Implications of contamination and surface area ratios for Langmuir probe diagnostics on CubeSats

NASA Astrophysics Data System (ADS)

Suresh, P.; Swenson, C.

2009-12-01

Theories describing the current collected by a biased probe under various conditions are necessary for such observation to be used to accurately determine plasma properties. Langmuir probes are routinely used on spacecraft to measure plasma parameters such as density, temperature, and vehicle charging. The collected current is a function of the potential between the surrounding plasma and probe surface. There have been both observations of and concepts for unaccounted variations of this potential which limit the application of Langmuir probe theory for determining plasma properties. These variations occur due to spatial variations of the work function across the probe surface due to non-uniformity of the crystalline surface properties and surface contamination of the probe. Currently we do not have theoretical expressions which consider these factors as first principles in their derivation. In the event of these surface potential variations, the analysis of the plasma using the currently available theories of the Langmuir probe yield erroneous results. We present a theory which models the current as a function of the surface potential variations. Another consideration for Langmuir probes on CubeSats is the ratio of the probe area to the return current collection area. If the area ratio is unfavorable this can also lead to erroneous results in the interpretation of observations. A mathematical formulation of the current collected by the probe for contaminated surfaces is presented and compared with data from a Langmuir probe flown on a sounding rocket mission. The implications of using Langmuir probes on CubeSats given the engineering limitations of probe cleanliness and area ratios are reviewed.

Study of the transverse and longitudinal electric field components of surface plasmon polaritons on flat metal film by polarization-resolved Fourier-space microscopy

NASA Astrophysics Data System (ADS)

Liu, C.; Ong, H. C.

2018-01-01

We have employed a polarization-resolved Fourier-space surface plasmon resonance microscope to determine the electric field component ratio of surface plasmon polaritons (SPPs) propagating on a flat gold film. By using a metallic nanoparticle as a probe to capture the radiation damping of the SPP scattered waves, we find the angular far-field distribution is related to the transverse and longitudinal fields of SPPs. The experiment is supported by analytical and numerical calculations. Our results present a simple but useful approach to probe the behaviors of SPPs such as the transverse spin density as well as the energy density.

Contact pin-printing of albumin-fungicide conjugate for silicon nitride-based sensors biofunctionalization: Multi-technique surface analysis for optimum immunoassay performance

NASA Astrophysics Data System (ADS)

Gajos, Katarzyna; Budkowski, Andrzej; Tsialla, Zoi; Petrou, Panagiota; Awsiuk, Kamil; Dąbczyński, Paweł; Bernasik, Andrzej; Rysz, Jakub; Misiakos, Konstantinos; Raptis, Ioannis; Kakabakos, Sotirios

2017-07-01

Mass fabrication of integrated biosensors on silicon chips is facilitated by contact pin-printing, applied for biofunctionalization of individual Si3N4-based transducers at wafer-scale. To optimize the biofunctionalization for immunochemical (competitive) detection of fungicide thiabendazole (TBZ), Si3N4 surfaces are modified with (3-aminopropyl)triethoxysilane and examined after: immobilization of BSA-TBZ conjugate (probe) from solutions with different concentration, blocking with bovine serum albumin (BSA), and immunoreaction with a mouse monoclonal antibody against TBZ. Nanostructure, surface density, probe composition and coverage uniformity of protein layers are evaluated with Atomic Force Microscopy, Spectroscopic Ellipsometry, Time-of-Flight Secondary Ion Mass Spectrometry and X-ray Photoelectron Spectroscopy. Contact pin-printing of overlapping probe spots is compared with hand spotted areas. Contact pin-printing resulted in two-fold increase of immobilized probe surface density as compared to hand spotting. Regarding BSA-TBZ immobilization, an incomplete monolayer develops into a bilayer as the concentration of BSA-TBZ molecules in the printing solution increases from 25 to 100 μg/mL. Upon blocking, however, a complete protein monolayer is formed for all the BSA-TBZ concentrations used. Free surface sites are filled with BSA for low surface coverage with BSA-TBZ, whereas loosely bound BSA-TBZ molecules are removed from the BSA-TBZ bilayer. As a consequence immunoreaction efficiency increases with the printing probe concentration.

Tunneling magnetic force microscopy

NASA Technical Reports Server (NTRS)

Burke, Edward R.; Gomez, Romel D.; Adly, Amr A.; Mayergoyz, Isaak D.

1993-01-01

We have developed a powerful new tool for studying the magnetic patterns on magnetic recording media. This was accomplished by modifying a conventional scanning tunneling microscope. The fine-wire probe that is used to image surface topography was replaced with a flexible magnetic probe. Images obtained with these probes reveal both the surface topography and the magnetic structure. We have made a thorough theoretical analysis of the interaction between the probe and the magnetic fields emanating from a typical recorded surface. Quantitative data about the constituent magnetic fields can then be obtained. We have employed these techniques in studies of two of the most important issues of magnetic record: data overwrite and maximizing data-density. These studies have shown: (1) overwritten data can be retrieved under certain conditions; and (2) improvements in data-density will require new magnetic materials. In the course of these studies we have developed new techniques to analyze magnetic fields of recorded media. These studies are both theoretical and experimental and combined with the use of our magnetic force scanning tunneling microscope should lead to further breakthroughs in the field of magnetic recording.

Growth of carbon nanofibers on tipless cantilevers: process development and applications in scanning probe microscopy

NASA Astrophysics Data System (ADS)

Cui, Hongtao; Kalinin, Sergei; Yang, Xiaojing; Lowndes, Douglas

2005-03-01

Carbon nanofibers (CNFs) are grown on tipless cantilevers as probe tips for scanning probe microscopy. A catalyst dot pattern is formed on the surface of the tipless cantilever using electron beam lithography and CNF growth is performed in a direct-current plasma enhanced chemical vapor deposition reactor. Because the CNF is aligned with the electric field near the edge of the cantilever during growth, it is tilted with respect to the cantilever surface, which compensates partially for the probe tilt introduced when used in scanning probe microscopy. CNFs with different shapes and tip radii can be produced by variation of experimental conditions. The tip geometries of the CNF probes are defined by their catalyst particles, whose magnetic nature also imparts a capability for imaging magnetic samples. We have demonstrated their use in both atomic force and magnetic force surface imaging. These probe tips may provide information on magnetic phenomena at the nanometer scale in connection with the drive for ever-increasing storage density of magnetic hard disks.

Electrostatic-probe measurements of plasma parameters for two reentry flight experiments at 25000 feet per second

NASA Technical Reports Server (NTRS)

Jones, W. L., Jr.; Cross, A. E.

1972-01-01

Unique plasma diagnostic measurements at high altitudes from two geometrically similar blunt body reentry spacecraft using electrostatic probe rakes are presented. The probes measured the positive ion density profiles (shape and magnitude) during the two flights. The probe measurements were made at eight discrete points (1 cm to 7 cm) from the vehicle surface in the aft flow field of the spacecraft over the altitude range of 85.3 to 53.3 km (280,000 to 175,000 ft) with measured densities of 10 to the 8th power to 10 to the 12th power electrons/cu cm, respectively. Maximum reentry velocity for each spacecraft was approximately 7620 meters/second (25,000 ft/sec). In the first flight experiment, water was periodically injected into a flow field which was contaminated by ablation products from the spacecraft nose region. The nonablative nose of the second spacecraft thereby minimized flow field contamination. Comparisons of the probe measured density profiles with theoretical calculations are presented with discussion as to the probable cause of significant disagreement. Also discussed are the correlation of probe measurements with vehicle angle of attack motions and the good high altitude agreement between electron densities inferred from the probe measurements, VHF antenna measurements, and microwave reflectometer diagnostic measurements.

Coupled Ablation, Heat Conduction, Pyrolysis, Shape Change and Spallation of the Galileo Probe

NASA Technical Reports Server (NTRS)

Milos, Frank S.; Chen, Y.-K.; Rasky, Daniel J. (Technical Monitor)

1995-01-01

The Galileo probe enters the atmosphere of Jupiter in December 1995. This paper presents numerical methodology and detailed results of our final pre-impact calculations for the heat shield response. The calculations are performed using a highly modified version of a viscous shock layer code with massive radiation coupled with a surface thermochemical ablation and spallation model and with the transient in-depth thermal response of the charring and ablating heat shield. The flowfield is quasi-steady along the trajectory, but the heat shield thermal response is dynamic. Each surface node of the VSL grid is coupled with a one-dimensional thermal response calculation. The thermal solver includes heat conduction, pyrolysis, and grid movement owing to surface recession. Initial conditions for the heat shield temperature and density were obtained from the high altitude rarefied-flow calculations of Haas and Milos. Galileo probe surface temperature, shape, mass flux, and element flux are all determined as functions of time along the trajectory with spallation varied parametrically. The calculations also estimate the in-depth density and temperature profiles for the heat shield. All this information is required to determine the time-dependent vehicle mass and drag coefficient which are necessary inputs for the atmospheric reconstruction experiment on board the probe.

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

Steigies, C. T.; Barjatya, A.

Langmuir probes are standard instruments for plasma density measurements on many sounding rockets. These probes can be operated in swept-bias as well as in fixed-bias modes. In swept-bias Langmuir probes, contamination effects are frequently visible as a hysteresis between consecutive up and down voltage ramps. This hysteresis, if not corrected, leads to poorly determined plasma densities and temperatures. With a properly chosen sweep function, the contamination parameters can be determined from the measurements and correct plasma parameters can then be determined. In this paper, we study the contamination effects on fixed-bias Langmuir probes, where no hysteresis type effect is seenmore » in the data. Even though the contamination is not evident from the measurements, it does affect the plasma density fluctuation spectrum as measured by the fixed-bias Langmuir probe. We model the contamination as a simple resistor-capacitor circuit between the probe surface and the plasma. We find that measurements of small scale plasma fluctuations (meter to sub-meter scale) along a rocket trajectory are not affected, but the measured amplitude of large scale plasma density variation (tens of meters or larger) is attenuated. From the model calculations, we determine amplitude and cross-over frequency of the contamination effect on fixed-bias probes for different contamination parameters. The model results also show that a fixed bias probe operating in the ion-saturation region is affected less by contamination as compared to a fixed bias probe operating in the electron saturation region.« less

Chemoselective covalent coupling of oligonucleotide probes to self-assembled monolayers.

PubMed

Devaraj, Neal K; Miller, Gregory P; Ebina, Wataru; Kakaradov, Boyko; Collman, James P; Kool, Eric T; Chidsey, Christopher E D

2005-06-22

A chemoselective route to routinely and rapidly attach oligonucleotide probes to well-defined surfaces is presented. Cu(I) tris(benzyltriazolylmethyl)amine-catalyzed coupling of terminal acetylenes to azides on a self-assembled monolayer is used instead of traditional nucleophilic-electrophilic coupling reactions. The reaction proceeds well even in the presence of purposely introduced nucleophilic and electrophilic impurities. The density of oligonucleotide probes can be controlled by controlling the amount of azide functionality. Although most of our work was done on gold surfaces, this technique should be readily applicable to any surface on which an azide-containing monolayer can be assembled as we have preliminarily demonstrated by derivatizing azidotrimethoxysilane-modified glass slides with fluorescein-containing oligonucleotides.

Electron temperature and density probe for small aeronomy satellites

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

Oyama, K.-I.; Institute of Space and Plasma Sciences, National Cheng Kung University, Tainan, Taiwan; International Center for Space Weather Study and education, Kyushu University, Fukuoka

2015-08-15

A compact and low power consumption instrument for measuring the electron density and temperature in the ionosphere has been developed by modifying the previously developed Electron Temperature Probe (ETP). A circuit block which controls frequency of the sinusoidal signal is added to the ETP so that the instrument can measure both T{sub e} in low frequency mode and N{sub e} in high frequency mode from the floating potential shift of the electrode. The floating potential shift shows a minimum at the upper hybrid resonance frequency (f{sub UHR}). The instrument which is named “TeNeP” can be used for tiny satellites whichmore » do not have enough conductive surface area for conventional DC Langmuir probe measurements. The instrument also eliminates the serious problems associated with the contamination of satellite surface as well as the sensor electrode.« less

Electrical potential-assisted DNA hybridization. How to mitigate electrostatics for surface DNA hybridization.

PubMed

Tymoczko, Jakub; Schuhmann, Wolfgang; Gebala, Magdalena

2014-12-24

Surface-confined DNA hybridization reactions are sensitive to the number and identity of DNA capture probes and experimental conditions such as the nature and the ionic strength of the electrolyte solution. When the surface probe density is high or the concentration of bulk ions is much lower than the concentration of ions within the DNA layer, hybridization is significantly slowed down or does not proceed at all. However, high-density DNA monolayers are attractive for designing high-sensitivity DNA sensors. Thus, circumventing sluggish DNA hybridization on such interfaces allows a high surface concentration of target DNA and improved signal/noise ratio. We present potential-assisted hybridization as a strategy in which an external voltage is applied to the ssDNA-modified interface during the hybridization process. Results show that a significant enhancement of hybridization can be achieved using this approach.

Probing Interfacial Processes on Graphene Surface by Mass Detection

NASA Astrophysics Data System (ADS)

Kakenov, Nurbek; Kocabas, Coskun

2013-03-01

In this work we studied the mass density of graphene, probed interfacial processes on graphene surface and examined the formation of graphene oxide by mass detection. The graphene layers were synthesized by chemical vapor deposition method on copper foils and transfer-printed on a quartz crystal microbalance (QCM). The mass density of single layer graphene was measured by investigating the mechanical resonance of the QCM. Moreover, we extended the developed technique to probe the binding dynamics of proteins on the surface of graphene, were able to obtain nonspecific binding constant of BSA protein of graphene surface in aqueous solution. The time trace of resonance signal showed that the BSA molecules rapidly saturated by filling the available binding sites on graphene surface. Furthermore, we monitored oxidation of graphene surface under oxygen plasma by tracing the changes of interfacial mass of the graphene controlled by the shifts in Raman spectra. Three regimes were observed the formation of graphene oxide which increases the interfacial mass, the release of carbon dioxide and the removal of small graphene/graphene oxide flakes. Scientific and Technological Research Council of Turkey (TUBITAK) grant no. 110T304, 109T209, Marie Curie International Reintegration Grant (IRG) grant no 256458, Turkish Academy of Science (TUBA-Gebip).

Vacuum probe surface sampler

NASA Technical Reports Server (NTRS)

Zahlava, B. A. (Inventor)

1973-01-01

A vacuum probe surface sampler is described for rapidly sampling relatively large surface areas which possess relatively light loading densities of micro-organism, drug particles or the like. A vacuum head with a hollow handle connected to a suitable vacuum source is frictionally attached to a cone assembly terminating in a flared tip adapted to be passed over the surface to be sampled. A fine mesh screen carried by the vacuum head provides support for a membrane filter which collects the microorganisms or other particles. The head assembly is easily removed from the cone assembly without contacting the cone assembly with human hands.

The local work function: Concept and implications

NASA Astrophysics Data System (ADS)

Wandelt, K.

1997-02-01

The term 'local work function' is now widely applied. The present work discusses the common physical basis of 'photoemission of adsorbed xenon (PAX)' and 'two-photon photonemissionspectroscopy of image potential states' as local work function probes. New examples with bimetallic and defective surfaces are presented which demonstrate the capability of PAX measurements for the characterization of heterogeneous surfaces on an atomic scale. Finally, implications of the existence of short-range variations of the surface potential at surface steps are addressed. In particular, dynamical work function change measurements are a sensitive probe for the step-density at surfaces and, as such, a powerful in-situ method to monitor film growth.

Tomography of a Probe Potential Using Atomic Sensors on Graphene.

PubMed

Wyrick, Jonathan; Natterer, Fabian D; Zhao, Yue; Watanabe, Kenji; Taniguchi, Takashi; Cullen, William G; Zhitenev, Nikolai B; Stroscio, Joseph A

2016-12-27

Our ability to access and explore the quantum world has been greatly advanced by the power of atomic manipulation and local spectroscopy with scanning tunneling and atomic force microscopes, where the key technique is the use of atomically sharp probe tips to interact with an underlying substrate. Here we employ atomic manipulation to modify and quantify the interaction between the probe and the system under study that can strongly affect any measurement in low charge density systems, such as graphene. We transfer Co atoms from a graphene surface onto a probe tip to change and control the probe's physical structure, enabling us to modify the induced potential at a graphene surface. We utilize single Co atoms on a graphene field-effect device as atomic scale sensors to quantitatively map the modified potential exerted by the scanning probe over the whole relevant spatial and energy range.

A Steel Ball Surface Quality Inspection Method Based on a Circumferential Eddy Current Array Sensor.

PubMed

Zhang, Huayu; Xie, Fengqin; Cao, Maoyong; Zhong, Mingming

2017-07-01

To efficiently inspect surface defects on steel ball bearings, a new method based on a circumferential eddy current array (CECA) sensor was proposed here. The best probe configuration, in terms of the coil quality factor (Q-factor), magnetic field intensity, and induced eddy current density on the surface of a sample steel ball, was determined using 3-, 4-, 5-, and 6-coil probes, for analysis and comparison. The optimal lift-off from the measured steel ball, the number of probe coils, and the frequency of excitation current suitable for steel ball inspection were obtained. Using the resulting CECA sensor to inspect 46,126 steel balls showed a miss rate of ~0.02%. The sensor was inspected for surface defects as small as 0.05 mm in width and 0.1 mm in depth.

Interaction model between a liquid film and a spherical probe

NASA Astrophysics Data System (ADS)

Ledesma Alonso, Rene; Legendre, Dominique; Tordjeman, Philippe

2012-11-01

To find a liquid surface profile, when performing AFM measurements, probe interaction effects should be identified. Herein, the behavior of a liquid film free surface (thickness E, surface tension γ and density difference Δρ), disposed over a flat surface and in the presence of a spherical probe (radius R) is forecast. A bump-like surface shape is observed, due to the probe/film interaction (characterized by the Hamaker constant Hpl). In addition, the attraction between the film and the substrate (depicted by Hsl) opposes the axial and radial deformation ranges. Several parameters portray the equilibrium shape: Bond Bo = (ΔρgR2) / γ and modified Hamaker Ha = 4Hpl / (3 πγR2) numbers, Hamaker ratio A =Hls /Hpl , separation distance D / R and film thickness E / R . We focus on the effect of geometry, nevertheless special attention is given to the role of physical parameters. Employing an augmented Young-Laplace equation, the equilibrium profile is described by a strongly non-linear ODE. A critical distance, below which the irreversible wetting process of the spherical probe occurs, is predicted. Our results provide simple relationships between parameters, which determine the optimal scanning conditions over liquid films.

Adsorption of a cationic dye molecule on polystyrene microspheres in colloids: effect of surface charge and composition probed by second harmonic generation.

PubMed

Eckenrode, Heather M; Jen, Shih-Hui; Han, Jun; Yeh, An-Gong; Dai, Hai-Lung

2005-03-17

Nonlinear optical probe, second harmonic generation (SHG), of the adsorption of the dye molecule malachite green (MG), in cationic form at pH < or = 5, on polystyrene microspheres in aqueous solution is used to study the effect of surface charge and composition on molecular adsorption. Three types of polystyrene microspheres with different surface composition are investigated: (1) a sulfate terminated, anionic surface, (2) a neutral surface without any functional group termination, and (3) an amine terminated, cationic surface. The cationic dye was found to adsorb at all three surfaces, regardless of surface charge. The adsorption free energies, DeltaG's, measured for the three surfaces are -12.67, -12.39, and -10.46 kcal/mol, respectively, with the trend as expected from the charge interactions. The adsorption density on the anionic surface, where attractive charge-charge interaction dominates, is determined by the surface negative charge density. The adsorption densities on the neutral and cationic surfaces are on the other hand higher, perhaps as a result of a balance between minimizing repulsive charge interaction and maximizing attractive molecule-substrate and intermolecular interactions. The relative strength of the SH intensity per molecule, in combination of a model calculation, reveals that the C(2) axis of the MG molecule is nearly perpendicular to the surface on the anionic surface and tilts away from the surface norm when the surface is neutral and further away when cationic. Changing the pH of the solution may alter the surface charge and subsequently affect the adsorption configuration and SH intensity.

Electron collection theory for a D-region subsonic blunt electrostatic probe

NASA Technical Reports Server (NTRS)

Wai-Kwong Lai, T.

1974-01-01

Blunt probe theory for subsonic flow in a weakly ionized and collisional gas is reviewed, and an electron collection theory for the relatively unexplored case, Deybye length approximately 1, which occurs in the lower ionosphere (D-region), is developed. It is found that the dimensionless Debye length is no longer an electric field screening parameter, and the space charge field effect can be negelected. For ion collection, Hoult-Sonin theory is recognized as a correct description of the thin, ion density-perturbed layer adjacent the blunt probe surface. The large volume with electron density perturbed by a positively biased probe renders the usual thin boundary layer analysis inapplicable. Theories relating free stream conditions to the electron collection rate for both stationary and moving blunt probes are obtained. A model based on experimental nonlinear electron drift velocity data is proposed. For a subsonically moving probe, it is found that the perturbed region can be divided into four regions with distinct collection mechanisms.

Characterization and global modelling of low-pressure hydrogen-based RF plasmas suitable for surface cleaning processes

NASA Astrophysics Data System (ADS)

Škoro, Nikola; Puač, Nevena; Lazović, Saša; Cvelbar, Uroš; Kokkoris, George; Gogolides, Evangelos

2013-11-01

In this paper we present results of measurements and global modelling of low-pressure inductively coupled H2 plasma which is suitable for surface cleaning applications. The plasma is ignited at 1 Pa in a helicon-type reactor and is characterized using optical emission measurements (optical actinometry) and electrical measurements, namely Langmuir and catalytic probe. By comparing catalytic probe data obtained at the centre of the chamber with optical actinometry results, an approximate calibration of the actinometry method as a semi-quantititative measure of H density was achieved. Coefficients for conversion of actinometric ratios to H densities are tabulated and provided. The approximate validity region of the simple actinometry formula for low-pressure H2 plasma is discussed in the online supplementary data (stacks.iop.org/JPhysD/46/475206/mmedia). Best agreement with catalytic probe results was obtained for (Hβ, Ar750) and (Hβ, Ar811) actinometric line pairs. Additionally, concentrations of electrons and ions as well as plasma potential, electron temperature and ion fluxes were measured in the chamber centre at different plasma powers using a Langmuir probe. Moreover, a global model of an inductively coupled plasma was formulated using a compiled reaction set for H2/Ar gas mixture. The model results compared reasonably well with the results on H atom and charge particle densities and a sensitivity analysis of important input parameters was conducted. The influence of the surface recombination, ionization, and dissociation coefficients, and the ion-neutral collision cross-section on model results was demonstrated.

Virus-based surface patterning of biological molecules, probes, and inorganic materials.

PubMed

Ahn, Suji; Jeon, Seongho; Kwak, Eun-A; Kim, Jong-Man; Jaworski, Justyn

2014-10-01

An essential requirement for continued technological advancement in many areas of biology, physics, chemistry, and materials science is the growing need to generate custom patterned materials. Building from recent achievements in the site-specific modification of virus for covalent surface tethering, we show in this work that stable 2D virus patterns can be generated in custom geometries over large area glass surfaces to yield templates of biological, biochemical, and inorganic materials in high density. As a nanomaterial building block, filamentous viruses have been extensively used in recent years to produce materials with interesting properties, owing to their ease of genetic and chemical modification. By utilizing un-natural amino acids generated at specific locations on the filamentous fd bacteriophage protein coat, surface immobilization is carried out on APTES patterned glass resulting in precise geometries of covalently linked virus material. This technique facilitated the surface display of a high density of virus that were labeled with biomolecules, fluorescent probes, and gold nanoparticles, thereby opening the possibility of integrating virus as functional components for surface engineering. Copyright © 2014 Elsevier B.V. All rights reserved.

Doping Level of Boron-Doped Diamond Electrodes Controls the Grafting Density of Functional Groups for DNA Assays.

PubMed

Švorc, Ĺubomír; Jambrec, Daliborka; Vojs, Marian; Barwe, Stefan; Clausmeyer, Jan; Michniak, Pavol; Marton, Marián; Schuhmann, Wolfgang

2015-09-02

The impact of different doping levels of boron-doped diamond on the surface functionalization was investigated by means of electrochemical reduction of aryldiazonium salts. The grafting efficiency of 4-nitrophenyl groups increased with the boron levels (B/C ratio from 0 to 20,000 ppm). Controlled grafting of nitrophenyldiazonium was used to adjust the amount of immobilized single-stranded DNA strands at the surface and further on the hybridization yield in dependence on the boron doping level. The grafted nitro functions were electrochemically reduced to the amine moieties. Subsequent functionalization with a succinic acid introduced carboxyl groups for subsequent binding of an amino-terminated DNA probe. DNA hybridization significantly depends on the probe density which is in turn dependent on the boron doping level. The proposed approach opens new insights for the design and control of doped diamond surface functionalization for the construction of DNA hybridization assays.

Effects of surface nanostructuring and impurity doping on ultrafast carrier dynamics of silicon photovoltaic cells: a pump-probe study

NASA Astrophysics Data System (ADS)

Chen, Tianyu; Nam, Yoon-Ho; Wang, Xinke; Han, Peng; Sun, Wenfeng; Feng, Shengfei; Ye, Jiasheng; Song, Jae-Won; Lee, Jung-Ho; Zhang, Chao; Zhang, Yan

2018-01-01

We present femtosecond optical pump-terahertz probe studies on the ultrafast dynamical processes of photo-generated charge carriers in silicon photovoltaic cells with various nanostructured surfaces and doping densities. The pump-probe measurements provide direct insight on the lifetime of photo-generated carriers, frequency-dependent complex dielectric response along with photoconductivity of silicon photovoltaic cells excited by optical pump pulses. A lifetime of photo-generated carriers of tens of nanosecond is identified from the time-dependent pump-induced attenuation of the terahertz transmission. In addition, we find a large value of the imaginary part of the dielectric function and of the real part of the photoconductivity in silicon photovoltaic cells with micron length nanowires. We attribute these findings to the result of defect-enhanced electron-photon interactions. Moreover, doping densities of phosphorous impurities in silicon photovoltaic cells are also quantified using the Drude-Smith model with our measured frequency-dependent complex photoconductivities.

DNA hybridization activity of single-stranded DNA-conjugated gold nanoparticles used as probes for DNA detection

NASA Astrophysics Data System (ADS)

Kira, Atsushi; Matsuo, Kosuke; Nakajima, Shin-ichiro

2016-02-01

Colloidal nanoparticles (NPs) have potential applications in bio-sensing technologies as labels or signal enhancers. In order to meet demands for a development of biomolecular assays by a quantitative understanding of single-molecule, it is necessary to regulate accuracy of the NPs probes modified with biomolecules to optimize the characteristics of NPs. However, to our knowledge, there is little information about the structural effect of conjugated biomolecules to the NPs. In this study, we investigated the contribution of a density of single-stranded DNA (ssDNA) conjugating gold NP to hybridization activity. Hybridization activity decreased in accordance with increases in the density of attached ssDNAs, likely due to electrostatic repulsion generated by negatively charged phosphate groups in the ssDNA backbone. These results highlight the importance of controlling the density of ssDNAs attached to the surface of NPs used as DNA detection probes.

The Mass Surface Density Distribution of a High-Mass Protocluster forming from an IRDC and GMC

NASA Astrophysics Data System (ADS)

Lim, Wanggi; Tan, Jonathan C.; Kainulainen, Jouni; Ma, Bo; Butler, Michael

2016-01-01

We study the probability distribution function (PDF) of mass surface densities of infrared dark cloud (IRDC) G028.36+00.07 and its surrounding giant molecular cloud (GMC). Such PDF analysis has the potential to probe the physical processes that are controlling cloud structure and star formation activity. The chosen IRDC is of particular interest since it has almost 100,000 solar masses within a radius of 8 parsecs, making it one of the most massive, dense molecular structures known and is thus a potential site for the formation of a high-mass, "super star cluster". We study mass surface densities in two ways. First, we use a combination of NIR, MIR and FIR extinction maps that are able to probe the bulk of the cloud structure that is not yet forming stars. This analysis also shows evidence for flattening of the IR extinction law as mass surface density increases, consistent with increasing grain size and/or growth of ice mantles. Second, we study the FIR and sub-mm dust continuum emission from the cloud, especially utlizing Herschel PACS and SPIRE images. We first subtract off the contribution of the foreground diffuse emission that contaminates these images. Next we examine the effects of background subtraction and choice of dust opacities on the derived mass surface density PDF. The final derived PDFs from both methods are compared, including also with other published studies of this cloud. The implications for theoretical models and simulations of cloud structure, including the role of turbulence and magnetic fields, are discussed.

Self-assembled monolayers of alkyl-thiols on InAs: A Kelvin probe force microscopy study

NASA Astrophysics Data System (ADS)

Szwajca, A.; Wei, J.; Schukfeh, M. I.; Tornow, M.

2015-03-01

We report on the preparation and characterization of self-assembled monolayers from aliphatic thiols with different chain length and termination on InAs (100) planar surfaces. This included as first step the development and investigation of a thorough chemical InAs surface preparation step using a dedicated bromine/NH4OH-based etching process. Ellipsometry, contact angle measurements and atomic force microscopy (AFM) indicated the formation of smooth, surface conforming monolayers. The molecular tilt angles were obtained as 30 ± 10° with respect to the surface normal. Kelvin probe force microscopy (KPFM) measurements in hand with Parameterized Model number 5 (PM5) calculations of the involved molecular dipoles allowed for an estimation of the molecular packing densities on the surface. We obtained values of up to n = 1014 cm- 2 for the SAMs under study. These are close to what is predicted from a simple geometrical model that would calculate a maximum density of about n = 2.7 × 1014 cm- 2. We take this as additional conformation of the substrate smoothness and quality of our InAs-SAM hybrid layer systems.

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

Yoshimoto, Shinya, E-mail: yosshi@issp.u-tokyo.ac.jp; Shiozawa, Yuichiro; Koitaya, Takanori

Electronic states and electrical conductivity of the native oxide Si(111) surface adsorbed with an electron donor tetrakis(dimethylamino)ethylene (TDAE) were investigated using ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy (XPS), and independently driven four-probe conductivity measurements. The formation of positively charged TDAE species is confirmed by the downward shift of the vacuum level by 1.45 eV, the absence of HOMO level in the valence band, and observation of the positively charged state in the N 1s XPS spectra. Si 2p XPS spectra and four-probe conductivity measurements revealed that TDAE adsorption induces an increase in downward band bending and a reduction in electrical resistancemore » of the surface, respectively. The sheet conductivity and the electron density of the surface are 1.1 μS/◻ and 4.6 × 10{sup 9} cm{sup −2}, respectively, after TDAE adsorption, and they are as high as 350% of the original surface. These results demonstrate that the electron density of the semiconductor surface is successfully controlled by the electron donor molecule TDAE.« less

[Detection of transgenic crop with gene chip].

PubMed

Huang, Ying-Chun; Sun, Chun-Yun; Feng, Hong; Hu, Xiao-Dong; Yin, Hai-Bin

2003-05-01

Some selected available sequences of reporter genes,resistant genes, promoters and terminators are amplified by PCR for the probes of transgenic crop detection gene chip. These probes are arrayed at definite density and printed on the surface of amino-slides by bioRobot MicroGrid II. Results showed that gene chip worked quickly and correctly, when transgenic rice, pawpaw,maize and soybean were applied.

Spacecraft surface charging within geosynchronous orbit observed by the Van Allen Probes

DOE PAGES

Sarno-Smith, Lois K.; Larsen, Brian A.; Skoug, Ruth M.; ...

2016-02-27

Using the Helium Oxygen Proton Electron (HOPE) and Electric Field and Waves (EFW) instruments from the Van Allen Probes, we explored the relationship between electron energy fluxes in the eV and keV ranges and spacecraft surface charging. We present statistical results on spacecraft charging within geosynchronous orbit by L and MLT. An algorithm to extract the H+ charging line in the HOPE instrument data was developed to better explore intense charging events. Also, this study explored how spacecraft potential relates to electron number density, electron pressure, electron temperature, thermal electron current, and low-energy ion density between 1 and 210 eV.more » It is demonstrated that it is imperative to use both EFW potential measurements and the HOPE instrument ion charging line for examining times of extreme spacecraft charging of the Van Allen Probes. The results of this study show that elevated electron energy fluxes and high-electron pressures are present during times of spacecraft charging but these same conditions may also occur during noncharging times. Furthermore, we also show noneclipse significant negative charging events on the Van Allen Probes.« less

Near-surface density profiling of Fe ion irradiated Si (100) using extremely asymmetric x-ray diffraction by variation of the wavelength

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

Khanbabaee, B., E-mail: khanbabaee@physik.uni-siegen.de; Pietsch, U.; Facsko, S.

