for Li(G4) TFSI shows that at HOPG, friction forces at all potentials are low. The TFSI - anion rich boundary layer at positive potentials is more lubricating than the Li + cation rich boundary layer at negative potentials. These results suggest that boundary layers at all potentials are smooth and energy is predominantly dissipated via stick-slip events. In contrast, friction at Au(111) for Li(G4) TFSI is significantly higher at positive potentials than at negative potentials, which is comparable to that at HOPG at the same potential. The similarity of boundary layer friction at negatively charged HOPG and Au(111) surfaces indicates that the boundary layer compositions are similar and rich in Li + cations for both surfaces at negative potentials. However, at Au(111), the TFSI - rich boundary layer is less lubricating than the Li + rich boundary layer, which implies that anion reorientations rather than stick-slip events are the predominant energy dissipation pathways. This is confirmed by the boundary friction of Li(G4) NO 3 at Au(111), which shows similar friction to Li(G4) TFSI at negative potentials due to the same cation rich boundary layer composition, but even higher friction at positive potentials, due to higher energy dissipation in the NO 3 - rich boundary layer.

Graphene oxide electrochemistry: the electrochemistry of graphene oxide modified electrodes reveals coverage dependent beneficial electrocatalysis

PubMed Central

Smith, Graham C.

2017-01-01

The modification of electrode surfaces is widely implemented in order to try and improve electron transfer kinetics and surface interactions, most recently using graphene related materials. Currently, the use of ‘as is’ graphene oxide (GO) has been largely overlooked, with the vast majority of researchers choosing to reduce GO to graphene or use it as part of a composite electrode. In this paper, ‘as is’ GO is explored and electrochemically characterized using a range of electrochemical redox probes, namely potassium ferrocyanide(II), N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD), dopamine hydrochloride and epinephrine. Furthermore, the electroanalytical efficacy of GO is explored towards the sensing of dopamine hydrochloride and epinephrine via cyclic voltammetry. The electrochemical response of GO is benchmarked against pristine graphene and edge plane-/basal plane pyrolytic graphite (EPPG and BPPG respectively) alternatives, where the GO shows an enhanced electrochemical/electroanalytical response. When using GO as an electrode material, the electrochemical response of the analytes studied herein deviate from that expected and exhibit altered electrochemical responses. The oxygenated species encompassing GO strongly influence and dominate the observed voltammetry, which is crucially coverage dependent. GO electrocatalysis is observed, which is attributed to the presence of beneficial oxygenated species dictating the response in specific cases, demonstrating potential for advantageous electroanalysis to be realized. Note however, that crucial coverage based regions are observed at GO modified electrodes, owing to the synergy of edge plane sites and oxygenated species. We report the true beneficial electrochemistry of GO, which has enormous potential to be beneficially used in various electrochemical applications ‘as is’ rather than be simply used as a precursor to making graphene and is truly a fascinating member of the graphene family. PMID:29291099

Chirality in adsorption on solid surfaces.

PubMed

Zaera, Francisco

2017-12-07

In the present review we survey the main advances made in recent years on the understanding of chemical chirality at solid surfaces. Chirality is an important topic, made particularly relevant by the homochiral nature of the biochemistry of life on Earth, and many chiral chemical reactions involve solid surfaces. Here we start our discussion with a description of surface chirality and of the different ways that chirality can be bestowed on solid surfaces. We then expand on the studies carried out to date to understand the adsorption of chiral compounds at a molecular level. We summarize the work published on the adsorption of pure enantiomers, of enantiomeric mixtures, and of prochiral molecules on chiral and achiral model surfaces, especially on well-defined metal single crystals but also on other flat substrates such as highly ordered pyrolytic graphite. Several phenomena are identified, including surface reconstruction and chiral imprinting upon adsorption of chiral agents, and the enhancement or suppression of enantioselectivity seen in some cases upon adsorption of enantiomixtures of chiral compounds. The possibility of enhancing the enantiopurity of adsorbed layers upon the addition of chiral seeds and the so-called "sergeants and soldiers" phenomenon are presented. Examples are provided where the chiral behavior has been associated with either thermodynamic or kinetic driving forces. Two main approaches to the creation of enantioselective surface sites are discussed, namely, via the formation of supramolecular chiral ensembles made out of small chiral adsorbates, and by adsorption of more complex chiral molecules capable of providing suitable chiral environments for reactants by themselves, via the formation of individual adsorbate:modifier adducts on the surface. Finally, a discussion is offered on the additional effects generated by the presence of the liquid phase often required in practical applications such as enantioselective crystallization, chiral chromatography, and enantioselective catalysis.

A novel strategy to improve the sensitivity of antibiotics determination based on bioelectrocatalysis at molecularly imprinted polymer film electrodes.

PubMed

Lian, Wenjing; Liu, Shuang; Wang, Lei; Liu, Hongyun

2015-11-15

A new strategy for the sensitive detection of kanamycin (KA) and other antibiotics based on molecularly imprinted polymer (MIP) and bioelectrocatalysis was developed in the present study. The KA-polypyrrole MIP films were electropolymerized on the surface of pyrolytic graphite (PG) electrodes, with pyrrole (PY) serving as the monomer and KA as the template. Because KA is electro-inactive, electroactive K3[Fe(CN)6] was used as the probe in the cyclic voltammetric (CV) measurements. The difference of the CV reduction peaks of K3[Fe(CN)6] at electrodes between the MIP films after KA removal and KA-rebinding MIP films could thus be used to determine KA quantitatively. When horseradish peroxidase (HRP) and H2O2 were added into the testing solution, the detection sensitivity of the system was greatly amplified because the electrochemical reduction of H2O2 could be catalyzed by HRP and mediated by K3[Fe(CN)6]. With the bioelectrocatalysis amplification, the limit of detection (LOD) for KA fell as low as 28 nM, approximately two orders of magnitude lower than that for the MIP films in the absence of enzymatic catalysis. The strategy demonstrated the generality. Not only KA but also other antibiotics, such as oxytetracycline (OTC), could be determined by this method. More significantly, in addition to the K3[Fe(CN)6]-HRP-H2O2 system, other bioelectrocatalysis systems, such as Fc(COOH)2-GOD-glucose (Fc(COOH)2=ferrocenedicarboxylic acid, GOD=glucose oxidase), could also be used to amplify the CV signal and realize the sensitive detection of KA for the MIP film system, thereby illustrating the great potential and prospects of the strategy. Copyright © 2015 Elsevier B.V. All rights reserved.

NanoSIMS Determination of Carbon and Oxygen Isotopic Compositions of Presolar Graphites from the Murchison Meteorite

NASA Technical Reports Server (NTRS)

Stadermann, F. J.; Croat, T. K.; Bernatowicz, T.

2004-01-01

Graphite from the Murchison density separate KFC1 (2.15 - 2.20 g/cu cm) has previously been studied by combined SEM/EDX and ion microprobe analysis. These studies found several distinct morphological types of graphites and C isotopic compositions that vary over more than 3 orders of magnitude, clearly establishing their presolar origin. Subsequent TEM measurements of a subset of these particles found abundant embedded crystals of metal (Zr, Mo, Ti, Ru) carbides which were incorporated during the growth of the graphites. A new TEM study of a large set of KFC1 graphites led to the discovery of another type of presolar material, Ru-Fe metal. Here we report results of the C and O isotopic measurements in the same graphite sections, which makes it possible for the first time to directly correlate isotopic and TEM data of KFC1 grains.

Pyrolytic carbon-coated nuclear fuel

DOEpatents

Lindemer, Terrence B.; Long, Jr., Ernest L.; Beatty, Ronald L.

1978-01-01

An improved nuclear fuel kernel having at least one pyrolytic carbon coating and a silicon carbon layer is provided in which extensive interaction of fission product lanthanides with the silicon carbon layer is avoided by providing sufficient UO.sub.2 to maintain the lanthanides as oxides during in-reactor use of said fuel.

Electrochemical treatment of evaporated residue of soak liquor generated from leather industry.

PubMed

Boopathy, R; Sekaran, G

2013-09-15

The organic and suspended solids present in soak liquor, generated from leather industry, demands treatment. The soak liquor is being segregated and evaporated in solar evaporation pans/multiple effect evaporator due to non availability of viable technology for its treatment. The residue left behind in the pans/evaporator does not carry any reuse value and also faces disposal threat due to the presence of high concentration of sodium chloride, organic and bacterial impurities. In the present investigation, the aqueous evaporated residue of soak liquor (ERSL) was treated by electrochemical oxidation. Graphite/graphite and SS304/graphite systems were used in electrochemical oxidation of organics in ERSL. Among these, graphite/graphite system was found to be effective over SS304/graphite system. Hence, the optimised conditions for the electrochemical oxidation of organics in ERSL using graphite/graphite system was evaluated by response surface methodology (RSM). The mass transport coefficient (km) was calculated based on pseudo-first order rate kinetics for both the electrode systems (graphite/graphite and SS304/graphite). The thermodynamic properties illustrated the electrochemical oxidation was exothermic and non-spontaneous in nature. The calculated specific energy consumption at the optimum current density of 50 mA cm(-2) was 0.41 kWh m(-3) for the removal of COD and 2.57 kWh m(-3) for the removal of TKN. Copyright © 2013 Elsevier B.V. All rights reserved.

IDENTIFICATION OF CHLOROMETHANE FROMATION PATHS DURING ELECTROCHEMICAL DECHLORINATION OF TCE USING GRAPHITE ELECTRODES

EPA Science Inventory

The purpose of this research is to investigate the formation of chloromethane during TCE dechlorination in a mixed electrochemical reactor using graphite electrodes. Chloromethane was the major chlorinated organic compound detected in previous dechlorination experiments. In order...

IDENTIFICATION OF CHLOROMETHANE FORMATION PATHS DURING ELECTROCHEMICAL DECHLORINATION OF TCE USING GRAPHITE ELECTRODES

EPA Science Inventory

The purpose of this research is to investigate the formation of chloromethane during TCE dechlorination in a mixed electrochemical reactor using graphite electrodes. Chloromethane was the major chlorinated organic compound detected in previous dechlorination experiments. In order...

Coatings for Graphite Fibers

NASA Technical Reports Server (NTRS)

Galasso, F. S.; Scola, D. A.; Veltri, R. D.

1980-01-01

Several approaches for applying high resistance coatings continuously to graphite yarn were investigated. Two of the most promising approaches involved (1) chemically vapor depositing (CVD) SiC coatings on the surface of the fiber followed by oxidation, and (2) drawing the graphite yarn through an organo-silicone solution followed by heat treatments. In both methods, coated fibers were obtained which exhibited increased electrical resistances over untreated fibers and which were not degraded. This work was conducted in a previous program. In this program, the continuous CVD SiC coating process used on HTS fiber was extended to the coating of HMS, Celion 6000, Celion 12000 and T-300 graphite fiber. Electrical resistances three order of magnitude greater than the uncoated fiber were measured with no significant degradation of the fiber strength. Graphite fibers coated with CVD Si3N4 and BN had resistances greater than 10(exp 6) ohm/cm. Lower pyrolysis temperatures were used in preparing the silica-like coatings also resulting in resistances as high as three orders of magnitude higher than the uncoated fiber. The epoxy matrix composites prepared using these coated fibers had low shear strengths indicating that the coatings were weak.