2014-10-20

In this work, we report on correlations between surface density variations and ion parameters during ion beam-induced surface patterning process. The near-surface density variations of irradiated Si(100) surfaces were investigated after off-normal irradiation with 5 keV Fe ions at different fluences. In order to reduce the x-ray probing depth to a thickness below 5 nm, the extremely asymmetrical x-ray diffraction by variation of wavelength was applied, exploiting x-ray refraction at the air-sample interface. Depth profiling was achieved by measuring x-ray rocking curves as function of varying wavelengths providing incidence angles down to 0°. The density variation was extracted from the deviationsmore » from kinematical Bragg angle at grazing incidence angles due to refraction of the x-ray beam at the air-sample interface. The simulations based on the dynamical theory of x-ray diffraction revealed that while a net near-surface density decreases with increasing ion fluence which is accompanied by surface patterning, there is a certain threshold of ion fluence to surface density modulation. Our finding suggests that the surface density variation can be relevant with the mechanism of pattern formation.« less

A robust molecular probe for Ångstrom-scale analytics in liquids

PubMed Central

Nirmalraj, Peter; Thompson, Damien; Dimitrakopoulos, Christos; Gotsmann, Bernd; Dumcenco, Dumitru; Kis, Andras; Riel, Heike

2016-01-01

Traditionally, nanomaterial profiling using a single-molecule-terminated scanning probe is performed at the vacuum–solid interface often at a few Kelvin, but is not a notion immediately associated with liquid–solid interface at room temperature. Here, using a scanning tunnelling probe functionalized with a single C60 molecule stabilized in a high-density liquid, we resolve low-dimensional surface defects, atomic interfaces and capture Ångstrom-level bond-length variations in single-layer graphene and MoS2. Atom-by-atom controllable imaging contrast is demonstrated at room temperature and the electronic structure of the C60–metal probe complex within the encompassing liquid molecules is clarified using density functional theory. Our findings demonstrates that operating a robust single-molecular probe is not restricted to ultra-high vacuum and cryogenic settings. Hence the scope of high-precision analytics can be extended towards resolving sub-molecular features of organic elements and gauging ambient compatibility of emerging layered materials with atomic-scale sensitivity under experimentally less stringent conditions. PMID:27516157

High quality-factor quartz tuning fork glass probe used in tapping mode atomic force microscopy for surface profile measurement

NASA Astrophysics Data System (ADS)

Chen, Yuan-Liu; Xu, Yanhao; Shimizu, Yuki; Matsukuma, Hiraku; Gao, Wei

2018-06-01

This paper presents a high quality-factor (Q-factor) quartz tuning fork (QTF) with a glass probe attached, used in frequency modulation tapping mode atomic force microscopy (AFM) for the surface profile metrology of micro and nanostructures. Unlike conventionally used QTFs, which have tungsten or platinum probes for tapping mode AFM, and suffer from a low Q-factor influenced by the relatively large mass of the probe, the glass probe, which has a lower density, increases the Q-factor of the QTF probe unit allowing it to obtain better measurement sensitivity. In addition, the process of attaching the probe to the QTF with epoxy resin, which is necessary for tapping mode AFM, is also optimized to further improve the Q-factor of the QTF glass probe. The Q-factor of the optimized QTF glass probe unit is demonstrated to be very close to that of a bare QTF without a probe attached. To verify the effectiveness and the advantages of the optimized QTF glass probe unit, the probe unit is integrated into a home-built tapping mode AFM for conducting surface profile measurements of micro and nanostructures. A blazed grating with fine tool marks of 100 nm, a microprism sheet with a vertical amplitude of 25 µm and a Fresnel lens with a steep slope of 90 degrees are used as measurement specimens. From the measurement results, it is demonstrated that the optimized QTF glass probe unit can achieve higher sensitivity as well as better stability than conventional probes in the measurement of micro and nanostructures.

Poly-adenine-mediated fluorescent spherical nucleic acid probes for live-cell imaging of endogenous tumor-related mRNA.

PubMed

Zhu, Dan; Zhao, Dongxia; Huang, Jiaxuan; Zhu, Yu; Chao, Jie; Su, Shao; Li, Jiang; Wang, Lihua; Shi, Jiye; Zuo, Xiaolei; Weng, Lixing; Li, Qian; Wang, Lianhui

2018-05-16

Identification of tumor-related mRNA in living cells hold great promise for early cancer diagnosis and pathological research. Herein, we present poly-adenine (polyA)-mediated fluorescent spherical nucleic acid (FSNA) probes for intracellular mRNA detection with regulable sensitivities by programmably adjusting the loading density of DNA on gold nano-interface. Gold nanoparticles (AuNPs) functionalized with polyA-tailed recognition sequences were hybridized to fluorescent "reporter" strands to fabricate fluorescence-quenched FSNA probes. While exposed to target gene, the "reporter" strands were released from FSNA through strand displacement and fluorescence was recovered. With polyA20 tail as the attaching block, the detection limit of FSNA probes was calculated to be 0.31 nM, which is ~55 fold lower than that of thiolated probes without surface density regulation. Quantitative intracellular mRNA detection and imaging could be achieved with polyA-mediated FSNA probes within 2 hours, indicating their application potential in rapid and sensitive intracellular target imaging. Copyright © 2018. Published by Elsevier Inc.

Analysis by oxygen atom number density measurement of high-speed hydrophilic treatment of polyimide using atmospheric pressure microwave plasma

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

Ono, S.

2015-03-30

This paper describes the fundamental experimental data of the plasma surface modification of the polyimide using atmospheric pressure microwave plasma source. The experimental results were discussed from the point of view of the radical’s behavior, which significantly affects the modification mechanism. The purpose of the study is to examine how the value of the oxygen atom density will affect the hydrophilic treatment in the upstream region of the plasma where gas temperature is very high. The surface modification experiments were performed by setting the polyimide film sample in the downstream region of the plasma. The degree of the modification wasmore » measured by a water contact angle measurement. The water contact angle decreased less than 30 degrees within 1 second treatment time in the upstream region. Very high speed modification was observed. The reason of this high speed modification seems that the high density radical which contributes the surface modification exist in the upstream region of the plasma. This tendency is supposed to the measured relatively high electron density (~10{sup 15}cm{sup −3}) at the center of the plasma. We used the electric heating catalytic probe method for oxygen radical measurement. An absolute value of oxygen radical density was determined by catalytic probe measurement and the results show that ~10{sup 15}cm{sup −3} of the oxygen radical density in the upstream region and decreases toward downstream region. The experimental results of the relation of the oxygen radical density and hydrophilic modification of polyimide was discussed.« less

2D microwave imaging reflectometer electronics.

PubMed

Spear, A G; Domier, C W; Hu, X; Muscatello, C M; Ren, X; Tobias, B J; Luhmann, N C

2014-11-01

A 2D microwave imaging reflectometer system has been developed to visualize electron density fluctuations on the DIII-D tokamak. Simultaneously illuminated at four probe frequencies, large aperture optics image reflections from four density-dependent cutoff surfaces in the plasma over an extended region of the DIII-D plasma. Localized density fluctuations in the vicinity of the plasma cutoff surfaces modulate the plasma reflections, yielding a 2D image of electron density fluctuations. Details are presented of the receiver down conversion electronics that generate the in-phase (I) and quadrature (Q) reflectometer signals from which 2D density fluctuation data are obtained. Also presented are details on the control system and backplane used to manage the electronics as well as an introduction to the computer based control program.

Wireless sensor node for surface seawater density measurements.

PubMed

Baronti, Federico; Fantechi, Gabriele; Roncella, Roberto; Saletti, Roberto

2012-01-01

An electronic meter to measure surface seawater density is presented. It is based on the measurement of the difference in displacements of a surface level probe and a weighted float, which according to Archimedes' law depends on the density of the water. The displacements are simultaneously measured using a high-accuracy magnetostrictive sensor, to which a custom electronic board provides a wireless connection and power supply so that it can become part of a wireless sensor network. The electronics are designed so that different kinds of wireless networks can be used, by simply changing the wireless module and the relevant firmware of the microcontroller. Lastly, laboratory and at-sea tests are presented and discussed in order to highlight the functionality and the performance of a prototype of the wireless density meter node in a Bluetooth radio network. The experimental results show a good agreement of the values of the calculated density compared to reference hydrometer readings.

Wireless Sensor Node for Surface Seawater Density Measurements

PubMed Central

Baronti, Federico; Fantechi, Gabriele; Roncella, Roberto; Saletti, Roberto

2012-01-01

An electronic meter to measure surface seawater density is presented. It is based on the measurement of the difference in displacements of a surface level probe and a weighted float, which according to Archimedes’ law depends on the density of the water. The displacements are simultaneously measured using a high-accuracy magnetostrictive sensor, to which a custom electronic board provides a wireless connection and power supply so that it can become part of a wireless sensor network. The electronics are designed so that different kinds of wireless networks can be used, by simply changing the wireless module and the relevant firmware of the microcontroller. Lastly, laboratory and at-sea tests are presented and discussed in order to highlight the functionality and the performance of a prototype of the wireless density meter node in a Bluetooth radio network. The experimental results show a good agreement of the values of the calculated density compared to reference hydrometer readings. PMID:22736986

Refined gravity determination at small bodies through landing probes

NASA Astrophysics Data System (ADS)

Bellerose, J.

2012-02-01

Very small objects of the near-Earth population have not been visited to date, and may be among the next targets for human exploration. As density is a strong indication of the body origin and intrinsic properties, determining the mass is one of the most important goals. The past missions to Eros and Itokawa resulted in mass and density estimates to less than five percent error, allowing precise mission planning while giving new insights on the body structure. Current mass determination techniques have limitations in the low gravity regime, and spacecraft tracking at very small asteroids is challenging. We investigate the constraints on measuring the mass at very small near-Earth objects, and their consequences on proximity operation planning. An alternative option to spacecraft radio tracking is to use surface probes. The near-surface and landing dynamics can be observed and tracked by the host spacecraft, providing higher resolution measurements of the NEA gravity pull. We show analytical methods to estimate the performance of given proximity operations, and simulations of spacecraft and probe dynamics at NEAs less than 100 m in diameter.

Advanced concentration analysis of atom probe tomography data: Local proximity histograms and pseudo-2D concentration maps.

PubMed

Felfer, Peter; Cairney, Julie

2018-06-01

Analysing the distribution of selected chemical elements with respect to interfaces is one of the most common tasks in data mining in atom probe tomography. This can be represented by 1D concentration profiles, 2D concentration maps or proximity histograms, which represent concentration, density etc. of selected species as a function of the distance from a reference surface/interface. These are some of the most useful tools for the analysis of solute distributions in atom probe data. In this paper, we present extensions to the proximity histogram in the form of 'local' proximity histograms, calculated for selected parts of a surface, and pseudo-2D concentration maps, which are 2D concentration maps calculated on non-flat surfaces. This way, local concentration changes at interfaces or and other structures can be assessed more effectively. Copyright © 2018 Elsevier B.V. All rights reserved.

Multiple epitope presentation and surface density control enabled by chemoselective immobilization lead to enhanced performance in IgE-binding fingerprinting on peptide microarrays.

PubMed

Gori, Alessandro; Cretich, Marina; Vanna, Renzo; Sola, Laura; Gagni, Paola; Bruni, Giulia; Liprino, Marta; Gramatica, Furio; Burastero, Samuele; Chiari, Marcella

2017-08-29

Multiple ligand presentation is a powerful strategy to enhance the affinity of a probe for its corresponding target. A promising application of this concept lies in the analytical field, where surface immobilized probes interact with their corresponding targets in the context of complex biological samples. Here we investigate the effect of multiple epitope presentation (MEP) in the challenging context of IgE-detection in serum samples using peptide microarrays, and evaluate the influence of probes surface density on the assay results. Using the milk allergen alpha-lactalbumin as a model, we have synthesized three immunoreactive epitope sequences in a linear, branched and tandem form and exploited a chemoselective click strategy (CuAAC) for their immobilization on the surface of two biosensors, a microarray and an SPR chip both modified with the same clickable polymeric coating. We first demonstrated that a fine tuning of the surface peptide density plays a crucial role to fully exploit the potential of oriented and multiple peptide display. We then compared the three multiple epitope presentations in a microarray assay using sera samples from milk allergic patients, confirming that a multiple presentation, in particular that of the tandem construct, allows for a more efficient characterization of IgE-binding fingerprints at a statistically significant level. To gain insights on the binding parameters that characterize antibody/epitopes affinity, we selected the most reactive epitope of the series (LAC1) and performed a Surface Plasmon Resonance Imaging (SPRi) analysis comparing different epitope architectures (linear versus branched versus tandem). We demonstrated that the tandem peptide provides an approximately twofold increased binding capacity with respect to the linear and branched peptides, that could be attributed to a lower rate of dissociation (K d ). Copyright © 2017 Elsevier B.V. All rights reserved.

Compressive Strength of Cometary Surfaces Derived from Radar Observations

NASA Astrophysics Data System (ADS)

ElShafie, A.; Heggy, E.

2014-12-01

Landing on a comet nucleus and probing it, mechanically using harpoons, penetrometers and drills, and electromagnetically using low frequency radar waves is a complex task that will be tackled by the Rosetta mission for Comet 67P/Churyumov-Gerasimenko. The mechanical properties (i.e. density, porosity and compressive strength) and the electrical properties (i.e. the real and imaginary parts of the dielectric constant) of the comet nucleus, constrain both the mechanical and electromagnetic probing capabilities of Rosetta, as well as the choice of landing site, the safety of the landing, and subsurface data interpretation. During landing, the sounding radar data that will be collected by Rosetta's CONSERT experiment can be used to probe the comet's upper regolith layer by assessing its dielectric properties, which are then inverted to retrieve the surface mechanical properties. These observations can help characterize the mechanical properties of the landing site, which will optimize the operation of the anchor system. In this effort, we correlate the mechanical and electrical properties of cometary analogs to each other, and derive an empirical model that can be used to retrieve density, porosity and compressive strength from the dielectric properties of the upper regolith inverted from CONSERT observations during the landing phase. In our approach we consider snow as a viable cometary material analog due to its low density and its porous nature. Therefore, we used the compressive strength and dielectric constant measurements conducted on snow at a temperature of 250 K and a density range of 0.4-0.9 g/cm3 in order to investigate the relation between compressive strength and dielectric constant under cometary-relevant density range. Our results suggest that compressive strength increases linearly as function of the dielectric constant over the observed density range mentioned above. The minimum and maximum compressive strength of 0.5 and 4.5 MPa corresponded to a dielectric constant of 2.2 and 3.4 over the density range of 0.4-0.9 g/cm3. This preliminary correlation will be applied to the case of porous and dust contaminated snow under different temperatures to assess the surface mechanical properties for Comet 67P.

Snow Densification and Recent Accumulation Along the iSTAR Traverse, Pine Island Glacier, Antarctica

NASA Astrophysics Data System (ADS)

Morris, E. M.; Mulvaney, R.; Arthern, R. J.; Davies, D.; Gurney, R. J.; Lambert, P.; De Rydt, J.; Smith, A. M.; Tuckwell, R. J.; Winstrup, M.

2017-12-01

Neutron probe measurements of snow density from 22 sites in the Pine Island Glacier basin have been used to determine mean annual accumulation using an automatic annual layer identification routine. A mean density profile which can be used to convert radar two-way travel times to depth has been derived, and the effect of annual fluctuations in density on estimates of the depth of radar reflectors is shown to be insignificant, except very near the surface. Vertical densification rates have been derived from the neutron probe density profiles and from deeper firn core density profiles available at 9 of the sites. These rates are consistent with the rates predicted by the Herron and Langway model for stage 1 densification (by grain-boundary sliding, grain growth and intracrystalline deformation) and stage 2 densification (predominantly by sintering), except in a transition zone extending from ≈8 to ≈13 m from the surface in which 10-14% of the compaction occurs. Profiles of volumetric strain rate at each site show that in this transition zone the rates are consistent with the Arthern densification model. Comparison of the vertical densification rates and volumetric strain rates indicates that the expected relation to mean annual accumulation breaks down at high accumulation rates even when corrections are made for horizontal ice velocity divergence.

Scanned-probe field-emission studies of vertically aligned carbon nanofibers

NASA Astrophysics Data System (ADS)

Merkulov, Vladimir I.; Lowndes, Douglas H.; Baylor, Larry R.

2001-02-01

Field emission properties of dense and sparse "forests" of randomly placed, vertically aligned carbon nanofibers (VACNFs) were studied using a scanned probe with a small tip diameter of ˜1 μm. The probe was scanned in directions perpendicular and parallel to the sample plane, which allowed for measuring not only the emission turn-on field at fixed locations but also the emission site density over large surface areas. The results show that dense forests of VACNFs are not good field emitters as they require high extracting (turn-on) fields. This is attributed to the screening of the local electric field by the neighboring VACNFs. In contrast, sparse forests of VACNFs exhibit moderate-to-low turn-on fields as well as high emission site and current densities, and long emission lifetime, which makes them very promising for various field emission applications.

Effect of Molecular Crowding on the Response of an Electrochemical DNA Sensor

PubMed Central

Ricci, Francesco; Lai, Rebecca Y.; Heeger, Alan J.; Plaxco, Kevin W.; Sumner, James J.

2009-01-01

E-DNA sensors, the electrochemical equivalent of molecular beacons, appear to be a promising means of detecting oligonucleotides. E-DNA sensors are comprised of a redox-modified (here, methylene blue or ferrocene) DNA stem-loop covalently attached to an interrogating electrode. Because E-DNA signaling arises due to binding-induced changes in the conformation of the stem-loop probe, it is likely sensitive to the nature of the molecular packing on the electrode surface. Here we detail the effects of probe density, target length, and other aspects of molecular crowding on the signaling properties, specificity, and response time of a model E-DNA sensor. We find that the highest signal suppression is obtained at the highest probe densities investigated, and that greater suppression is observed with longer and bulkier targets. In contrast, sensor equilibration time slows monotonically with increasing probe density, and the specificity of hybridization is not significantly affected. In addition to providing insight into the optimization of electrochemical DNA sensors, these results suggest that E-DNA signaling arises due to hybridization-linked changes in the rate, and thus efficiency, with which the redox moiety collides with the electrode and transfers electrons. PMID:17488132

Investigation of Coatings for Langmuir Probes in an Oxygen-Rich Space Environment

NASA Astrophysics Data System (ADS)

Samaniego, J. I.; Wang, X.; Andersson, L.; Malaspina, D.; Ergun, R.; Horanyi, M.

2017-12-01

The surface properties of the Langmuir probes, such as the one on the MAVEN mission, will change after exposure to upper planetary atmospheres where high concentrations of atomic oxygen and other oxidizing compounds are present. TiN (Titanium Nitride) or DAG (a resin based graphite dispersion) are the most common coatings for current Langmuir probes, yet both of these coatings pose issues when exposed to oxygen-rich space environment. TiN showed reduced surface conductivity while the DAG layers erode with exposure to oxygen. It is known that Iridium (Ir) and Rhenium (Rh) are difficult to oxidize and maintain high conductivity even in their oxidized forms, suggesting them to be good candidates for probe coatings. Oxidation of most metals creates a resistive layer on the surface of the probe that will affect the amount of current being collected at a given voltage during the probe sweep and therefore affect the accuracy of plasma parameters determined by the Langmuir probe (e.g. density, temperature). We present the results of the oxidation effect on the current-voltage curves (I-V curves) and therefore the resulting measured plasma parameters of Ir and Rh wire probes compared with other control metals and coatings (Cu, Ni, TiN) in controlled plasma environments. The oxidation process is performed in an oxygen plasma chamber in which both O+ and O2+ are created and accelerated toward the probes with energies < 10 eV. An argon plasma chamber is used to compare the probe's I-V curves before and after the oxidation process. Our preliminary results indicate that iridium shows the least effect of oxidation on the probe measurements. The second objective of this study is to identify methods that can be used in orbit to clean the surface of Langmuir probes to minimize the effect of exposure to oxidizing compounds.

Development of scanning graphene Hall probes for magnetic microscopy

NASA Astrophysics Data System (ADS)

Schaefer, Brian T.; Wang, Lei; McEuen, Paul L.; Nowack, Katja C.

We discuss our progress on developing scanning Hall probes fabricated from hexagonal boron nitride (hBN)-encapsulated graphene, with the goal to image magnetic fields with submicron resolution. In contrast to scanning superconducting quantum interference device (SQUID) microscopy, this technique is compatible with a large applied magnetic field and not limited to cryogenic temperatures. The field sensitivity of a Hall probe depends inversely on carrier density, while the primary source of noise in the measurement is Johnson noise originating from the device resistance. hBN-encapsulated graphene demonstrates high carrier mobility at low carrier densities, therefore making it an ideal material for sensitive Hall probes. Furthermore, engineering the dielectric environment of graphene by encapsulating in hBN reduces low-frequency charge noise and disorder from the substrate. We outline our plans for adapting these devices for scanning, including characterization of the point spread function with a scanned current loop and fabrication of a deep-etched structure that enables positioning the sensitive area within 100 nanometers of the sample surface.

Cone penetrometer fiber optic raman spectroscopy probe assembly

DOEpatents

Kyle, Kevin R.; Brown, Steven B.

2000-01-01

A chemically and mechanically robust optical Raman spectroscopy probe assembly that can be incorporated in a cone penetrometer (CPT) for subsurface deployment. This assembly consists of an optical Raman probe and a penetrometer compatible optical probe housing. The probe is intended for in-situ chemical analysis of chemical constituents in the surrounding environment. The probe is optically linked via fiber optics to the light source and the detection system at the surface. A built-in broadband light source provides a strobe method for direct measurement of sample optical density. A mechanically stable sapphire window is sealed directly into the side-wall of the housing using a metallic, chemically resistant, hermetic seal design. This window permits transmission of the interrogation light beam and the resultant signal. The spectroscopy probe assembly is capable of accepting Raman, Laser induced Fluorescence, reflectance, and other optical probes with collimated output for CPT deployment.

Radioactive contamination mapping of northeastern and eastern Japan by a car-borne survey system, Radi-Probe.

PubMed

Kobayashi, Shingo; Shinomiya, Takayuki; Kitamura, Hisashi; Ishikawa, Takahiro; Imaseki, Hitoshi; Oikawa, Masakazu; Kodaira, Satoshi; Miyaushiro, Norihiro; Takashima, Yoshio; Uchihori, Yukio

2015-01-01

We constructed a new car-borne survey system called Radi-Probe with a portable germanium gamma-ray spectrometer onboard a cargo truck, to identify radionuclides and quantify surface contamination from the accident at Fukushima Dai-ichi Nuclear Power Station. The system can quickly survey a large area and obtain ambient dose equivalent rates and gamma-ray energy spectra with good energy resolution. We also developed a new calibration method for the system to deal with an actual nuclear disaster, and quantitative surface deposition densities of radionuclides, such as (134)Cs and (137)Cs, and kerma rates of each radionuclide can be calculated. We carried out car-borne survey over northeastern and eastern Japan (Tohoku and Kanto regions of Honshu) from 25 September through 7 October 2012. We discuss results of the distribution of ambient dose equivalent rate H(∗)(10), (134)Cs and (137)Cs surface deposition densities, spatial variation of (134)Cs/(137)Cs ratio, and the relationship between surface deposition densities of (134)Cs/(137)Cs and H(∗)(10). The ratio of (134)Cs/(137)Cs was nearly constant within our measurement precision, with average 1.06 ± 0.04 in northeastern and eastern Japan (decay-corrected to 11 March, 2011), although small variations from the average were observed. Copyright © 2014 Elsevier Ltd. All rights reserved.

Isotopic tracing for calculating the surface density of arginine-glycine-aspartic acid-containing peptide on allogeneic bone.

PubMed

Hou, Xiao-bin; Hu, Yong-cheng; He, Jin-quan

2013-02-01

To investigate the feasibility of determining the surface density of arginine-glycine-aspartic acid (RGD) peptides grafted onto allogeneic bone by an isotopic tracing method involving labeling these peptides with (125) I, evaluating the impact of the input concentration of RGD peptides on surface density and establishing the correlation between surface density and their input concentration. A synthetic RGD-containing polypeptide (EPRGDNYR) was labeled with (125) I and its specific radioactivity calculated. Reactive solutions of RGD peptide with radioactive (125) I-RGD as probe with input concentrations of 0.01 mg/mL, 0.10 mg/mL, 0.50 mg/mL, 1.00 mg/mL, 2.00 mg/mL and 4.00 mg/mL were prepared. Using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide as a cross-linking agent, reactions were induced by placing allogeneic bone fragments into reactive solutions of RGD peptide of different input concentrations. On completion of the reactions, the surface densities of RGD peptides grafted onto the allogeneic bone fragments were calculated by evaluating the radioactivity and surface areas of the bone fragments. The impact of input concentration of RGD peptides on surface density was measured and a curve constructed. Measurements by a radiodensity γ-counter showed that the RGD peptides had been labeled successfully with (125) I. The allogeneic bone fragments were radioactive after the reaction, demonstrating that the RGD peptides had been successfully grafted onto their surfaces. It was also found that with increasing input concentration, the surface density increased. It was concluded that the surface density of RGD peptides is quantitatively related to their input concentration. With increasing input concentration, the surface density gradually increases to saturation value. © 2013 Chinese Orthopaedic Association and Wiley Publishing Asia Pty Ltd.

Carrier dynamics and surface vibration-assisted Auger recombination in porous silicon

NASA Astrophysics Data System (ADS)

Zakar, Ammar; Wu, Rihan; Chekulaev, Dimitri; Zerova, Vera; He, Wei; Canham, Leigh; Kaplan, Andrey

2018-04-01

Excitation and recombination dynamics of the photoexcited charge carriers in porous silicon membranes were studied using a femtosecond pump-probe technique. Near-infrared pulses (800 nm, 60 fs) were used for the pump while, for the probe, we employed different wavelengths in the range between 3.4 and 5 μ m covering the medium wavelength infrared range. The data acquired in these experiments consist of simultaneous measurements of the transmittance and reflectance as a function of the delay time between the pump and probe for different pump fluences and probe wavelengths. To evaluate the results, we developed an optical model based on the two-dimensional Maxwell-Garnett formula, incorporating the free-carrier Drude contribution and nonuniformity of the excitation by the Wentzel-Kramers-Brillouin model. This model allowed the retrieval of information about the carrier density as a function of the pump fluence, time, and wavelength. The carrier density data were analyzed to reveal that the recombination dynamics is governed by Shockley-Read-Hall and Auger processes, whereas the diffusion has an insignificant contribution. We show that, in porous silicon samples, the Auger recombination process is greatly enhanced at the wavelength corresponding to the infrared-active vibrational modes of the molecular impurities on the surface of the pores. This observation of surface-vibration-assisted Auger recombination is not only for porous silicon in particular, but for low-dimension and bulk semiconductors in general. We estimate the time constants of Shockley-Read-Hall and Auger processes, and demonstrate their wavelength dependence for the excited carrier density in the range of 1018-10191 /cm3 . We demonstrate that both processes are enhanced by up to three orders of magnitude with respect to the bulk counterpart. In addition, we provide a plethora of the physical parameters evaluated from the experimental data, such as the dielectric function and its dependence on the injection level of the free carriers, charge-carrier scattering time related high-frequency conductivity, and the free-carrier absorption at the midwave infrared range.

Nanoscale electrical property studies of individual GeSi quantum rings by conductive scanning probe microscopy.

PubMed

Lv, Yi; Cui, Jian; Jiang, Zuimin M; Yang, Xinju

2012-11-29

The nanoscale electrical properties of individual self-assembled GeSi quantum rings (QRs) were studied by scanning probe microscopy-based techniques. The surface potential distributions of individual GeSi QRs are obtained by scanning Kelvin microscopy (SKM). Ring-shaped work function distributions are observed, presenting that the QRs' rim has a larger work function than the QRs' central hole. By combining the SKM results with those obtained by conductive atomic force microscopy and scanning capacitance microscopy, the correlations between the surface potential, conductance, and carrier density distributions are revealed, and a possible interpretation for the QRs' conductance distributions is suggested.

Probing surface states in PbS nanocrystal films using pentacene field effect transistors: controlling carrier concentration and charge transport in pentacene.

PubMed

Park, Byoungnam; Whitham, Kevin; Bian, Kaifu; Lim, Yee-Fun; Hanrath, Tobias

2014-12-21

We used a bilayer field effect transistor (FET) consisting of a thin PbS nanocrystals (NCs) film interfaced with vacuum-deposited pentacene to probe trap states in NCs. We interpret the observed threshold voltage shift in context of charge carrier trapping by PbS NCs and relate the magnitude of the threshold voltage shift to the number of trapped carriers. We explored a series of NC surface ligands to modify the interface between PbS NCs and pentacene and demonstrate the impact of interface chemistry on charge carrier density and the FET mobility in a pentacene FET.

Symmetry energy III: Isovector skins

NASA Astrophysics Data System (ADS)

Danielewicz, Paweł; Singh, Pardeep; Lee, Jenny

2017-02-01

Isoscalar density is a sum of neutron and proton densities and isovector is a normalized difference. Here, we report the experimental evidence for the displacement of the isovector and isoscalar surfaces in nuclei, by ∼ 0.9 fm from each other. We analyze data on quasielastic (QE) charge exchange (p,n) reactions, concurrently with proton and neutron elastic scattering data for the same target nuclei, following the concepts of the isoscalar and isovector potentials combined into Lane optical potential. The elastic data largely probe the geometry of the isoscalar potential and the (p,n) data largely probe a relation between the geometries of the isovector and isoscalar potentials. The targets include 48Ca, 90Zr, 120Sn and 208Pb and projectile incident energy values span the range of (10-50) MeV. In our fit to elastic and QE charge-exchange data, we allow the values of isoscalar and isovector radii, diffusivities and overall potential normalizations to float away from those in the popular Koning and Delaroche parametrization. We find that the best-fit isovector radii are consistently larger than isoscalar and the best-fit isovector surfaces are steeper. Upon identifying the displacement of the potential surfaces with the displacement of the surfaces for the densities in the Skyrme-Hartree-Fock calculations, and by supplementing the results with those from analyzing excitation energies to isobaric analog states in the past, we arrive at the slope and value of the symmetry energy at normal density of 70 < L < 101 MeV and 33.5 < aaV < 36.4 MeV, respectively.

Strong influence of coadsorbate interaction on CO desorption dynamics on Ru(0001) probed by ultrafast x-ray spectroscopy and ab initio simulations

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

Xin, H.; LaRue, J.; Oberg, H.

2015-04-16

We show that coadsorbed oxygen atoms have a dramatic influence on the CO desorption dynamics from Ru(0001). In contrast to the precursor-mediated desorption mechanism on Ru(0001), the presence of surface oxygen modifies the electronic structure of Ru atoms such that CO desorption occurs predominantly via the direct pathway. This phenomenon is directly observed in an ultrafast pump-probe experiment using a soft x-ray free-electron laser to monitor the dynamic evolution of the valence electronic structure of the surface species. This is supported with the potential of mean force along the CO desorption path obtained from density-functional theory calculations. Charge density distributionmore » and frozen-orbital analysis suggest that the oxygen-induced reduction of the Pauli repulsion, and consequent increase of the dative interaction between the CO 5σ and the charged Ru atom, is the electronic origin of the distinct desorption dynamics. Ab initio molecular dynamics simulations of CO desorption from Ru(0001) and oxygen-coadsorbed Ru(0001) provide further insights into the surface bond-breaking process.« less

Vibrational Surface Electron-Energy-Loss Spectroscopy Probes Confined Surface-Phonon Modes

NASA Astrophysics Data System (ADS)

Lourenço-Martins, Hugo; Kociak, Mathieu

2017-10-01

Recently, two reports [Krivanek et al. Nature (London) 514, 209 (2014), 10.1038/nature13870, Lagos et al. Nature (London) 543, 529 (2017), 10.1038/nature21699] have demonstrated the amazing possibility to probe vibrational excitations from nanoparticles with a spatial resolution much smaller than the corresponding free-space phonon wavelength using electron-energy-loss spectroscopy (EELS). While Lagos et al. evidenced a strong spatial and spectral modulation of the EELS signal over a nanoparticle, Krivanek et al. did not. Here, we show that discrepancies among different EELS experiments as well as their relation to optical near- and far-field optical experiments [Dai et al. Science 343, 1125 (2014), 10.1126/science.1246833] can be understood by introducing the concept of confined bright and dark surface phonon modes, whose density of states is probed by EELS. Such a concise formalism is the vibrational counterpart of the broadly used formalism for localized surface plasmons [Ouyang and Isaacson Philos. Mag. B 60, 481 (1989), 10.1080/13642818908205921, García de Abajo and Aizpurua Phys. Rev. B 56, 15873 (1997), 10.1103/PhysRevB.56.15873, García de Abajo and Kociak Phys. Rev. Lett. 100, 106804 (2008), 10.1103/PhysRevLett.100.106804, Boudarham and Kociak Phys. Rev. B 85, 245447 (2012), 10.1103/PhysRevB.85.245447]; it makes it straightforward to predict or interpret phenomena already known for localized surface plasmons such as environment-related energy shifts or the possibility of 3D mapping of the related surface charge densities [Collins et al. ACS Photonics 2, 1628 (2015), 10.1021/acsphotonics.5b00421].

In-surface confinement of topological insulator nanowire surface states

NASA Astrophysics Data System (ADS)

Chen, Fan W.; Jauregui, Luis A.; Tan, Yaohua; Manfra, Michael; Klimeck, Gerhard; Chen, Yong P.; Kubis, Tillmann

2015-09-01

The bandstructures of [110] and [001] Bi2Te3 nanowires are solved with the atomistic 20 band tight binding functionality of NEMO5. The theoretical results reveal: The popular assumption that all topological insulator (TI) wire surfaces are equivalent is inappropriate. The Fermi velocity of chemically distinct wire surfaces differs significantly which creates an effective in-surface confinement potential. As a result, topological insulator surface states prefer specific surfaces. Therefore, experiments have to be designed carefully not to probe surfaces unfavorable to the surface states (low density of states) and thereby be insensitive to the TI-effects.

Influence of surface oxidation on ion dynamics and capacitance in porous and nonporous carbon electrodes

DOE PAGES

Dyatkin, Boris; Zhang, Yu; Mamontov, Eugene; ...

2016-04-07

Here, we investigate the influence of surface chemistry and ion confinement on capacitance and electrosorption dynamics of room-temperature ionic liquids (RTILs) in supercapacitors. Using air oxidation and vacuum annealing, we produced defunctionalized and oxygen-rich surfaces of carbide-derived carbons (CDCs) and graphene nanoplatelets (GNPs). While oxidized surfaces of porous CDCs improve capacitance and rate handling abilities of ions, defunctionalized nonporous GNPs improve charge storage densities on planar electrodes. Quasi-elastic neutron scattering (QENS) and inelastic neutron scattering (INS) probed the structure, dynamics, and orientation of RTIL ions confined in divergently functionalized pores. Oxidized, ionophilic surfaces draw ions closer to pore surfaces andmore » enhance potential-driven ion transport during electrosorption. Molecular dynamics (MD) simulations corroborated experimental data and demonstrated the significance of surface functional groups on ion orientations, accumulation densities, and capacitance.« less

Study of plasma parameters in a pulsed plasma accelerator using triple Langmuir probe

NASA Astrophysics Data System (ADS)

Borthakur, S.; Talukdar, N.; Neog, N. K.; Borthakur, T. K.

2018-01-01

A Triple Langmuir Probe (TLP) has been used to study plasma parameters of a transient plasma produced in a newly developed Pulsed Plasma Accelerator system. In this experiment, a TLP with a capacitor based current mode biasing circuit was used that instantaneously gives voltage traces in an oscilloscope which are directly proportional to the plasma electron temperature and density. The electron temperature (Te) and plasma density (ne) of the plasma are measured with the help of this probe and found to be 24.13 eV and 3.34 × 1021/m3 at the maximum energy (-15 kV) of the system, respectively. An attempt was also made to analyse the time-dependent fluctuations in plasma parameters detected by the highly sensitive triple probe. In addition to this, the variation of these parameters under different discharge voltages was studied. The information obtained from these parameters is the initial diagnostics of a new device which is to be dedicated to study the impact of high heat flux plasma stream upon material surfaces inside an ITER like tokamak.

Effect of dopant density on contact potential difference across n-type GaAs homojunctions using Kelvin Probe Force Microscopy

NASA Astrophysics Data System (ADS)

Boumenou, C. Kameni; Urgessa, Z. N.; Djiokap, S. R. Tankio; Botha, J. R.; Nel, J.

2018-04-01

In this study, cross-sectional surface potential imaging of n+/semi-insulating GaAs junctions is investigated by using amplitude mode kelvin probe force microscopy. The measurements have shown two different potential profiles, related to the difference in surface potential between the semi-insulating (SI) substrate and the epilayers. It is shown that the contact potential difference (CPD) between the tip and the sample is higher on the semi-insulating substrate side than on the n-type epilayer side. This change in CPD across the interface has been explained by means of energy band diagrams indicating the relative Fermi level positions. In addition, it has also been found that the CPD values across the interface are much smaller than the calculated values (on average about 25% of the theoretical values) and increase with the electron density. Therefore, the results presented in study are only in qualitative agreement with the theory.

Excitation-dependent carrier lifetime and diffusion length in bulk CdTe determined by time-resolved optical pump-probe techniques

NASA Astrophysics Data System (ADS)

Ščajev, Patrik; Miasojedovas, Saulius; Mekys, Algirdas; Kuciauskas, Darius; Lynn, Kelvin G.; Swain, Santosh K.; JarašiÅ«nas, Kestutis

2018-01-01

We applied time-resolved pump-probe spectroscopy based on free carrier absorption and light diffraction on a transient grating for direct measurements of the carrier lifetime and diffusion coefficient D in high-resistivity single crystal CdTe (codoped with In and Er). The bulk carrier lifetime τ decreased from 670 ± 50 ns to 60 ± 10 ns with increase of excess carrier density N from 1016 to 5 × 1018 cm-3 due to the excitation-dependent radiative recombination rate. In this N range, the carrier diffusion length dropped from 14 μm to 6 μm due to lifetime decrease. Modeling of in-depth (axial) and in-plane (lateral) carrier diffusion provided the value of surface recombination velocity S = 6 × 105 cm/s for the untreated surface. At even higher excitations, in the 1019-3 × 1020 cm-3 density range, D increase from 5 to 20 cm2/s due to carrier degeneracy was observed.

Probing surface sites of TiO2: reactions with [HRe(CO)5] and [CH3Re(CO)5].

PubMed

Lobo-Lapidus, Rodrigo J; Gates, Bruce C

2010-10-04

Two carbonyl complexes of rhenium, [HRe(CO)(5)] and [CH(3)Re(CO)(5)], were used to probe surface sites of TiO(2) (anatase). These complexes were adsorbed from the gas phase onto anatase powder that had been treated in flowing O(2) or under vacuum to vary the density of surface OH sites. Infrared (IR) spectra demonstrate the variation in the number of sites, including Ti(+3)-OH and Ti(+4)-OH. IR and extended X-ray absorption fine structure (EXAFS) spectra show that chemisorption of the rhenium complexes led to their decarbonylation, with formation of surface-bound rhenium tricarbonyls, when [HRe(CO)(5)] was adsorbed, or rhenium tetracarbonyls, when [CH(3)Re(CO)(5)] was adsorbed. These reactions were accompanied by the formation of water and surface carbonates and removal of terminal hydroxyl groups associated with Ti(+3) and Ti(+4) ions on the anatase. Data characterizing the samples after adsorption of [HRe(CO)(5)] or [CH(3)Re(CO)(5)] determined a ranking of the reactivity of the surface OH sites, with the Ti(+3)-OH groups being the more reactive towards the rhenium complexes but the less likely to be dehydroxylated. The two rhenium pentacarbonyl probes provided complementary information, suggesting that the carbonate species originate from carbonyl ligands initially bonded to the rhenium and from hydroxyl groups of the titania surface, with the reaction leading to the formation of water and bridging hydroxyl groups on the titania. The results illustrate the value of using a family of organometallic complexes as probes of oxide surface sites.

LETTER TO THE EDITOR: The quasi-coherent signature of enhanced Dα H-mode in Alcator C-Mod

NASA Astrophysics Data System (ADS)

Snipes, J. A.; La Bombard, B.; Greenwald, M.; Hutchinson, I. H.; Irby, J.; Lin, Y.; Mazurenko, A.; Porkolab, M.

2001-04-01

The steady-state H-mode regime found at moderate to high density in Alcator C-Mod, known as enhanced Dα (EDA) H-mode, appears to be maintained by a continuous quasi-coherent (QC) mode in the steep edge gradient region. Large amplitude density and magnetic fluctuations with typical frequencies of about 100 kHz are driven by the QC mode. These fluctuations are measured in the steep edge gradient region by inserting a fast-scanning probe containing two poloidally separated Langmuir probes and a poloidal field pick-up coil. As the probe approaches the plasma edge, clear magnetic fluctuations were measured within about 2 cm of the last-closed flux surface (LCFS). The mode amplitude falls off rapidly with distance from the plasma centre with an exponential decay length of kr≈1.5 cm-1, measured 10 cm above the outboard midplane. The root-mean-square amplitude of the fluctuation extrapolated to the LCFS was θ≈5 G. The density fluctuations, on the other hand, were visible on the Langmuir probe only when it was within a few millimetres of the LCFS. The potential and density fluctuations were sufficiently in phase to enhance particle transport at the QC mode frequency. These results show that the QC signature of the EDA H-mode is an electromagnetic mode that appears to be responsible for the enhanced particle transport in the plasma edge.

Remote Sensing of the Solar Wind Density, Speed, and Temperature in the Region between the Sun and Parker Solar Probe

NASA Astrophysics Data System (ADS)

Davila, J. M.; Reginald, N. L.

2017-12-01

A coronagraph is the tool of choice to understand and observe the structure of the corona from space. The novel coronagraph concept presented her provides a new scientific capability that will allow the measurement of density, temperature, and flow velocity in the solar atmosphere. This instrument will provide the first remote sensing measurement of the global solar wind temperature, density, and flow speed in the regions between 3 and 8 Rsun. It is in this region that the manority of the solar wind acceleration takes place, and where the ion compsition of the solar wind is "frozen in". This is also the region of the corona that links the surface of the Sun to the Parker Solar Probe and to Solar Orbiter. The observations suggested here would dramatically improve our understanding of solar wind formation and evolution in this critical region.

Probing functional groups at the gas-aerosol interface using heterogeneous titration reactions: a tool for predicting aerosol health effects?

PubMed

Setyan, Ari; Sauvain, Jean-Jacques; Guillemin, Michel; Riediker, Michael; Demirdjian, Benjamin; Rossi, Michel J

2010-12-17

The complex chemical and physical nature of combustion and secondary organic aerosols (SOAs) in general precludes the complete characterization of both bulk and interfacial components. The bulk composition reveals the history of the growth process and therefore the source region, whereas the interface controls--to a large extent--the interaction with gases, biological membranes, and solid supports. We summarize the development of a soft interrogation technique, using heterogeneous chemistry, for the interfacial functional groups of selected probe gases [N(CH(3))(3), NH(2)OH, CF(3)COOH, HCl, O(3), NO(2)] of different reactivity. The technique reveals the identity and density of surface functional groups. Examples include acidic and basic sites, olefinic and polycyclic aromatic hydrocarbon (PAH) sites, and partially and completely oxidized surface sites. We report on the surface composition and oxidation states of laboratory-generated aerosols and of aerosols sampled in several bus depots. In the latter case, the biomarker 8-hydroxy-2'-deoxyguanosine, signaling oxidative stress caused by aerosol exposure, was isolated. The increase in biomarker levels over a working day is correlated with the surface density N(i)(O3) of olefinic and/or PAH sites obtained from O(3) uptakes as well as with the initial uptake coefficient, γ(0), of five probe gases used in the field. This correlation with γ(0) suggests the idea of competing pathways occurring at the interface of the aerosol particles between the generation of reactive oxygen species (ROS) responsible for oxidative stress and cellular antioxidants.

Three-dimensional atom probe tomography of oxide, anion, and alkanethiolate coatings on gold.

PubMed

Zhang, Yi; Hillier, Andrew C

2010-07-15

We have used three-dimensional atom probe tomography to analyze several nanometer-thick and monomolecular films on gold surfaces. High-purity gold wire was etched by electropolishing to create a sharp tip suitable for field evaporation with a radius of curvature of <100 nm. The near-surface region of a freshly etched gold tip was examined with the atom probe at subnanometer spatial resolution and with atom-level composition accuracy. A thin contaminant layer, primarily consisting of water and atmospheric gases, was observed on a fresh tip. This sample exhibited crystalline lattice spacings consistent with the interlayer spacing of {200} lattice planes of bulk gold. A thin oxide layer was created on the gold surface via plasma oxidation, and the thickness and composition of this layer was measured. Clear evidence of a nanometer-thick oxide layer was seen coating the gold tip, and the atomic composition of the oxide layer was consistent with the expected stoichiometry for gold oxide. Monomolecular anions layers of Br(-) and I(-) were created via adsorption from aqueous solutions onto the gold. Atom probe data verified the presence of the monomolecular anion layers on the gold surface, with ion density values consistent with literature values. A hexanethiolate monolayer was coated onto the gold tip, and atom probe analysis revealed a thin film whose ion fragments were consistent with the molecular composition of the monolayer and a surface coverage similar to that expected from literature. Details of the various coating compositions and structures are presented, along with discussion of the reconstruction issues associated with properly analyzing these thin-film systems.

Propulsion Instruments for Small Hall Thruster Integration

NASA Technical Reports Server (NTRS)

Johnson, Lee K.; Conroy, David G.; Spanjers, Greg G.; Bromaghim, Daron R.

2001-01-01

Planning and development are underway for the propulsion instrumentation necessary for the next AFRL electric propulsion flight project, which includes both a small Hall thruster and a micro-PPT. These instruments characterize the environment induced by the thruster and the associated data constitute part of a 'user's manual' for these thrusters. Several instruments probe the back-flow region of the thruster plume, and the data are intended for comparison with detailed numerical models in this region. Specifically, an ion probe is under development to determine the energy and species distributions, and a Langmuir probe will be employed to characterize the electron density and temperature. Other instruments directly measure the effects of thruster operation on spacecraft thermal control surfaces, optical surfaces, and solar arrays. Specifically, radiometric, photometric, and solar-cell-based sensors are under development. Prototype test data for most sensors should be available, together with details of the instrumentation subsystem and spacecraft interface.

Characterization of atomic oxygen from an ECR plasma source

NASA Astrophysics Data System (ADS)

Naddaf, M.; Bhoraskar, V. N.; Mandale, A. B.; Sainkar, S. R.; Bhoraskar, S. V.

2002-11-01

A low-power microwave-assisted electron cyclotron resonance (ECR) plasma system is shown to be a powerful and effective source of atomic oxygen (AO) useful in material processing. A 2.45 GHz microwave source with maximum power of 600 W was launched into the cavity to generate the ECR plasma. A catalytic nickel probe was used to determine the density of AO. The density of AO is studied as a function of pressure and axial position of the probe in the plasma chamber. It was found to vary from ~1×1020 to ~10×1020 atom m-3 as the plasma pressure was varied from 0.8 to 10 mTorr. The effect of AO in oxidation of silver is investigated by gravimetric analysis. The stoichiometric properties of the oxide are studied using the x-ray photoelectron spectroscopy as well as energy dispersive x-ray analysis. The degradation of the silver surface due to sputtering effect was viewed by scanning electron spectroscopy. The sputtering yield of oxygen ions in the plasma is calculated using the TRIM code. The effects of plasma pressure and the distance from the ECR zone on the AO density were also investigated. The density of AO measured by oxidation of silver is in good agreement with results obtained from the catalytic nickel probe.

Laser Driven Compression Equations of State and Hugoniot Pressure Measurements in Thick Solid Metallic Targets at ˜0.17-13 TW/cm2

NASA Astrophysics Data System (ADS)

Remo, John L.

2010-10-01

An electro-optic laser probe was developed to obtain parameters for high energy density equations of state (EoS), Hugoniot pressures (PH), and strain rates for high energy density laser irradiation intensity, I, experiments at ˜170 GW/cm2 (λ = 1064 nm) to ˜13 TW/cm2 (λ = 527 nm) on Al, Cu, Ti, Fe, Ni metal targets in a vacuum. At I ˜7 TW/cm2 front surface plasma pressures and temperatures reached 100's GPa and over two million K. Rear surface PH ranged from 7-120 GPa at average shock wave transit velocities 4.2-8.5 km/s, depending on target thickness and I. A surface plasma compression ˜100's GPa generated an impulsive radial expanding shock wave causing compression, rarefactions, and surface elastic and plastic deformations depending on I. A laser/fiber optic system measured rear surface shock wave emergence and particle velocity with ˜3 GHz resolution by monitoring light deflection from diamond polished rear surfaces of malleable metallic targets, analogous to an atomic force microscope. Target thickness, ˜0.5-2.9 mm, prevented front surface laser irradiation penetration, due to low radiation skin depth, from altering rear surface reflectivity (refractive index). At ˜10 TW electromagnetic plasma pulse noise generated from the target chamber overwhelmed detector signals. Pulse frequency analysis using Moebius loop antennae probed transient noise characteristics. Average shock (compression) and particle (rear surface displacement) velocity measurements determined rear surface PH and GPa) EoS that are compared with gas guns.

Effect of surface roughness and subsurface damage on grazing-incidence x-ray scattering and specular reflectance.

PubMed

Lodha, G S; Yamashita, K; Kunieda, H; Tawara, Y; Yu, J; Namba, Y; Bennett, J M

1998-08-01

Grazing-incidence specular reflectance and near-specular scattering were measured at Al-K(alpha) (1.486-keV, 8.34-?) radiation on uncoated dielectric substrates whose surface topography had been measured with a scanning probe microscope and a mechanical profiler. Grazing-incidence specular reflectance was also measured on selected substrates at the Cu-K(alpha) (8.047-keV, 1.54-?) wavelength. Substrates included superpolished and conventionally polished fused silica; SiO(2) wafers; superpolished and precision-ground Zerodur; conventionally polished, float-polished, and precision-ground BK-7 glass; and superpolished and precision-ground silicon carbide. Roughnesses derived from x-ray specular reflectance and scattering measurements were in good agreement with topographic roughness values measured with a scanning probe microscope (atomic force microscope) and a mechanical profiler that included similar ranges of surface spatial wavelengths. The specular reflectance was also found to be sensitive to the density of polished surface layers and subsurface damage down to the penetration depth of the x rays. Density gradients and subsurface damage were found in the superpolished fused-silica and precision-ground Zerodur samples. These results suggest that one can nondestructively evaluate subsurface damage in transparent materials using grazing-incidence x-ray specular reflectance in the 1.5-8-keV range.

In situ oligonucleotide synthesis on poly(dimethylsiloxane): a flexible substrate for microarray fabrication

PubMed Central

Moorcroft, Matthew J.; Meuleman, Wouter R. A.; Latham, Steven G.; Nicholls, Thomas J.; Egeland, Ryan D.; Southern, Edwin M.

2005-01-01

In this paper, we demonstrate in situ synthesis of oligonucleotide probes on poly(dimethylsiloxane) (PDMS) microchannels through use of conventional phosphoramidite chemistry. PDMS polymer was moulded into a series of microchannels using standard soft lithography (micro-moulding), with dimensions <100 μm. The surface of the PDMS was derivatized by exposure to ultraviolet/ozone followed by vapour phase deposition of glycidoxypropyltrimethoxysilane and reaction with poly(ethylene glycol) spacer, resulting in a reactive surface for oligonucleotide coupling. High, reproducible yields were achieved for both 6mer and 21mer probes as assessed by hybridization to fluorescent oligonucleotides. Oligonucleotide surface density was comparable with that obtained on glass substrates. These results suggest PDMS as a stable and flexible alternative to glass as a suitable substrate in the fabrication and synthesis of DNA microarrays. PMID:15870385

Label-Free Potentiometry for Detecting DNA Hybridization Using Peptide Nucleic Acid and DNA Probes

PubMed Central

Goda, Tatsuro; Singi, Ankit Balram; Maeda, Yasuhiro; Matsumoto, Akira; Torimura, Masaki; Aoki, Hiroshi; Miyahara, Yuji

2013-01-01

Peptide nucleic acid (PNA) has outstanding affinity over DNA for complementary nucleic acid sequences by forming a PNA-DNA heterodimer upon hybridization via Watson-Crick base-pairing. To verify whether PNA probes on an electrode surface enhance sensitivity for potentiometric DNA detection or not, we conducted a comparative study on the hybridization of PNA and DNA probes on the surface of a 10-channel gold electrodes microarray. Changes in the charge density as a result of hybridization at the solution/electrode interface on the self-assembled monolayer (SAM)-formed microelectrodes were directly transformed into potentiometric signals using a high input impedance electrometer. The charge readout allows label-free, reagent-less, and multi-parallel detection of target oligonucleotides without any optical assistance. The differences in the probe lengths between 15- to 22-mer dramatically influenced on the sensitivity of the PNA and DNA sensors. Molecular type of the capturing probe did not affect the degree of potential shift. Theoretical model for charged rod-like duplex using the Gouy-Chapman equation indicates the dominant effect of electrostatic attractive forces between anionic DNA and underlying electrode at the electrolyte/electrode interface in the potentiometry. PMID:23435052

Probing ultrafast dynamics of solid-density plasma generated by high-contrast intense laser pulses

NASA Astrophysics Data System (ADS)

Jana, Kamalesh; Blackman, David R.; Shaikh, Moniruzzaman; Lad, Amit D.; Sarkar, Deep; Dey, Indranuj; Robinson, Alex P. L.; Pasley, John; Ravindra Kumar, G.

2018-01-01

We present ultrafast dynamics of solid-density plasma created by high-contrast (picosecond contrast ˜10-9), high-intensity (˜4 × 1018 W/cm2) laser pulses using time-resolved pump-probe Doppler spectrometry. Experiments show a rapid rise in blue-shift at early time delay (2-4.3 ps) followed by a rapid fall (4.3-8.3 ps) and then a slow rise in blue-shift at later time delays (>8.3 ps). Simulations show that the early-time observations, specifically the absence of any red-shifting of the reflected probe, can only be reproduced if the front surface is unperturbed by the laser pre-pulse at the moment that the high intensity pulse arrives. A flexible diagnostic which is capable of diagnosing the presence of low-levels of pre-plasma formation would be useful for potential applications in laser-produced proton and ion production, such as cancer therapy and security imaging.

Plasma Potential and Langmuir Probe Measurements in the Near-field Plume of the NASA 300M Hall Thruster

NASA Technical Reports Server (NTRS)

Herman, Daniel A; Shastry, Rohit; Huang, Wensheng; Soulas, George C.; KamHawi, Hani

2012-01-01

In order to aid in the design of high-power Hall thrusters and provide experimental validation for existing modeling efforts, plasma potential and Langmuir probe measurements were performed in the near-field plume of the NASA 300M Hall thruster. A probe array consisting of a Faraday probe, Langmuir probe, and emissive probe was used to interrogate the plume from approximately 0.1 - 2.0 DT,m downstream of the thruster exit plane at four operating conditions: 300 V, 400 V, and 500 V at 20 kW as well as 300 V at 10 kW. Results show that the acceleration zone and high-temperature region were contained within 0.3 DT,m from the exit plane at all operating conditions. Isothermal lines were shown to strongly follow magnetic field lines in the nearfield, with maximum temperatures ranging from 19 - 27 eV. The electron temperature spatial distribution created large drops in measured floating potentials in front of the magnetic pole surfaces where the plasma density was small, which suggests strong sheaths at these surfaces. The data taken have provided valuable information for future design and modeling validation, and complements ongoing internal measurement efforts on the NASA 300 M.

Measurement of the lunar neutron density profile. [Apollo 17 flight

NASA Technical Reports Server (NTRS)

Woolum, D. S.; Burnett, D. S.; Furst, M.; Weiss, J. R.

1974-01-01

An in situ measurement of the lunar neutron density from 20 to 400 g/sq cm depth between the lunar surface was made by the Apollo 17 Lunar Neutron Probe Experiment using particle tracks produced by the B10(n, alpha)Li7 reaction. Both the absolute magnitude and depth profile of the neutron density are in good agreement with past theoretical calculations. The effect of cadmium absorption on the neutron density and in the relative Sm149 to Gd157 capture rates obtained experimentally implies that the true lunar Gd157 capture rate is about one half of that calculated theoretically.

A Floating Potential Method for Determining Ion Density

NASA Astrophysics Data System (ADS)

Evans, John D.; Chen, Francis F.

2001-10-01

The density n in partially ionized discharges is often found from the saturation ion current Ii of a cylindrical Langmuir probe. Collisionless probe theories, however, disagree with measured I - V curves probably because of collisions^1. We use a heuristic method that yields n from probe data agreeing with microwave interferometry. Probe current I is raised to the 4/3 power and fitted to a straight line on an I^4/3-V plot. The line is extrapolated to the floating potential V_f, thus approximating I_i(V_f). The sheath thickness d_sh for V = Vf is calculated from the Child-Langmuir (CL) law, and applying the Bohm sheath criterion to the surface at r_sh = Rp + d_sh yields n when Ii = I_i(V_f). This method works, but it cannot be justified by theory. Neglected are (a) cylindrical convergence of the ion charge, (b) finite ion energy at r = r_sh, (c) ions orbiting the probe, and (d) escape of ions axially. The Allen-Boyd-Reynolds theory, which treats (a) and (b) and neglects (c) and (d), gives too low n's. Apparently the errors self-cancel, and the simple Vf method gives the right result. ^1 F.F. Chen, Phys. Plasmas 8, 3029 (2001).

Plasma potential and electron temperature evaluated by ball-pen and Langmuir probes in the COMPASS tokamak

NASA Astrophysics Data System (ADS)

Dimitrova, M.; Popov, Tsv K.; Adamek, J.; Kovačič, J.; Ivanova, P.; Hasan, E.; López-Bruna, D.; Seidl, J.; Vondráček, P.; Dejarnac, R.; Stöckel, J.; Imríšek, M.; Panek, R.; the COMPASS Team

2017-12-01

The radial distributions of the main plasma parameters in the scrape-off-layer of the COMPASS tokamak are measured during L-mode and H-mode regimes by using both Langmuir and ball-pen probes mounted on a horizontal reciprocating manipulator. The radial profile of the plasma potential derived previously from Langmuir probes data by using the first derivative probe technique is compared with data derived using ball-pen probes. A good agreement can be seen between the data acquired by the two techniques during the L-mode discharge and during the H-mode regime within the inter-ELM periods. In contrast with the first derivative probe technique, the ball-pen probe technique does not require a swept voltage and, therefore, the temporal resolution is only limited by the data acquisition system. In the electron temperature evaluation, in the far scrape-off layer and in the limiter shadow, where the electron energy distribution is Maxwellian, the results from both techniques match well. In the vicinity of the last closed flux surface, where the electron energy distribution function is bi-Maxwellian, the ball-pen probe technique results are in agreement with the high-temperature components of the electron distribution only. We also discuss the application of relatively large Langmuir probes placed in parallel and perpendicularly to the magnetic field lines to studying the main plasma parameters. The results obtained by the two types of the large probes agree well. They are compared with Thomson scattering data for electron temperatures and densities. The results for the electron densities are compared also with the results from ASTRA code calculation of the electron source due to the ionization of the neutrals by fast electrons and the origin of the bi-Maxwellian electron energy distribution function is briefly discussed.

Application of electron stimulated desorption techniques to measure the isotherm and the mean residence time of hydrogen physisorbed on a metal surface

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

Arakawa, Ichiro, E-mail: ich.arakawa@gakushuin.ac.jp; Shimizu, Hideyuki; Kawarabuki, Taku

2015-03-15

Electron stimulated desorption techniques were applied to probe the density of H{sub 2} physisorbed on a cold surface. The adsorption isotherm of H{sub 2} on a copper surface was measured in the equilibrium pressure range between 10{sup −9} and 10{sup −4} Pa at surface temperatures of 6.5 and 4.2 K. The mean residence times of H{sub 2} on copper were obtained from the observation of the time development of the surface density in a transitional state approaching equilibrium, and are 50–500 s for the coverage between 1 and 0.18 at 4.2 K of the substrate temperature. The adsorption energies of 1.18–1.27 kJ/mol, and themore » condensation coefficient of 0.074–0.018 were also deduced.« less

Detection of Matrix Crack Density of CFRP using an Electrical Potential Change Method with Multiple Probes

NASA Astrophysics Data System (ADS)

Todoroki, Akira; Omagari, Kazuomi

Carbon Fiber Reinforced Plastic (CFRP) laminates are adopted for fuel tank structures of next generation space rockets or automobiles. Matrix cracks may cause fuel leak or trigger fatigue damage. A monitoring system of the matrix crack density is required. The authors have developed an electrical resistance change method for the monitoring of delamination cracks in CFRP laminates. Reinforcement fibers are used as a self-sensing system. In the present study, the electric potential method is adopted for matrix crack density monitoring. Finite element analysis (FEA) was performed to investigate the possibility of monitoring matrix crack density using multiple electrodes mounted on a single surface of a specimen. The FEA reveals the matrix crack density increases electrical resistance for a target segment between electrodes. Experimental confirmation was also performed using cross-ply laminates. Eight electrodes were mounted on a single surface of a specimen using silver paste after polishing of the specimen surface with sandpaper. The two outermost electrodes applied electrical current, and the inner electrodes measured electric voltage changes. The slope of electrical resistance during reloading is revealed to be an appropriate index for the detection of matrix crack density.

Electric-field noise from carbon-adatom diusion on a Au(110) surface: first-principles calculations and experiments

NASA Astrophysics Data System (ADS)

Sadeghpour, Hossein; Kim, Eunja; Safavi-Naini, Arghavan; Weck, Philippe; Hite, Dustin; McKay, Kyle; Pappas, David

2017-04-01

The decoherence of trapped-ion quantum gates due to heating of their motional modes is a fundamental science and engineering challenge. Mitigating this noise, is fundamental to efficient and scalable operations in ion microtraps. To understand heating at the trap-electrode surfaces, we investigate the possible source of noise by focusing on the diffusion of carbon-containing adsorbates onto the Au(110) surface. Using density functional theory and detailed scanning probe microscopy, we show that the diffusive motion of carbon adatom on gold surface significantly affect the energy landscape and adatom dipole moment variation. A model for the diffusion noise, which varies quadratically with the variation of the dipole moment, qualitatively reproduces the measured noise spectrum, and the estimate of the noise spectral density is in accord with measured values.

In-flight calibration of mesospheric rocket plasma probes

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

Havnes, Ove; University Studies Svalbard; Hartquist, Thomas W.

Many effects and factors can influence the efficiency of a rocket plasma probe. These include payload charging, solar illumination, rocket payload orientation and rotation, and dust impact induced secondary charge production. As a consequence, considerable uncertainties can arise in the determination of the effective cross sections of plasma probes and measured electron and ion densities. We present a new method for calibrating mesospheric rocket plasma probes and obtaining reliable measurements of plasma densities. This method can be used if a payload also carries a probe for measuring the dust charge density. It is based on that a dust probe's effectivemore » cross section for measuring the charged component of dust normally is nearly equal to its geometric cross section, and it involves the comparison of variations in the dust charge density measured with the dust detector to the corresponding current variations measured with the electron and/or ion probes. In cases in which the dust charge density is significantly smaller than the electron density, the relation between plasma and dust charge density variations can be simplified and used to infer the effective cross sections of the plasma probes. We illustrate the utility of the method by analysing the data from a specific rocket flight of a payload containing both dust and electron probes.« less

In-flight calibration of mesospheric rocket plasma probes.

PubMed

Havnes, Ove; Hartquist, Thomas W; Kassa, Meseret; Morfill, Gregor E

2011-07-01

Many effects and factors can influence the efficiency of a rocket plasma probe. These include payload charging, solar illumination, rocket payload orientation and rotation, and dust impact induced secondary charge production. As a consequence, considerable uncertainties can arise in the determination of the effective cross sections of plasma probes and measured electron and ion densities. We present a new method for calibrating mesospheric rocket plasma probes and obtaining reliable measurements of plasma densities. This method can be used if a payload also carries a probe for measuring the dust charge density. It is based on that a dust probe's effective cross section for measuring the charged component of dust normally is nearly equal to its geometric cross section, and it involves the comparison of variations in the dust charge density measured with the dust detector to the corresponding current variations measured with the electron and/or ion probes. In cases in which the dust charge density is significantly smaller than the electron density, the relation between plasma and dust charge density variations can be simplified and used to infer the effective cross sections of the plasma probes. We illustrate the utility of the method by analysing the data from a specific rocket flight of a payload containing both dust and electron probes.

A novel probe density controllable electrochemiluminescence biosensor for ultra-sensitive detection of Hg2+ based on DNA hybridization optimization with gold nanoparticles array patterned self-assembly platform.