HiMAT structural development design methodology. [aeroelastic tailoring of the canard and wing box and distributed load tests

NASA Technical Reports Server (NTRS)

Price, M. A.

1979-01-01

In order to improve aerodynamic performance, a twist criterion was used to design the canard and wing lifting surfaces of two graphite-epoxy research aircraft. To meet that twist criterion, the lifting surfaces were tailored using graphite-epoxy tape. The outer surface of the aircraft is essentially constructed of 95 percent graphite epoxy materials. The analytical tools and methodology used to design those lifting surfaces are described. One aircraft was subjected to an 8g ground test in order to verify structural integrity and to determine how well the desired twist was achieved. Test results are presented and the reductions of both flight and ground strain test gages and their associated stresses are discussed.

"Bricks and mortar" self-assembly approach to graphitic mesoporous carbon nanocomposites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fulvio, P. F.; Mayes, R.; Wang, X. Q.

2011-04-20

Mesoporous carbon materials do not have sufficient ordering at the atomic scale to exhibit good electronic conductivity. To date, mesoporous carbons having uniform mesopores and high surface areas have been prepared from partially-graphitizable precursors in the presence of templates. High temperature thermal treatments above 2000 °C, which are usually required to increase conductivity, result in a partial or total collapse of the mesoporous structures and reduced surface areas induced by growth of graphitic domains, limiting their applications in electric double layer capacitors and lithium-ion batteries. In this work, we successfully implemented a “brick-and-mortar” approach to obtain ordered graphitic mesoporous carbonmore » nanocomposites with tunable mesopore sizes below 850 °C without using graphitization catalysts or high temperature thermal treatments. Phenolic resin-based mesoporous carbons act as mortar to highly conductive carbon blacks and carbon onions (bricks). The capacitance and resistivity of final materials can be tailored by changing the mortar to brick ratios.« less

Brick-and-Mortar Self-Assembly Approach to Graphitic Mesoporous Carbon Nanocomposites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dai, Sheng; Fulvio, Pasquale F; Mayes, Richard T

2011-01-01

Mesoporous carbon materials do not have sufficient ordering at the atomic scale to exhibit good electronic conductivity. To date, mesoporous carbons having uniform mesopores and high surface areas have been prepared from partially-graphitizable precursors in the presence of templates. High temperature thermal treatments above 2000 C, which are usually required to increase conductivity, result in a partial or total collapse of the mesoporous structures and reduced surface areas induced by growth of graphitic domains, limiting their applications in electric double layer capacitors and lithium-ion batteries. In this work, we successfully implemented a 'brick-and-mortar' approach to obtain ordered graphitic mesoporous carbonmore » nanocomposites with tunable mesopore sizes below 850 C without using graphitization catalysts or high temperature thermal treatments. Phenolic resin-based mesoporous carbons act as mortar to highly conductive carbon blacks and carbon onions (bricks). The capacitance and resistivity of final materials can be tailored by changing the mortar to brick ratios.« less

Pyrolysis reaction models of waste tires: Application of Master-Plots method for energy conversion via devolatilization.

PubMed

Irmak Aslan, Dilan; Parthasarathy, Prakash; Goldfarb, Jillian L; Ceylan, Selim

2017-10-01

Land applied disposal of waste tires has far-reaching environmental, economic, and human health consequences. Pyrolysis represents a potential waste management solution, whereby the solid carbonaceous residue is heated in the absence of oxygen to produce liquid and gaseous fuels, and a solid char. The design of an efficient conversion unit requires information on the reaction kinetics of pyrolysis. This work is the first to probe the appropriate reaction model of waste tire pyrolysis. The average activation energy of pyrolysis was determined via iso-conversional methods over a mass fraction conversion range between 0.20 and 0.80 to be 162.8±23.2kJmol -1 . Using the Master Plots method, a reaction order of three was found to be the most suitable model to describe the pyrolytic decomposition. This suggests that the chemical reactions themselves (cracking, depolymerization, etc.), not diffusion or boundary layer interactions common with carbonaceous biomasses, are the rate-limiting steps in the pyrolytic decomposition of waste tires. Copyright © 2017 Elsevier Ltd. All rights reserved.

Method for applying pyrolytic carbon coatings to small particles

DOEpatents

Beatty, Ronald L.; Kiplinger, Dale V.; Chilcoat, Bill R.

1977-01-01

A method for coating small diameter, low density particles with pyrolytic carbon is provided by fluidizing a bed of particles wherein at least 50 per cent of the particles have a density and diameter of at least two times the remainder of the particles and thereafter recovering the small diameter and coated particles.

Retrofitting hetrotrophically cultivated algae biomass as pyrolytic feedstock for biogas, bio-char and bio-oil production encompassing biorefinery.

PubMed

Sarkar, Omprakash; Agarwal, Manu; Naresh Kumar, A; Venkata Mohan, S

2015-02-01

Algal biomass grown hetrotrophically in domestic wastewater was evaluated as pyrolytic feedstock for harnessing biogas, bio-oil and bio-char. Freshly harvested microalgae (MA) and lipid extracted microalgae (LEMA) were pyrolysed in packed bed reactor in the presence and absence of sand as additive. MA (without sand additive) depicted higher biogas (420 ml/g; 800 °C; 3 h) and bio-oil (0.70 ml/g; 500 °C; 3 h). Sand addition enhanced biogas production (210 ml/g; 600 °C; 2 h) in LEMA operation. The composition of bio-gas and bio-oil was found to depend on the nature of feedstock as well as the process conditions viz., pyrolytic-temperature, retention time and presence of additive. Sand additive improved the H2 composition while pyrolytic temperature increment caused a decline in CO2 fraction. Bio-char productivity increased with increasing temperature specifically with LEMA. Integration of thermo-chemical process with microalgae cultivation showed to yield multiple resources and accounts for environmental sustainability in the bio-refinery framework. Copyright © 2014 Elsevier Ltd. All rights reserved.

Overliming detoxification of pyrolytic sugar syrup for direct fermentation of levoglucosan to ethanol.

PubMed

Chi, Zhanyou; Rover, Marjorie; Jun, Erin; Deaton, Mark; Johnston, Patrick; Brown, Robert C; Wen, Zhiyou; Jarboe, Laura R

2013-12-01

The application of pyrolytic sugars for biofuel production through fermentation is challenged by inhibitory contaminant compounds. Inhibition is so severe that only 0.25% sugar syrup can be used. In this study, overliming was tested as a simple detoxification method, using the Escherichia coli KO11+ lgk to directly convert levoglucosan into ethanol. After treatment with at least 14.8 g/L of Ca(OH)2, fermentation with 2% (w/v) pyrolytic sugar syrup was observed with no inhibition of ethanol production. Further investigation of treatment time and temperature showed that 8-16 h of treatment at 20°C, and 1-4 h of treatment at 60°C are necessary to obtain consistent ethanol production. The samples treated with 18.5 g/L Ca(OH)2 at 60°C for 4 h showed no inhibition at 2.5%. Multiple contaminants removed by the overliming treatment were identified. This study demonstrates that overliming is a promising method for detoxification of pyrolytic sugars for fermentation. Copyright © 2013 Elsevier Ltd. All rights reserved.

Ultraviolet photoelectron spectroscopy reveals energy-band dispersion for π-stacked 7,8,15,16-tetraazaterrylene thin films in a donor–acceptor bulk heterojunction

NASA Astrophysics Data System (ADS)

Aghdassi, Nabi; Wang, Qi; Ji, Ru-Ru; Wang, Bin; Fan, Jian; Duhm, Steffen

2018-05-01

7,8,15,16-tetraazaterrylene (TAT) thin films grown on highly oriented pyrolytic graphite (HOPG) substrates were studied extensively with regard to their intrinsic and interfacial electronic properties by means of ultraviolet photoelectron spectroscopy (UPS). Merely weak substrate–adsorbate interaction occurs at the TAT/HOPG interface, with interface energetics being only little affected by the nominal film thickness. Photon energy-dependent UPS performed perpendicular to the molecular planes of TAT multilayer films at room temperature clearly reveals band-like intermolecular dispersion of the TAT highest occupied molecular orbital (HOMO) energy. Based on a comparison with a tight-binding model, a relatively narrow bandwidth of 54 meV is derived, which points to the presence of an intermediate regime between hopping and band-like hole transport. Upon additional deposition of 2,2‧:5‧,2″:5″,2″‧-quaterthiophene (4T), a 4T:TAT donor–acceptor bulk heterojunction with a considerable HOMO-level offset at the donor–acceptor interface is formed. The 4T:TAT bulk heterojunction likewise exhibits intermolecular dispersion of the TAT HOMO energy, yet with a significant decreased bandwidth.

Surface science approach to Pt/carbon model catalysts: XPS, STM and microreactor studies

NASA Astrophysics Data System (ADS)

Motin, Abdul Md.; Haunold, Thomas; Bukhtiyarov, Andrey V.; Bera, Abhijit; Rameshan, Christoph; Rupprechter, Günther

2018-05-01

Pt nanoparticles supported on carbon are an important technological catalyst. A corresponding model catalyst was prepared by physical vapor deposition (PVD) of Pt on sputtered HOPG (highly oriented pyrolytic graphite). The carbon substrate before and after sputtering as well as the Pt/HOPG system before and after Pt deposition and annealing were examined by XPS and STM. This yielded information on the surface density of defects, which serve as nucleation centres for Pt, and on the size distribution (mean size/height) of the Pt nanoparticles. Two different model catalysts were prepared with mean sizes of 2.0 and 3.6 nm, both turned out to be stable upon UHV-annealing to 300 °C. After transfer into a UHV-compatible flow microreactor and subsequent cleaning in UHV and under mbar pressure, the catalytic activity of the Pt/HOPG model system for ethylene hydrogenation was examined under atmospheric pressure flow conditions. This enabled to determine temperature-dependent conversion rates, turnover frequencies (TOFs) and activation energies. The catalytic results obtained are in line with the characteristics of technological Pt/C, demonstrating the validity of the current surface science based model catalyst approach.

Covalent Attachment of the Water-insoluble Ni(P Cy 2 N Phe 2 ) 2 Electrocatalyst to Electrodes Showing Reversible Catalysis in Aqueous Solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodríguez-Maciá, Patricia; Priyadarshani, Nilusha; Dutta, Arnab

Hydrogenases are a diverse group of metalloenzymes which catalyze the reversible conversion between molecular hydrogen and protons at high rates. The catalytic activity of these enzymes does not require overpotential because their active site has been evolutionarily optimized to operate fast and efficiently. These enzymes have inspired the development of molecular catalysts, which have dramatically improved in efficiency in recent years, to the point that some synthetic catalysts even outperform hydrogenases under certain conditions. In this work, we use a reversible noble-metal-free homogeneous catalyst, the [Ni(PCy2NPhe2)2]2+ complex, and we covalently immobilize it on a functionalized highly oriented pyrolytic graphite “edge”more » (HOPGe) electrode surface. This catalyst is not water soluble, but once it is surface-confined on the electrode, it maintains its catalytic properties in aqueous solutions, showing reversibility for H2 oxidation/reduction. Immobilization of the [Ni(PCy2NPhe2)2]2+ complex onto a multi-walled carbon nanotubes coated electrode leads to even higher catalytic current densities and enhanced stability.« less

Method of making carbon-carbon composites

DOEpatents

Engle, Glen B.