PubMed

Gao, Wenhua; Zhang, An; Chen, Yunsheng; Chen, Zixuan; Chen, Yaowen; Lu, Fushen; Chen, Zhanguang

2013-11-15

Biosensor based on DNA hybridization holds great potential to get higher sensitivity as the optimal DNA hybridization efficiency can be achieved by controlling the distribution and orientation of probe strands on the transducer surface. In this work, an innovative strategy is reported to tap the sensitivity potential of current electrochemiluminescence (ECL) biosensing system by dispersedly anchoring the DNA beacons on the gold nanoparticles (GNPs) array which was electrodeposited on the glassy carbon electrode surface, rather than simply sprawling the coil-like strands onto planar gold surface. The strategy was developed by designing a "signal-on" ECL biosensing switch fabricated on the GNPs nanopatterned electrode surface for enhanced ultra-sensitivity detection of Hg(2+). A 57-mer hairpin-DNA labeled with ferrocene as ECL quencher and a 13-mer DNA labeled with Ru(bpy)3(2+) as reporter were hybridized to construct the signal generator in off-state. A 31-mer thymine (T)-rich capture-DNA was introduced to form T-T mismatches with the loop sequence of the hairpin-DNA in the presence of Hg(2+) and induce the stem-loop open, meanwhile the ECL "signal-on" was triggered. The peak sensitivity with the lowest detection limit of 0.1 nM was achieved with the optimal GNPs number density while exorbitant GNPs deposition resulted in sensitivity deterioration for the biosensor. We expect the present strategy could lead the renovation of the existing probe-immobilized ECL genosensor design to get an even higher sensitivity in ultralow level of target detection such as the identification of genetic diseases and disorders in basic research and clinical application. Copyright © 2013 Elsevier B.V. All rights reserved.

Single-molecule interfacial electron transfer dynamics in solar energy conversion

NASA Astrophysics Data System (ADS)

Dhital, Bharat

This dissertation work investigated the parameters affecting the interfacial electron transfer (ET) dynamics in dye-semiconductor nanoparticles (NPs) system by using single-molecule fluorescence spectroscopy and imaging combined with electrochemistry. The influence of the molecule-substrate electronic coupling, the molecular structure, binding geometry on the surface and the molecule-attachment surface chemistry on interfacial charge transfer processes was studied on zinc porphyrin-TiO2 NP systems. The fluorescence blinking measurement on TiO2 NP demonstrated that electronic coupling regulates dynamics of charge transfer processes at the interface depending on the conformation of molecule on the surface. Moreover, semiconductor surface charge induced electronic coupling of molecule which is electrostatically adsorbed on the semiconductor surface also predominantly alters the ET dynamics. Furthermore, interfacial electric field and electron accepting state density dependent ET dynamics has been dissected in zinc porphyrin-TiO2 NP system by observing the single-molecule fluorescence blinking dynamics and fluorescence lifetime with and without applied bias. The significant difference in fluorescence fluctuation and lifetime suggested the modulation of charge transfer dynamics at the interface with external electric field perturbation. Quasi-continuous distribution of fluorescence intensity with applied negative potential was attributed to the faster charge recombination due to reduced density of electron accepting states. The driving force and electron accepting state density ET dependent dynamics has also been probed in zinc porphyrin-TiO2 NP and zinc porphyrin-indium tin oxide (ITO) systems. Study of a molecule adsorbed on two different semiconductors (ITO and TiO2), with large difference in electron densities and distinct driving forces, allows us to observe the changes in rates of back electron transfer process reflected by the suppressed fluorescence blinking of molecule on ITO surface. Finally, the electric field effect on the interface properties has been probed by using surface-enhanced Raman spectroscopy and supported by density functional theory calculations in alizarin-TiO2 system. The perturbation, created by the external potential, has been observed to cause a shift and/or splitting interfacial bond vibrational mode, typical indicator of the coupling energy changes between alizarin and TiO2. Such splitting provides evidence for electric field-dependent electronic coupling changes that have a significant impact on the interfacial electron transfer dynamics.

Measurement of electron density using reactance cutoff probe

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

You, K. H.; Seo, B. H.; Kim, J. H.

2016-05-15

This paper proposes a new measurement method of electron density using the reactance spectrum of the plasma in the cutoff probe system instead of the transmission spectrum. The highly accurate reactance spectrum of the plasma-cutoff probe system, as expected from previous circuit simulations [Kim et al., Appl. Phys. Lett. 99, 131502 (2011)], was measured using the full two-port error correction and automatic port extension methods of the network analyzer. The electron density can be obtained from the analysis of the measured reactance spectrum, based on circuit modeling. According to the circuit simulation results, the reactance cutoff probe can measure themore » electron density more precisely than the previous cutoff probe at low densities or at higher pressure. The obtained results for the electron density are presented and discussed for a wide range of experimental conditions, and this method is compared with previous methods (a cutoff probe using the transmission spectrum and a single Langmuir probe).« less

Pressure effects on collective density fluctuations in water and protein solutions

PubMed Central

Russo, Daniela; Laloni, Alessio; Filabozzi, Alessandra; Heyden, Matthias

2017-01-01

Neutron Brillouin scattering and molecular dynamics simulations have been used to investigate protein hydration water density fluctuations as a function of pressure. Our results show significant differences between the pressure and density dependence of collective dynamics in bulk water and in concentrated protein solutions. Pressure-induced changes in the tetrahedral order of the water HB network have direct consequences for the high-frequency sound velocity and damping coefficients, which we find to be a sensitive probe for changes in the HB network structure as well as the wetting of biomolecular surfaces. PMID:29073065

Surface diffusion of a carbon-adatom on Au(110) surfaces

NASA Astrophysics Data System (ADS)

Kim, E.; Safavi-Naini, A.; Hite, D. A.; McKay, K. S.; Pappas, D. P.; Weck, P. F.; Sadeghpour, H. R.

We have investigated the surface diffusion of carbon-adatom on gold surfaces using density functional theory and detailed scanning probe microscopy. The decoherence of trapped-ion quantum gates due to heating of their motional modes is a fundamental science and engineering problem. In an effort to understand heating at the trap-electrode surfaces, we investigate the possible source of noise by focusing on the diffusion of carbon-containing adsorbates onto the Au(110) surface. In this study, we show how the diffusive motion of carbon adatom on gold surface significantly affects the energy landscape and adatom dipole moment variation. A simple model for the diffusion noise, which varies quadratically with the variation of the dipole moment, qualitatively reproduces the measured noise spectrum, and the estimate of the noise spectral density is in accord with measured values. Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the United States Department of Energy's NNSA under Contract DE-AC04-94AL85000.

Correlation between the Knight shift of chemisorbed CO and the Fermi level local density of states at clean platinum catalyst surfaces

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

Tong, Y.Y.; Rice, C.; Godbout, N.

1999-04-07

Due to its fundamental importance in heterogeneous catalysis, as well as in electrocatalysis, the chemisorption and reaction of CO on transition metal surfaces has been an important focus of modern surface science. Here, the NMR spectroscopy of {sup 13}CO adsorbed onto transition metal surfaces has been shown to be a very powerful probe of molecular structure and dynamics of CO itself, as well as a probe of the electronic properties of the transition metal surfaces onto which it is adsorbed. The authors have investigated the {sup 195}Pt and {sup 13}C nuclear magnetic resonance (NMR) spectroscopy of clean-surface platinum catalysts andmore » of CO chemisorbed onto Pt catalysts surfaces. They use Knight shift, relaxation, and J-coupling data to deduce information about the Fermi level local density of states (E{sub f}-LDOS) at catalyst surfaces. There is a linear correlation between the Knight shifts of chemisorbed CO and the clean surface E{sub f}-LDOS of platinum onto which the CO is bound, as determined by {sup 13}C and {sup 195}Pt NMR. The correlation amounts to {approximately} 12 ppm/Ry{sup {minus}1} {center_dot} atom{sup {minus}1}, the same as that which can be deduced for CO on palladium, as well as from the electrode potential dependence of {sup 13}C Knight shifts and infrared vibrational frequencies, {nu}{sub CO}, and the relationship between {nu}{sub CO} and the E{sub f}-LDOS at clean platinum surfaces. The ability to now directly relate meal and adsorbate electronic properties opens up new avenues for investigating metal-ligand interactions in heterogeneous catalysis and electrocatalysis.« less

The dynamics of superclusters - Initial determination of the mass density of the universe at large scales

NASA Technical Reports Server (NTRS)

Ford, H. C.; Ciardullo, R.; Harms, R. J.; Bartko, F.

1981-01-01

The radial velocities of cluster members of two rich, large superclusters have been measured in order to probe the supercluster mass densities, and simple evolutionary models have been computed to place limits upon the mass density within each supercluster. These superclusters represent true physical associations of size of about 100 Mpc seen presently at an early stage of evolution. One supercluster is weakly bound, the other probably barely bound, but possibly marginally unbound. Gravity has noticeably slowed the Hubble expansion of both superclusters. Galaxy surface-density counts and the density enhancement of Abell clusters within each supercluster were used to derive the ratio of mass densities of the superclusters to the mean field mass density. The results strongly exclude a closed universe.

Multi-Paradigm Multi-Scale Simulations for Fuel Cell Catalysts and Membranes

DTIC Science & Technology

2006-01-01

transfer studies on model systems. . Applying newly developed density functionals QM ( X3LYP ) for estimating the thermodynamics and kinetic energy...Density functional theory methods We have used many QM methods to probe chemical reaction mechanisms and find that the B3LYP and X3LYP [6] flavors of DFT...carried out QM calculations on the surface reactivity of the Pt and PtRu anode catalysts. This QM uses a new ab initio DFT-GGA method ( X3LYP ) [6

Aerogel-Positronium Technology for the Detection of Small Quantities of Organic and/or Toxic Materials

NASA Technical Reports Server (NTRS)

Petkov, Mihail P.; Jones, Steven M.

2010-01-01

The Ps-aerogel system [Ps is positronium (an electron-positron-hydrogen-like atom)] has been evaluated and optimized as a potential tool for planetary exploration missions. Different configurations of use were assessed, and the results provide a quantitative measure of the expected performance. The aerogel density is first optimized to attain maximum production of Ps that reaches the pores of the aerogel. This has been accomplished, and the optimum aerogel density is .70 mg/cm3. The aerogel is used as a concentrator for target volatile moieties, which accumulate in its open porosity over an extended period of time. For the detection of the accumulated materials, the use of Ps as a probe for the environment at the pore surface, has been proposed. This concept is based on two steps: (1) using aerogel to produce Ps and (2) using the propensity of Ps to interact differently with organic and inorganic matter. The active area of such a detector will comprise aerogel with a certain density, specific surface area, and gas permeability optimized for Ps production and gas diffusion and adsorption. The aerogel is a natural adsorber of organic molecules, which adhere to its internal surface, where their presence is detected by the Ps probe. Initial estimates indicate that, e.g., trace organic molecules in the Martian atmosphere, can be detected at the ppm level, which rivals current methods having significantly higher complexity, volume, mass, and power consumption (e.g. Raman, IR).

Divertor sheath power studies in DIII-D using fixed Langmuir probes and three-dimensional modeling of tile heat flows

NASA Astrophysics Data System (ADS)

Donovan, D.; Nygren, R.; Buchenauer, D.; Watkins, J.; Rudakov, D.; Leonard, A.; Wong, C. P. C.; Makowski, M.

2014-04-01

Experimental results are presented from the three-Langmuir probe (LP) diagnostic head of the divertor material evaluation system (DiMES) on DIII-D that confirm the size of the projected current collection area of the LPs, which is essential for properly measuring ion saturation current density (Jsat) and the sheath power transmission factor (SPTF). Also using the 3-LP DiMES head, the hypothesis that collisional effects on plasma density occurring in the magnetic sheath of the tile are responsible for a lower than expected SPTF is tested and deemed not to have a significant impact on the SPTF. Three-dimensional thermal modeling of wall tiles is presented that accounts for lateral heat conduction, temperature dependence of tile material properties and radiative heat loss from the tile surface. This modeling was developed to be used in the analysis of temperature profiles of the divertor embedded thermocouple (TC) array to obtain more accurate interpretations of TC temperature profiles to infer divertor surface heat flux than have previously been accomplished using more basic one-dimensional methods.

Atmospheric electromagnetic pulse propagation effects from thick targets in a terawatt laser target chamber.

PubMed

Remo, John L; Adams, Richard G; Jones, Michael C

2007-08-20

Generation and effects of atmospherically propagated electromagnetic pulses (EMPs) initiated by photoelectrons ejected by the high density and temperature target surface plasmas from multiterawatt laser pulses are analyzed. These laser radiation pulse interactions can significantly increase noise levels, thereby obscuring data (sometimes totally) and may even damage sensitive probe and detection instrumentation. Noise effects from high energy density (approximately multiterawatt) laser pulses (approximately 300-400 ps pulse widths) interacting with thick approximately 1 mm) metallic and dielectric solid targets and dielectric-metallic powder mixtures are interpreted as transient resonance radiation associated with surface charge fluctuations on the target chamber that functions as a radiating antenna. Effective solutions that minimize atmospheric EMP effects on internal and proximate electronic and electro-optical equipment external to the system based on systematic measurements using Moebius loop antennas, interpretations of signal periodicities, and dissipation indicators determining transient noise origin characteristics from target emissions are described. Analytic models for the effect of target chamber resonances and associated noise current and temperature in a probe diode laser are described.

Atmospheric electromagnetic pulse propagation effects from thick targets in a terawatt laser target chamber

NASA Astrophysics Data System (ADS)

Remo, John L.; Adams, Richard G.; Jones, Michael C.

2007-08-01

Generation and effects of atmospherically propagated electromagnetic pulses (EMPs) initiated by photoelectrons ejected by the high density and temperature target surface plasmas from multiterawatt laser pulses are analyzed. These laser radiation pulse interactions can significantly increase noise levels, thereby obscuring data (sometimes totally) and may even damage sensitive probe and detection instrumentation. Noise effects from high energy density (approximately multiterawatt) laser pulses (˜300-400 ps pulse widths) interacting with thick (˜1 mm) metallic and dielectric solid targets and dielectric-metallic powder mixtures are interpreted as transient resonance radiation associated with surface charge fluctuations on the target chamber that functions as a radiating antenna. Effective solutions that minimize atmospheric EMP effects on internal and proximate electronic and electro-optical equipment external to the system based on systematic measurements using Moebius loop antennas, interpretations of signal periodicities, and dissipation indicators determining transient noise origin characteristics from target emissions are described. Analytic models for the effect of target chamber resonances and associated noise current and temperature in a probe diode laser are described.

Excitation-dependent carrier lifetime and diffusion length in bulk CdTe determined by time-resolved optical pump-probe techniques

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

Ščajev, Patrik; Miasojedovas, Saulius; Mekys, Algirdas

We applied time-resolved pump-probe spectroscopy based on free carrier absorption and light diffraction on a transient grating for direct measurements of the carrier lifetime and diffusion coefficient D in high-resistivity single crystal CdTe (codoped with In and Er). The bulk carrier lifetime t decreased from 670 +/-50 ns to 60 +/- 10 ns with increase of excess carrier density N from 10 16 to 5 x 10 18cm -3 due to the excitation-dependent radiative recombination rate. In this N range, the carrier diffusion length dropped from 14 um to 6 um due to lifetime decrease. Modeling of in-depth (axial) andmore » in-plane (lateral) carrier diffusion provided the value of surface recombination velocity S = 6 x 10 5 cm/s for the untreated surface. At even higher excitations, in the 10 19-3 x 10 20 cm -3 density range, D increase from 5 to 20 cm^2/s due to carrier degeneracy was observed.« less

Excitation-dependent carrier lifetime and diffusion length in bulk CdTe determined by time-resolved optical pump-probe techniques

DOE PAGES

Ščajev, Patrik; Miasojedovas, Saulius; Mekys, Algirdas; ...

2018-01-14

We applied time-resolved pump-probe spectroscopy based on free carrier absorption and light diffraction on a transient grating for direct measurements of the carrier lifetime and diffusion coefficient D in high-resistivity single crystal CdTe (codoped with In and Er). The bulk carrier lifetime t decreased from 670 +/-50 ns to 60 +/- 10 ns with increase of excess carrier density N from 10 16 to 5 x 10 18cm -3 due to the excitation-dependent radiative recombination rate. In this N range, the carrier diffusion length dropped from 14 um to 6 um due to lifetime decrease. Modeling of in-depth (axial) andmore » in-plane (lateral) carrier diffusion provided the value of surface recombination velocity S = 6 x 10 5 cm/s for the untreated surface. At even higher excitations, in the 10 19-3 x 10 20 cm -3 density range, D increase from 5 to 20 cm^2/s due to carrier degeneracy was observed.« less

Atmospheric electromagnetic pulse propagation effects from thick targets in a terawatt laser target chamber

DOE PAGES

Remo, John L.; Adams, Richard G.; Jones, Michael C.

2007-08-16

Generation and effects of atmospherically propagated electromagnetic pulses (EMPs) initiated by photoelectrons ejected by the high density and temperature target surface plasmas from multiterawatt laser pulses are analyzed. These laser radiation pulse interactions can significantly increase noise levels, thereby obscuring data (sometimes totally) and may even damage sensitive probe and detection instrumentation. Noise effects from high energy density (approximately multiterawatt) laser pulses (~300–400 ps pulse widths) interacting with thick (~1 mm) metallic and dielectric solid targets and dielectric–metallic powder mixtures are interpreted as transient resonance radiation associated with surface charge fluctuations on the target chamber that functions as a radiatingmore » antenna. Effective solutions that minimize atmospheric EMP effects on internal and proximate electronic and electro-optical equipment external to the system based on systematic measurements using Moebius loop antennas, interpretations of signal periodicities, and dissipation indicators determining transient noise origin characteristics from target emissions are described. Analytic models for the effect of target chamber resonances and associated noise current and temperature in a probe diode laser are described.« less

Identification of the spatial location of deep trap states in AlGaN/GaN heterostructures by surface photovoltage spectroscopy

NASA Astrophysics Data System (ADS)

Jana, Dipankar; Porwal, S.; Sharma, T. K.

2017-12-01

Spatial and spectral origin of deep level defects in molecular beam epitaxy grown AlGaN/GaN heterostructures are investigated by using surface photovoltage spectroscopy (SPS) and pump-probe SPS techniques. A deep trap center ∼1 eV above the valence band is observed in SPS measurements which is correlated with the yellow luminescence feature in GaN. Capture of electrons and holes is resolved by performing temperature dependent SPS and pump-probe SPS measurements. It is found that the deep trap states are distributed throughout the sample while their dominance in SPS spectra depends on the density, occupation probability of deep trap states and the background electron density of GaN channel layer. Dynamics of deep trap states associated with GaN channel layer is investigated by performing frequency dependent photoluminescence (PL) and SPS measurements. A time constant of few millisecond is estimated for the deep defects which might limit the dynamic performance of AlGaN/GaN based devices.

Monte Carlo simulations of protein micropatterning in biomembranes: effects of immobile sticky obstacles

NASA Astrophysics Data System (ADS)

Arnold, Andreas M.; Sevcsik, Eva; Schütz, Gerhard J.

2016-09-01

Single molecule trajectories of lipids and proteins can yield valuable information about the nanoscopic organization of the plasma membrane itself. The interpretation of such trajectories, however, is complicated, as the mobility of molecules can be affected by the presence of immobile obstacles, and the transient binding of the tracers to these obstacles. We have previously developed a micropatterning approach that allows for immobilizing a plasma membrane protein and probing the diffusional behavior of a putative interaction partner in living cells. Here, we provide guidelines on how this micropatterning approach can be extended to quantify interaction parameters between plasma membrane constituents in their natural environment. We simulated a patterned membrane system and evaluated the effect of different surface densities of patterned immobile obstacles on the relative mobility as well as the surface density of diffusing tracers. In the case of inert obstacles, the size of the obstacle can be assessed from its surface density at the percolation threshold, which in turn can be extracted from the diffusion behavior of the tracer. For sticky obstacles, 2D dissociation constants can be determined from the tracer diffusion or surface density.

An electrochemiluminescent DNA sensor based on nano-gold enhancement and ferrocene quenching.

PubMed

Yao, Wu; Wang, Lun; Wang, Haiyan; Zhang, Xiaolei; Li, Ling; Zhang, Na; Pan, Le; Xing, Nannan

2013-02-15

An electrochemiluminescent DNA (ECL-DNA) sensor based on nano-gold signal enhancement (i.e. gold nanoparticles, GNP) and ferrocene signal quenching was investigated. The Au electrode was first modified with GNPs through electrodeposition method, followed by subsequent immobilization of single-stranded probe DNA labeled with ruthenium complex. The resulting sensor produced a higher ECL signal due to its higher density of self-assembled probe DNAs on the surface. Upon the hybridization of probe DNA with complementary target DNA labeled with ferrocene, ECL intensity decreased significantly due to spatial separation of ECL label from the electrode surface. As a result, the ECL signal was simultaneously quenched by ferrocene. The effects of both nano-gold electrodeposition time and ferrocene on the performance of ECL-DNA sensor were studied in detail and possible reasons for these effects were suggested as well. The reported ECL-DNA sensor showed great sensitivity and may provide an alternative approach for DNA detection in diagnostics and gene analysis. Copyright © 2012 Elsevier B.V. All rights reserved.

U-bent plastic optical fiber based plasmonic biosensor for nucleic acid detection

NASA Astrophysics Data System (ADS)

Gowri, A.; Sai, V. V. R.

2017-05-01

This study presents the development of low cost, rapid and highly sensitive plasmonic sandwich DNA biosensor using U-bent plastic optical fiber (POF) probes with high evanescent wave absorbance sensitivity and gold nanoparticles (AuNP) as labels. Plastic optical fiber (PMMA core and fluorinated polymer as cladding) offer ease in machinability and handling due to which optimum U-bent geometry (with fiber and bend diameter of 0.5 and 1.5 mm respectively) for high sensitivity could be achieved. A sensitive fiber optic DNA biosensor is realized by (i) modifying the PMMA surface using ethylenediamine (EDA) in order to maximize the immobilization of capture oligonucleotides (ONs) and (ii) conjugating probe ONs to AuNP labels of optimum size ( 35 nm) with high extinction coefficient and optimal ON surface density. The sandwich hybridization assay on U-bent POF probes results in increase in optical absorbance through the probe with increase in target ON concentration due to the presence of increased number of AuNPs. The absorbance of light passing through the U-bent probe due to the presence of AuNP labels on its surface as result of sandwich DNA hybridization is measured using a halogen lamp and a fiber optic spectrometer. A picomolar limit of detection of target ON (0.2 pM or 1 pg/ml or 5 attomol in 25 μL) is achieved with this biosensing scheme, indicating its potential for the development of a highly sensitive DNA biosensor.

Crystal step edges can trap electrons on the surfaces of n-type organic semiconductors.

PubMed

He, Tao; Wu, Yanfei; D'Avino, Gabriele; Schmidt, Elliot; Stolte, Matthias; Cornil, Jérôme; Beljonne, David; Ruden, P Paul; Würthner, Frank; Frisbie, C Daniel

2018-05-30

Understanding relationships between microstructure and electrical transport is an important goal for the materials science of organic semiconductors. Combining high-resolution surface potential mapping by scanning Kelvin probe microscopy (SKPM) with systematic field effect transport measurements, we show that step edges can trap electrons on the surfaces of single crystal organic semiconductors. n-type organic semiconductor crystals exhibiting positive step edge surface potentials display threshold voltages that increase and carrier mobilities that decrease with increasing step density, characteristic of trapping, whereas crystals that do not have positive step edge surface potentials do not have strongly step density dependent transport. A device model and microelectrostatics calculations suggest that trapping can be intrinsic to step edges for crystals of molecules with polar substituents. The results provide a unique example of a specific microstructure-charge trapping relationship and highlight the utility of surface potential imaging in combination with transport measurements as a productive strategy for uncovering microscopic structure-property relationships in organic semiconductors.

Hole Fermi surface in Bi2Se3 probed by quantum oscillations

NASA Astrophysics Data System (ADS)

Piot, B. A.; Desrat, W.; Maude, D. K.; Orlita, M.; Potemski, M.; Martinez, G.; Hor, Y. S.

2016-04-01

Transport and torque magnetometry measurements are performed at high magnetic fields and low temperatures in a series of p-type (Ca-doped) Bi2Se3 crystals. The angular dependence of the Shubnikov-de Haas and de Haas-van Alphen quantum oscillations enables us to determine the Fermi surface of the bulk valence band states as a function of the carrier density. At low density, the angular dependence exhibits a downturn in the oscillations frequency between 0∘ and 90∘, reflecting a bag-shaped hole Fermi surface. The detection of a single frequency for all tilt angles rules out the existence of a Fermi surface with different extremal cross sections down to 24 meV. There is therefore no signature of a camelback in the valence band of our bulk samples, in accordance with the direct band gap predicted by G W calculations.

Electric-field noise from carbon-adatom diffusion on a Au(110) surface: First-principles calculations and experiments

DOE PAGES

Kim, E.; Safavi-Naini, A.; Hite, D. A.; ...

2017-03-01

The decoherence of trapped-ion quantum bits due to heating of their motional modes is a fundamental science and engineering problem. This heating is attributed to electric-field noise arising from processes on the trap-electrode surfaces. In this work, we address the source of this noise by focusing on the diffusion of carbon-containing adsorbates on the surface of Au(110). We show by detailed scanned probe microscopy and density functional theory how the carbon adatom diffusion on the gold surface changes the energy landscape, and how the adatom dipole moment varies with the diffusive motion. Lastly, a simple model for the diffusion noise,more » which varies quadratically with the variation of the dipole moment, qualitatively reproduces the measured noise spectrum, and the estimate of the noise spectral density is in accord with measured values.« less

Electric-field noise from carbon-adatom diffusion on a Au(110) surface: First-principles calculations and experiments

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

Kim, E.; Safavi-Naini, A.; Hite, D. A.

The decoherence of trapped-ion quantum bits due to heating of their motional modes is a fundamental science and engineering problem. This heating is attributed to electric-field noise arising from processes on the trap-electrode surfaces. In this work, we address the source of this noise by focusing on the diffusion of carbon-containing adsorbates on the surface of Au(110). We show by detailed scanned probe microscopy and density functional theory how the carbon adatom diffusion on the gold surface changes the energy landscape, and how the adatom dipole moment varies with the diffusive motion. Lastly, a simple model for the diffusion noise,more » which varies quadratically with the variation of the dipole moment, qualitatively reproduces the measured noise spectrum, and the estimate of the noise spectral density is in accord with measured values.« less

EFFECTS OF LASER RADIATION ON MATTER: Growth of periodic structures on the surface of germanium subjected to pulsed laser radiation

NASA Astrophysics Data System (ADS)

Barsukov, D. O.; Gusakov, G. M.; Frolov, A. I.

1991-12-01

An experimental investigation was made of the dynamics of growth of periodic surface structures due to the interaction with pulsed laser radiation. Samples of Ge were subjected to laser pulses (λ = 1.06 μm, τ = 70 ns) with energy densities in the range 0.5-5.5 J/cm2. An investigation was made of the dynamics of the first-order diffraction of probe (λ = 0.53 μm) laser pulses with a time resolution 4 ns when p- and s-polarized laser radiation was incident at angles close to normal. A strong nonlinearity of the growth of such periodic surface structures was observed. The energy density from which such growth began depended on the quality of the polished Ge surface. The parameters of the dynamics of the growth of these structures were estimated.

Determination of plasma density from data on the ion current to cylindrical and planar probes

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

Voloshin, D. G., E-mail: dvoloshin@mics.msu.su; Vasil’eva, A. N.; Kovalev, A. S.

2016-12-15

To improve probe methods of plasma diagnostics, special probe measurements were performed and numerical models describing ion transport to a probe with allowance for collisions were developed. The current–voltage characteristics of cylindrical and planar probes were measured in an RF capacitive discharge in argon at a frequency of 81 MHz and plasma densities of 10{sup 10}–10{sup 11} cm{sup –3}, typical of modern RF reactors. 1D and 2D numerical models based on the particle-in-cell method with Monte Carlo collisions for simulating ion motion and the Boltzmann equilibrium for electrons are developed to describe current collection by a probe. The models weremore » used to find the plasma density from the ion part of the current–voltage characteristic, study the effect of ion collisions, and verify simplified approaches to determining the plasma density. A 1D hydrodynamic model of the ion current to a cylindrical probe with allowance for ion collisions is proposed. For a planar probe, a method to determine the plasma density from the averaged numerical results is developed. A comparative analysis of different approaches to calculating the plasma density from the ion current to a probe is performed.« less

Evaluation of a Magnetically-Filtered Faraday Probe for Measuring the ion Current Density Profile of a Hall Thruster

DTIC Science & Technology

2004-07-01

The ability of a magnetically-filtered Faraday probe (MFFP) to obtain the ion current density profile of a Hall thruster is investigated. The MFFP is...MFFP, boxed Faraday probe (BFP), and nude Faraday probe are used to measure the ion current density profile of a 5 kW Hall thruster operated over the

A molecular Rayleigh scattering setup to measure density fluctuations in thermal boundary layers

NASA Astrophysics Data System (ADS)

Panda, J.

2016-12-01

A Rayleigh scattering-based density fluctuation measurement system was set up inside a low-speed wind tunnel of NASA Ames Research Center. The immediate goal was to study the thermal boundary layer on a heated flat plate. A large number of obstacles had to be overcome to set up the system, such as the removal of dust particles using air filters, the use of photoelectron counting electronics to measure low intensity light, an optical layout to minimize stray light contamination, the reduction in tunnel vibration, and an expanded calibration process to relate photoelectron arrival rate to air density close to the plate surface. To measure spectra of turbulent density fluctuations, a two-PMT cross-correlation system was used to minimize the shot noise floor. To validate the Rayleigh measurements, temperature fluctuations spectra were calculated from density spectra and then compared with temperature spectra measured with a cold-wire probe operated in constant current mode. The spectra from the downstream half of the plate were found to be in good agreement with cold-wire probe, whereas spectra from the leading edge differed. Various lessons learnt are discussed. It is believed that the present effort is the first measurement of density fluctuations spectra in a boundary layer flow.

Cassini/Huygens Science Instruments, Spacecraft, and Mission

NASA Technical Reports Server (NTRS)

Jaffe, Leonard D.; Herrell, Linda M.

1997-01-01

The Cassini spacecraft will take 18 scientific instruments to Saturn. After launch and a seven-year cruise, Cassini will arrive at Saturn and separate into a Saturn orbiter and an atmospheric probe, called Huygens, which will descend to the surface of Titan. The orbiter will orbit the planet for four years, making close flybys of five satellites, including multiple flybys of Titan. Communication with Earth is at X-band; the maximum downlink rate from Saturn is 166 x 10(exp 3) bps. Orbiter instruments are body mounted; the spacecraft must be turned to point some of them toward objects of interest. The orbiter carries 12 instruments. Optical instruments provide imagery and spectrometry. Radar supplies imaging, altimetry, and radiometry. Radio links contribute information about intervening material and gravity fields. Other instruments measure electromagnetic fields and the properties of plasma, energetic particles, and dust particles. The probe is spin stabilized. It returns data via an S-band link to the orbiter. The probe's six instruments include sensors to determine atmospheric physical properties and composition. Radiometric and optical sensors will produce data on thermal balance and obtain images of Titan's atmosphere and surface. Doppler measurements between probe and orbiter will provide wind profiles. Surface sensors will measure impact acceleration, thermal and electrical properties, and, if the surface is liquid, density and refractive index. This design will enable Cassini to determine the composition; the physical, morphological, and geological nature; and the physical and chemical processes of the atmospheres, surfaces, and magnetosphere of the Saturnian system. This paper briefly describes the Cassini mission and spacecraft and, in somewhat more detail, the scientific instruments.

Triboelectrification-Enabled Self-Powered Data Storage.

PubMed

Kuang, Shuang Yang; Zhu, Guang; Wang, Zhong Lin

2018-02-01

Data storage by any means usually requires an electric driving power for writing or reading. A novel approach for self-powered, triboelectrification-enabled data storage (TEDS) is presented. Data are incorporated into a set of metal-based surface patterns. As a probe slides across the patterned surface, triboelectrification between the scanning probe and the patterns produces alternatively varying voltage signal in quasi-square wave. The trough and crest of the quasi-square wave signal are coded as binary bits of "0" and "1," respectively, while the time span of the trough and the crest is associated with the number of bits. The storage of letters and sentences is demonstrated through either square-shaped or disc-shaped surface patterns. Based on experimental data and numerical calculation, the theoretically predicted maximum data storage density could reach as high as 38.2 Gbit in -2 . Demonstration of real-time data retrieval is realized with the assistance of software interface. For the TEDS reported in this work, the measured voltage signal is self-generated as a result of triboelectrification without the reliance on an external power source. This feature brings about not only low power consumption but also a much more simplified structure. Therefore, this work paves a new path to a unique approach of high-density data storage that may have widespread applications.