1991-01-01

A process for making a carbon-carbon composite having a combination of high crystallinity, high strength, high modulus and high thermal and electrical conductivity. High-modulus/high-strength mesophase derived carbon fibers are woven into a suitable cloth. Layers of this easily graphitizable woven cloth are covered with petroleum or coal tar pitch and pressed at a temperature a few degrees above the softening point of the pitch to form a green laminated composite. The green composite is restrained in a suitable fixture and heated slowly to carbonize the pitch binder. The carbonized composite is then impregnated several times with pitch by covering the composite with hot pitch under pressure. The composites are given a heat treatment between each impregnation step to crack up the infiltrated carbon and allow additional pitch to enter the microstructure during the next impregnation cycle. The impregnated composites are then given a final heat treatment in the range 2500.degree. to 3000.degree. C. to fully graphitize the fibers and the matrix carbon. The composites are then infiltrated with pyrolytic carbon by chemical vapor deposition in the range 1000.degree. to 1300.degree. C. at a reduced pressure for approximately one hundred and fifty (150) hours.

Preparation of monolayers of [MnIII 6CrIII]3+ single-molecule magnets on HOPG, mica and silicon surfaces and characterization by means of non-contact AFM

NASA Astrophysics Data System (ADS)

Gryzia, Aaron; Predatsch, Hans; Brechling, Armin; Hoeke, Veronika; Krickemeyer, Erich; Derks, Christine; Neumann, Manfred; Glaser, Thorsten; Heinzmann, Ulrich

2011-08-01

We report on the characterization of various salts of [ Mn III 6 Cr III ] 3+ complexes prepared on substrates such as highly oriented pyrolytic graphite (HOPG), mica, SiO2, and Si3N4. [ Mn III 6 Cr III ] 3+ is a single-molecule magnet, i.e., a superparamagnetic molecule, with a blocking temperature around 2 K. The three positive charges of [ Mn III 6 Cr III ] 3+ were electrically neutralized by use of various anions such as tetraphenylborate (BPh4 -), lactate (C3H5O3 -), or perchlorate (ClO4 -). The molecule was prepared on the substrates out of solution using the droplet technique. The main subject of investigation was how the anions and substrates influence the emerging surface topology during and after the preparation. Regarding HOPG and SiO2, flat island-like and hemispheric-shaped structures were created. We observed a strong correlation between the electronic properties of the substrate and the analyzed structures, especially in the case of mica where we observed a gradient in the analyzed structures across the surface.

Ultraviolet photoelectron spectroscopy reveals energy-band dispersion for π-stacked 7,8,15,16-tetraazaterrylene thin films in a donor-acceptor bulk heterojunction.

PubMed

Aghdassi, Nabi; Wang, Qi; Ji, Ru-Ru; Wang, Bin; Fan, Jian; Duhm, Steffen

2018-05-11

7,8,15,16-tetraazaterrylene (TAT) thin films grown on highly oriented pyrolytic graphite (HOPG) substrates were studied extensively with regard to their intrinsic and interfacial electronic properties by means of ultraviolet photoelectron spectroscopy (UPS). Merely weak substrate-adsorbate interaction occurs at the TAT/HOPG interface, with interface energetics being only little affected by the nominal film thickness. Photon energy-dependent UPS performed perpendicular to the molecular planes of TAT multilayer films at room temperature clearly reveals band-like intermolecular dispersion of the TAT highest occupied molecular orbital (HOMO) energy. Based on a comparison with a tight-binding model, a relatively narrow bandwidth of 54 meV is derived, which points to the presence of an intermediate regime between hopping and band-like hole transport. Upon additional deposition of 2,2':5',2″:5″,2″'-quaterthiophene (4T), a 4T:TAT donor-acceptor bulk heterojunction with a considerable HOMO-level offset at the donor-acceptor interface is formed. The 4T:TAT bulk heterojunction likewise exhibits intermolecular dispersion of the TAT HOMO energy, yet with a significant decreased bandwidth.

Comparison of DNA-Reactive Metabolites from Nitrosamine and Styrene Using Voltammetric DNA/Microsomes Sensors

PubMed Central

Krishnan, Sadagopan; Bajrami, Besnik; Mani, Vigneshwaran; Pan, Shenmin; Rusling, James F.

2012-01-01

Voltammetric sensors made with films of polyions, double-stranded DNA and liver microsomes adsorbed layer-by-layer onto pyrolytic graphite electrodes were evaluated for reactive metabolite screening. This approach features simple, inexpensive screening without enzyme purification for applications in drug or environmental chemical development. Cytochrome P450 enzymes (CYPs) in the liver microsomes were activated by an NADPH regenerating system or by electrolysis to metabolize model carcinogenic compounds nitrosamine and styrene. Reactive metabolites formed in the films were trapped as adducts with nucleobases on DNA. The DNA damage was detected by square-wave voltammetry (SWV) using Ru(bpy)32+ as a DNA-oxidation catalyst. These sensors showed a larger rate of increase in signal vs. reaction time for a highly toxic nitrosamine than for the moderately toxic styrene due to more rapid reactive metabolite-DNA adduct formation. Results were consistent with reported in vivo TD50 data for the formation of liver tumors in rats. Analogous polyion/ liver microsome films prepared on 500 nm silica nanoparticles (nanoreactors) and reacted with nitrosamine or styrene, provided LC-MS or GC analyses of metabolite formation rates that correlated well with sensor response. PMID:23100998

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oloff, L.-P., E-mail: oloff@physik.uni-kiel.de; Hanff, K.; Stange, A.

With the advent of ultrashort-pulsed extreme ultraviolet sources, such as free-electron lasers or high-harmonic-generation (HHG) sources, a new research field for photoelectron spectroscopy has opened up in terms of femtosecond time-resolved pump-probe experiments. The impact of the high peak brilliance of these novel sources on photoemission spectra, so-called vacuum space-charge effects caused by the Coulomb interaction among the photoemitted probe electrons, has been studied extensively. However, possible distortions of the energy and momentum distributions of the probe photoelectrons caused by the low photon energy pump pulse due to the nonlinear emission of electrons have not been studied in detail yet.more » Here, we systematically investigate these pump laser-induced space-charge effects in a HHG-based experiment for the test case of highly oriented pyrolytic graphite. Specifically, we determine how the key parameters of the pump pulse—the excitation density, wavelength, spot size, and emitted electron energy distribution—affect the measured time-dependent energy and momentum distributions of the probe photoelectrons. The results are well reproduced by a simple mean-field model, which could open a path for the correction of pump laser-induced space-charge effects and thus toward probing ultrafast electron dynamics in strongly excited materials.« less

Nano-structured variable capacitor based on P(VDF-TrFE) copolymer and carbon nanotubes

NASA Astrophysics Data System (ADS)

Lakbita, I.; El-Hami, K.

2018-02-01

A newly organic capacitor was conceived with a variable capacitance using the inverse piezoelectric effect. The device consists of two parallel plates of carbon nanotubes (CNTs), known for their large surface area, high sensitivity and high electric conductivity, separated by a thin film of a dielectric layer of Polyinylidene fluoride and trifluoroehtylene (P(VDF-TrFE)) promising material for piezoelectric and ferroelectric properties. The obtained architecture is the CNT/PVDF-TrFE/CNT capacitor device. In this study, an ultra-thin film of P(VDF-TrFE) (54/46) with thickness of 20 nm was elaborated on highly oriented pyrolytic graphite (HOPG) by spin-coating. The morphology of the ultra-thin film and the mechanical behavior of CNT/P(VDF-TrFE)/CNT system were studied using the atomic force microscopy (AFM) combined with a lock-in amplifier in contact mode. All changes in applied voltage induce a change in thin film thickness according to the inverse piezoelectric effect that affect, consequently the capacitance. The results showed that the ratio of capacitance change ΔC to initial capacitance C0 is ΔC/C0=5%. This value is sufficient to use P(VDF-TrFE) as variable organic capacitor.

Preparation of graphite dispersed copper composite with intruding graphite particles in copper plate

NASA Astrophysics Data System (ADS)

Noor, Abdul Muizz Mohd; Ishikawa, Yoshikazu; Yokoyama, Seiji

2017-01-01

In this study, it was attempted that copper-graphite composite was prepared locally on the surface of a copper plate with using a spot welding machine. Experiments were carried out with changing the compressive load, the repetition number of the compression and the electrical current in order to study the effect of them on carbon content and Vickers hardness on the copper plate surface. When the graphite was pushed into copper plate only with the compressive load, the composite was mainly hardened by the work hardening. The Vickers hardness increased linearly with an increase in the carbon content. When an electrical current was energized through the composite at the compression, the copper around the graphite particles were heated to the temperature above approximately 2100 K and melted. The graphite particles partially or entirely dissolved into the melt. The graphite particles were precipitated from the melt under solidification. In addition, this high temperature caused the improvement of wetting of copper to graphite. This high temperature caused the annealing, and reduced the Vickers hardness. Even in this case, the Vickers hardness increased with an increase in the carbon content. This resulted from the dispersion hardening.

Porous carbon-coated graphite electrodes for energy production from salinity gradient using reverse electrodialysis

NASA Astrophysics Data System (ADS)

Lee, Su-Yoon; Jeong, Ye-Jin; Chae, So-Ryong; Yeon, Kyeong-Ho; Lee, Yunkyu; Kim, Chan-Soo; Jeong, Nam-Jo; Park, Jin-Soo

2016-04-01

Performance of graphite foil electrodes coated by porous carbon black (i.e., Vulcan) was investigated in comparison with metal electrodes for reverse electrodialysis (RED) application. The electrode slurry that was used for fabrication of the porous carbon-coated graphite foil is composed of 7.2 wt% of carbon black (Vulcan X-72), 0.8 wt% of a polymer binder (polyvinylidene fluoride, PVdF), and 92.0 wt% of a mixing solvent (dimethylacetamide, DMAc). Cyclic voltammograms of both the porous carbon (i.e., Vulcan)-coated graphite foil electrode and the graphite foil electrode without Vulcan showed good reversibility in the hexacyanoferrate(III) (i.e., Fe(CN)63-) and hexacyanoferrate(II) (i.e., Fe(CN)64-) redox couple and 1 M Na2SO4 at room temperature. However, anodic and cathodic current of the Vulcan-coated graphite foil electrode was much higher than those of the graphite foil electrode. Using a bench-scale RED stack, the current-voltage polarization curve of the Vulcan-coated graphite electrode was compared to that of metal electrodes such as iridium (Ir) and platinum (Pt). From the results, it was confirmed that resistance of four different electrodes increased with the following order: the Vulcan-coated graphite foil

Effect of lightning strike on bromine intercalated graphite fiber/epoxy composites

NASA Technical Reports Server (NTRS)

Gaier, James R.; Slabe, Melissa E.; Brink, Norman O.

1991-01-01

Laminar composites were fabricated from pristine and bromine intercalated pitch based graphite fibers. It was found that laminar composites could be fabricated using either pristine or intercalated graphite fibers using standard fabrication techniques. The intercalated graphite fiber composites had electrical properties which were markedly improved over both the corresponding pitch based and polyacrylonitrile (PAN) based composites. Despite composites resistivities more than an order of magnitude lower for pitch based fiber composites, the lightning strike resistance was poorer than that of the Pan based fiber composites. This leads to the conclusion that the mechanical properties of the pitch fibers are more important than electrical or thermal properties in determining the lightning strike resistance. Based on indicated lightning strike tolerance for high elongation to failure materials, the use of vapor grown, rather than pitch based graphite fibers appears promising.

Electronic structure imperfections and chemical bonding at graphene interfaces

NASA Astrophysics Data System (ADS)

Schultz, Brian Joseph

The manifestation of novel phenomena upon scaling to finite size has inspired a paradigm shift in materials science that takes advantage of the distinctive electrical and physical properties of nanomaterials. Remarkably, the simple honeycomb arrangement of carbon atoms in a single atomic layer has become renowned for exhibiting never-before-seen electronic and physical phenomena. This archetypal 2-dimensional nanomaterial is known as graphene, a single layer of graphite. Early reports in the 1950's eluded to graphene-like nanostructures that were evidenced from exfoliation of oxidized graphite followed by chemical reduction, absorbed carbon on transition metals, and thermal decomposition of SiC. Furthermore, the earliest tight binding approximation calculations in the 1950's held clues that a single-layer of graphite would behave drastically different than bulk graphite. Not until 2004, when Giem and Novoselov first synthesized graphene by mechanical exfoliation from highly-oriented pyrolytic graphite did the field of graphene-based research bloom within the scientific community. Since 2004, the availability and relatively straight forward synthesis of single-layer graphene (SLG) enabled the observation of remarkable phenomena including: massless Dirac fermions, extremely high mobilities of its charge carriers, room temperature half-integer quantum Hall effect, the Rashba effect, and the potential for ballistic conduction over macroscopic distances. These enticing electronic properties produce the drive to study graphene for use in truly nanoscale electrical interconnects, integrated circuits, transparent conducting electrodes, ultra-high frequency transistors, and spintronic devices, just to name a few. Yet, for almost all real world applications graphene will need to be interfaced with other materials, metals, dielectrics, organics, or any combination thereof that in turn are constituted from various inorganic and organic components. Interfacing graphene, a nanomaterial with lateral dimensions in the hundreds of microns if not larger, with a corresponding atomic vertical thickness poses significant difficulties. Graphene's unique structure is dominated by surface area or potentially hybridized interfaces; consequently, the true realization of this remarkable nanomaterial in device constructs relies on engineering graphene interfaces at the surface in order to controllably mold the electronic structure. Near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy and the transmission mode analogue scanning transmission X-ray microscopy (STXM) are particularly useful tools to study the unoccupied states of graphene and graphene interfaces. In addition, polarized NEXAFS and STXM studies provide information on surface orientation, bond sterics, and the extent of substrate alignment before and after interfacial hybridization. The work presented in this dissertation is fundamentally informed by NEXAFS and STXM measurements on graphene/metal, graphene/dielectric, and graphene/organic interfaces. We start with a general review of the electronic structure of freestanding graphene and graphene interfaces in Chapter 1. In Chapter 2, we investigate freestanding single-layer graphene via STXM and NEXAFS demonstrating that electronic structure heterogeneities from synthesis and processing are ubiquitous in 2-dimensional graphene. We show the mapping of discrete charge transfer regions as a result of doped impurities that decorate the surfaces of graphene and that transfer processing imparts local electronic corrugations or ripples. In corroboration with density functional theory, definitive assignments to the spectral features, global steric orientations of the localized domains, and quantitative charge transfer schemes are evidenced. In the following chapters, we deliberately (Chapter 3) incorporate substitutional nitrogen into reduced graphene oxide to induce C--N charge redistribution and improve global conductivity, (Chapter 4) fabricate graphene/metal interfaces and metal/graphene/metal sandwich structures evidencing classical anisotropic umpolung chemistry from carbon pz-orbrital charge pinning, and (Chapter 5) engineer graphene/dielectric interfaces showing electron depletion from carbon atoms at the HfO2/graphene interface. The fabrication of graphene interfaces remains a critical gap for successful commercialization of graphene-based devices, yet we demonstrate that interfacial hybridization, anisotropic charge redistribution, local chemical bonding, and discrete electronic hybridization regimes play a critical role in the electronic structure at graphene interfaces.

Comparative study on pyrolysis of lignocellulosic and algal biomass using pyrolysis-gas chromatography/mass spectrometry.

PubMed

Li, Kai; Zhang, Liqiang; Zhu, Liang; Zhu, Xifeng

2017-06-01

The cornstalk and chlorella were selected as the representative of lignocelulosic and algal biomass, and the pyrolysis experiments of them were carried out using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The physicochemical properties of samples and the pyrolytic product distribution were presented. And then the compositional differences between the two kinds of pyrolytic products were studied, the relevant pyrolysis mechanisms were analyzed systematically. Pyrolytic vapor from lignocellulosic biomass contained more phenolic and carbonyl compounds while that from algal biomass contained more long-chain fatty acids, nitrogen-containing compounds and fewer carbonyl compounds. Maillard reaction is conducive to the conversion of carbonyl compounds to nitrogenous heterocyclic compounds with better thermal stability. Copyright © 2017 Elsevier Ltd. All rights reserved.

Diffusivity and solubility of hydrogen in the carbon fibre composite SEP N11

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alberici, S.; Perujo, A.; Camposilvan, J.

1995-10-01

In this paper we present the hydrogen diffusivity and solubility in the carbon fibre composite (CFC) SEP N11 with tri-directional fibres structure that is a possible candidate as armour material for plasma facing components (PFC). The technique used for these measurements is a gas evolution method and the measurements were carried out in the temperature range 900 - 1200 K with a loading hydrogen pressure of 100 kPa. The results obtained showed that the Sieverts` constant K{sub s} is of the same order of magnitude as those previously obtained for several graphites, while the diffusivity is about five to sixmore » orders of magnitude higher as compared to graphites. Furthermore, CFC presents an endothermic behaviour in contrast to graphites. 10 refs., 3 figs.« less

Fixed-bed adsorption study of methylene blue onto pyrolytic tire char

NASA Astrophysics Data System (ADS)

Makrigianni, Vassiliki; Giannakas, Aris; Papadaki, Maria; Albanis, Triantafyllos; Konstantinou, Ioannis

2016-04-01

In this work, the adsorption efficiency of acid treated pyrolytic tire char to cationic methylene blue (MB) dye adsorption from aqueous solutions was investigated by fixed-bed adsorption column experiments. The effects of the initial dye concentration (10 - 40 mg L-1) and feed flow rate (50 - 150 mL min -1) with a fixed bed height (15 cm) were studied in order to determine the breakthrough characteristics of the adsorption system. The Adams-Bohart, Yoon-Nelson and Thomas model were applied to the adsorption of MB onto char at different operational conditions to predict the breakthrough curves and to determine the characteristic parameters of the column. The results showed that the maximum adsorbed quantities decreased with increasing flow rate and increased with increasing initial MB concentration. Breakthrough time and exhaustion time increased with decreasing inlet dye concentration and flow rate. In contrast with Adams-Bohart model, Yoon-Nelson model followed by Thomas model were found more suitable to describe the fixed-bed adsorption of methylene blue by char. The correlation coefficient values R2 for both models at different operating conditions are higher than 0.9 and the low average relative error values provided very good fittings of experimental data at different operating conditions. Higher adsorption capacity of 3.85 mg g -1 was obtained at 15 cm of adsorbent bed height, flow rate of 100 mL min -1and initial MB concentration of 40 mg L-1. Although that activated carbons exhibited higher adsorption capacities in the literature, acid-treated pyrolytic tire char was found to be considerably efficient adsorbent for the removal of MB dye column taking into account the advantages of the simpler production process compared to activated carbons, as well as, the availability of waste tire feedstock and concurrent waste tire management.

Preparation of graphite intercalation compounds containing oligo and polyethers

NASA Astrophysics Data System (ADS)

Zhang, Hanyang; Lerner, Michael M.

2016-02-01

Layered host-polymer nanocomposites comprising polymeric guests between inorganic sheets have been prepared with many inorganic hosts, but there is limited evidence for the incorporation of polymeric guests into graphite. Here we report for the first time the preparation, and structural and compositional characterization of graphite intercalation compounds (GICs) containing polyether bilayers. The new GICs are obtained by either (1) reductive intercalation of graphite with an alkali metal in the presence of an oligo or polyether and an electrocatalyst, or (2) co-intercalate exchange of an amine for an oligo or polyether in a donor-type GIC. Structural characterization of products using powder X-ray diffraction, Raman spectroscopy, and thermal analyses supports the formation of well-ordered, first-stage GICs containing alkali metal cations and oligo or polyether bilayers between reduced graphene sheets.Layered host-polymer nanocomposites comprising polymeric guests between inorganic sheets have been prepared with many inorganic hosts, but there is limited evidence for the incorporation of polymeric guests into graphite. Here we report for the first time the preparation, and structural and compositional characterization of graphite intercalation compounds (GICs) containing polyether bilayers. The new GICs are obtained by either (1) reductive intercalation of graphite with an alkali metal in the presence of an oligo or polyether and an electrocatalyst, or (2) co-intercalate exchange of an amine for an oligo or polyether in a donor-type GIC. Structural characterization of products using powder X-ray diffraction, Raman spectroscopy, and thermal analyses supports the formation of well-ordered, first-stage GICs containing alkali metal cations and oligo or polyether bilayers between reduced graphene sheets. Electronic supplementary information (ESI) available: Domain size, additional Raman spectra info, compositional calculation, and packing fractions. See DOI: 10.1039/c5nr08226a

High Peak Power Ka-Band Gyrotron Oscillator Experiments with Slotted and Unslotted Cavities.

DTIC Science & Technology

1987-11-10

cylindrical graphite cathode by explosive plasma formation. (In order to optimize the compression ratio for these experiments, a graphite cathode was employed...48106 Attn: S.B. Segall I copy Lawrence Livermore National Laboratory P.O. Box 808 Livermore, California 94550 Attn: Dr. D. Prosnitz 1 copy Dr. T.J

Electrocatalytic Dechlorination Of A PCB Congener At A Palladized Granular Graphite-Packed Electrode: Reaction Equilibrium And Mechanism

EPA Science Inventory

Our previous study on the electrocatalytic dechlorination of 2-chlorobiphenyl at a Pd-loaded granular graphite-packed electrode demonstrated that the process did not follow the first order kinetics. The rate constant varied with the applied potential at the beginning, but later b...