Absolute Molecular Orientation of Isopropanol at Ceria (100) Surfaces: Insight into Catalytic Selectivity from the Interfacial Structure

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

Doughty, Benjamin; Goverapet Srinivasan, Sriram; Bryantsev, Vyacheslav S.

The initial mechanistic steps underlying heterogeneous chemical catalysis can be described in a framework where the composition, structure, and orientation of molecules adsorbed to reactive interfaces are known. However, extracting this vital information is the limiting step in most cases due in part to challenges in probing the interfacial monolayer with enough chemical specificity to characterize the surface molecular constituents. These challenges are exacerbated at complex or spatially heterogeneous interfaces where competing processes and a distribution of local environments can uniquely drive chemistry. To address these limitations, this work presents a distinctive combination of materials synthesis, surface specific optical experiments,more » and theory to probe and understand molecular structure at catalytic interfaces. Specifically, isopropanol was adsorbed to surfaces of the model CeO 2 catalyst that were synthesized with only the (100) facet exposed. Vibrational sum-frequency generation was used to probe the molecular monolayer, and with the guidance of density functional theory calculations, was used to extract the structure and absolute molecular orientation of isopropanol at the CeO 2 (100) surface. Our results show that isopropanol is readily deprotonated at the surface, and through the measured absolute molecular orientation of isopropanol, we obtain new insight into the selectivity of the (100) surface to form propylene. Our findings reveal key insight into the chemical and physical phenomena taking place at pristine interfaces thereby pointing to intuitive structural arguments to describe catalytic selectivity in more complex systems.« less

Absolute Molecular Orientation of Isopropanol at Ceria (100) Surfaces: Insight into Catalytic Selectivity from the Interfacial Structure

DOE PAGES

Doughty, Benjamin; Goverapet Srinivasan, Sriram; Bryantsev, Vyacheslav S.; ...

2017-06-12

The initial mechanistic steps underlying heterogeneous chemical catalysis can be described in a framework where the composition, structure, and orientation of molecules adsorbed to reactive interfaces are known. However, extracting this vital information is the limiting step in most cases due in part to challenges in probing the interfacial monolayer with enough chemical specificity to characterize the surface molecular constituents. These challenges are exacerbated at complex or spatially heterogeneous interfaces where competing processes and a distribution of local environments can uniquely drive chemistry. To address these limitations, this work presents a distinctive combination of materials synthesis, surface specific optical experiments,more » and theory to probe and understand molecular structure at catalytic interfaces. Specifically, isopropanol was adsorbed to surfaces of the model CeO 2 catalyst that were synthesized with only the (100) facet exposed. Vibrational sum-frequency generation was used to probe the molecular monolayer, and with the guidance of density functional theory calculations, was used to extract the structure and absolute molecular orientation of isopropanol at the CeO 2 (100) surface. Our results show that isopropanol is readily deprotonated at the surface, and through the measured absolute molecular orientation of isopropanol, we obtain new insight into the selectivity of the (100) surface to form propylene. Our findings reveal key insight into the chemical and physical phenomena taking place at pristine interfaces thereby pointing to intuitive structural arguments to describe catalytic selectivity in more complex systems.« less

The hairpin resonator: A plasma density measuring technique revisited

NASA Astrophysics Data System (ADS)

Piejak, R. B.; Godyak, V. A.; Garner, R.; Alexandrovich, B. M.; Sternberg, N.

2004-04-01

A microwave resonator probe is a resonant structure from which the relative permittivity of the surrounding medium can be determined. Two types of microwave resonator probes (referred to here as hairpin probes) have been designed and built to determine the electron density in a low-pressure gas discharge. One type, a transmission probe, is a functional equivalent of the original microwave resonator probe introduced by R. L. Stenzel [Rev. Sci. Instrum. 47, 603 (1976)], modified to increase coupling to the hairpin structure and to minimize plasma perturbation. The second type, a reflection probe, differs from the transmission probe in that it requires only one coaxial feeder cable. A sheath correction, based on the fluid equations for collisionless ions in a cylindrical electron-free sheath, is presented here to account for the sheath that naturally forms about the hairpin structure immersed in plasma. The sheath correction extends the range of electron density that can be accurately measured with a particular wire separation of the hairpin structure. Experimental measurements using the hairpin probe appear to be highly reproducible. Comparisons with Langmuir probes show that the Langmuir probe determines an electron density that is 20-30% lower than the hairpin. Further comparisons, with both an interferometer and a Langmuir probe, show hairpin measurements to be in good agreement with the interferometer while Langmuir probe measurements again result in a lower electron density.

Development of atomic radical monitoring probe and its application to spatial distribution measurements of H and O atomic radical densities in radical-based plasma processing

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

Takahashi, Shunji; Katagiri Engineering Co., Ltd., 3-5-34 Shitte Tsurumi-ku, Yokohama 230-0003; Takashima, Seigo

2009-09-01

Atomic radicals such as hydrogen (H) and oxygen (O) play important roles in process plasmas. In a previous study, we developed a system for measuring the absolute density of H, O, nitrogen, and carbon atoms in plasmas using vacuum ultraviolet absorption spectroscopy (VUVAS) with a compact light source using an atmospheric pressure microplasma [microdischarge hollow cathode lamp (MHCL)]. In this study, we developed a monitoring probe for atomic radicals employing the VUVAS with the MHCL. The probe size was 2.7 mm in diameter. Using this probe, only a single port needs to be accessed for radical density measurements. We successfullymore » measured the spatial distribution of the absolute densities of H and O atomic radicals in a radical-based plasma processing system by moving the probe along the radial direction of the chamber. This probe allows convenient analysis of atomic radical densities to be carried out for any type of process plasma at any time. We refer to this probe as a ubiquitous monitoring probe for atomic radicals.« less

The Sheath-less Planar Langmuir Probe

NASA Astrophysics Data System (ADS)

Cooke, D. L.

2017-12-01

The Langmuir probe is one of the oldest plasma diagnostics, provided the plasma density and species temperature from analysis of a current-voltage curve as the voltage is swept over a practically chosen range. The analysis depends on a knowledge or theory of the many factors that influence the current-voltage curve including, probe shape, size, nearby perturbations, and the voltage reference. For applications in Low Earth Orbit, the Planar Langmuir Probe, PLP, is an attractive geometry because the ram ion current is very constant over many Volts of a sweep, allowing the ion density and electron temperature to be determined independently with the same instrument, at different points on the sweep. However, when the physical voltage reference is itself small and electrically floating as with a small spacecraft, the spacecraft and probe system become a double probe where the current collection theory depends on the interaction of the spacecraft with the plasma which is generally not as simple as the probe itself. The Sheath-less PLP, SPLP, interlaces on a single ram facing surface, two variably biased probe elements, broken into many small and intertwined segments on a scale smaller than the plasma Debye length. The SPLP is electrically isolated from the rest of the spacecraft. For relative bias potentials of a few volts, the ion current to all segments of each element will be constant, while the electron currents will vary as a function of the element potential and the electron temperature. Because the segments are small, intertwined, and floating, the assembly will always present the same floating potential to the plasma, with minimal growth as a function of voltage, thus sheath-less and still planar. This concept has been modelled with Nascap, and tested with a physical model inserted into a Low Earth Orbit-like chamber plasma. Results will be presented.

International Conference on the Physics of Semiconductors (17th) Held in San Francisco, California on August 6-10, 1984

DTIC Science & Technology

1984-09-30

experimental probe of the Landau level density of states, which we find to be distinctly non -gaussian and in qualitative agreement with theoretical predictions...dispersion on the cleaved Si(111)2xi surface. For good single domain 2x1 surfaces different experimental groups agree on a highly dispersive dangling-bond...work underlies the operation of new devices proposed II] and realized experimentally : a gate controlled microwave generator (2,3J and a charge

Structural properties of oligonucleotide monolayers on gold surfaces probed by fluorescence investigations.

PubMed

Rant, Ulrich; Arinaga, Kenji; Fujita, Shozo; Yokoyama, Naoki; Abstreiter, Gerhard; Tornow, Marc

2004-11-09

We present optical investigations on the conformation of oligonucleotide layers on Au surfaces. Our studies concentrate on the effect of varying surface coverage densities on the structural properties of layers of 12- and 24mer single-stranded DNA, tethered to the Au surface at one end while being labeled with a fluorescent marker at the opposing end. The distance-dependent energy transfer from the marker dye to the metal surface, which causes quenching of the observed fluorescence, is used to provide information on the orientation of the DNA strands relative to the surface. Variations in the oligonucleotide coverage density, as determined from electrochemical quantification, over 2 orders of magnitude are achieved by employing different preparation conditions. The observed enhancement in fluorescence intensity with increasing DNA coverage can be related to a model involving mutual steric interactions of oligonucleotides on the surface, as well as fluorescence quenching theory. Finally, the applicability of the presented concepts for investigations of heterogeneous monolayers is demonstrated by means of studying the coadsorption of mercaptohexanol onto DNA-modified Au surfaces.

Atomic force microscopy evaluation of aqueous interfaces of immobilized hyaluronan.

PubMed

Morra, Marco; Cassinelli, Clara; Pavesio, Alessandra; Renier, Davide

2003-03-15

Hyaluronan (HA) was immobilized on aminated glass surfaces in three different ways: by simple ionic interaction and by covalent linking at low density and at full density. In agreement with previous reports, in vitro experiments show that the outcome of fibroblast adhesion tests is markedly affected by the details of the coupling procedure, suggesting that different interfacial forces are operating at the aqueous/HA interface in the three cases investigated. The interfacial properties of the HA-coated surfaces were probed by force-distance curves obtained with the atomic force microscope (AFM). This approach readily shows significant differences among the tested samples, which are directly related to the coupling strategy and to results of cell adhesion tests. In particular, the range of interaction between the tip and the surface is much lower when HA is covalently linked than when it is ionically coupled, suggesting a more compact surface structure in the former case. Increasing HA surface density minimizes the interaction force between the surface and the AFM tip, likely reflecting more complete shielding by the HA chains of the underlying substrate. In summary, these measurements clearly show the different nature of the aqueous interfaces tested, and underline the role of this analytical approach in the development and control of finely tuned biomaterial surfaces.

Formation and properties of surface-anchored polymer assemblies with tunable physico-chemical characteristics

NASA Astrophysics Data System (ADS)

Wu, Tao

We describe two new methodologies leading to the formation of novel surface-anchored polymer assemblies on solid substrates. While the main goal is to understand the fundamentals pertaining to the preparation and properties of the surface-bound polymer assemblies (including neutral and chargeable polymers), several examples also are mentioned throughout the Thesis that point out to practical applications of such structures. The first method is based on generating assemblies comprising anchored polymers with a gradual variation of grafting densities on solid substrates. These structures are prepared by first covering the substrate with a molecular gradient of the polymerization initiator, followed by polymerization from these substrate-bound initiator centers ("grafting from"). We apply this technique to prepare grafting density gradients of poly(acryl amide) (PAAm) and poly(acrylic acid) (PAA) on silica-covered substrates. We show that using the grafting density gradient geometry, the characteristics of surface-anchored polymers in both the low grafting density ("mushroom") regime as well as the high grafting density ("brush") regime can be accessed conveniently on a single sample. We use a battery of experimental methods, including Fourier transform infrared spectroscopy (FTIR), Near-edge absorption fine structure spectroscopy (NEXAFS), contact angle, ellipsometry, to study the characteristics of the surface-bound polymer layers. We also probe the scaling laws of neutral polymer as a function of grafting density, and for weak polyelectrolyte, in addition to the grafting density, we study the affect of solution ionic strength and pH values. In the second novel method, which we coined as "mechanically assisted polymer assembly" (MAPA), we form surface anchored polymers by "grafting from" polymerization initiators deposited on elastic surfaces that have been previously extended uniaxially by a certain length increment, Deltax. Upon releasing the strain in the substrate after completion of polymerization, we show the grafting density of the polymers grafted to flexible substrates can be tuned as a function of Deltax.

Intrasulcal Electrocorticography in Macaque Monkeys with Minimally Invasive Neurosurgical Protocols

PubMed Central

Matsuo, Takeshi; Kawasaki, Keisuke; Osada, Takahiro; Sawahata, Hirohito; Suzuki, Takafumi; Shibata, Masahiro; Miyakawa, Naohisa; Nakahara, Kiyoshi; Iijima, Atsuhiko; Sato, Noboru; Kawai, Kensuke; Saito, Nobuhito; Hasegawa, Isao

2011-01-01

Electrocorticography (ECoG), multichannel brain-surface recording and stimulation with probe electrode arrays, has become a potent methodology not only for clinical neurosurgery but also for basic neuroscience using animal models. The highly evolved primate's brain has deep cerebral sulci, and both gyral and intrasulcal cortical regions have been implicated in important functional processes. However, direct experimental access is typically limited to gyral regions, since placing probes into sulci is difficult without damaging the surrounding tissues. Here we describe a novel methodology for intrasulcal ECoG in macaque monkeys. We designed and fabricated ultra-thin flexible probes for macaques with micro-electro-mechanical systems technology. We developed minimally invasive operative protocols to implant the probes by introducing cutting-edge devices for human neurosurgery. To evaluate the feasibility of intrasulcal ECoG, we conducted electrophysiological recording and stimulation experiments. First, we inserted parts of the Parylene-C-based probe into the superior temporal sulcus to compare visually evoked ECoG responses from the ventral bank of the sulcus with those from the surface of the inferior temporal cortex. Analyses of power spectral density and signal-to-noise ratio revealed that the quality of the ECoG signal was comparable inside and outside of the sulcus. Histological examination revealed no obvious physical damage in the implanted areas. Second, we placed a modified silicone ECoG probe into the central sulcus and also on the surface of the precentral gyrus for stimulation. Thresholds for muscle twitching were significantly lower during intrasulcal stimulation compared to gyral stimulation. These results demonstrate the feasibility of intrasulcal ECoG in macaques. The novel methodology proposed here opens up a new frontier in neuroscience research, enabling the direct measurement and manipulation of electrical activity in the whole brain. PMID:21647392

Studies of RF sheaths and diagnostics on IShTAR

NASA Astrophysics Data System (ADS)

Crombé, K.; Devaux, S.; D'Inca, R.; Faudot, E.; Faugel, H.; Fünfgelder, H.; Heuraux, S.; Jacquot, J.; Louche, F.; Moritz, J.; Ochoukov, R.; Tripsky, M.; Van Eester, D.; Wauters, T.; Noterdaeme, J.-M.

2015-12-01

IShTAR (Ion cyclotron Sheath Test ARrangement) is a linear magnetised plasma test facility for RF sheaths studies at the Max-Planck-Institut für Plasmaphysik in Garching. In contrast to a tokamak, a test stand provides more liberty to impose the parameters and gives better access for the instrumentation and antennas. The project will support the development of diagnostic methods for characterising RF sheaths and validate and improve theoretical predictions. The cylindrical vacuum vessel has a diameter of 1 m and is 1.1 m long. The plasma is created by an external cylindrical plasma source equipped with a helical antenna that has been designed to excite the m=1 helicon mode. In inductive mode, plasma densities and electron temperatures have been characterised with a planar Langmuir probe as a function of gas pressure and input RF power. A 2D array of RF compensated Langmuir probes and a spectrometer are planned. A single strap RF antenna has been designed; the plasma-facing surface is aligned to the cylindrical plasma to ease the modelling. The probes will allow direct measurements of plasma density profiles in front of the RF antenna, and thus a detailed study of the density modifications induced by RF sheaths, which influences the coupling. The RF antenna frequency has been chosen to study different plasma wave interactions: the accessible plasma density range includes an evanescent and propagative behaviour of slow or fast waves, and allows the study of the effect of the lower hybrid resonance layer.

The study of surface wetting, nanobubbles and boundary slip with an applied voltage: A review

PubMed Central

Pan, Yunlu; Zhao, Xuezeng

2014-01-01

Summary The drag of fluid flow at the solid–liquid interface in the micro/nanoscale is an important issue in micro/nanofluidic systems. Drag depends on the surface wetting, nanobubbles, surface charge and boundary slip. Some researchers have focused on the relationship between these interface properties. In this review, the influence of an applied voltage on the surface wettability, nanobubbles, surface charge density and slip length are discussed. The contact angle (CA) and contact angle hysteresis (CAH) of a droplet of deionized (DI) water on a hydrophobic polystyrene (PS) surface were measured with applied direct current (DC) and alternating current (AC) voltages. The nanobubbles in DI water and three kinds of saline solution on a PS surface were imaged when a voltage was applied. The influence of the surface charge density on the nanobubbles was analyzed. Then the slip length and the electrostatic force on the probe were measured on an octadecyltrichlorosilane (OTS) surface with applied voltage. The influence of the surface charge on the boundary slip and drag of fluid flow has been discussed. Finally, the influence of the applied voltage on the surface wetting, nanobubbles, surface charge, boundary slip and the drag of liquid flow are summarized. With a smaller surface charge density which could be achieved by applying a voltage on the surface, larger and fewer nanobubbles, a larger slip length and a smaller drag of liquid flow could be found. PMID:25161839

The study of surface wetting, nanobubbles and boundary slip with an applied voltage: A review.

PubMed

Pan, Yunlu; Bhushan, Bharat; Zhao, Xuezeng

2014-01-01

The drag of fluid flow at the solid-liquid interface in the micro/nanoscale is an important issue in micro/nanofluidic systems. Drag depends on the surface wetting, nanobubbles, surface charge and boundary slip. Some researchers have focused on the relationship between these interface properties. In this review, the influence of an applied voltage on the surface wettability, nanobubbles, surface charge density and slip length are discussed. The contact angle (CA) and contact angle hysteresis (CAH) of a droplet of deionized (DI) water on a hydrophobic polystyrene (PS) surface were measured with applied direct current (DC) and alternating current (AC) voltages. The nanobubbles in DI water and three kinds of saline solution on a PS surface were imaged when a voltage was applied. The influence of the surface charge density on the nanobubbles was analyzed. Then the slip length and the electrostatic force on the probe were measured on an octadecyltrichlorosilane (OTS) surface with applied voltage. The influence of the surface charge on the boundary slip and drag of fluid flow has been discussed. Finally, the influence of the applied voltage on the surface wetting, nanobubbles, surface charge, boundary slip and the drag of liquid flow are summarized. With a smaller surface charge density which could be achieved by applying a voltage on the surface, larger and fewer nanobubbles, a larger slip length and a smaller drag of liquid flow could be found.

Differential heating: A versatile method for thermal conductivity measurements in high-energy-density matter

DOE PAGES

Ping, Y.; Fernandez-Panella, A.; Sio, H.; ...

2015-09-04

We propose a method for thermal conductivity measurements of high energy density matter based on differential heating. A temperature gradient is created either by surface heating of one material or at an interface between two materials by different energy deposition. The subsequent heat conduction across the temperature gradient is observed by various time-resolved probing techniques. Conceptual designs of such measurements using laser heating, proton heating, and x-ray heating are presented. As a result, the sensitivity of the measurements to thermal conductivity is confirmed by simulations.

Integrating AlGaN/GaN high electron mobility transistor with Si: A comparative study of integration schemes

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

Mohan, Nagaboopathy; Raghavan, Srinivasan; Centre for Nano Science and Engineering, Indian Institute of Science, Bangalore 560012

2015-10-07

AlGaN/GaN high electron mobility transistor stacks deposited on a single growth platform are used to compare the most common transition, AlN to GaN, schemes used for integrating GaN with Si. The efficiency of these transitions based on linearly graded, step graded, interlayer, and superlattice schemes on dislocation density reduction, stress management, surface roughness, and eventually mobility of the 2D-gas are evaluated. In a 500 nm GaN probe layer deposited, all of these transitions result in total transmission electron microscopy measured dislocations densities of 1 to 3 × 10{sup 9}/cm{sup 2} and <1 nm surface roughness. The 2-D electron gas channels formed atmore » an AlGaN-1 nm AlN/GaN interface deposited on this GaN probe layer all have mobilities of 1600–1900 cm{sup 2}/V s at a carrier concentration of 0.7–0.9 × 10{sup 13}/cm{sup 2}. Compressive stress and changes in composition in GaN rich regions of the AlN-GaN transition are the most effective at reducing dislocation density. Amongst all the transitions studied the step graded transition is the one that helps to implement this feature of GaN integration in the simplest and most consistent manner.« less

Making Mn substitutional impurities in InAs using a scanning tunneling microscope.

PubMed

Song, Young Jae; Erwin, Steven C; Rutter, Gregory M; First, Phillip N; Zhitenev, Nikolai B; Stroscio, Joseph A

2009-12-01

We describe in detail an atom-by-atom exchange manipulation technique using a scanning tunneling microscope probe. As-deposited Mn adatoms (Mn(ad)) are exchanged one-by-one with surface In atoms (In(su)) to create a Mn surface-substitutional (Mn(In)) and an exchanged In adatom (In(ad)) by an electron tunneling induced reaction Mn(ad) + In(su) --> Mn(In) + In(ad) on the InAs(110) surface. In combination with density-functional theory and high resolution scanning tunneling microscopy imaging, we have identified the reaction pathway for the Mn and In atom exchange.

Ordered adsorption of coagulation factor XII on negatively charged polymer surfaces probed by sum frequency generation vibrational spectroscopy.

PubMed

Chen, Xiaoyun; Wang, Jie; Paszti, Zoltan; Wang, Fulin; Schrauben, Joel N; Tarabara, Volodymyr V; Schmaier, Alvin H; Chen, Zhan

2007-05-01

Electrostatic interactions between negatively charged polymer surfaces and factor XII (FXII), a blood coagulation factor, were investigated by sum frequency generation (SFG) vibrational spectroscopy, supplemented by several analytical techniques including attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), quartz crystal microbalance (QCM), zeta-potential measurement, and chromogenic assay. A series of sulfonated polystyrenes (sPS) with different sulfonation levels were synthesized as model surfaces with different surface charge densities. SFG spectra collected from FXII adsorbed onto PS and sPS surfaces with different surface charge densities showed remarkable differences in spectral features and especially in spectral intensity. Chromogenic assay experiments showed that highly charged sPS surfaces induced FXII autoactivation. ATR-FTIR and QCM results indicated that adsorption amounts on the PS and sPS surfaces were similar even though the surface charge densities were different. No significant conformational change was observed from FXII adsorbed onto surfaces studied. Using theoretical calculations, the possible contribution from the third-order nonlinear optical effect induced by the surface electric field was evaluated, and it was found to be unable to yield the SFG signal enhancement observed. Therefore it was concluded that the adsorbed FXII orientation and ordering were the main reasons for the remarkable SFG amide I signal increase on sPS surfaces. These investigations indicate that negatively charged surfaces facilitate or induce FXII autoactivation on the molecular level by imposing specific orientation and ordering on the adsorbed protein molecules.

Development of 3D online contact measurement system for intelligent manufacturing based on stereo vision

NASA Astrophysics Data System (ADS)

Li, Peng; Chong, Wenyan; Ma, Yongjun

2017-10-01

In order to avoid shortcomings of low efficiency and restricted measuring range exsited in traditional 3D on-line contact measurement method for workpiece size, the development of a novel 3D contact measurement system is introduced, which is designed for intelligent manufacturing based on stereo vision. The developed contact measurement system is characterized with an intergarted use of a handy probe, a binocular stereo vision system, and advanced measurement software.The handy probe consists of six track markers, a touch probe and the associated elcetronics. In the process of contact measurement, the hand probe can be located by the use of the stereo vision system and track markers, and 3D coordinates of a space point on the workpiece can be mearsured by calculating the tip position of a touch probe. With the flexibility of the hand probe, the orientation, range, density of the 3D contact measurenent can be adptable to different needs. Applications of the developed contact measurement system to high-precision measurement and rapid surface digitization are experimentally demonstrated.

Nano Scale Mechanical Analysis of Biomaterials Using Atomic Force Microscopy

NASA Astrophysics Data System (ADS)

Dutta, Diganta

The atomic force microscope (AFM) is a probe-based microscope that uses nanoscale and structural imaging where high resolution is desired. AFM has also been used in mechanical, electrical, and thermal engineering applications. This unique technique provides vital local material properties like the modulus of elasticity, hardness, surface potential, Hamaker constant, and the surface charge density from force versus displacement curve. Therefore, AFM was used to measure both the diameter and mechanical properties of the collagen nanostraws in human costal cartilage. Human costal cartilage forms a bridge between the sternum and bony ribs. The chest wall of some humans is deformed due to defective costal cartilage. However, costal cartilage is less studied compared to load bearing cartilage. Results show that there is a difference between chemical fixation and non-chemical fixation treatments. Our findings imply that the patients' chest wall is mechanically weak and protein deposition is abnormal. This may impact the nanostraws' ability to facilitate fluid flow between the ribs and the sternum. At present, AFM is the only tool for imaging cells' ultra-structure at the nanometer scale because cells are not homogeneous. The first layer of the cell is called the cell membrane, and the layer under it is made of the cytoskeleton. Cancerous cells are different from normal cells in term of cell growth, mechanical properties, and ultra-structure. Here, force is measured with very high sensitivity and this is accomplished with highly sensitive probes such as a nano-probe. We performed experiments to determine ultra-structural differences that emerge when such cancerous cells are subject to treatments such as with drugs and electric pulses. Jurkat cells are cancerous cells. These cells were pulsed at different conditions. Pulsed and non-pulsed Jurkat cell ultra-structures were investigated at the nano meter scale using AFM. Jurkat cell mechanical properties were measured under different conditions. In addition, AFM was used to measure the charge density of cell surface in physiological conditions. We found that the treatments changed the cancer cells' ultra-structural and mechanical properties at the nanometer scale. Finally, we used AFM to characterize many non-biological materials with relevance to biomedical science. Various metals, polymers, and semi-conducting materials were characterized in air and multiple liquid media through AFM - techniques from which a plethora of industries can benefit. This applies especially to the fledging solar industry which has found much promise in nanoscopic insights. Independent of the material being examined, a reliable method to measure the surface force between a nano probe and a sample surface in a variety of ionic concentrations was also found in the process of procuring these measurements. The key findings were that the charge density increases with the increase of the medium's ionic concentration.

Analysis of the plasma-wall interaction in the Heliotron E device

NASA Astrophysics Data System (ADS)

Motojima, O.; Mizuuchi, T.; Besshou, S.; Iiyoshi, A.; Uo, K.; Yamashina, T.; Mohri, M.; Satake, T.; Hashiba, M.; Amemiya, S.; Miwa, H.

1984-12-01

The plasma-wall interaction (PWI) of the currentless plasmas with temperature To, Tio ≤ 1.1 keV, density N¯e = (2-10)× 1013/cm3, and volume-averaged beta value of β$¯≤ 2% was investigated. We have observed that PWI took place mainly where the divertor field line intersected the chamber wall (called divertor traces). Boundary plasmas were measured with electrostatic probes, which showed the presence of the divertor region with the parameters in the range of Ned = 1010-1011/cm3 and Ted = 10-50 eV. Surface analysis techniques (ESCA, AES, and RBS) were applied to analyze the surface probes (Si, graphite and stainless steel) and the test pieces (SiC, TiC, and stainless steel), which were irradiated by plasmas for short and long times respectively.

Quantitative determination of the lateral density and intermolecular correlation between proteins anchored on the membrane surfaces using grazing incidence small-angle X-ray scattering and grazing incidence X-ray fluorescence.

PubMed

Abuillan, Wasim; Vorobiev, Alexei; Hartel, Andreas; Jones, Nicola G; Engstler, Markus; Tanaka, Motomu

2012-11-28

As a physical model of the surface of cells coated with densely packed, non-crystalline proteins coupled to lipid anchors, we functionalized the surface of phospholipid membranes by coupling of neutravidin to biotinylated lipid anchors. After the characterization of fine structures perpendicular to the plane of membrane using specular X-ray reflectivity, the same membrane was characterized by grazing incidence small angle X-ray scattering (GISAXS). Within the framework of distorted wave Born approximation and two-dimensional Percus-Yevick function, we can analyze the form and structure factors of the non-crystalline, membrane-anchored proteins for the first time. As a new experimental technique to quantify the surface density of proteins on the membrane surface, we utilized grazing incidence X-ray fluorescence (GIXF). Here, the mean intermolecular distance between proteins from the sulfur peak intensities can be calculated by applying Abelé's matrix formalism. The characteristic correlation distance between non-crystalline neutravidin obtained by the GISAXS analysis agrees well with the intermolecular distance calculated by GIXF, suggesting a large potential of the combination of GISAXS and GIXF in probing the lateral density and correlation of non-crystalline proteins displayed on the membrane surface.

Positive Voltage Hazard to EMU Crewman from Currents through Plasma

NASA Technical Reports Server (NTRS)

Koontz, Steven L.; Kramer, Leonard; Hamilton, Doug; Mikatarian, Ronald

2010-01-01

This paper describes the model of the EMU with a human body in the circuit that has been used by NASA to evaluate the low positive voltage hazard. The model utilizes the electron collection characterization from on orbit Langmuir probe data as representative of electron collection to a positive charged surface with a wide range of on orbit plasma temperature and density conditions. The data has been unified according to non-linear theoretical temperature and density variation of the electron saturated probe current collection theory and used as a model for the electron collection at EMU surfaces. Vulnerable paths through the EMU connecting through the crewman s body have been identified along with electrical impedance of the exposed body parts. The body impedance information is merged with the electron collection characteristics in circuit simulation software (SPICE). The assessment shows that currents can be on the order of 20 mA for a 15 V exposure and of order 4 mA at 3V. These currents formally violate NASA protocol for electric current exposures however the human factors associated with subjective consequences of noxious stimuli from low voltage exposure during the stressful conditions of EVA are an area of active inquiry.

Visualization and Enumeration of Marine Planktonic Archaea and Bacteria by Using Polyribonucleotide Probes and Fluorescent In Situ Hybridization

PubMed Central

DeLong, Edward F.; Taylor, Lance Trent; Marsh, Terence L.; Preston, Christina M.

1999-01-01

Fluorescent in situ hybridization (FISH) using rRNA-specific oligonucleotide probes has emerged as a popular technique for identifying individual microbial cells. In natural samples, however, the signal derived from fluor-labeled oligonucleotide probes often is undetectable above background fluorescence in many cells. To circumvent this difficulty, we applied fluorochrome-labeled polyribonucleotide probes to identify and enumerate marine planktonic archaea and bacteria. The approach greatly enhanced the sensitivity and applicability of FISH with seawater samples, allowing confident identification and enumeration of planktonic cells to ocean depths of 3,400 m. Quantitative whole-cell hybridization experiments using these probes accounted for 90 to 100% of the total 4′,6-diamidino-2-phenylindole (DAPI)-stained cells in most samples. As predicted in a previous study (R. Massana, A. E. Murray, C. M. Preston, and E. F. DeLong, Appl. Environ. Microbiol. 63:50–56, 1997), group I and II marine archaea predominate in different zones in the water column, with maximal cell densities of 105/ml. The high cell densities of archaea, extending from surface waters to abyssal depths, suggest that they represent a large and significant fraction of the total picoplankton biomass in coastal ocean waters. The data also show that the vast majority of planktonic prokaryotes contain significant numbers of ribosomes, rendering them easily detectable with polyribonucleotide probes. These results imply that the majority of planktonic cells visualized by DAPI do not represent lysed cells or “ghosts,” as was suggested in a previous report. PMID:10584017

Spectroscopic infrared extinction mapping as a probe of grain growth in IRDCs

NASA Astrophysics Data System (ADS)

Lim, Wanggi; Carey, Sean J.

2014-07-01

We present photometric and spectroscopic tests of MIR to FIR extinction laws toward IRDC G028.36+00.07, a potential site of massive star formation. Lim & Tan (2014, hereafter LT14) developed methods of FIR extinction mapping of this source using Spitzer-MIPS 24 micron and Herschel-PACS 70 micron images, and extending the MIR 8 micron mapping methods of (Butler & Tan 2012, hereafter BT12), finding evidence for grain growth in the highest mass surface density regions. Here we present initial results of spectroscopic infrared extinction (SIREX) mapping using Spitzer-IRS (14 to 38 micron) data of the same IRDC. These methods allow us to measure the SED of the diffuse Galactic ISM, which we compare to theoretical models of Draine & Li (2007), as well as to search for opacity law variations with mass surface density within the IRDC. By comparison with theoretical dust models, e.g., Ossenkopf & Henning (1994) and Ormel et al. (2011), we are able to search for compositional signatures of the grain ices, such as water and methanol. We find evidence for generally flatter MIR to FIR extinction laws as mass surface density increases, strengthening the evidence for grain and ice mantle growth in higher density regions.

DNA-modified electrodes fabricated using copper-free click chemistry for enhanced protein detection.