Pyrolytic-carbon coating in carbon nanotube foams for better performance in supercapacitors

NASA Astrophysics Data System (ADS)

He, Nanfei; Yildiz, Ozkan; Pan, Qin; Zhu, Jiadeng; Zhang, Xiangwu; Bradford, Philip D.; Gao, Wei

2017-03-01

Nowadays, the wide-spread adoption of supercapacitors has been hindered by their inferior energy density to that of batteries. Here we report the use of our pyrolytic-carbon-coated carbon nanotube foams as lightweight, compressible, porous, and highly conductive current collectors in supercapacitors, which are infiltrated with chemically-reduced graphene oxide and later compressed via mechanical and capillary forces to generate the active electrodes. The pyrolytic carbon coatings, introduced by chemical vapor infiltration, wrap around the CNT junctions and increase the surface roughness. When active materials are infiltrated, the pyrolytic-carbon coatings help prevent the π-stacking, enlarge the accessible surface area, and increase the electrical conductivity of the scaffold. Our best-performing device offers 48% and 57% higher gravimetric energy and power density, 14% and 23% higher volumetric energy and power density, respectively, and two times higher knee frequency, than the device with commercial current collectors, while the "true-performance metrics" are strictly followed in our measurements. We have further clarified the solution resistance, charge transfer resistance/capacitance, double-layer capacitance, and Warburg resistance in our system via comprehensive impedance analysis, which will shed light on the design and optimization of similar systems.

Formation of the reduced form of furaneol® (2,5-dimethyl-4-hydroxy-tetrahydrofuran-3-one) during the Maillard reaction through catalysis of amino acid metal salts.

PubMed

Nashalian, Ossanna; Wang, Xi; Yaylayan, Varoujan A

2016-11-01

Under pyrolytic conditions the acidity/basicity of Maillard reaction mixtures can be controlled through the use of hydrochloride or sodium salts of amino acids to generate a diversity of products. When the degradation of glucose was studied under pyrolytic conditions using excess sodium glycinate the reaction was found to generate a major unknown peak having a molecular ion at m/z 130. Subsequent in-depth isotope labelling studies indicated that acetol was an important precursor of this compound under pyrolytic and aqueous heating conditions. The dimerisation and cyclisation of acetol into 2,5-dimethyl-4-hydroxy-tetrahydrofuran-3-one was found to be catalysed by amino acid metal salts. Also, ESI/qTOF/MS studies indicated that the unknown peak has expected molecular formula of C6H10O3. Finally, a peak having the same retention time and mass spectrum was also generated pyrolytically when furaneol® was reduced with NaBH4 confirming the initial hypothesis regarding the unknown peak to be the reduced form of furaneol®. Copyright © 2016 Elsevier Ltd. All rights reserved.

Effect of Reacting Surface Density on the Overall Graphite Oxidation Rate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang H. Oh; Eung Kim; Jong Lim

2009-05-01

Graphite oxidation in an air-ingress accident is presently a very important issue for the reactor safety of the very high temperature gas cooled-reactor (VHTR), the concept of the next generation nuclear plant (NGNP) because of its potential problems such as mechanical degradation of the supporting graphite in the lower plenum of the VHTR might lead to core collapse if the countermeasure is taken carefully. The oxidation process of graphite has known to be affected by various factors, including temperature, pressure, oxygen concentration, types of graphite, graphite shape and size, flow distribution, etc. However, our recent study reveals that the internalmore » pore characteristics play very important roles in the overall graphite oxidation rate. One of the main issues regarding graphite oxidation is the potential core collapse problem that may occur following the degradation of graphite mechanical strength. In analyzing this phenomenon, it is very important to understand the relationship between the degree of oxidization and strength degradation. In addition, the change of oxidation rate by graphite oxidation degree characterization by burn-off (ratio of the oxidized graphite density to the original density) should be quantified because graphite strength degradation is followed by graphite density decrease, which highly affects oxidation rates and patterns. Because the density change is proportional to the internal pore surface area, they should be quantified in advance. In order to understand the above issues, the following experiments were performed: (1)Experiment on the fracture of the oxidized graphite and validation of the previous correlations, (2) Experiment on the change of oxidation rate using graphite density and data collection, (3) Measure the BET surface area of the graphite. The experiments were performed using H451 (Great Lakes Carbon Corporation) and IG-110 (Toyo Tanso Co., Ltd) graphite. The reason for the use of those graphite materials is because their chemical and mechanical characteristics are well identified by the previous investigations, and therefore it was convenient for us to access the published data, and to apply and validate our new methodologies. This paper presents preliminary results of compressive strength vs. burn-off and surface area density vs. burn-off, which can be used for the nuclear graphite selection for the NGNP.« less

Facile Synthesis of Pre-Doping Lithium-Ion Into Nitrogen-Doped Graphite Negative Electrode for Lithium-Ion Capacitor.

PubMed

Lee, Seul-Yi; Kim, Ji-Il; Rhee, Kyong Yop; Park, Soo-Jin

2015-09-01

Nitrogen-doped graphite, prepared via the thermal decomposition of melamine into a carbon matrix for use as the negative electrode in lithium-ion capacitors (LICs), was evaluated by electrochemical measurements. Furthermore, in order to study the performance of pre-doped lithium components as a function of nitrogen-doped material, the pre-doped lithium graphite was allowed to react with a lithium salt solution. The results showed that the nitrogen functional groups in the graphite largely influenced the pre-doped lithium components, thereby contributing to the discharge capacity and cycling performance. We confirmed that the large initial irreversible capacity could be significantly decreased by using pre-doped lithium components obtained through the nitrogen-doping method.

Pyrolytic conversion of plastic and rubber waste to hydrocarbons with basic salt catalysts

DOEpatents

Wingfield, Jr., Robert C.; Braslaw, Jacob; Gealer, Roy L.

1985-01-01

The invention relates to a process for improving the pyrolytic conversion of waste selected from rubber and plastic to low molecular weight olefinic materials by employing basis salt catalysts in the waste mixture. The salts comprise alkali or alkaline earth compounds, particularly sodium carbonate, in an amount of greater than about 1 weight percent based on the waste feed.

The First Discovery of Presolar Graphite Grains from the Highly Reducing Qingzhen (EH3) Meteorite

NASA Astrophysics Data System (ADS)

Xu, Yuchen; Lin, Yangting; Zhang, Jianchao; Hao, Jialong

2016-07-01

Presolar graphite grains have been extensively studied, but are limited in carbonaceous chondrites, particularly in Murchison (CM2) and Orgueil (CI1), which sampled materials from the oxidizing regions in the solar nebula. Here, we report the first discovery of presolar graphite grains from the Qingzhen (EH3) enstatite chondrite which formed under a highly reducing condition. Eighteen presolar graphite grains were identified by C-isotope mapping of the low-density fraction (1.75-1.85 g cm-3) from Qingzhen acid residue. Another 58 graphite spherules were found in different areas of the same sample mount using a scanning electron microscope and were classified into three morphologies, including cauliflower, onion, and cauliflower-onion. The Raman spectra of these spherules vary from ordered, disordered, and glassy to kerogen-like, suggestive of a wide range of thermal metamorphisms. NanoSIMS analysis of the C- and Si-isotopes of these graphite spherules confirmed 23 presolar grains. The other 35 graphite spherules have no significant isotopic anomalies, but they share similar morphologies and Raman spectra with the presolar ones. Another three grains were identified during NanoSIMS analysis. Of all the 44 presolar graphite grains identified, six grains show 28Si-excesses, suggestive of supernovae origins, and four grains are 12C- and 29,30Si-rich, consistent with low-metallicity asymptotic giant branch star origins. Another two graphite spherules have extremely low 12C/13C ratios with marginal solar Si-isotopes. The morphologies, Raman spectra, and C- and Si-isotopic distributions of the presolar graphite grains from the Qingzhen enstatite chondrite are similar to those of the low-density fractions from Murchison carbonaceous chondrites. This study suggests a homogeneous distribution of presolar graphite grains in the solar nebula.

Nanoscale Electrochemistry of sp(2) Carbon Materials: From Graphite and Graphene to Carbon Nanotubes.

PubMed

Unwin, Patrick R; Güell, Aleix G; Zhang, Guohui

2016-09-20

Carbon materials have a long history of use as electrodes in electrochemistry, from (bio)electroanalysis to applications in energy technologies, such as batteries and fuel cells. With the advent of new forms of nanocarbon, particularly, carbon nanotubes and graphene, carbon electrode materials have taken on even greater significance for electrochemical studies, both in their own right and as components and supports in an array of functional composites. With the increasing prominence of carbon nanomaterials in electrochemistry comes a need to critically evaluate the experimental framework from which a microscopic understanding of electrochemical processes is best developed. This Account advocates the use of emerging electrochemical imaging techniques and confined electrochemical cell formats that have considerable potential to reveal major new perspectives on the intrinsic electrochemical activity of carbon materials, with unprecedented detail and spatial resolution. These techniques allow particular features on a surface to be targeted and models of structure-activity to be developed and tested on a wide range of length scales and time scales. When high resolution electrochemical imaging data are combined with information from other microscopy and spectroscopy techniques applied to the same area of an electrode surface, in a correlative-electrochemical microscopy approach, highly resolved and unambiguous pictures of electrode activity are revealed that provide new views of the electrochemical properties of carbon materials. With a focus on major sp(2) carbon materials, graphite, graphene, and single walled carbon nanotubes (SWNTs), this Account summarizes recent advances that have changed understanding of interfacial electrochemistry at carbon electrodes including: (i) Unequivocal evidence for the high activity of the basal surface of highly oriented pyrolytic graphite (HOPG), which is at least as active as noble metal electrodes (e.g., platinum) for outer-sphere redox processes. (ii) Demonstration of the high activity of basal plane HOPG toward other reactions, with no requirement for catalysis by step edges or defects, as exemplified by studies of proton-coupled electron transfer, redox transformations of adsorbed molecules, surface functionalization via diazonium electrochemistry, and metal electrodeposition. (iii) Rationalization of the complex interplay of different factors that determine electrochemistry at graphene, including the source (mechanical exfoliation from graphite vs chemical vapor deposition), number of graphene layers, edges, electronic structure, redox couple, and electrode history effects. (iv) New methodologies that allow nanoscale electrochemistry of 1D materials (SWNTs) to be related to their electronic characteristics (metallic vs semiconductor SWNTs), size, and quality, with high resolution imaging revealing the high activity of SWNT sidewalls and the importance of defects for some electrocatalytic reactions (e.g., the oxygen reduction reaction). The experimental approaches highlighted for carbon electrodes are generally applicable to other electrode materials and set a new framework and course for the study of electrochemical and interfacial processes.

HF/H2O2 treated graphite felt as the positive electrode for vanadium redox flow battery

NASA Astrophysics Data System (ADS)

He, Zhangxing; Jiang, Yingqiao; Meng, Wei; Jiang, Fengyun; Zhou, Huizhu; Li, Yuehua; Zhu, Jing; Wang, Ling; Dai, Lei

2017-11-01

In order to improve the electrochemical performance of the positive graphite felt electrode in vanadium flow redox battery, a novel method is developed to effectively modify the graphite felt by combination of etching of HF and oxidation of H2O2. After the etching of HF for the graphite felt at ambient temperature, abundant oxygen-containing functional groups were further introduced on the surface of graphite felt by hydrothermal treatment using H2O2 as oxidant. Benefiting from the surface etching and introduction of functional groups, mass transfer and electrode process can be improved significantly on the surface of graphite felt. VO2+/VO2+ redox reaction on the graphite felt modified by HF and H2O2 jointly (denote: GF-HF/H2O2) exhibits superior electrochemical kinetics in comparison with the graphite felt modified by single HF or H2O2 treatment. The cell using GF-HF/H2O2 as the positive electrode was assembled and its electrochemical properties were evaluated. The increase of energy efficiency of 4.1% for GF-HF/H2O2 at a current density of 50 mA cm-2 was obtained compared with the pristine graphite felt. The cell using GF-HF/H2O2 also demonstrated higher discharge capacity. Our study revealed that HF/H2O2 treatment is an efficient method to enhance the electrochemical performance of graphite felt, further improving the comprehensive energy storage performance of the vanadium flow redox battery.

Role of nuclear grade graphite in controlling oxidation in modular HTGRs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Windes, Willaim; Strydom, G.; Kane, J.

2014-11-01

The passively safe High Temperature Gas-cooled Reactor (HTGR) design is one of the primary concepts considered for Generation IV and Small Modular Reactor (SMR) programs. The helium cooled, nuclear grade graphite moderated core achieves extremely high operating temperatures allowing either industrial process heat or electricity generation at high efficiencies. In addition to their neutron moderating properties, nuclear grade graphite core components provide excellent high temperature stability, thermal conductivity, and chemical compatibility with the high temperature nuclear fuel form. Graphite has been continuously used in nuclear reactors since the 1940’s and has performed remarkably well over a wide range of coremore » environments and operating conditions. Graphite moderated, gas-cooled reactor designs have been safely used for research and power production purposes in multiple countries since the inception of nuclear energy development. However, graphite is a carbonaceous material, and this has generated a persistent concern that the graphite components could actually burn during either normal or accident conditions [ , ]. The common assumption is that graphite, since it is ostensibly similar to charcoal and coal, will burn in a similar manner. While charcoal and coal may have the appearance of graphite, the internal microstructure and impurities within these carbonaceous materials are very different. Volatile species and trapped moisture provide a source of oxygen within coal and charcoal allowing them to burn. The fabrication process used to produce nuclear grade graphite eliminates these oxidation enhancing impurities, creating a dense, highly ordered form of carbon possessing high thermal diffusivity and strongly (covalently) bonded atoms.« less

Controlling the Surface Chemistry of Graphite by Engineered Self-Assembled Peptides

PubMed Central

Khatayevich, Dmitriy; So, Christopher R.; Hayamizu, Yuhei; Gresswell, Carolyn; Sarikaya, Mehmet

2012-01-01

The systematic control over surface chemistry is a long-standing challenge in biomedical and nanotechnological applications for graphitic materials. As a novel approach, we utilize graphite-binding dodecapeptides that self-assemble into dense domains to form monolayer thick long-range ordered films on graphite. Specifically, the peptides are rationally designed through their amino acid sequences to predictably display hydrophilic and hydrophobic characteristics while maintaining their self-assembly capabilities on the solid substrate. The peptides are observed to maintain a high tolerance for sequence modification, allowing the control over surface chemistry via their amino acid sequence. Furthermore, through a single step co-assembly of two different designed peptides, we predictably and precisely tune the wettability of the resulting functionalized graphite surfaces from 44 to 83 degrees. The modular molecular structures and predictable behavior of short peptides demonstrated here give rise to a novel platform for functionalizing graphitic materials that offers numerous advantages, including non-invasive modification of the substrate, bio-compatible processing in an aqueous environment, and simple fusion with other functional biological molecules. PMID:22428620

Effect of high-power-laser with and without graphite coating on bonding of resin cement to lithium disilicate ceramic.

PubMed

Feitosa, Fernanda A; de Araújo, Rodrigo M; Tay, Franklin R; Niu, Lina; Pucci, César R

2017-12-12

The present study evaluated the effect of different high-power-laser surface treatments on the bond strength between resin cement and disilicate ceramic. Lithium disilicate ceramic specimens with truncated cones shape were prepared and divided into 5 groups: HF (hydrofluoric acid-etching), Er:YAG laser + HF, Graphite + Er:YAG laser + HF, Nd:YAG laser + HF, and Graphite + Nd:YAG laser + HF. The treated ceramic surfaces were characterized with scanning electron microscopy and surface roughness measurement. Hourglasses-shaped ceramic- resin bond specimens were prepared, thermomechanically cycled and stressed to failure under tension. The results showed that for both the factors "laser" and "graphite", statistically significant differences were observed (p < 0.05). Multiple-comparison tests performed on the "laser" factor were in the order: Er:YAG > Nd:YAG (p < 0.05), and on the "graphite" factor were in the order: graphite coating < without coating (p < 0.05). The Dunnett test showed that Er:YAG + HF had significantly higher tensile strength (p = 0.00). Higher surface roughness was achieved after Er:YAG laser treatment. Thus Er:YAG laser treatment produces higher bond strength to resin cement than other surface treatment protocols. Surface-coating with graphite does not improve bonding of the laser-treated lithium disilicate ceramic to resin cement.

Raman studies of the interactions of fibrous carbon nanomaterials with albumin

NASA Astrophysics Data System (ADS)

Wesełucha-Birczyńska, Aleksandra; Morajka, Krzysztof; Stodolak-Zych, Ewa; Długoń, Elżbieta; Dużyja, Maria; Lis, Tomasz; Gubernat, Maciej; Ziąbka, Magdalena; Błażewicz, Marta

2018-05-01

Adsorption or immobilization of proteins on synthetic surfaces is a key issue in the context of the biocompatibility of implant materials, especially those intended for the needs of cardiac surgery but also for the construction of biosensors or nanomaterials used as drug carriers. The subject of research was the analysis of Raman spectra of two types of fibrous carbon nanomaterials, of great potential for biomedical applications, incubated with human serum albumin (HSA). The first nanomaterial has been created on the layer of MWCNTs deposited by electrophoretic method (EPD) and then covered by thin film of pyrolytic carbon introduced by chemical vapor deposition process (CVD). The second material was formed from carbonized nanofibers prepared via electrospinning (ESCNFs) of polyacrylonitrile (PAN) precursor and then covered with pyrolytic carbon (CVD). The G-band blue-shift towards the position of about 1600 cm-1, observed for both studied surfaces, clearly indicates the albumin (HSA) adhesion to the surface. The G and G' (2D) peak shift was employed to assess the stress build up on the carbon nanomaterials. The surface nano- and micro-topography as well as the method of ordering the carbon nanomaterial has a significant influence on the mode of surface-protein interaction.

Cobalt ion-coordinated self-assembly synthesis of nitrogen-doped ordered mesoporous carbon nanosheets for efficiently catalyzing oxygen reduction.

PubMed

Wang, Haitao; Wang, Wei; Asif, Muhammad; Yu, Yang; Wang, Zhengyun; Wang, Junlei; Liu, Hongfang; Xiao, Junwu

2017-10-19

The design and synthesis of a promising porous carbon-based electrocatalyst with an ordered and uninterrupted porous structure for oxygen reduction reaction (ORR) is still a significant challenge. Herein, an efficient catalyst based on cobalt-embedded nitrogen-doped ordered mesoporous carbon nanosheets (Co/N-OMCNS) is successfully prepared through a two-step procedure (cobalt ion-coordinated self-assembly and carbonization process) using 3-aminophenol as a nitrogen source, cobalt acetate as a cobalt source and Pluronic F127 as a mesoporous template. This work indicates that the formation of a two dimensional nanosheet structure is directly related to the extent of the cobalt ion coordination interaction. Moreover, the critical roles of pyrolysis temperature in nitrogen doping and ORR catalytic activity are also investigated. Benefiting from the high surface area and graphitic degree, high contents of graphitic N and pyridinic N, ordered interconnected mesoporous carbon framework, as well as synergetic interaction between the cobalt nanoparticles and protective nitrogen doped graphitic carbon layer, the resultant optimal catalyst Co/N-OMCNS-800 (pyrolyzed at 800 °C) exhibits comparable ORR catalytic activity to Pt/C, superior tolerance to methanol crossover and stability.

Balanced improvement of high performance concrete material properties with modified graphite nanomaterials

NASA Astrophysics Data System (ADS)

Peyvandi, Amirpasha

Graphite nanomaterials offer distinct features for effective reinforcement of cementitious matrices in the pre-crack and post-crack ranges of behavior. Thoroughly dispersed and well-bonded nanomaterials provide for effective control of the size and propagation of defects (microcracks) in matrix, and also act as closely spaced barriers against diffusion of moisture and aggressive solutions into concrete. Modified graphite nanomaterials can play multi-faceted roles towards enhancing the mechanical, physical and functional attributes of concrete materials. Graphite nanoplatelets (GP) and carbon nanofibers (CNF) were chosen for use in cementitious materials. Experimental results highlighted the balanced gains in diverse engineering properties of high-performance concrete realized by introduction of graphite nanomaterials. Nuclear Magnetic Resonance (NMR) spectroscopy was used in order to gain further insight into the effects of nanomaterials on the hydration process and structure of cement hydrates. NMR exploits the magnetic properties of certain atomic nuclei, and the sensitivity of these properties to local environments to generate data which enables determination of the internal structure, reaction state, and chemical environment of molecules and bulk materials. 27 Al and 29Si NMR spectroscopy techniques were employed in order to evaluate the effects of graphite nanoplatelets on the structure of cement hydrates, and their resistance to alkali-silica reaction (ASR), chloride ion diffusion, and sulfate attack. Results of 29Si NMR spectroscopy indicated that the percent condensation of C-S-H in cementitious paste was lowered in the presence of nanoplatelets at the same age. The extent of chloride diffusion was assessed indirectly by detecting Friedel's salt as a reaction product of chloride ions with aluminum-bearing cement hydrates. Graphite nanoplatelets were found to significantly reduce the concentration of Friedel's salt at different depths after various periods of exposure to chloride solutions, pointing at the benefits of nanoplatelets towards enhancement of concrete resistance to chloride ion diffusion. It was also found that the intensity of Thaumasite, a key species marking sulfate attack on cement hydrates, was lowered with the addition of graphite nanoplatelets in concrete exposed to sulfate solutions. Experimental evaluations were conducted on scaled-up production of concrete nanocomposite in precast concrete plants. Full-scale reinforced concrete pipes and beams were produced using concrete nanocomposites. Durability and structural tests indicated that the use of graphite nanoplatelets, alone or in combination with synthetic (PVA) fibers, produced significant gains in the durability characteristics, and also benefited the structural performance of precast reinforced concrete products. The material and scaled-up structural investigations conducted in the project concluded that lower-cost graphite nanomaterials (e.g., graphite nanoplatelets) offer significant potentials as multi-functional additives capable of enhancing the barrier, durability and mechanical performance of concrete materials. The benefits of graphite nanomaterials tend to be more pronounced in higher-performance concrete materials.