PubMed

Furst, Ariel L; Hill, Michael G; Barton, Jacqueline K

2013-12-31

A method of DNA monolayer formation has been developed using copper-free click chemistry that yields enhanced surface homogeneity and enables variation in the amount of DNA assembled; extremely low-density DNA monolayers, with as little as 5% of the monolayer being DNA, have been formed. These DNA-modified electrodes (DMEs) were characterized visually, with AFM, and electrochemically, and were found to facilitate DNA-mediated reduction of a distally bound redox probe. These low-density monolayers were found to be more homogeneous than traditional thiol-modified DNA monolayers, with greater helix accessibility through an increased surface area-to-volume ratio. Protein binding efficiency of the transcriptional activator TATA-binding protein (TBP) was also investigated on these surfaces and compared to that on DNA monolayers formed with standard thiol-modified DNA. Our low-density monolayers were found to be extremely sensitive to TBP binding, with a signal decrease in excess of 75% for 150 nM protein. This protein was detectable at 4 nM, on the order of its dissociation constant, with our low-density monolayers. The improved DNA helix accessibility and sensitivity of our low-density DNA monolayers to TBP binding reflects the general utility of this method of DNA monolayer formation for DNA-based electrochemical sensor development.

Influence of the Ambient Electric Field on Measurements of the Actively Controlled Spacecraft Potential by MMS

NASA Astrophysics Data System (ADS)

Torkar, K.; Nakamura, R.; Andriopoulou, M.; Giles, B. L.; Jeszenszky, H.; Khotyaintsev, Y. V.; Lindqvist, P.-A.; Torbert, R. B.

2017-12-01

Space missions with sophisticated plasma instrumentation such as Magnetospheric Multiscale, which employs four satellites to explore near-Earth space benefit from a low electric potential of the spacecraft, to improve the plasma measurements and therefore carry instruments to actively control the potential by means of ion beams. Without control, the potential varies in anticorrelation with plasma density and temperature to maintain an equilibrium between the plasma current and the one of photoelectrons produced at the surface and overcoming the potential barrier. A drawback of the controlled, almost constant potential is the difficulty to use it as convenient estimator for plasma density. This paper identifies a correlation between the spacecraft potential and the ambient electric field, both measured by double probes mounted at the end of wire booms, as the main responsible for artifacts in the potential data besides the known effect of the variable photoelectron production due to changing illumination of the surface. It is shown that the effect of density variations is too weak to explain the observed correlation with the electric field and that a correction of the artifacts can be achieved to enable the reconstruction of the uncontrolled potential and plasma density in turn. Two possible mechanisms are discussed: the asymmetry of the current-voltage characteristic determining the probe to plasma potential and the fact that a large equipotential structure embedded in an electric field results in asymmetries of both the emission and spatial distribution of photoelectrons, which results in an increase of the spacecraft potential.

Hydrodynamic size-dependent cellular uptake of aqueous QDs probed by fluorescence correlation spectroscopy.

PubMed

Dong, Chaoqing; Irudayaraj, Joseph

2012-10-11

Aqueous quantum dots (QDs) directly synthesized with various thiol ligands have been investigated as imaging probes in living cells. However, the effect of the surface chemistry of these ligands on QDs' cellular uptakes and their intracellular fate remains poorly understood. In this work, four CdTe QDs were directly synthesized under aqueous conditions using four different thiols as stabilizers and their interactions with cells were investigated. Fluorescence correlation spectroscopy (FCS), X-ray photoelectron spectroscopy (XPS), and zeta potential measurements on QDs primarily show that the surface structure of these QDs is highly dependent on the thiol ligands used in the preparation of QDs' precursors, including its layer thicknesses, densities, and surface charges. Subsequently, FCS integrated with the maximum-entropy-method-based FCS (MEMFCS) was used to investigate the concentration distribution and dynamics of these QDs in living A-427 cells. Our findings indicate that QDs' surface characteristics affect cell membrane adsorption and subsequent internalization. More critically, we show that the cellular uptake of aqueous QDs is dependent on their hydrodynamic diameter and might have the potential to escape trapped environments to accumulate in the cytoplasm.

The use of the ion probe mass spectrometer in the measurement of hydrogen concentration gradients in Monel K 500

NASA Technical Reports Server (NTRS)

Truhan, J. J., Jr.; Hehemann, R. F.

1974-01-01

The ion probe mass spectrometer was used to measure hydrogen concentration gradients in cathodically charged Monel K 500. Initial work with the ion probe involved the calibration of the instrument and the establishment of a suitable experimental procedure for this application. Samples of Monel K 500 were cathodically charged in a weak sulfuric acid solution. By varying the current density, different levels of hydrogen were introduced into the samples. Hydrogen concentration gradients were taken by ion sputtering on the surface of these samples and monitoring the behavior of the hydrogen mass peak as a function of time. An attempt was made to determine the relative amounts of hydrogen in the bulk and grain boundaries by analyzing a fresh fracture surface with a higher proportion of grain boundary area. It was found that substantially more hydrogen was detected in the grain boundaries than in the bulk, confirming the predictions of previous workers. A sputter rate determination was made in order to establish the rate of erosion.

Surface reconstruction of InAs (001) depending on the pressure and temperature examined by density functional thermodynamics.

PubMed

Yeu, In Won; Park, Jaehong; Han, Gyuseung; Hwang, Cheol Seong; Choi, Jung-Hae

2017-09-06

A detailed understanding of the atomic configuration of the compound semiconductor surface, especially after reconstruction, is very important for the device fabrication and performance. While there have been numerous experimental studies using the scanning probe techniques, further theoretical studies on surface reconstruction are necessary to promote the clear understanding of the origins and development of such subtle surface structures. In this work, therefore, a pressure-temperature surface reconstruction diagram was constructed for the model case of the InAs (001) surface considering both the vibrational entropy and configurational entropy based on the density functional theory. Notably, the equilibrium fraction of various reconstructions was determined as a function of the pressure and temperature, not as a function of the chemical potential, which largely facilitated the direct comparison with the experiments. By taking into account the entropy effects, the coexistence of the multiple reconstructions and the fractional change of each reconstruction by the thermodynamic condition were predicted and were in agreement with the previous experimental observations. This work provides the community with a useful framework for such type of theoretical studies.

Mapping Hydrophobicity on the Protein Molecular Surface at Atom-Level Resolution

PubMed Central

Nicolau Jr., Dan V.; Paszek, Ewa; Fulga, Florin; Nicolau, Dan V.

2014-01-01

A precise representation of the spatial distribution of hydrophobicity, hydrophilicity and charges on the molecular surface of proteins is critical for the understanding of the interaction with small molecules and larger systems. The representation of hydrophobicity is rarely done at atom-level, as this property is generally assigned to residues. A new methodology for the derivation of atomic hydrophobicity from any amino acid-based hydrophobicity scale was used to derive 8 sets of atomic hydrophobicities, one of which was used to generate the molecular surfaces for 35 proteins with convex structures, 5 of which, i.e., lysozyme, ribonuclease, hemoglobin, albumin and IgG, have been analyzed in more detail. Sets of the molecular surfaces of the model proteins have been constructed using spherical probes with increasingly large radii, from 1.4 to 20 Å, followed by the quantification of (i) the surface hydrophobicity; (ii) their respective molecular surface areas, i.e., total, hydrophilic and hydrophobic area; and (iii) their relative densities, i.e., divided by the total molecular area; or specific densities, i.e., divided by property-specific area. Compared with the amino acid-based formalism, the atom-level description reveals molecular surfaces which (i) present an approximately two times more hydrophilic areas; with (ii) less extended, but between 2 to 5 times more intense hydrophilic patches; and (iii) 3 to 20 times more extended hydrophobic areas. The hydrophobic areas are also approximately 2 times more hydrophobicity-intense. This, more pronounced “leopard skin”-like, design of the protein molecular surface has been confirmed by comparing the results for a restricted set of homologous proteins, i.e., hemoglobins diverging by only one residue (Trp37). These results suggest that the representation of hydrophobicity on the protein molecular surfaces at atom-level resolution, coupled with the probing of the molecular surface at different geometric resolutions, can capture processes that are otherwise obscured to the amino acid-based formalism. PMID:25462574

Thomson scattering measurements from asymmetric interpenetrating plasma flows

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

Ross, J. S., E-mail: ross36@llnl.gov; Moody, J. D.; Fiuza, F.

2014-11-15

Imaging Thomson scattering measurements of collective ion-acoustic fluctuations have been utilized to determine ion temperature and density from laser produced counter-streaming asymmetric flows. Two foils are heated with 8 laser beams each, 500 J per beam, at the Omega Laser facility. Measurements are made 4 mm from the foil surface using a 60 J 2ω probe laser with a 200 ps pulse length. Measuring the electron density and temperature from the electron-plasma fluctuations constrains the fit of the multi-ion species, asymmetric flows theoretical form factor for the ion feature such that the ion temperatures, ion densities, and flow velocities formore » each plasma flow are determined.« less

Prediction of Particle Number Density and Particle Properties in the Flow Field Observed by the Nephelometer Experiment on the Galileo Probe

NASA Technical Reports Server (NTRS)

Naughton, Jonathan W.

1998-01-01

This report summarizes the work performed to assist in the analysis of data returned from the Galileo Probe's Nephelometer instrument. A computation of the flow field around the Galileo Probe during its descent through the Jovian atmosphere was simulated. The behavior of cloud particles that passed around the Galileo probe was then computed and the number density in the vicinity of the Nephelometer instrument was predicted. The results of our analysis support the finding that the number density of cloud particles was not the same in each of the four sampling volumes of the Nephelometer instrument. The number densities calculated in this study are currently being used to assist in the reanalysis of the data returned from the Galileo Probe.

Nanoscale patterning of Si surface using SPM scratching

NASA Astrophysics Data System (ADS)

Ogino, T.; Nishimura, S.; Shirakashi, J.

2008-03-01

Nanolithography of Si surface using scanning probe microscopy (SPM) scratching with a diamond-coated tip was systematically investigated at a low force regime below 9 μN. The groove patterns with controlled width and depth could be achieved by adjusting the applied force, scan direction and the number of scan cycles. There was no effect of scan speed on the groove size. The minimum groove width of 10 nm was obtained on Si surfaces. Furthermore, more complex nanostructures such as line and space patterns of 30 nm pith and dot arrays of 2.6×1010 cm-2 density were realized. SPM scratching with a diamond-coated tip allows nanoscale patterning of Si surfaces to be performed simply.

Electrochemical DNA sensor for anthrax toxin activator gene atxA-detection of PCR amplicons.

PubMed

Das, Ritu; Goel, Ajay K; Sharma, Mukesh K; Upadhyay, Sanjay

2015-12-15

We report the DNA probe functionalized electrochemical genosensor for the detection of Bacillus anthracis, specific towards the regulatory gene atxA. The DNA sensor is fabricated on electrochemically deposited gold nanoparticle on self assembled layer of (3-Mercaptopropyl) trimethoxysilane (MPTS) on GC electrode. DNA hybridization is monitored by differential pulse voltammogram (DPV). The modified GC electrode is characterized by atomic force microscopy (AFM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) method. We also quantified the DNA probe density on electrode surface by the chronocoulometric method. The detection is specific and selective for atxA gene by DNA probe on the electrode surface. No report is available for the detection of B. anthracis by using atxA an anthrax toxin activator gene. In the light of real and complex sample, we have studied the PCR amplicons of 303, 361 and 568 base pairs by using symmetric and asymmetric PCR approaches. The DNA probe of atxA gene efficiently hybridizes with different base pairs of PCR amplicons. The detection limit is found to be 1.0 pM (S/N ratio=3). The results indicate that the DNA sensor is able to detect synthetic target as well as PCR amplicons of different base pairs. Copyright © 2015 Elsevier B.V. All rights reserved.

Studies of RF sheaths and diagnostics on IShTAR

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

Crombé, K., E-mail: Kristel.Crombe@UGent.be; LPP-ERM/KMS, Royal Military Academy, Brussels; Devaux, S.

2015-12-10

IShTAR (Ion cyclotron Sheath Test ARrangement) is a linear magnetised plasma test facility for RF sheaths studies at the Max-Planck-Institut für Plasmaphysik in Garching. In contrast to a tokamak, a test stand provides more liberty to impose the parameters and gives better access for the instrumentation and antennas. The project will support the development of diagnostic methods for characterising RF sheaths and validate and improve theoretical predictions. The cylindrical vacuum vessel has a diameter of 1 m and is 1.1 m long. The plasma is created by an external cylindrical plasma source equipped with a helical antenna that has been designed tomore » excite the m=1 helicon mode. In inductive mode, plasma densities and electron temperatures have been characterised with a planar Langmuir probe as a function of gas pressure and input RF power. A 2D array of RF compensated Langmuir probes and a spectrometer are planned. A single strap RF antenna has been designed; the plasma-facing surface is aligned to the cylindrical plasma to ease the modelling. The probes will allow direct measurements of plasma density profiles in front of the RF antenna, and thus a detailed study of the density modifications induced by RF sheaths, which influences the coupling. The RF antenna frequency has been chosen to study different plasma wave interactions: the accessible plasma density range includes an evanescent and propagative behaviour of slow or fast waves, and allows the study of the effect of the lower hybrid resonance layer.« less

Rain, winds and haze during the Huygens probe's descent to Titan's surface

USGS Publications Warehouse

Tomasko, M.G.; Archinal, B.; Becker, T.; Bezard, B.; Bushroe, M.; Combes, M.; Cook, D.; Coustenis, A.; De Bergh, C.; Dafoe, L.E.; Doose, L.; Doute, S.; Eibl, A.; Engel, S.; Gliem, F.; Grieger, B.; Holso, K.; Howington-Kraus, E.; Karkoschka, E.; Keller, H.U.; Kirk, R.; Kramm, R.; Kuppers, M.; Lanagan, P.; Lellouch, E.; Lemmon, M.; Lunine, J.; McFarlane, E.; Moores, J.; Prout, G.M.; Rizk, B.; Rosiek, M.; Rueffer, P.; Schroder, S.E.; Schmitt, B.; See, C.; Smith, P.; Soderblom, L.; Thomas, N.; West, R.

2005-01-01

The irreversible conversion of methane into higher hydrocarbons in Titan's stratosphere implies a surface or subsurface methane reservoir. Recent measurements from the cameras aboard the Cassini orbiter fail to see a global reservoir, but the methane and smog in Titan's atmosphere impedes the search for hydrocarbons on the surface. Here we report spectra and high-resolution images obtained by the Huygens Probe Descent Imager/Spectral Radiometer instrument in Titan's atmosphere. Although these images do not show liquid hydrocarbon pools on the surface, they do reveal the traces of once flowing liquid. Surprisingly like Earth, the brighter highland regions show complex systems draining into flat, dark lowlands. Images taken after landing are of a dry riverbed. The infrared reflectance spectrum measured for the surface is unlike any other in the Solar System; there is a red slope in the optical range that is consistent with an organic material such as tholins, and absorption from water ice is seen. However, a blue slope in the near-infrared suggests another, unknown constituent. The number density of haze particles increases by a factor of just a few from an altitude of 150 km to the surface, with no clear space below the tropopause. The methane relative humidity near the surface is 50 per cent. ?? 2005 Nature Publishing Group.

Microwave Interferometric Density Measurements of a Pulsed Helicon Source

NASA Astrophysics Data System (ADS)

Scime, Ethan; Scime, Earl; Thompson, Derek

2017-10-01

The intense rf environment of a helicon plasma source is problematic for electrostatic probe measurements of plasma density, particularly at low neutral pressures. Here we present measurements of the line-integrated plasma density in a helicon plasma source using a multi-frequency (20-40 GHz) microwave interferometer. The design of the diagnostic and the data acquisition system are presented, as well as a comparison to density profiles obtained with a moveable electrostatic probe. A parametric fit to the probe profile measurements is used to determine the peak density from the microwave density measurements. This work supported by U.S. National Science Foundation Grant No. PHY-1360278.

Density measurements in low pressure, weakly magnetized, RF plasmas: experimental verification of the sheath expansion effect

NASA Astrophysics Data System (ADS)

Zhang, Yunchao; Charles, Christine; Boswell, Roderick W.

2017-07-01

This experimental study shows the validity of Sheridan's method in determining plasma density in low pressure, weakly magnetized, RF plasmas using ion saturation current data measured by a planar Langmuir probe. The ion density derived from Sheridan's method which takes into account the sheath expansion around the negatively biased probe tip, presents a good consistency with the electron density measured by a cylindrical RF-compensated Langmuir probe using the Druyvesteyn theory. The ion density obtained from the simplified method which neglects the sheath expansion effect, overestimates the true density magnitude, e.g., by a factor of 3 to 12 for the present experiment.

Spectral probes of the holographic Fermi ground state: Dialing between the electron star and AdS Dirac hair

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

Cubrovic, Mihailo; Liu Yan; Schalm, Koenraad

2011-10-15

We argue that the electron star and the anti-de Sitter (AdS) Dirac hair solution are two limits of the free charged Fermi gas in AdS. Spectral functions of holographic duals to probe fermions in the background of electron stars have a free parameter that quantifies the number of constituent fermions that make up the charge and energy density characterizing the electron star solution. The strict electron star limit takes this number to be infinite. The Dirac hair solution is the limit where this number is unity. This is evident in the behavior of the distribution of holographically dual Fermi surfaces.more » As we decrease the number of constituents in a fixed electron star background the number of Fermi surfaces also decreases. An improved holographic Fermi ground state should be a configuration that shares the qualitative properties of both limits.« less

The Dragonfly Nearby Galaxies Survey. IV. A Giant Stellar Disk in NGC 2841

NASA Astrophysics Data System (ADS)

Zhang, Jielai; Abraham, Roberto; van Dokkum, Pieter; Merritt, Allison; Janssens, Steven

2018-03-01

Neutral gas is commonly believed to dominate over stars in the outskirts of galaxies, and investigations of the disk-halo interface are generally considered to be in the domain of radio astronomy. This may simply be a consequence of the fact that deep H I observations typically probe to a lower-mass surface density than visible wavelength data. This paper presents low-surface-brightness, optimized visible wavelength observations of the extreme outskirts of the nearby spiral galaxy NGC 2841. We report the discovery of an enormous low-surface brightness stellar disk in this object. When azimuthally averaged, the stellar disk can be traced out to a radius of ∼70 kpc (5 R 25 or 23 inner disk scale lengths). The structure in the stellar disk traces the morphology of H I emission and extended UV emission. Contrary to expectations, the stellar mass surface density does not fall below that of the gas mass surface density at any radius. In fact, at all radii greater than ∼20 kpc, the ratio of the stellar mass to gas mass surface density is a constant 3:1. Beyond ∼30 kpc, the low-surface-brightness stellar disk begins to warp, which may be an indication of a physical connection between the outskirts of the galaxy and infall from the circumgalactic medium. A combination of stellar migration, accretion, and in situ star formation might be responsible for building up the outer stellar disk, but whatever mechanisms formed the outer disk must also explain the constant ratio between stellar and gas mass in the outskirts of this galaxy.

On the origin of the ionosphere at Moon : a study using results from Chandrayaan-I S-band radio occultation experiment and a photochemical model

NASA Astrophysics Data System (ADS)

Kailasam Madathil, Ambili; Bhardwaj, Anil; Choudhary, Raj Kumar

2016-07-01

Using Chandrayaan-1 communication link between orbiter and ground (S-band frequency), the presence of ionosphere at Moon has been explored using Radio Occultation technique. Results obtained from the observations conducted between July 30 and August 14, 2009 show evidence for a possible existence of the Ionosphere at Moon. A few seconds before the occultation of Chandrayaan-1 radio signals, extra fluctuation in the rate of change of difference between the theoretically estimated Doppler and observed Doppler was observed. The fluctuation was more pronounced when the probing radio waves were crossing through the day-night terminator. Using standard onion-peeling technique to invert the phase changes in radio signals to the refractivity of the medium, we estimated the bending angle and hence the electron density profiles for the Lunar medium. The estimated electron density near the Lunar surface was of the order of 400 - 1000 cm ^{-3} which decreased monotonically with increasing altitude till about 40 km above the surface where it became negligible. The observed electron density was compared with the results from a model which was developed based on CHACE measurements abroad Moon Impact Probe of Chandrayaan-I. The model included the photo chemical reactions and solar wind interactions of the lunar plasma. We propose that the ionosphere over Moon could have molecular origin with H _{2}O ^{+},CO_{2} ^{+} and H_{3}O ^{+} as dominant ions.

Controlling the dual mechanisms of oxide interface doping

NASA Astrophysics Data System (ADS)

Dai, Weitao; Cen, Cheng

The formation of two dimensional electron gas (2DEG) at LaAlO3/SrTiO3 interfaces involves multiple electronic and structural causes. The interplay between them makes the investigation of individual mechanism very challenging. Here we demonstrate the nanoscale selective control of two interface doping pathways: charge transfers from surface adsorbed protons and oxygen vacancies created in LaAlO3 layers. The selective control is achieved by combining intensive electric field generated by conducting AFM probe which controls both the creation/migration of oxygen vacancies and the surface proton density, with plasma assisted surface hydroxylation and solvent based proton solvation that act mainly on surface adsorbates. Robust nanoscale reversible metal-insulator transition was achieved at the interfaces with the LaAlO3 layer thicker than the critic thickness. Different combinations of the experimental methods and doping mechanisms enable highly flexible tuning of the 2DEG's carrier density, mobility and sensitivity to ambient environments. The reversible and independent controls of surface states and vacancies add to the fundamental material research capabilities and can benefit future exploration of designed 2DEG nanoelectronics.

Measurement of Electron Density Using the Multipole Resonance Probe, Langmuir Probe and Optical Emission Spectroscopy in Low Pressure Plasmas with Different Electron Energy Distribution Functions

NASA Astrophysics Data System (ADS)

Oberberg, Moritz; Bibinov, Nikita; Ries, Stefan; Awakowicz, Peter; Institute of Electrical Engineering; Plasma Technology Team

2016-09-01

In recently publication, the young diagnostic tool Multipole Resonance Probe (MRP) for electron density measurements was introduced. It is based on active plasma resonance spectroscopy (APRS). The probe was simulated und evaluated for different devices. The geometrical and electrical symmetry simplifies the APRS model, so that the electron density can be easily calculated from the measured resonance. In this work, low pressure nitrogen mixture plasmas with different electron energy distribution functions (EEDF) are investigated. The results of the MRP measurement are compared with measurements of a Langmuir Probe (LP) and Optical Emission Spectroscopy (OES). Probes and OES measure in different regimes of kinetic electron energy. Both probes measure electrons with low kinetic energy (<10 eV), whereas the OES is influenced by electrons with high kinetic energy which are needed for transitions of molecule bands. By the determination of the absolute intensity of N2(C-B) and N2+(B-X)electron temperature and density can be calculated. In a non-maxwellian plasma, all plasma diagnostics need to be combined.

Characterizing the performance of an affordable, multichannel conductivity probe for density measurements in stratified flows

NASA Astrophysics Data System (ADS)

Subramanian, Balaji; Carminati, Marco; Luzzatto-Fegiz, Paolo

2017-11-01

In stratified flows, conductivity (combined with temperature) is often used to measure density. The conductivity probes typically used can resolve very fine spatial scales, but on the downside they are fragile, expensive, sensitive to environmental noise and have only single channel capability. Recently a low-cost, robust, arduino-based probe called Conduino was developed, which can be valuable in a wide range of applications where resolving extremely small spatial scales is not needed. This probe uses micro-USB connectors as actual conductivity sensors with a custom designed electronic board for simultaneous acquisition from multiple probes, with conductivity resolution comparable to commercially available PME conductivity probe. A detailed assessment of performance of this Conduino probe is described here. To establish time response and sensitivity as a function of electrode geometry, we build a variety of shapes for different kinds of applications, with tip spacing ranging from 0.5-2.5 mm, and with electrode length ranging from 2.3-6 mm. We set up a two-layer density profile and traverse it rapidly, yielding a time response comparable to PME. The Conduino's multi-channel capability is used to operate probe arrays, which helps to construct density fields in stratified flows.

Cone-Probe Rake Design and Calibration for Supersonic Wind Tunnel Models

NASA Technical Reports Server (NTRS)

Won, Mark J.

1999-01-01

A series of experimental investigations were conducted at the NASA Langley Unitary Plan Wind Tunnel (UPWT) to calibrate cone-probe rakes designed to measure the flow field on 1-2% scale, high-speed wind tunnel models from Mach 2.15 to 2.4. The rakes were developed from a previous design that exhibited unfavorable measurement characteristics caused by a high probe spatial density and flow blockage from the rake body. Calibration parameters included Mach number, total pressure recovery, and flow angularity. Reference conditions were determined from a localized UPWT test section flow survey using a 10deg supersonic wedge probe. Test section Mach number and total pressure were determined using a novel iterative technique that accounted for boundary layer effects on the wedge surface. Cone-probe measurements were correlated to the surveyed flow conditions using analytical functions and recursive algorithms that resolved Mach number, pressure recovery, and flow angle to within +/-0.01, +/-1% and +/-0.1deg , respectively, for angles of attack and sideslip between +/-8deg. Uncertainty estimates indicated the overall cone-probe calibration accuracy was strongly influenced by the propagation of measurement error into the calculated results.

Characterization of low-pressure microwave and radio frequency discharges in oxygen applying optical emission spectroscopy and multipole resonance probe

NASA Astrophysics Data System (ADS)

Steves, Simon; Styrnoll, Tim; Mitschker, Felix; Bienholz, Stefan; Nikita, Bibinov; Awakowicz, Peter

2013-11-01

Optical emission spectroscopy (OES) and multipole resonance probe (MRP) are adopted to characterize low-pressure microwave (MW) and radio frequency (RF) discharges in oxygen. In this context, both discharges are usually applied for the deposition of permeation barrier SiOx films on plastic foils or the inner surface of plastic bottles. For technological reasons the MW excitation is modulated and a continuous wave (cw) RF bias is used. The RF voltage produces a stationary low-density plasma, whereas the high-density MW discharge is pulsed. For the optimization of deposition process and the quality of the deposited barrier films, plasma conditions are characterized using OES and MRP. To simplify the comparison of applied diagnostics, both MW and RF discharges are studied separately in cw mode. The OES and MRP diagnostic methods complement each other and provide reliable information about electron density and electron temperature. In the MW case, electron density amounts to ne = (1.25 ± 0.26) × 1017 m-3, and kTe to 1.93 ± 0.20 eV, in the RF case ne = (6.8 ± 1.8)×1015 m-3 and kTe = 2.6 ± 0.35 eV. The corresponding gas temperatures are 760±40 K and 440±20 K.

The Ocean`s Thermohaline Circulation in a Fish Tank

NASA Astrophysics Data System (ADS)

Lavender, K.; Joyce, P.; Graziano, L.; Harris, S.; Jaroslow, G.; Lea, C.; Schell, J.; Witting, J.

2005-12-01

This demonstration develops intuition about density stratification, a concept critical to understanding the ocean`s thermohaline circulation. In addition, students learn how temperature and salinity affect density, how these characteristics may be density-compensating, and students gain practice in graphing and interpreting vertical profiles and temperature-salinity (T-S) diagrams. The demonstration requires a rectangular fish tank (5-10 gallons) with a plexiglass partition, preparation of three colored ''water masses'' representing surface water (warm and fresh), ''mystery'' Mediterranean Water (warm and salty), and North Atlantic Deep Water (NADW; cold and salty), a kitchen sponge, and a temperature and salinity probe. Density may be computed using an Equation of State calculator (e.g. online version at http://fermi.jhuapl.edu/denscalc.html). The larger side of the fish tank is filled halfway with NADW, then surface water is layered on top by carefully pouring it on a floating sponge. A student volunteer measures the temperature and salinity of the two water masses, while another computes the densities. Students draw vertical profiles and T-S diagrams representing the temperature, salinity, and density of the water column. The properties of the ''mystery'' water are measured and students predict what will happen when the water is poured on the opposite side of the partition and is allowed to overflow into the layered water. If the density gradients are sufficiently large, a beautiful internal wave develops as the mystery water overflows the sill and becomes intermediate Mediterranean Water. If time permits, having a student blow on the surface illustrates the limited influence of ''wind'' with depth; an internal wave may by forced by depressing the thermocline with a large, flat spoon; and pouring extra NADW on the sponge floating at the surface may illustrate deep convection.

Langmuir-Probe Measurements in Flowing-Afterglow Plasmas

NASA Technical Reports Server (NTRS)

Johnsen, R.; Shunko, E. V.; Gougousi, T.; Golde, M. F.

1994-01-01

The validity of the orbital-motion theory for cylindrical Langmuir probes immersed in flowing- afterglow plasmas is investigated experimentally. It is found that the probe currents scale linearly with probe area only for electron-collecting but not for ion-collecting probes. In general, no agreement is found between the ion and electron densities derived from the probe currents. Measurements in recombining plasmas support the conclusion that only the electron densities derived from probe measurements can be trusted to be of acceptable accuracy. This paper also includes a brief derivation of the orbital-motion theory, a discussion of perturbations of the plasma by the probe current, and the interpretation of plasma velocities obtained from probe measurements.

Determining Core Plasmaspheric Electron Densities with the Van Allen Probes

NASA Astrophysics Data System (ADS)

De Pascuale, S.; Hartley, D.; Kurth, W. S.; Kletzing, C.; Thaller, S. A.; Wygant, J. R.

2016-12-01

We survey three methods for obtaining electron densities inside of the core plasmasphere region (L < 4) to the perigee of the Van Allen Probes (L 1.1) from September 2012 to December 2014. Using the EMFISIS instrument on board the Van Allen Probes, electron densities are extracted from the upper hybrid resonance to an uncertainty of 10%. Some measurements are subject to larger errors given interpretational issues, especially at low densities (L > 4) resulting from geomagnetic activity. At high densities EMFISIS is restricted by an upper observable limit near 3000 cm-3. As this limit is encountered above perigee, we employ two additional methods validated against EMFISIS measurements to determine electron densities deep within the plasmasphere (L < 2). EMFISIS can extrapolate density estimates to lower L by calculating high densities, in good agreement with the upper hybrid technique when applicable, from plasma wave properties. Calibrated measurements, from the Van Allen Probes EFW potential instrument, also extend into this range. In comparison with the published EMFISIS database we provide a metric for the validity of core plasmaspheric density measurements obtained from these methods and an empirical density model for use in wave and particle simulations.

Star Formation-Driven Winds in the Early Universe

NASA Astrophysics Data System (ADS)

Peek, Matthew; Lundgren, Britt; Brammer, Gabriel

2018-01-01

Measuring the extent of star formation-driven winds from galaxies in the early universe is crucial for understanding of how galaxies evolve over cosmic time. Using WFC3/IR grism data from the Hubble Space Telescope (HST), we have measured the star formation rates and star formation rate surface densities of several hundred galaxies at redshift (z) = 1, when the universe was roughly half its present age. The galaxies we examine are also probed by background quasars, whose spectra provide information about the extent of metal-enriched gas in their halos. We use a computational pipeline to measure the density of the star formation in each galaxy and correlate these measurements with detections of Mg II absorption in nearby quasar spectra from the Sloan Digital Sky Survey. Our preliminary results support a model in which galaxies with high SFR surface densities drive metal-enriched gas out of the disk and into these galaxies’ extended halos, where that gas is detected in the spectra of more distant quasars.

Huygens Probe In-Situ Measurements : An Update

NASA Astrophysics Data System (ADS)

Lorenz, Ralph D.

2015-04-01

The global Titan perspective afforded by ongoing Cassini observations, and prospects for future in-situ exploration, have prompted a re-examination of Huygens data, yielding a number of recent new results. Gravity waves have been detected (Lorenz, Ferri and Young, Icarus, 2014) in the HASI descent temperature data, with ~2K amplitude. These waves are seen above about 60km, and analysis suggests they may therefore be controlled by interaction of upward-propagating waves with the zonal wind field. A curious cessation of detection of sound pulses by a Surface Science Package ultrasound instrument about 15 minutes after the probe landed appears to be best explained (Lorenz et al., Planetary and Space Science, 2014) by an accumulation of polyatomic vapors such as ethane, sweated out of the ground by the warm probe. Such gases have high acoustic attenuation, and were independently measured by the probe GCMS. The Huygens probe carried two radar altimeters. While their principal function was merely to trigger observation sequences at specific altitudes on the science instruments, the surface range history, and the Automatic Gain Control (AGC) housekeeping data, provide some useful information on Titan's surface (Lorenz et al., submitted). Small-scale topographic variations, and the surface radar reflectivity characteristics implied by the AGC variation with height, are discussed. A new integrated timeline product, which arranges second-by-second measurements from several Huygens sensors on a convenient, common tabulation, has been recently archived on the PDS Atmospheres node. Finally, a troubling discrepancy exists between radio occultation and infrared soundings from Cassini, and Huygens methane and temperature measurements in the lower stratosphere. The interdependence of these parameters will be discussed. In particular the possible role of the assumed probe mass history (depending on the unmeasured ablation from the heat shield) and the assumed zonal wind profile on the recovered temperature profile to these factors is examined. It is noted that the speed relative to the atmosphere in the late part of entry, when the hypersonic entry speed has been largely bled away by drag, is particularly sensitive to assumed winds, and it is in this altitude region where the recovered density (or temperature) profile discrepancy may be highest.

Measurement of the magnetic field inside the holes of a drilled bulk high-Tc superconductor

NASA Astrophysics Data System (ADS)

Lousberg, Gregory P.; Fagnard, Jean-François; Noudem, Jacques G.; Ausloos, Marcel; Vanderheyden, Benoit; Vanderbemden, Philippe

2009-04-01

We use macroscopic holes drilled in a bulk YBCO superconductor to probe its magnetic properties in the volume of the sample. The sample is subjected to an AC magnetic flux with a density ranging from 30 to 130 mT and the flux in the superconductor is probed by miniature coils inserted in the holes. In a given hole, three different penetration regimes can be observed: (i) the shielded regime, where no magnetic flux threads the hole; (ii) the gradual penetration regime, where the waveform of the magnetic field has a clipped sine shape whose fundamental component scales with the applied field; and (iii) the flux concentration regime, where the waveform of the magnetic field is nearly a sine wave, with an amplitude exceeding that of the applied field by up to a factor of two. The distribution of the penetration regimes in the holes is compared with that of the magnetic flux density at the top and bottom surfaces of the sample, and is interpreted with the help of optical polarized light micrographs of these surfaces. We show that the measurement of the magnetic field inside the holes can be used as a local characterization of the bulk magnetic properties of the sample.

Measuring the mechanical properties of molecular conformers

NASA Astrophysics Data System (ADS)

Jarvis, S. P.; Taylor, S.; Baran, J. D.; Champness, N. R.; Larsson, J. A.; Moriarty, P.

2015-09-01

Scanning probe-actuated single molecule manipulation has proven to be an exceptionally powerful tool for the systematic atomic-scale interrogation of molecular adsorbates. To date, however, the extent to which molecular conformation affects the force required to push or pull a single molecule has not been explored. Here we probe the mechanochemical response of two tetra(4-bromophenyl)porphyrin conformers using non-contact atomic force microscopy where we find a large difference between the lateral forces required for manipulation. Remarkably, despite sharing very similar adsorption characteristics, variations in the potential energy surface are capable of prohibiting probe-induced positioning of one conformer, while simultaneously permitting manipulation of the alternative conformational form. Our results are interpreted in the context of dispersion-corrected density functional theory calculations which reveal significant differences in the diffusion barriers for each conformer. These results demonstrate that conformational variation significantly modifies the mechanical response of even simple porpyhrins, potentially affecting many other flexible molecules.

First principles investigation of heterogeneous catalysis on metal oxide surfaces

NASA Astrophysics Data System (ADS)

Ghoussoub, Mireille

Metal oxides possess unique electronic and structural properties that render them highly favourable for applications in heterogeneous catalysis. In this study, computational atomistic modelling based on Density Functional Theory was used to investigate the reduction of carbon dioxide over hydroxylated indium oxide nanoparticles, as well at the activation of methane over oxygen-covered bimetallic surfaces. The first study employed metadynamics-biased ab initio molecular dynamics to obtain the free energy surface of the various reaction steps at finite temperature. In the second study, the nudged elastic band method was used to probe the C-H activation mechanisms for different surface configurations. In both cases, activation energies, reaction energies, transition state structures, and charge analysis results are used to explain the underlying mechanistic pathways.

In-plane conductance of thin films as a probe of surface chemical environment: Adsorbate effects on film electronic properties of indium tin oxide and gold

NASA Astrophysics Data System (ADS)

Swint, Amy Lynn

Changes in the in-plane conductance of conductive thin films are observed as a result of chemical adsorption at the surface. Reaction of the indium tin oxide (ITO) surface with Bronsted acids (bases) leads to increases (decreases) in its in-plane conductance as measured by a four-point probe configuration. The conductance varies monotonically with pH suggesting that the degree of surface protonation or hydroxylation controls the surface charge density, which in turn affects the width of the n-type depletion layer, and ultimately the in-plane conductance. Measurements at constant pH with a series of tetraalkylammonium hydroxide species of varying cation size indicate that surface dipoles also affect ITO conductance by modulating the magnitude of the surface polarization. Modulating the double layer with varying aqueous salt solutions also affects ITO conductance, though not to the same degree as strong Bronsted acids and bases. Solvents of varying dielectric constant and proton donating ability (ethanol, dimethylformamide) decrease ITO conductance relative to H2O. In addition, changing solvent gives rise to thermally-derived conductance transients, which result from exothermic solvent mixing. The self-assembly of alkanethiols at the surface increases the conductance of ITO films, most likely through carrier population effects. In all cases examined the combined effects of surface charge, adsorbed dipole layer magnitude and carrier injection are responsible for altering the ITO conductance. Besides being directly applicable to the control of electronic properties, these results also point to the use of four-point probe resistance measurements in condensed phase sensing applications. Ultrasensitive conductance-based gas phase sensing of organothiol adsorption to gold nanowires is accomplished with a limit of detection in the 105 molecule range. Further refinement of the inherently low noise resistance measurement may lead to observation of single adsorption events at the gold surface.

Effect of the magnetic field on measurements of the electron density and temperature by cylindrical probes in the Earth's ionosphere

NASA Astrophysics Data System (ADS)

Gubsky, V. F.

2009-12-01

In the 1960s and 1970s, quite simply produced cylindrical Langmuir probes were used in the USSR both on satellites (Kosmos-378, Intercosmos-2, -4, -8, -10, -19) and to measure the electron density and temperature on vertical launched rockets (Vertical’-4, -6, -10) within the Intercosmos program. These measurements were first made at middle latitudes. With increasing inclination of the orbits of launched satellites (satellites had no stabilization), falling sections were sometimes observed on probe characteristics in the electron saturation region. The Intercosmos-Bulgaria-1300 satellite, which was stabilized along three axes and was equipped with a cylindrical probe whose longitudinal axis was always directed downward to the Earth, was launched in 1981. This satellite allowed definite conclusions on the effect of the geomagnetic field on the form of the probe characteristic and, hence, on the determination of the electron density and temperature. Probe characteristics with falling sections are presented. These measurements are compared with those performed in a laboratory plasma. The appearance of negative sections on the probe characteristics is shown to be due to the effect of the geomagnetic field. The degree of this effect depends both on the electron density and temperature and on the probe voltage.

Electronic structure of hydrogenated diamond: Microscopical insight into surface conductivity

NASA Astrophysics Data System (ADS)

Iacobucci, S.; Alippi, Paola; Calvani, P.; Girolami, M.; Offi, F.; Petaccia, L.; Trucchi, D. M.

2016-07-01

We have correlated the surface conductivity of hydrogen-terminated diamond to the electronic structure in the Fermi region. Significant density of electronic states (DOS) in proximity of the Fermi edge has been measured by photoelectron spectroscopy (PES) on surfaces exposed to air, corresponding to a p -type electric conductive regime, while upon annealing a depletion of the DOS has been achieved, resembling the diamond insulating state. The surface and subsurface electronic structure has been determined, exploiting the different probing depths of PES applied in a photon energy range between 7 and 31 eV. Ab initio density functional calculations including surface charge depletion and band-bending effects favorably compare with electronic states measured by angular-resolved photoelectron spectroscopy. Such states are organized in the energy-momentum space in a twofold structure: one, bulk-derived, band disperses in the Γ -X direction with an average hole effective mass of (0.43 ±0.02 ) m0 , where m0 is the bare electron mass; a second flatter band, with an effective mass of (2.2 ±0.9 ) m0 , proves that a hole gas confined in the topmost layers is responsible for the conductivity of the (2 ×1 ) hydrogen-terminated diamond (100 ) surface.

Epitaxial growth of pentacene on alkali halide surfaces studied by Kelvin probe force microscopy.

PubMed

Neff, Julia L; Milde, Peter; León, Carmen Pérez; Kundrat, Matthew D; Eng, Lukas M; Jacob, Christoph R; Hoffmann-Vogel, Regina

2014-04-22

In the field of molecular electronics, thin films of molecules adsorbed on insulating surfaces are used as the functional building blocks of electronic devices. Control of the structural and electronic properties of the thin films is required for reliably operating devices. Here, noncontact atomic force and Kelvin probe force microscopies have been used to investigate the growth and electrostatic landscape of pentacene on KBr(001) and KCl(001) surfaces. We have found that, together with molecular islands of upright standing pentacene, a new phase of tilted molecules appears near step edges on KBr. Local contact potential differences (LCPD) have been studied with both Kelvin experiments and density functional theory calculations. Our images reveal that differently oriented molecules display different LCPD and that their value is independent of the number of molecular layers. These results point to the formation of an interface dipole, which may be explained by a partial charge transfer from the pentacene to the surface. Moreover, the monitoring of the evolution of the pentacene islands shows that they are strongly affected by dewetting: Multilayers build up at the expense of monolayers, and in the Kelvin images, previously unknown line defects appear, which reveal the epitaxial growth of pentacene crystals.

A dual wavelength imaging system for plasma-surface interaction studies on the National Spherical Torus Experiment Upgrade

DOE PAGES

Scotti, F.; Soukhanovskii, V. A.

2015-12-09

A two-channel spectral imaging system based on a charge injection device radiation-hardened intensified camera was built for studies of plasma-surface interactions on divertor plasma facing components in the National Spherical Torus Experiment Upgrade (NSTX-U) tokamak. By means of commercially available mechanically referenced optical components, the two-wavelength setup images the light from the plasma, relayed by a fiber optic bundle, at two different wavelengths side-by-side on the same detector. Remotely controlled filter wheels are used for narrow band pass and neutral density filters on each optical path allowing for simultaneous imaging of emission at wavelengths differing in brightness up to 3more » orders of magnitude. Applications on NSTX-U will include the measurement of impurity influxes in the lower divertor strike point region and the imaging of plasma-material interaction on the head of the surface analysis probe MAPP (Material Analysis and Particle Probe). Furthermore, the diagnostic setup and initial results from its application on the lithium tokamak experiment are presented.« less

Quantifying Interfacial pH Variation at Molecular Length Scales Using a Concurrent Non-Faradaic Reaction.

PubMed

Ryu, Jaeyune; Wuttig, Anna; Surendranath, Yogesh

2018-05-15

We quantify changes in the interfacial pH local to the electrochemical double layer during electrocatalysis, using a concurrent non-faradaic probe reaction. In the absence of electrocatalysis, nanostructured Pt/C surfaces mediate the reaction of H2 with cis-2-butene-1,4-diol to form a mixture of 1,4-butanediol and n-butanol with a selectivity that is linearly dependent on the bulk solution pH. We show that kinetic branching occurs from a common surface-bound intermediate, ensuring that this probe reaction is uniquely sensitive to the interfacial pH within molecular length scales of the surface. We use the pH-dependent selectivity of this reaction to track changes in interfacial pH during concurrent hydrogen oxidation electrocatalysis and find that the local pH can vary dramatically, > 3 units, relative to the bulk value even at modest current densities in well-buffered electrolytes. This work highlights the key role that interfacial pH variation plays in modulating inner-sphere electrocatalysis. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A computer program for borehole compensation of dual-detector density well logs

USGS Publications Warehouse

Scott, James Henry

1978-01-01

The computer program described in this report was developed for applying a borehole-rugosity and mudcake compensation algorithm to dual-density logs using the following information: the water level in the drill hole, hole diameter (from a caliper log if available, or the nominal drill diameter if not), and the two gamma-ray count rate logs from the near and far detectors of the density probe. The equations that represent the compensation algorithm and the calibration of the two detectors (for converting countrate or density) were derived specifically for a probe manufactured by Comprobe Inc. (5.4 cm O.D. dual-density-caliper); they are not applicable to other probes. However, equivalent calibration and compensation equations can be empirically determined for any other similar two-detector density probes and substituted in the computer program listed in this report. * Use of brand names in this report does not necessarily constitute endorsement by the U.S. Geological Survey.

Nebular and Stellar Dust Extinction Across the Disk of Emission-line Galaxies on Kiloparsec Scales

NASA Astrophysics Data System (ADS)

Hemmati, Shoubaneh; Mobasher, Bahram; Darvish, Behnam; Nayyeri, Hooshang; Sobral, David; Miller, Sarah

2015-11-01

We investigate the resolved kiloparsec-scale stellar and nebular dust distribution in eight star-forming galaxies at z ∼ 0.4 in the Great Observatories Origins Deep Survey fields. This is to get a better understanding of the effect of dust attenuation on measurements of physical properties and its variation with redshift. Constructing the observed spectral energy distributions (SEDs) per pixel, based on seven bands of photometric data from Hubble Space Telescope/Advanced Camera for Surveys and WFC3, we performed pixel-by-pixel SED fits to population synthesis models and estimated the small-scale distribution of stellar dust extinction. We use Hα/Hβ nebular emission line ratios from Keck/DEIMOS high-resolution spectra at each spatial resolution element to measure the amount of attenuation faced by ionized gas at different radii from the centers of galaxies. We find a good agreement between the integrated and median of resolved color excess measurements in our galaxies. The ratio of integrated nebular to stellar dust extinction is always greater than unity, but does not show any trend with stellar mass or star formation rate (SFR). We find that inclination plays an important role in the variation of the nebular to stellar excess ratio. The stellar color excess profiles are found to have higher values at the center compared to outer parts of the disk. However, for lower mass galaxies, a similar trend is not found for the nebular color excess. We find that the nebular color excess increases with stellar mass surface density. This explains the absence of radial trend in the nebular color excess in lower mass galaxies which lack a large radial variation of stellar mass surface density. Using standard conversions of SFR surface density to gas mass surface density, and the relation between dust mass surface density and color excess, we find no significant variation in the dust-to-gas ratio in regions with high gas mass surface densities over the scales probed in this study.

Local Charge Injection and Extraction on Surface-Modified Al2O3 Nanoparticles in LDPE.

PubMed

Borgani, Riccardo; Pallon, Love K H; Hedenqvist, Mikael S; Gedde, Ulf W; Haviland, David B

2016-09-14

We use a recently developed scanning probe technique to image with high spatial resolution the injection and extraction of charge around individual surface-modified aluminum oxide nanoparticles embedded in a low-density polyethylene (LDPE) matrix. We find that the experimental results are consistent with a simple band structure model where localized electronic states are available in the band gap (trap states) in the vicinity of the nanoparticles. This work offers experimental support to a previously proposed mechanism for enhanced insulating properties of nanocomposite LDPE and provides a powerful experimental tool to further investigate such properties.

Aspheric surface measurement using capacitive probes

NASA Astrophysics Data System (ADS)

Tao, Xin; Yuan, Daocheng; Li, Shaobo

2017-02-01

With the application of aspheres in optical fields, high precision and high efficiency aspheric surface metrology becomes a hot research topic. We describe a novel method of non-contact measurement of aspheric surface with capacitive probe. Taking an eccentric spherical surface as the object of study, the averaging effect of capacitive probe measurement and the influence of tilting the capacitive probe on the measurement results are investigated. By comparing measurement results from simultaneous measurement of the capacitive probe and contact probe of roundness instrument, this paper indicates the feasibility of using capacitive probes to test aspheric surface and proposes the compensation method of measurement error caused by averaging effect and the tilting of the capacitive probe.

Reliability design and assessment of a micro-probe using the results of a tensile test of a beryllium-copper alloy thin film

NASA Astrophysics Data System (ADS)

Park, Jun-Hyub; Shin, Myung-Soo

2011-09-01

This paper describes the results of tensile tests for a beryllium-copper (BeCu) alloy thin film and the application of the results to the design of a probe. The copper alloy films were fabricated by electroplating. To obtain the tensile characteristics of the film, the dog-bone type specimen was fabricated by the etching method. The tensile tests were performed with the specimen using a test machine developed by the authors. The BeCu alloy has an elastic modulus of 119 GPa and the 0.2% offset yield and ultimate tensile strengths of 1078 MPa and 1108 MPa, respectively. The design and manufacture of a smaller probe require higher pad density and smaller pad-pitch chips. It should be effective in high-frequency testing. For the design of a new micro-probe, we investigated several design parameters that may cause problems, such as the contact force and life, using the tensile properties and the design of experiment method in conjunction with finite element analysis. The optimal dimensions of the probe were found using the response surface method. The probe with optimal dimensions was manufactured by a precision press process. It was verified that the manufactured probe satisfied the life, the contact force and the over drive through the compression tests and the life tests of the probes.

Probing the molecular-level control of aluminosilicate dissolution: A sensitive solid-state NMR proxy for reactive surface area

NASA Astrophysics Data System (ADS)

Washton, Nancy M.; Brantley, Susan L.; Mueller, Karl T.

2008-12-01

For two suites of volcanic aluminosilicate glasses, the accessible and reactive sites for covalent attachment of the fluorine-containing (3,3,3-trifluoropropyl)dimethylchlorosilane (TFS) probe molecule were measured by quantitative 19F nuclear magnetic resonance (NMR) spectroscopy. The first set of samples consists of six rhyolitic and dacitic glasses originating from volcanic activity in Iceland and one rhyolitic glass from the Bishop Tuff, CA. Due to differences in the reactive species present on the surfaces of these glasses, variations in the rate of acid-mediated dissolution (pH 4) for samples in this suite cannot be explained by variations in geometric or BET-measured surface area. In contrast, the rates scale directly with the surface density of TFS-reactive sites as measured by solid-state NMR. These data are consistent with the inference that the TFS-reactive M-OH species on the glass surface, which are known to be non-hydrogen-bonded Q 3 groups, represent loci accessible to and affected by proton-mediated dissolution. The second suite of samples, originating from a chronosequence in Kozushima, Japan, is comprised of four rhyolites that have been weathered for 1.1, 1.8, 26, and 52 ka. The number of TFS-reactive sites per gram increases with duration of weathering in the laboratory for the "Icelandic" samples and with duration of field weathering for both "Icelandic" and Japanese samples. One hypothesis is consistent with these and published modeling, laboratory, and field observations: over short timescales, dissolution is controlled by fast-dissolving sites, but over long timescales, dissolution is controlled by slower-dissolving sites, the surface density of which is proportional to the number of TFS-reactive Q 3 sites. These latter sites are not part of a hydrogen-bonded network on the surface of the glasses, and measurement of their surface site density allows predictions of trends in reactive surface area. The TFS treatment method, which is easily monitored by quantitative 19F solid-state NMR, therefore provides a chemically specific and quantifiable proxy to understand the nature of how sites on dissolving silicates control dissolution. Furthermore, 27Al NMR techniques are shown here to be useful in identifying clays on the glass surfaces, and these methods are therefore effective for quantifying concentrations of weathering impurities. Our interpretations offer a testable hypothesis for the mechanism of proton-promoted dissolution for low-iron aluminosilicate minerals and glasses and suggest that future investigations of reactive surfaces with high-sensitivity NMR techniques are warranted.

Correcting magnetic probe perturbations on current density measurements of current carrying plasmas.

PubMed

Knoblauch, P; Raspa, V; Di Lorenzo, F; Lazarte, A; Clausse, A; Moreno, C

2010-09-01

A method to infer the current density distribution in the current sheath of a plasma focus discharge from a magnetic probe is formulated and then applied to experimental data obtained in a 1.1 kJ device. Distortions on the magnetic probe signal caused by current redistribution and by a time-dependent total discharge current are considered simultaneously, leading to an integral equation for the current density. Two distinct, easy to implement, numerical procedures are given to solve such equation. Experimental results show the coexistence of at least two maxima in the current density structure of a nitrogen sheath.

Dust Abundance Variations in the Magellanic Clouds: Probing the Life-cycle of Metals with All-sky Surveys

NASA Astrophysics Data System (ADS)

Roman-Duval, Julia; Bot, Caroline; Chastenet, Jeremy; Gordon, Karl

2017-06-01

Observations and modeling suggest that dust abundance (gas-to-dust ratio, G/D) depends on (surface) density. Variations of the G/D provide timescale constraints for the different processes involved in the life cycle of metals in galaxies. Recent G/D measurements based on Herschel data suggest a factor of 5-10 decrease in dust abundance between the dense and diffuse interstellar media (ISM) in the Magellanic Clouds. However, the relative nature of the Herschel measurements precludes definitive conclusions as to the magnitude of those variations. We investigate variations of the dust abundance in the LMC and SMC using all-sky far-infrared surveys, which do not suffer from the limitations of Herschel on their zero-point calibration. We stack the dust spectral energy distribution (SED) at 100, 350, 550, and 850 microns from IRAS and Planck in intervals of gas surface density, model the stacked SEDs to derive the dust surface density, and constrain the relation between G/D and gas surface density in the range 10-100 M ⊙ pc-2 on ˜80 pc scales. We find that G/D decreases by factors of 3 (from 1500 to 500) in the LMC and 7 (from 1.5× {10}4 to 2000) in the SMC between the diffuse and dense ISM. The surface-density-dependence of G/D is consistent with elemental depletions, and with simple modeling of the accretion of gas-phase metals onto dust grains. This result has important implications for the sub-grid modeling of galaxy evolution, and for the calibration of dust-based gas-mass estimates, both locally and at high redshift.

Pressure cell for investigations of solid-liquid interfaces by neutron reflectivity.

PubMed

Kreuzer, Martin; Kaltofen, Thomas; Steitz, Roland; Zehnder, Beat H; Dahint, Reiner

2011-02-01

We describe an apparatus for measuring scattering length density and structure of molecular layers at planar solid-liquid interfaces under high hydrostatic pressure conditions. The device is designed for in situ characterizations utilizing neutron reflectometry in the pressure range 0.1-100 MPa at temperatures between 5 and 60 °C. The pressure cell is constructed such that stratified molecular layers on crystalline substrates of silicon, quartz, or sapphire with a surface area of 28 cm(2) can be investigated against noncorrosive liquid phases. The large substrate surface area enables reflectivity to be measured down to 10(-5) (without background correction) and thus facilitates determination of the scattering length density profile across the interface as a function of applied load. Our current interest is on the stability of oligolamellar lipid coatings on silicon surfaces against aqueous phases as a function of applied hydrostatic pressure and temperature but the device can also be employed to probe the structure of any other solid-liquid interface.

Electrochemical Deposition of Nanostructured Conducting Polymer Coatings on Neural Prosthetic Devices

NASA Astrophysics Data System (ADS)

Yang, Junyan; Martin, David

2003-03-01

Micromachined neural prosthetic devices facilitate the functional stimulation of and recording from the central nervous system (CNS). These devices have been fabricated to consist of silicon shanks that have gold or iridium sites along their surface. Our goal is to improve the biocompatibility and long-term performance of the neural prosthetic probes when they are implanted chronically in the brain. In our most recent efforts we have established that electrochemical polymerization can be used to deposit fuzzy coatings of conducting polymers specifically on the electrode sites. For neural prosthetic devices that are intended for long term implantation, we need to develop surfaces that provide intimate contact and promote efficient signal transport at the interface of the microelectrode array and brain tissue. We have developed methods to rapidly and reliably fabricate nanostructured conducting polymer coatings on the electrode probes using templated and surfactant-mediated techniques. Conducting polymer nanomushrooms and nanohairs of polypyrrole (PPy) were electrochemically polymerized onto the functional sites of neural probes by using either nanoporous block copolymers thin films, "track-etched" polycarbonate films or anodic aluminium oxide membranes as templates. Nanofibers of conducting polymers have also been successfully obtained by polymerizations in the presence of surfactants. The influence of current density, monomer concentration, surfactant concentration, and deposition charge on the thickness and morphology of the nanostructured conducting polymer coatings has been studied by optical, scanned probe, scanning electron and transmission electron microscopy. As compared with the normal nodular morphology of polypyrrole, the nanostructured morphologies grown from the neural electrode result in fuzzy coatings with extremely high surface area. The electrical properties of the polymer coatings were studied by Impedance Spectroscopy (IS) and Cyclic Voltammetry (CV). The significant drop in impedance in magnitude and phase angle is consistent with an increase of the surface area due to the roughened surface morphology.

Flame exposure time on Langmuir probe degradation, ion density, and thermionic emission for flame temperature.

PubMed

Doyle, S J; Salvador, P R; Xu, K G

2017-11-01

The paper examines the effect of exposure time of Langmuir probes in an atmospheric premixed methane-air flame. The effects of probe size and material composition on current measurements were investigated, with molybdenum and tungsten probe tips ranging in diameter from 0.0508 to 0.1651 mm. Repeated prolonged exposures to the flame, with five runs of 60 s, resulted in gradual probe degradations (-6% to -62% area loss) which affected the measurements. Due to long flame exposures, two ion saturation currents were observed, resulting in significantly different ion densities ranging from 1.16 × 10 16 to 2.71 × 10 19 m -3 . The difference between the saturation currents is caused by thermionic emissions from the probe tip. As thermionic emission is temperature dependent, the flame temperature could thus be estimated from the change in current. The flame temperatures calculated from the difference in saturation currents (1734-1887 K) were compared to those from a conventional thermocouple (1580-1908 K). Temperature measurements obtained from tungsten probes placed in rich flames yielded the highest percent error (9.66%-18.70%) due to smaller emission current densities at lower temperatures. The molybdenum probe yielded an accurate temperature value with only 1.29% error. Molybdenum also demonstrated very low probe degradation in comparison to the tungsten probe tips (area reductions of 6% vs. 58%, respectively). The results also show that very little exposure time (<5 s) is needed to obtain a valid ion density measurement and that prolonged flame exposures can yield the flame temperature but also risks damage to the Langmuir probe tip.

The gas-phase metallicities of star-forming galaxies in aperture-matched SDSS samples follow potential rather than mass or average surface density

NASA Astrophysics Data System (ADS)

D'Eugenio, Francesco; Colless, Matthew; Groves, Brent; Bian, Fuyan; Barone, Tania M.

2018-05-01

We present a comparative study of the relation between the aperture-based gas-phase metallicity and three structural parameters of star-forming galaxies: mass (M ≡ M*), average potential (Φ ≡ M*/Re) and average surface mass density (Σ ≡ M_*/R_e^2; where Re is the effective radius). We use a volume-limited sample drawn from the publicly available SDSS DR7, and base our analysis on aperture-matched sampling by selecting sets of galaxies where the SDSS fibre probes a fixed fraction of Re. We find that between 0.5 and 1.5 Re, the gas-phase metallicity correlates more tightly with Φ than with either {M} or Σ, in that for all aperture-matched samples, the potential-metallicity relation has (i) less scatter, (ii) higher Spearman rank correlation coefficient and (iii) less residual trend with Re than either the mass-metallicity relation and the average surface density-metallicity relation. Our result is broadly consistent with the current models of gas enrichment and metal loss. However, a more natural explanation for our findings is a local relation between the gas-phase metallicity and escape velocity.

A Kinematical Detection of Two Embedded Jupiter-mass Planets in HD 163296

NASA Astrophysics Data System (ADS)

Teague, Richard; Bae, Jaehan; Bergin, Edwin A.; Birnstiel, Tilman; Foreman-Mackey, Daniel

2018-06-01

We present the first kinematical detection of embedded protoplanets within a protoplanetary disk. Using archival Atacama Large Millimetre Array (ALMA) observations of HD 163296, we demonstrate a new technique to measure the rotation curves of CO isotopologue emission to sub-percent precision relative to the Keplerian rotation. These rotation curves betray substantial deviations caused by local perturbations in the radial pressure gradient, likely driven by gaps carved in the gas surface density by Jupiter-mass planets. Comparison with hydrodynamic simulations shows excellent agreement with the gas rotation profile when the disk surface density is perturbed by two Jupiter-mass planets at 83 and 137 au. As the rotation of the gas is dependent upon the pressure of the total gas component, this method provides a unique probe of the gas surface density profile without incurring significant uncertainties due to gas-to-dust ratios or local chemical abundances that plague other methods. Future analyses combining both methods promise to provide the most accurate and robust measures of embedded planetary mass. Furthermore, this method provides a unique opportunity to explore wide-separation planets beyond the mm continuum edge and to trace the gas pressure profile essential in modeling grain evolution in disks.

WOx supported on γ-Al2O3 with different morphologies as model catalysts for alkanol dehydration

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

Shi, Dachuan; Wang, Huamin; Kovarik, Libor

2018-04-21

The distinctive morphological and surface characteristics of platelet-like γ-Al2O3 were compared to a regular, commercial γ-Al2O3. γ-Al2O3 platelets display dominant (110) surface facets and higher densities of coordinative unsaturated penta-coordinate Al3+ (Al3+penta) sites than regular γ-Al2O3, as measured by solid-state magic-angle spinning nuclear magnetic resonance spectroscopy (MAS NMR). Such Al3+penta sites are also the preferred surface anchoring sites for tungsten oxide (WOx) species consistent with NMR analysis indicating that these sites are consumed upon WOx adsorption. The higher Al3+penta density on γ-Al2O3 platelets leads to greater WOx dispersion (or smaller WOx clusters), as demonstrated by scanning transmission electron microscopy andmore » ultraviolet–visible spectroscopy, and WOx species at intermediate WOx surface concentration are the most active for the probe reaction of 2-butanol dehydration. WOx on γ-Al2O3 platelets approaches the highest turnover rates at higher surface densities than WOx on regular γ-Al2O3, yet with similar highest rate values for both series of catalysts. This indicates that different Al2O3 supports mainly affect the dispersion of supported WOx rather than the intrinsic reactivity of individual WOx clusters with similar size.« less

WO x supported on γ-Al 2 O 3 with different morphologies as model catalysts for alkanol dehydration

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

Shi, Dachuan; Wang, Huamin; Kovarik, Libor

The distinctive morphological and surface characteristics of platelet-like γ-Al2O3 were compared to a regular, commercial γ-Al2O3. γ-Al2O3 platelets display dominant (110) surface facets and higher densities of coordinative unsaturated penta-coordinate Al3+ (Al3+penta) sites than regular γ-Al2O3, as measured by solid-state magic-angle spinning nuclear magnetic resonance spectroscopy (MAS NMR). Such Al3+penta sites are also the preferred surface anchoring sites for tungsten oxide (WOx) species consistent with NMR analysis indicating that these sites are consumed upon WOx adsorption. The higher Al3+penta density on γ-Al2O3 platelets leads to greater WOx dispersion (or smaller WOx clusters), as demonstrated by scanning transmission electron microscopy andmore » ultraviolet–visible spectroscopy, and WOx species at intermediate WOx surface concentration are the most active for the probe reaction of 2-butanol dehydration. WOx on γ-Al2O3 platelets approaches the highest turnover rates at higher surface densities than WOx on regular γ-Al2O3, yet with similar highest rate values for both series of catalysts. This indicates that different Al2O3 supports mainly affect the dispersion of supported WOx rather than the intrinsic reactivity of individual WOx clusters with similar size.« less

Diagnostics of hydrogen plasma with in situ optical emission and silicon probes

NASA Astrophysics Data System (ADS)

Lee, Szetsen; Chung, Yi-Jie

2005-11-01

In this work, an approach has been adopted to explore plasma properties by combining an in situ optical emission technique with a contact angle measurement. Hydrogen plasma was generated with a radio-frequency power source. The plasma parameters such as number densities and temperatures were derived from the optical emission spectroscopic data. Small silicon chips were placed at various positions inside a discharge tube as probes for the plasma conditions. The hydrogen-plasma-treated silicon chip surfaces were characterized with the contact angle measurement method. The change of wettability on the silicon surface was observed with various plasma treatment times. The spectroscopic information about the plasma is correlated with the results of the surface characterization. It is found that the rate of the increasing hydrophilicity is sensitive to the amount of helium added and the location in the discharge tube. A simple model describing the relation between the surface coverage area of water droplet and the variation of contact angle has been established. We have proposed plasma excitation and reaction mechanisms for the observed correlation between plasma temperatures and the wettability of the silicon surface. It shows that small silicon chips can serve as "litmus tests" for the plasma conditions without introducing too much perturbation.

Perceiving the vertical distances of surfaces by means of a hand-held probe.

PubMed

Chan, T C; Turvey, M T

1991-05-01

Nine experiments were conducted on the haptic capacity of people to perceive the distances of horizontal surfaces solely on the basis of mechanical stimulation resulting from contacting the surfaces with a vertically held rod. Participants touched target surfaces with rods inside a wooden cabinet and reported the perceived surface location with an indicator outside the cabinet. The target surface, rod, and the participant's hand were occluded, and the sound produced in exploration was muffled. Properties of the probe (length, mass, moment of inertia, center of mass, and shape) were manipulated, along with surface distance and the method and angle of probing. Results suggest that for the most common method of probing, namely, tapping, perceived vertical distance is specific to a particular relation among the rotational inertia of the probe, the distance of the point of contact with the surface from the probe's center of percussion, and the inclination at contact of the probe to the surface. They also suggest that the probe length and the distance probed are independently perceivable. The results were discussed in terms of information specificity versus percept-percept coupling and parallels between selective attention in haptic and visual perception.