Synthesis and characterization of SiC based composite materials for immobilizing radioactive graphite

NASA Astrophysics Data System (ADS)

Wang, Qing; Teng, Yuancheng; Wu, Lang; Zhang, Kuibao; Zhao, Xiaofeng; Hu, Zhuang

2018-06-01

In order to immobilize high-level radioactive graphite, silicon carbide based composite materials{ (1-x) SiC· x MgAl2O4 (0.1 ≤ x≤0.4) } were fabricated by solid-state reaction at 1370 °C for 2 h in vacuum. Residual graphite and precipitated corundum were observed in the as-synthesized product, which attributed to the interface reaction of element silicon and magnesium compounds. To further understand the reasons for the presence of graphite and corundum, the effects of mole ratio of Si/C, MgAl2O4 content and non-stoichiometry of MgAl2O4 on the synthesis were investigated. To immobilize graphite better, residual graphite should be eliminated. The target product was obtained when the mole ratio of Si/C was 1.3:1, MgAl2O4 content was x = 0.2, and the mole ratio of Al to Mg in non-stoichiometric MgAl2O4 was 1.7:1. In addition, the interface reaction between magnesium compounds and silicon not graphite was displayed by conducting a series of comparative experiments. The key factor for the occurrence of interface reaction is that oxygen atom is transferred from magnesium compound to SiO gas. Infrared and Raman spectrum revealed the increased disorders of graphite after being synthesized.

Lithium storage in structurally tunable carbon anode derived from sustainable source

DOE PAGES

Lim, Daw Gen; Kim, Kyungho; Razdan, Mayuri; ...

2017-09-01

Here, a meticulous solid state chemistry approach has been developed for the synthesis of carbon anode from a sustainable source. The reaction mechanism of carbon formation during pyrolysis of sustainable feed-stock was studied in situ by employing Raman microspectroscopy. No Raman spectral changes observed below 160°C (thermally stable precursor) followed by color change, however above 280°C characteristic D and G bands of graphitic carbon are recorded. Derived carbon particles exhibited high specific surface area with low structural ordering (active carbons) to low specific surface area with high graphitic ordering as a function of increasing reaction temperature. Carbons synthesized at 600°Cmore » demonstrated enhanced reversible lithiation capacity (390 mAh g -1), high charge-discharge rate capability, and stable cycle life. On the contrary, carbons synthesized at higher temperatures (>1200°C) produced more graphite-like structure yielding longer specific capacity retention with lower reversible capacity.« less

Low temperature simulation of subliming boundary layer flow in Jupiter atmosphere

NASA Technical Reports Server (NTRS)

Chen, C. J.

1976-01-01

A low-temperature approximate simulation for the sublimation of a graphite heat shield under Jovian entry conditions is studied. A set of algebraic equations is derived to approximate the governing equation and boundary conditions, based on order-of-magnitude analysis. Characteristic quantities such as the wall temperature and the subliming velocity are predicted. Similarity parameters that are needed to simulate the most dominant phenomena of the Jovian entry flow are also given. An approximate simulation of the sublimation of the graphite heat shield is performed with an air-dry-ice model. The simulation with the air-dry-ice model may be carried out experimentally at a lower temperature of 3000 to 6000 K instead of the entry temperature of 14,000 K. The rate of graphite sublimation predicted by the present algebraic approximation agrees to the order of magnitude with extrapolated data. The limitations of the simulation method and its utility are discussed.

Manufacture of fiber-epoxy test specimens: Including associated jigs and instrumentation

NASA Technical Reports Server (NTRS)

Mathur, S. B.; Felbeck, D. K.

1980-01-01

Experimental work on the manufacture and strength of graphite-epoxy composites is considered. The correct data and thus a true assessment of the strength properties based on a proper and scientifically modeled test specimen with engineered design, construction, and manufacture has led to claims of a very broad spread in optimized values. Such behavior is in the main due to inadequate control during manufacture of test specimen, improper curing, and uneven scatter in the fiber orientation. The graphite fibers are strong but brittle. Even with various epoxy matrices and volume fraction, the fracture toughness is still relatively low. Graphite-epoxy prepreg tape was investigated as a sandwich construction with intermittent interlaminar bonding between the laminates in order to produce high strength, high fracture toughness composites. The quality and control of manufacture of the multilaminate test specimen blanks was emphasized. The dimensions, orientation and cure must be meticulous in order to produce the desired mix.

Effect of Graphitic Content on Carbon Supported Catalyst Performance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patel, Anant; Artyushkova, Kateryna; Atanassov, Plamen

2011-07-01

The effect of graphitic content on carbon supported platinum catalysts was investigated in order to investigate its influence on catalyst performance. Four catalysts of varying surface areas and graphitic content were analyzed using XPS, HREELS, and tested using RDE experiments. The catalysts were also heat treated at 150oC and 100%RH as means to uniformly age them. The heat treated samples were analyzed using the same methods to determine what changes had occurred due to this aging process. When compared to the BOL catalysts, heat treated catalysts displayed increased graphitic carbon and platinum metalic content, however they also showed depressed catalyticmore » activity. The primary cause is still under investigation, though it is believed to be related to loss of amorphous carbon content.« less

Analysis of HEMCL Railgun Insulator Damage

DTIC Science & Technology

2006-06-01

pyrolytic epoxy degradation and glass fiber softening and liquification in the insulator, it is determined that rail-to-rail plasmas are present behind...produces epoxy decomposition products in the form of gases, oils , waxes and chars solid (heavily cross-linked residues) [4]. The nature of the... pyrolytic decomposition product (wax) of the epoxy as in the fired specimens. Figures 6 and 7 are typical examples of glass fiber softening and

Biological conversion of pyrolytic products to ethanol and lipids

NASA Astrophysics Data System (ADS)

Lian, Jieni

Pyrolysis is a promising technology that can convert up to 75 % of lignocellulosic biomass into crude bio-oil. However, due to the complex chemical compositions of bio-oil, its further refining into fuels and high value chemicals faces great challenges. This dissertation research proposed new technologies for biological conversion of pyrolytic products derived from cellulose and hemicellulose, such as anhydrosugars and carbolic acids to fuels and chemicals. First, the pyrolytic anhydrosugars (chiefly levoglucosan (LG)) were hydrolysed into glucose followed by neutralization, detoxification and fermentation to produce ethanol by ethanogenetic yeast and lipids by oleaginous yeasts. Second, a novel process for the conversion of C1-C4 pyrolytic products to lipid with oleaginous yeasts was investigated. Third, oleaginous yeasts that can directly convert LG to lipids were studied and a recombined yeast with LG kinase was constructed for the direct convertion of LG into lipids. This allowed a reduction of existing process for LG fermentation from four steps into two steps and eliminated the need for acids and bases as well as the disposal of chemicals. The development of genetic modified organisms with LG kinase opens a promising avenue for the direct LG fermentation to produce a wide range of fuels and chemicals. The simplification of LG utilization process would enhance the economic viability of this technology.

Determination of boron in blood, urine and bone by electrothermal atomic absorption spectrometry using zirconium and citric acid as modifiers

NASA Astrophysics Data System (ADS)

Burguera, Marcela; Burguera, José Luis; Rondón, Carlos; Carrero, Pablo

2001-10-01

A comparative study of various potential chemical modifiers (Au, Ba, Be, Ca, Cr, Ir, La, Lu, Mg, Ni, Pd, Pt, Rh, Ru, Sr, V, W, and Zr), and different 'coating' treatments (Zr, W, and W+Rh) of the pyrolytic graphite platform of a longitudinally heated graphite tube atomizer for thermal stabilization and determination of boron was undertaken. The use of Au, Ba, Be, Cr, Ir, Pt, Rh, Ru, Sr and V as modifiers, and of W+Rh coating produced erratic, and noisy signals, while the addition of La, Ni and Pd as modifiers, and the W coating had positive effects, but with too high background absorption signals, rendering their use unsuitable for boron determination even in aqueous solutions. The atomic absorption signal for boron was increased and stabilized when the platform was coated with Zr, and by the addition of Ca, Mg, Lu, W or Zr as modifiers. Only the addition of 10 μg of Zr as a modifier onto Zr-treated platforms allowed the use of a higher pyrolysis temperature without analyte losses. The memory effect was minimized by incorporating a cleaning step with 10 μl of 50 g l -1 NH 4F HF after every three boron measurements. The addition of 10 μl of 15 g l -1 citric acid together with Zr onto Zr-treated platforms significantly improved the characteristic mass to m0=282 pg, which is adequate for biological samples such as urine and bone, although the sensitivity was still inadequate for the determination of boron in blood of subjects without supplementary diet. Under optimized conditions, the detection limit (3σ) was 60 μg l -1. The amount of boron found in whole blood, urine and femur head samples from patients with osteoporosis was in agreement with values previously reported in the literature.

The role of mineral surface chemistry in modified dextrin adsorption.

PubMed

Beaussart, Audrey; Mierczynska-Vasilev, Agnieszka M; Harmer, Sarah L; Beattie, David A

2011-05-15

The adsorption of two modified dextrins (phenyl succinate dextrin--PS Dextrin; styrene oxide dextrin--SO Dextrin) on four different mineral surfaces has been studied using X-ray photoelectron spectroscopy (XPS), in situ atomic force microscopy (AFM) imaging, and captive bubble contact angle measurements. The four surfaces include highly orientated pyrolytic graphite (HOPG), freshly cleaved synthetic sphalerite (ZnS), and two surfaces produced through surface reactions of sphalerite: one oxidized in alkaline solution (pH 9, 1 h immersion); and one subjected to metal ion exchange between copper and zinc (i.e. copper activation: exposed to 1×10(-3) M CuSO(4) solution for 1 h). XPS measurements indicate that the different sphalerite surfaces contain varying amounts of sulfur, zinc, oxygen, and copper, producing substrates for polymer adsorption with a range of possible binding sites. AFM imaging has shown that the two polymers adsorb to a similar extent on HOPG, and that the two polymers display very different propensities for adsorption on the three sphalerite surface types, with freshly cleaved sphalerite encouraging the least adsorption, and copper activated and oxidized sphalerite encouraging significantly more adsorption. Contact angle measurements of the four surfaces indicate that synthetic sphalerite has a low contact angle upon fracture, and that oxidation on the timescale of one hour substantially alters the hydrophobicity. HOPG and copper-activated sphalerite were the most hydrophobic, as expected due to the carbon and di/poly-sulfide rich surfaces of the two samples, respectively. SO Dextrin is seen to have a significant impact on the wettability of HOPG and the surface reacted sphalerite samples, highlighting the difficulty in selectively separating sphalerite from carbonaceous unwanted minerals in flotation. PS Dextrin has the least effect on the hydrophobicity of the reacted sphalerite surfaces, whilst still significantly increasing the wettability of graphite, and thus has more potential for use as a polymer depressant in this separation. Copyright © 2011 Elsevier Inc. All rights reserved.

The role of chitosan as nanofiller of graphite oxide for the removal of toxic mercury ions.

PubMed

Kyzas, George Z; Travlou, Nikolina A; Deliyanni, Eleni A

2014-01-01

The present study focuses on the role of chitosan (CS) as nanofiller of graphite oxide (GO) in order to prepare composite materials with improved Hg(II) adsorption properties. The removal of Hg(II) from aqueous solutions was studied using adsorbents as graphite oxide (GO), graphite oxide nanofilled with chitosan (GO/CS) and magnetic chitosan (GO/mCS). Many possible interactions between materials and Hg(II) were observed after adsorption and explained via characterization with various techniques (SEM/EDAX, FTIR, XRD, DTG). The adsorption evaluation was done studying various parameters as the effect of pH (both in adsorption and desorption), contact time (pseudo-second order fitting), temperature (isotherms at 25, 45, 65 °C), in line with a brief thermodynamic analysis (ΔG(0), ΔH(0), ΔS(0)). The maximum adsorption capacity (fitting with Langmuir model) of GO at 25 °C was Qmax=187 mg/g, while after the CS nanofilling (formation of the composite GO/CS), Qmax was increased to 381 mg/g with a further enhancement for GO/mCS (Qmax=397 mg/g). Copyright © 2013 Elsevier B.V. All rights reserved.

Fluid-deposited graphitic inclusions in quartz: Comparison between KTB (German Continental Deep-Drilling) core samples and artificially reequilibrated natural inclusions

USGS Publications Warehouse

Pasteris, J.D.; Chou, I.-Ming

1998-01-01

We used Raman microsampling spectroscopy (RMS) to determine the degree of crystallinity of minute (2-15 ??m) graphite inclusions in quartz in two sets of samples: experimentally reequilibrated fluid inclusions in a natural quartz grain and biotite-bearing paragneisses from the KTB deep drillhole in SE Germany. Our sequential reequilibration experiments at 725??C on initially pure CO2 inclusions in a quartz wafer and the J. Krautheim (1993) experiments at 900-1100??C on organic compounds heated in gold or platinum capsules suggest that, at a given temperature, (1) fluid-deposited graphite will have a lower crystallinity than metamorphosed organic matter and (2) that the crystallinity of fluid-deposited graphite is affected by the composition of the fluid from which it was deposited. We determined that the precipitation of more-crystalline graphite is favored by lower fH2 (higher fO2), and that the crystallinity of graphite is established by the conditions (including gas fugacities) that pertain as the fluid first reaches graphite saturation. Graphite inclusions within quartz grains in the KTB rocks show a wide range in crystallinity index, reflecting three episodes of carbon entrapment under different metamorphic conditions. Isolated graphite inclusions have the spectral properties of totally ordered, completely crystalline graphite. Such crystallinity suggests that the graphite was incorporated from the surrounding metasedimentary rocks, which underwent metamorphism at upper amphibolite-facies conditions. Much of the fluid-deposited graphite in fluid inclusions, however, shows some spectral disorder. The properties of that graphite resemble those of experimental precipitates at temperatures in excess of 700??C and at elevated pressures, suggesting that the inclusions represent precipitates from C-O-H fluids trapped under conditions near those of peak metamorphism at the KTB site. In contrast, graphite that is intimately associated with chlorite and other (presumably low-temperature) silicates in inclusions is highly disordered and spectrally resembles kerogens. This graphite probably was deposited during later greenschist-facies retrograde metamorphism at about 400-500??C. The degree of crystallinity of fluid-deposited graphite is shown to be a much more complex function of temperature than is the crystallinity of metamorphic graphite. To some extent, experiments can provide temperature-calibration of the crystallinity index. However, the difference in time scales between experimental runs and geologic processes makes it difficult to infer specific temperatures for naturally precipitated graphite. Copyright ?? 1998 Elsevier Science Ltd.

Oxygen reduction reaction activity and structural stability of Pt-Au nanoparticles prepared by arc-plasma deposition.

PubMed

Takahashi, Shuntaro; Chiba, Hiroshi; Kato, Takashi; Endo, Shota; Hayashi, Takehiro; Todoroki, Naoto; Wadayama, Toshimasa

2015-07-28

The oxygen reduction reaction (ORR) activity and durability of various Au(x)/Pt100 nanoparticles (where x is the atomic ratio of Au against Pt) are evaluated herein. The samples were fabricated on a highly-oriented pyrolytic graphite substrate at 773 K through sequential arc-plasma depositions of Pt and Au. The electrochemical hydrogen adsorption charges (electrochemical surface area), particularly the characteristic currents caused by the corner and edge sites of the Pt nanoparticles, decrease with increasing Au atomic ratio (x). In contrast, the specific ORR activities of the Au(x)/Pt100 samples were dependent on the atomic ratios of Pt and Au: the Au28/Pt100 sample showed the highest specific activity among all the investigated samples (x = 0-42). As for ORR durability evaluated by applying potential cycles between 0.6 and 1.0 V in oxygen-saturated 0.1 M HClO4, Au28/Pt100 was the most durable sample against the electrochemical potential cycles. The results clearly showed that the Au atoms located at coordinatively-unsaturated sites, e.g. at the corners or edges of the Pt nanoparticles, can improve the ORR durability by suppressing unsaturated-site-induced degradation of the Pt nanoparticles.

Broadband optical properties of graphene and HOPG investigated by spectroscopic Mueller matrix ellipsometry

NASA Astrophysics Data System (ADS)

Song, Baokun; Gu, Honggang; Zhu, Simin; Jiang, Hao; Chen, Xiuguo; Zhang, Chuanwei; Liu, Shiyuan

2018-05-01

Optical properties of mono-graphene fabricated by chemical vapor deposition (CVD) and highly oriented pyrolytic graphite (HOPG) are comparatively studied by Mueller matrix ellipsometry (MME) over an ultra-wide energy range of 0.73-6.42 eV. A multilayer stacking model is constructed to describe the CVD mono-graphene, in which the roughness of the glass substrate and the water adsorption on the graphene are considered. We introduce a uniaxial anisotropic dielectric model to parameterize the optical constants of both the graphene and the HOPG. With the established models, broadband optical constants of the graphene and the HOPG are determined from the Mueller matrix spectra based on a point-by-point method and a non-linear regression method, respectively. Two significant absorption peaks at 4.75 eV and 6.31 eV are observed in the extinction coefficient spectra of the mono-graphene, which can be attributed to the von-Hove singularity (i.e., the π-to-π∗ exciton transition) near the M point and the σ-to-σ∗ exciton transition near the Γ point of the Brillouin zone, respectively. Comparatively, only a major absorption peak at 4.96 eV appears in the ordinary extinction coefficient spectra of the HOPG, which is mainly formed by the π-to-π∗ interband transition.

A collection system for dry solid residues from exhaled breath for analysis via atomic force microscopy.

PubMed

Morozov, Victor N; Mikheev, Andrey Y

2017-01-09

Exhaled air contains sub-micron droplets of lung liquid, which potentially bear biomarkers of lung diseases. After dehydration they form dry residue particles (DRPs). As a first step in developing techniques to characterize individual DRPs, a new electrostatic collector was designed in which DRPs are charged within a unipolar corona charger, concentrated in a cone funnel, and deposited onto a limited area of a highly oriented pyrolytic graphite surface. The collector captures 80%-90% of DRPs at an optimal flow rate of 0.15 l min -1 . Atomic force microscopy (AFM) revealed flattened round particles 20-50 nm high, with notable protrusions at their surface suggestive of an inhomogeneous internal structure. Exposure to humid air resulted in the DRPs spreading over the surface, with a 50%-200% decrease in their heights and an increase in their lateral dimensions so that their volume decreased by only 10% ± 3%. Exposure to saturated chloroform vapor resulted in drainage of 10%-15% of the DRP volume (presumably lipids), forming collar-shaped rings around each particle but leaving the core size and structure unchanged. AFM measurements combined with laser counter measurements of the DRP concentrations were used to estimate that one liter of air exhaled by volunteers contained less than 100 pg of dry residue material.

Integration of the ferromagnetic insulator EuO onto graphene.

PubMed

Swartz, Adrian G; Odenthal, Patrick M; Hao, Yufeng; Ruoff, Rodney S; Kawakami, Roland K

2012-11-27

We have demonstrated the deposition of EuO films on graphene by reactive molecular beam epitaxy in a special adsorption-controlled and oxygen-limited regime, which is a critical advance toward the realization of the exchange proximity interaction (EPI). It has been predicted that when the ferromagnetic insulator (FMI) EuO is brought into contact with graphene, an overlap of electronic wave functions at the FMI/graphene interface can induce a large spin splitting inside the graphene. Experimental realization of this effect could lead to new routes for spin manipulation, which is a necessary requirement for a functional spin transistor. Furthermore, EPI could lead to novel spintronic behavior such as controllable magnetoresistance, gate tunable exchange bias, and quantized anomalous Hall effect. However, experimentally, EuO has not yet been integrated onto graphene. Here we report the successful growth of high-quality crystalline EuO on highly oriented pyrolytic graphite and single-layer graphene. The epitaxial EuO layers have (001) orientation and do not induce an observable D peak (defect) in the Raman spectra. Magneto-optic measurements indicate ferromagnetism with a Curie temperature of 69 K, which is the value for bulk EuO. Transport measurements on exfoliated graphene before and after EuO deposition indicate only a slight decrease in mobility.

Formation, dissolution and properties of surface nanobubbles

NASA Astrophysics Data System (ADS)

Che, Zhizhao; Theodorakis, Panagiotis E.

2017-02-01

Surface nanobubbles are stable gaseous phases in liquids that form on solid substrates. While their existence has been confirmed, there are many open questions related to their formation and dissolution processes along with their structures and properties, which are difficult to investigate experimentally. To address these issues, we carried out molecular dynamics simulations based on atomistic force fields for systems comprised of water, air (N2 and O2), and a Highly Oriented Pyrolytic Graphite (HOPG) substrate. Our results provide insights into the formation/dissolution mechanisms of nanobubbles and estimates for their density, contact angle, and surface tension. We found that the formation of nanobubbles is driven by an initial nucleation process of air molecules and the subsequent coalescence of the formed air clusters. The clusters form favorably on the substrate, which provides an enhanced stability to the clusters. In contrast, nanobubbles formed in the bulk either move randomly to the substrate and spread or move to the water--air surface and pop immediately. Moreover, nanobubbles consist of a condensed gaseous phase with a surface tension smaller than that of an equivalent system under atmospheric conditions, and contact angles larger than those in the equivalent nanodroplet case. We anticipate that this study will provide useful insights into the physics of nanobubbles and will stimulate further research in the field by using all-atom simulations.