Impact of atmospheric refraction: how deeply can we probe exo-earth's atmospheres during primary eclipse observations?

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

Bétrémieux, Yan; Kaltenegger, Lisa, E-mail: betremieux@mpia.de

2014-08-10

Most models used to predict or fit exoplanet transmission spectra do not include all the effects of atmospheric refraction. Namely, the angular size of the star with respect to the planet can limit the lowest altitude, or highest density and pressure, probed during primary eclipses as no rays passing below this critical altitude can reach the observer. We discuss this geometrical effect of refraction for all exoplanets and tabulate the critical altitude, density, and pressure for an exoplanet identical to Earth with a 1 bar N{sub 2}/O{sub 2} atmosphere as a function of both the incident stellar flux (Venus, Earth,more » and Mars-like) at the top of the atmosphere and the spectral type (O5-M9) of the host star. We show that such a habitable exo-Earth can be probed to a surface pressure of 1 bar only around the coolest stars. We present 0.4-5.0 μm model transmission spectra of Earth's atmosphere viewed as a transiting exoplanet, and show how atmospheric refraction modifies the transmission spectrum depending on the spectral type of the host star. We demonstrate that refraction is another phenomenon that can potentially explain flat transmission spectra over some spectral regions.« less

Measurement of atmospheric pressure microplasma jet with Langmuir probes

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

Xu, Kunning G., E-mail: gabe.xu@uah.edu; Doyle, Steven J.

2016-09-15

A radio frequency argon microplasma jet at atmospheric-pressure is characterized using Langmuir probes. While optical methods are the typical diagnostic for these small scale plasmas, the simplicity and low cost of Langmuir probes makes them an attractive option. The plasma density and electron temperature are measured using existing high-pressure Langmuir probe theories developed for flames and arcs. The density and temperature vary from 1 × 10{sup 16} to 1 × 10{sup 19} m{sup −3} and 2.3 to 4.4 eV, respectively, depending on the operating condition. The density decreases while the electron temperature increases with axial distance from the jet exit. Themore » applicability of the probe theories as well as the effect of collisionality and jet mixing is discussed.« less

Non-invasive probe diagnostic method for electron temperature and ion current density in atmospheric pressure plasma jet source

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

Kim, Young-Cheol; Kim, Yu-Sin; Lee, Hyo-Chang

2015-08-15

The electrical probe diagnostics are very hard to be applied to atmospheric plasmas due to severe perturbation by the electrical probes. To overcome this, the probe for measuring electron temperature and ion current density is indirectly contacted with an atmospheric jet source. The plasma parameters are obtained by using floating harmonic analysis. The probe is mounted on the quartz tube that surrounds plasma. When a sinusoidal voltage is applied to a probe contacting on a quartz tube, the electrons near the sheath at dielectric tube are collected and the probe current has harmonic components due to probe sheath nonlinearity. Frommore » the relation of the harmonic currents and amplitude of the sheath voltage, the electron temperature near the wall can be obtained with collisional sheath model. The electron temperatures and ion current densities measured at the discharge region are in the ranges of 2.7–3.4 eV and 1.7–5.2 mA/cm{sup 2} at various flow rates and input powers.« less

Development of a Double Hemispherical Probe for Improved Space Plasma Measurements

NASA Astrophysics Data System (ADS)

Wang, X.; Samaniego, J. I.; Hsu, H.-W.; Horányi, M.; Wahlund, J.-E.; Ergun, R. E.; Bering, E. A.

2018-04-01

Langmuir probes have been widely used for space plasma measurements for decades. However, there are still challenges in the interpretation of their measurements. Due to the interaction of the ambient plasma with a spacecraft and an onboard probe itself, the local plasma conditions around the probe could be very different from the true ambient plasma of interest. These local plasma conditions are often anisotropic and/or inhomogeneous. Most of the Langmuir probes that are made of a single electrode have difficulties to remove these local plasma effects, introducing errors in the derived plasma characteristics. Directional probes are able to characterize anisotropic and inhomogeneous plasmas. The split Langmuir probe and the Segmented Langmuir Probe have been developed to characterize the plasma flow in the Earth's ionosphere. Here we introduce a new type of a directional Langmuir probe, the Double Hemispherical Probe (DHP), to improve the space plasma measurements in a broad range of scenarios: (a) low-density plasmas, (b) high surface-emission (photo and/or secondary electron emission) environments, (c) flowing plasmas, and (d) dust-rich plasma environments. The DHP consists of two identical hemispheres that are electrically insulated and swept with the same voltages simultaneously. The difference currents between the two hemispheres are used to characterize the anisotropic/inhomogeneous plasma conditions created around the probe, which will be then removed or minimized on the interpretation of their current-voltage curves. This paper describes the basic concept and design of the DHP sensor, as well as its initial results tested in the laboratory plasma environments.

Electron density measurements in STPX plasmas

NASA Astrophysics Data System (ADS)

Clark, Jerry; Williams, R.; Titus, J. B.; Mezonlin, E. D.; Akpovo, C.; Thomas, E.

2017-10-01

Diagnostics have been installed to measure the electron density of Spheromak Turbulent Physics Experiment (STPX) plasmas at Florida A. & M. University. An insertable probe, provided by Auburn University, consisting of a combination of a triple-tipped Langmuir probe and a radial array consisting of three ion saturation current / floating potential rings has been installed to measure instantaneous plasma density, temperature and plasma potential. As the ramp-up of the experimental program commences, initial electron density measurements from the triple-probe show that the electron density is on the order of 1019 particles/m3. For a passive measurement, a CO2 interferometer system has been designed and installed for measuring line-averaged densities and to corroborate the Langmuir measurements. We describe the design, calibration, and performance of these diagnostic systems on large volume STPX plasmas.

Real-Space Imaging of Carrier Dynamics of Materials Surfaces by Second-Generation Four-Dimensional Scanning Ultrafast Electron Microscopy.

PubMed

Sun, Jingya; Melnikov, Vasily A; Khan, Jafar I; Mohammed, Omar F

2015-10-01

In the fields of photocatalysis and photovoltaics, ultrafast dynamical processes, including carrier trapping and recombination on material surfaces, are among the key factors that determine the overall energy conversion efficiency. A precise knowledge of these dynamical events on the nanometer (nm) and femtosecond (fs) scales was not accessible until recently. The only way to access such fundamental processes fully is to map the surface dynamics selectively in real space and time. In this study, we establish a second generation of four-dimensional scanning ultrafast electron microscopy (4D S-UEM) and demonstrate the ability to record time-resolved images (snapshots) of material surfaces with 650 fs and ∼5 nm temporal and spatial resolutions, respectively. In this method, the surface of a specimen is excited by a clocking optical pulse and imaged using a pulsed primary electron beam as a probe pulse, generating secondary electrons (SEs), which are emitted from the surface of the specimen in a manner that is sensitive to the local electron/hole density. This method provides direct and controllable information regarding surface dynamics. We clearly demonstrate how the surface morphology, grains, defects, and nanostructured features can significantly impact the overall dynamical processes on the surface of photoactive-materials. In addition, the ability to access two regimes of dynamical probing in a single experiment and the energy loss of SEs in semiconductor-nanoscale materials will also be discussed.

Two-resonance probe for measuring electron density in low-pressure plasmas

NASA Astrophysics Data System (ADS)

Kim, D. W.; You, S. J.; Kim, S. J.; Kim, J. H.; Oh, W. Y.

2017-04-01

A technique for measuring double-checked electron density using two types of microwave resonance is presented. Simultaneous measurement of the resonances (plasma and quarter-wavelength resonator resonances), which were used for the cutoff probe (CP) and hairpin probe (HP), was achieved by the proposed microwave resonance probe. The developed two-resonance probe (TRP) consists of parallel separated coaxial cables exposing the radiation and detection tips. The structure resembles that of the CP, except the gapped coaxial cables operate not only as a microwave feeder for the CP but also as a U- shaped quarter-wavelength resonator for the HP. By virtue of this structure, the microwave resonances that have typically been used for measuring the electron density for the CP and HP were clearly identified on the microwave transmission spectrum of the TRP. The two types of resonances were measured experimentally under various power and pressure conditions for the plasma. A three-dimensional full-wave simulation model for the TRP is also presented and used to investigate and reproduce the resonances. The electron densities inferred from the resonances were compared and showed good agreement. Quantitative differences between the densities were attributed to the effects of the sheath width and spatial density gradient on the resonances. This accessible technique of using the TRP to obtain double-checked electron densities may be useful for comparative study and provides complementary uses for the CP and HP.

a Direct Probe for Chemical Potentials Difference Between Neutron and Protons in Heavy-Ion Collisions

NASA Astrophysics Data System (ADS)

Ma, Chun-Wang; Zhang, Yan-Li; Wang, Shan-Shan

We briefly introduce the newly proposed probe to the neutron and proton chemical potential (and density) difference, which is called as the isobaric yield ratio difference (IBD). The IBD probe is related to the chemical potential difference of neutrons and protons between two reactions, at the same time, the nuclear density difference between two reactions. The relationship between the IBD probe and the isoscaling method has also been discussed.

Electronegative plasma diagnostic by laser photo-detachment combined with negatively biased Langmuir probe

NASA Astrophysics Data System (ADS)

Oudini, N.; Sirse, N.; Taccogna, F.; Ellingboe, A. R.; Bendib, A.

2018-05-01

We propose a new technique for diagnosing negative ion properties using Langmuir probe assisted pulsed laser photo-detachment. While the classical technique uses a laser pulse to convert negative ions into electron-atom pairs and a positively biased Langmuir probe tracking the change of electron saturation current, the proposed method uses a negatively biased Langmuir probe to track the temporal evolution of positive ion current. The negative bias aims to avoid the parasitic electron current inherent to probe tip surface ablation. In this work, we show through analytical and numerical approaches that, by knowing electron temperature and performing photo-detachment at two different laser wavelengths, it is possible to deduce plasma electronegativity (ratio of negative ion to electron densities) α, and anisothermicity (ratio of electron to negative ion temperatures) γ-. We present an analytical model that links the change in the collected positive ion current to plasma electronegativity and anisothermicity. Particle-In-Cell simulation is used as a numerical experiment covering a wide range of α and γ- to test the new analysis technique. The new technique is sensitive to α in the range 0.5 < α < 10 and yields γ- for large α, where negative ion flux affects the probe sheath behavior, typically α > 1.

Methodology Development for the Reconstruction of the ESA Huygens Probe Entry and Descent Trajectory

NASA Astrophysics Data System (ADS)

Kazeminejad, B.

2005-01-01

The European Space Agency's (ESA) Huygens probe performed a successful entry and descent into Titan's atmosphere on January 14, 2005, and landed safely on the satellite's surface. A methodology was developed, implemented, and tested to reconstruct the Huygens probe trajectory from its various science and engineering measurements, which were performed during the probe's entry and descent to the surface of Titan, Saturn's largest moon. The probe trajectory reconstruction is an essential effort that has to be done as early as possible in the post-flight data analysis phase as it guarantees a correct and consistent interpretation of all the experiment data and furthermore provides a reference set of data for "ground-truthing" orbiter remote sensing measurements. The entry trajectory is reconstructed from the measured probe aerodynamic drag force, which also provides a means to derive the upper atmospheric properties like density, pressure, and temperature. The descent phase reconstruction is based upon a combination of various atmospheric measurements such as pressure, temperature, composition, speed of sound, and wind speed. A significant amount of effort was spent to outline and implement a least-squares trajectory estimation algorithm that provides a means to match the entry and descent trajectory portions in case of discontinuity. An extensive test campaign of the algorithm is presented which used the Huygens Synthetic Dataset (HSDS) developed by the Huygens Project Scientist Team at ESA/ESTEC as a test bed. This dataset comprises the simulated sensor output (and the corresponding measurement noise and uncertainty) of all the relevant probe instruments. The test campaign clearly showed that the proposed methodology is capable of utilizing all the relevant probe data, and will provide the best estimate of the probe trajectory once real instrument measurements from the actual probe mission are available. As a further test case using actual flight data the NASA Mars Pathfinder entry and descent trajectory and the space craft attitude was reconstructed from the 3-axis accelerometer measurements which are archived on the Planetary Data System. The results are consistent with previously published reconstruction efforts.

X-Ray Microdiffraction as a Probe to Reveal Flux Divergences in Interconnects

NASA Astrophysics Data System (ADS)

Spolenak, R.; Tamura, N.; Patel, J. R.

2006-02-01

Most reliability issues in interconnect systems occur at a local scale and many of them include the local build-up of stresses. Typical failure mechanisms are electromigration and stress voiding in interconnect lines and fatigue in surface acoustic wave devices. Thus a local probe is required for the investigation of these phenomena. In this paper the application of the Laue microdiffraction technique to investigate flux divergences in interconnect systems will be described. The deviatoric strain tensor of single grains can be correlated with the local microstructure, orientation and defect density. Especially the latter led to recent results about the correlation of stress build-up and orientation in Cu lines and electromigration-induced grain rotation in Cu and Al lines.

Balloon-borne Langmuir probe measurement of stratospheric ions in low latitudes

NASA Astrophysics Data System (ADS)

Banerjee, A.; Somayajulu, Y. V.; Subrahmanyam, P.

1984-12-01

A balloon carrying a Langmuir probe payload for measuring the positive and negative ion densities in the stratosphere was flown around midnight IST on Mar. 23, 1982 from the National Balloon Facility at Hyderabad, a low latitude station. The Langmuir probe with a guard ring arrangement is given a symmetrical probe voltage of triangular waveform with amplitude + or - 4.2 V and with a repetition frequency of 0.28 Hz. The balloon reached a ceiling altitude of 33 km and data were taken from 15 km up to the ceiling altitude. The altitude profiles of the ion density show a peak around 18 km with densities decreasing with altitude. The results are discussed in terms of cosmic ray production and ion chemistry. The structures in the positive ion density profile are interpreted in terms of the presence of aerosol layers.

Applied axial magnetic field effects on laboratory plasma jets: Density hollowing, field compression, and azimuthal rotation

DOE PAGES

Byvank, T.; Banasek, J. T.; Potter, W. M.; ...

2017-12-07

We experimentally measure the effects of an applied axial magnetic field (B z) on laboratory plasma jets and compare experimental results with numerical simulations using an extended magnetohydrodynamics code. A 1 MA peak current, 100 ns rise time pulse power machine is used to generate the plasma jet. On application of the axial field, we observe on-axis density hollowing and a conical formation of the jet using interferometry, compression of the applied B z using magnetic B-dot probes, and azimuthal rotation of the jet using Thomson scattering. Experimentally, we find densities ≤ 5×10 17 cm -3 on-axis relative to jetmore » densities of ≥ 3×10 18 cm -3. For aluminum jets, 6.5 ± 0.5 mm above the foil, we find on-axis compression of the applied 1.0 ± 0.1 T B z to a total 2.4 ± 0.3 T, while simulations predict a peak compression to a total 3.4 T at the same location. On the aluminum jet boundary, we find ion azimuthal rotation velocities of 15-20 km/s, while simulations predict 14 km/s at the density peak. We discuss possible sources of discrepancy between the experiments and simulations, including: surface plasma on B-dot probes, optical fiber spatial resolution, simulation density floors, and 2D vs. 3D simulation effects. Lastly, this quantitative comparison between experiments and numerical simulations helps elucidate the underlying physics that determine the plasma dynamics of magnetized plasma jets.« less

Applied axial magnetic field effects on laboratory plasma jets: Density hollowing, field compression, and azimuthal rotation

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

Byvank, T.; Banasek, J. T.; Potter, W. M.

We experimentally measure the effects of an applied axial magnetic field (B z) on laboratory plasma jets and compare experimental results with numerical simulations using an extended magnetohydrodynamics code. A 1 MA peak current, 100 ns rise time pulse power machine is used to generate the plasma jet. On application of the axial field, we observe on-axis density hollowing and a conical formation of the jet using interferometry, compression of the applied B z using magnetic B-dot probes, and azimuthal rotation of the jet using Thomson scattering. Experimentally, we find densities ≤ 5×10 17 cm -3 on-axis relative to jetmore » densities of ≥ 3×10 18 cm -3. For aluminum jets, 6.5 ± 0.5 mm above the foil, we find on-axis compression of the applied 1.0 ± 0.1 T B z to a total 2.4 ± 0.3 T, while simulations predict a peak compression to a total 3.4 T at the same location. On the aluminum jet boundary, we find ion azimuthal rotation velocities of 15-20 km/s, while simulations predict 14 km/s at the density peak. We discuss possible sources of discrepancy between the experiments and simulations, including: surface plasma on B-dot probes, optical fiber spatial resolution, simulation density floors, and 2D vs. 3D simulation effects. Lastly, this quantitative comparison between experiments and numerical simulations helps elucidate the underlying physics that determine the plasma dynamics of magnetized plasma jets.« less

Solid-Phase Nucleic Acid Sequence-Based Amplification and Length-Scale Effects during RNA Amplification.

PubMed

Ma, Youlong; Teng, Feiyue; Libera, Matthew

2018-06-05

Solid-phase oligonucleotide amplification is of interest because of possible applications to next-generation sequencing, multiplexed microarray-based detection, and cell-free synthetic biology. Its efficiency is, however, less than that of traditional liquid-phase amplification involving unconstrained primers and enzymes, and understanding how to optimize the solid-phase amplification process remains challenging. Here, we demonstrate the concept of solid-phase nucleic acid sequence-based amplification (SP-NASBA) and use it to study the effect of tethering density on amplification efficiency. SP-NASBA involves two enzymes, avian myeloblastosis virus reverse transcriptase (AMV-RT) and RNase H, to convert tethered forward and reverse primers into tethered double-stranded DNA (ds-DNA) bridges from which RNA - amplicons can be generated by a third enzyme, T7 RNA polymerase. We create microgels on silicon surfaces using electron-beam patterning of thin-film blends of hydroxyl-terminated and biotin-terminated poly(ethylene glycol) (PEG-OH, PEG-B). The tethering density is linearly related to the PEG-B concentration, and biotinylated primers and molecular beacon detection probes are tethered to streptavidin-activated microgels. While SP-NASBA is very efficient at low tethering densities, the efficiency decreases dramatically with increasing tethering density due to three effects: (a) a reduced hybridization efficiency of tethered molecular beacon detection probes; (b) a decrease in T7 RNA polymerase efficiency; (c) inhibition of T7 RNA polymerase activity by AMV-RT.

In-situ probing of coupled atomic restructuring and metallicity of oxide heterointerfaces induced by polar adsorbates

NASA Astrophysics Data System (ADS)

Ryu, S.; Zhou, H.; Paudel, T. R.; Irwin, J.; Podkaminer, J. P.; Bark, C. W.; Lee, D.; Kim, T. H.; Fong, D. D.; Rzchowski, M. S.; Tsymbal, E. Y.; Eom, C. B.

2017-10-01

Microscopic understanding of the surface-controlled conductivity of the two dimensional electron gas at complex oxide interfaces is crucial for developing functional interfaces. We observe conductivity and structural modification using in-situ synchrotron surface x-ray diffraction as the surface of a model LaAlO3/SrTiO3 (001) heterostructure is changed by polar adsorbates. We find that polar adsorbate-induced interfacial metallicity reduces polar distortions in the LaAlO3 layer. First-principles density functional theory calculations show that surface dipoles introduced by polar adsorbates lead to additional charge transfer and the reduction of polar displacements in the LaAlO3 layer, consistent with the experimental observations. Our study supports that internal structural deformations controlling functionalities can be driven without the application of direct electrical or thermal bias and offers a route to tuning interfacial properties. These results also highlight the important role of in-situ x-ray scattering with atomic resolution in capturing and exploring structural distortions and charge density changes caused by external perturbations such as chemical adsorption, redox reaction, and generation and/or annihilation of surface defects.

Dynamic Scaling and Island Growth Kinetics in Pulsed Laser Deposition of SrTiO 3

DOE PAGES

Eres, Gyula; Tischler, J. Z.; Rouleau, C. M.; ...

2016-11-11

We use real-time diffuse surface x-ray diffraction to probe the evolution of island size distributions and its effects on surface smoothing in pulsed laser deposition (PLD) of SrTiO 3. In this study, we show that the island size evolution obeys dynamic scaling and two distinct regimes of island growth kinetics. Our data show that PLD film growth can persist without roughening despite thermally driven Ostwald ripening, the main mechanism for surface smoothing, being shut down. The absence of roughening is concomitant with decreasing island density, contradicting the prevailing view that increasing island density is the key to surface smoothing inmore » PLD. We also report a previously unobserved crossover from diffusion-limited to attachment-limited island growth that reveals the influence of nonequilibrium atomic level surface transport processes on the growth modes in PLD. We show by direct measurements that attachment-limited island growth is the dominant process in PLD that creates step flowlike behavior or quasistep flow as PLD “self-organizes” local step flow on a length scale consistent with the substrate temperature and PLD parameters.« less

Dynamic Scaling and Island Growth Kinetics in Pulsed Laser Deposition of SrTiO 3

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

Eres, Gyula; Tischler, J. Z.; Rouleau, C. M.

We use real-time diffuse surface x-ray diffraction to probe the evolution of island size distributions and its effects on surface smoothing in pulsed laser deposition (PLD) of SrTiO 3. In this study, we show that the island size evolution obeys dynamic scaling and two distinct regimes of island growth kinetics. Our data show that PLD film growth can persist without roughening despite thermally driven Ostwald ripening, the main mechanism for surface smoothing, being shut down. The absence of roughening is concomitant with decreasing island density, contradicting the prevailing view that increasing island density is the key to surface smoothing inmore » PLD. We also report a previously unobserved crossover from diffusion-limited to attachment-limited island growth that reveals the influence of nonequilibrium atomic level surface transport processes on the growth modes in PLD. We show by direct measurements that attachment-limited island growth is the dominant process in PLD that creates step flowlike behavior or quasistep flow as PLD “self-organizes” local step flow on a length scale consistent with the substrate temperature and PLD parameters.« less

In-situ probing of coupled atomic restructuring and metallicity of oxide heterointerfaces induced by polar adsorbates

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

Ryu, S.; Zhou, H.; Paudel, T. R.

Microscopic understanding of the surface-controlled conductivity of the two dimensional electron gas at complex oxide interfaces is crucial for developing functional interfaces. We observe conductivity and structural modification using in-situ synchrotron surface x-ray diffraction as the surface of a model LaAlO3/SrTiO3 (001) heterostructure is changed by polar adsorbates. We find that polar adsorbate-induced interfacial metallicity reduces polar distortions in the LaAlO3 layer. First-principles density functional theory calculations show that surface dipoles introduced by polar adsorbates lead to additional charge transfer and the reduction of polar displacements in the LaAlO3 layer, consistent with the experimental observations. Our study supports that internalmore » structural deformations controlling functionalities can be driven without the application of direct electrical or thermal bias and offers a route to tuning interfacial properties. These results also highlight the important role of in-situ x-ray scattering with atomic resolution in capturing and exploring structural distortions and charge density changes caused by external perturbations such as chemical adsorption, redox reaction, and generation and/or annihilation of surface defects.« less

Calibrating ion density profile measurements in ion thruster beam plasma

NASA Astrophysics Data System (ADS)

Zhang, Zun; Tang, Haibin; Ren, Junxue; Zhang, Zhe; Wang, Joseph

2016-11-01

The ion thruster beam plasma is characterized by high directed ion velocity (104 m/s) and low plasma density (1015 m-3). Interpretation of measurements of such a plasma based on classical Langmuir probe theory can yield a large experimental error. This paper presents an indirect method to calibrate ion density determination in an ion thruster beam plasma using a Faraday probe, a retarding potential analyzer, and a Langmuir probe. This new method is applied to determine the plasma emitted from a 20-cm-diameter Kaufman ion thruster. The results show that the ion density calibrated by the new method can be as much as 40% less than that without any ion current density and ion velocity calibration.

Heating power at the substrate, electron temperature, and electron density in 2.45 GHz low-pressure microwave plasma

NASA Astrophysics Data System (ADS)

Kais, A.; Lo, J.; Thérèse, L.; Guillot, Ph.

2018-01-01

To control the temperature during a plasma treatment, an understanding of the link between the plasma parameters and the fundamental process responsible for the heating is required. In this work, the power supplied by the plasma onto the surface of a glass substrate is measured using the calorimetric method. It has been shown that the powers deposited by ions and electrons, and their recombination at the surface are the main contributions to the heating power. Each contribution is estimated according to the theory commonly used in the literature. Using the corona balance, the Modified Boltzmann Plot (MBP) is employed to determine the electron temperature. A correlation between the power deposited by the plasma and the results of the MBP has been established. This correlation has been used to estimate the electron number density independent of the Langmuir probe in considered conditions.

Gamma-ray lines from neutron stars as probes of fundamental physics

NASA Technical Reports Server (NTRS)

Brecher, K.

1978-01-01

The detection of gamma-ray lines produced at the surface of neutron stars will serve to test both the strong and gravitational interactions under conditions unavailable in terrestrial laboratories. Observation of a single redshifted gamma-ray line, combined with an estimate of the mass of the star will serve as a strong constraint on allowable equations of state of matter at supernuclear densities. Detection of two redshifted lines arising from different physical processes at the neutron star surface can provide a test of the strong principle of equivalence. Expected fluxes of nuclear gamma-ray lines from accreting neutron stars were calculated, including threshold, radiative transfer and redshift effects. The most promising probes of neutron star structure are the deuterium formation line and the positron annihilation line. Detection of sharp redshifted gamma-ray lines from X-ray sources such as Cyg X-1 would argue strongly in favor of a neutron star rather than black hole identification for the object.

Thermal stability of photovoltaic a-Si:H determined by neutron reflectometry

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

Qviller, A. J., E-mail: atlejq@ife.no; Haug, H.; You, C. C.

2014-12-08

Neutron and X-ray reflectometry were used to determine the layer structure and hydrogen content of thin films of amorphous silicon (a-Si:H) deposited onto crystalline silicon (Si) wafers for surface passivation in solar cells. The combination of these two reflectometry techniques is well suited for non-destructive probing of the structure of a-Si:H due to being able to probe buried interfaces and having sub-nanometer resolution. Neutron reflectometry is also unique in its ability to allow determination of density gradients of light elements such as hydrogen (H). The neutron scattering contrast between Si and H is strong, making it possible to determine themore » H concentration in the deposited a-Si:H. In order to correlate the surface passivation properties supplied by the a-Si:H thin films, as quantified by obtainable effective minority carrier lifetime, photoconductance measurements were also performed. It is shown that the minority carrier lifetime falls sharply when H has been desorbed from a-Si:H by annealing.« less

Quantification of evaporation induced error in atom probe tomography using molecular dynamics simulation.

PubMed

Chen, Shu Jian; Yao, Xupei; Zheng, Changxi; Duan, Wen Hui

2017-11-01

Non-equilibrium molecular dynamics was used to simulate the dynamics of atoms at the atom probe surface and five objective functions were used to quantify errors. The results suggested that before ionization, thermal vibration and collision caused the atoms to displace up to 1Å and 25Å respectively. The average atom displacements were found to vary between 0.2 and 0.5Å. About 9 to 17% of the atoms were affected by collision. Due to the effects of collision and ion-ion repulsion, the back-calculated positions were on average 0.3-0.5Å different from the pre-ionized positions of the atoms when the number of ions generated per pulse was minimal. This difference could increase up to 8-10Å when 1.5ion/nm 2 were evaporated per pulse. On the basis of the results, surface ion density was considered an important factor that needed to be controlled to minimize error in the evaporation process. Copyright © 2017. Published by Elsevier B.V.

Comparison of tungsten nano-tendrils grown in Alcator C-Mod and linear plasma devices

NASA Astrophysics Data System (ADS)

Wright, G. M.; Brunner, D.; Baldwin, M. J.; Bystrov, K.; Doerner, R. P.; Labombard, B.; Lipschultz, B.; De Temmerman, G.; Terry, J. L.; Whyte, D. G.; Woller, K. B.

2013-07-01

Growth of tungsten nano-tendrils ("fuzz") has been observed for the first time in the divertor region of a high-power density tokamak experiment. After 14 consecutive helium L-mode discharges in Alcator C-Mod, the tip of a tungsten Langmuir probe at the outer strike point was fully covered with a layer of nano-tendrils. The depth of the W fuzz layer (600 ± 150 nm) is consistent with an empirical growth formula from the PISCES experiment. Re-creating the C-Mod exposures as closely as possible in Pilot-PSI experiment can produce nearly-identical nano-tendril morphology and layer thickness at surface temperatures that agree with uncertainties with the C-Mod W probe temperature data. Helium concentrations in W fuzz layers are measured at 1-4 at.%, which is lower than expected for the observed sub-surface voids to be filled with several GPa of helium pressure. This possibly indicates that the void formation is not pressure driven.

Reproducibility of the cutoff probe for the measurement of electron density

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

Kim, D. W.; Oh, W. Y.; You, S. J., E-mail: sjyou@cnu.ac.kr

2016-06-15

Since a plasma processing control based on plasma diagnostics attracted considerable attention in industry, the reproducibility of the diagnostics using in this application has become a great interest. Because the cutoff probe is one of the potential candidates for this application, knowing the reproducibility of the cutoff probe measurement becomes quit important in the cutoff probe application research. To test the reproducibility of the cutoff probe measurement, in this paper, a comparative study among the different cutoff probe measurements was performed. The comparative study revealed remarkable result: the cutoff probe has a great reproducibility for the electron density measurement, i.e.,more » there are little differences among measurements by different probes made by different experimenters. The discussion including the reason for the result was addressed via this paper by using a basic measurement principle of cutoff probe and a comparative experiment with Langmuir probe.« less

STED Imaging of Golgi Dynamics with Cer-SiR: A Two-Component, Photostable, High-Density Lipid Probe for Live Cells.

PubMed

Erdmann, Roman S; Toomre, Derek; Schepartz, Alanna

2017-01-01

Long time-lapse super-resolution imaging in live cells requires a labeling strategy that combines a bright, photostable fluorophore with a high-density localization probe. Lipids are ideal high-density localization probes, as they are >100 times more abundant than most membrane-bound proteins and simultaneously demark the boundaries of cellular organelles. Here, we describe Cer-SiR, a two-component, high-density lipid probe that is exceptionally photostable. Cer-SiR is generated in cells via a bioorthogonal reaction of two components: a ceramide lipid tagged with trans-cyclooctene (Cer-TCO) and a reactive, photostable Si-rhodamine dye (SiR-Tz). These components assemble within the Golgi apparatus of live cells to form Cer-SiR. Cer-SiR is benign to cellular function, localizes within the Golgi at a high density, and is sufficiently photostable to enable visualization of Golgi structure and dynamics by 3D confocal or long time-lapse STED microscopy.

Polarity compensation mechanisms on the perovskite surface KTaO3(001)

NASA Astrophysics Data System (ADS)

Setvin, Martin; Reticcioli, Michele; Poelzleitner, Flora; Hulva, Jan; Schmid, Michael; Boatner, Lynn A.; Franchini, Cesare; Diebold, Ulrike

2018-02-01

The stacking of alternating charged planes in ionic crystals creates a diverging electrostatic energy—a “polar catastrophe”—that must be compensated at the surface. We used scanning probe microscopies and density functional theory to study compensation mechanisms at the perovskite potassium tantalate (KTaO3) (001) surface as increasing degrees of freedom were enabled. The as-cleaved surface in vacuum is frozen in place but immediately responds with an insulator-to-metal transition and possibly ferroelectric lattice distortions. Annealing in vacuum allows the formation of isolated oxygen vacancies, followed by a complete rearrangement of the top layers into an ordered pattern of KO and TaO2 stripes. The optimal solution is found after exposure to water vapor through the formation of a hydroxylated overlayer with ideal geometry and charge.

Surface emission from neutron stars and implications for the physics of their interiors.

PubMed

Ozel, Feryal

2013-01-01

Neutron stars are associated with diverse physical phenomena that take place in conditions characterized by ultrahigh densities as well as intense gravitational, magnetic and radiation fields. Understanding the properties and interactions of matter in these regimes remains one of the challenges in compact object astrophysics. Photons emitted from the surfaces of neutron stars provide direct probes of their structure, composition and magnetic fields. In this review, I discuss in detail the physics that governs the properties of emission from the surfaces of neutron stars and their various observational manifestations. I present the constraints on neutron star radii, core and crust composition, and magnetic field strength and topology obtained from studies of their broadband spectra, evolution of thermal luminosity, and the profiles of pulsations that originate on their surfaces.

Electric-field noise from carbon-adatom diffusion on a Au(110) surface: First-principles calculations and experiments

NASA Astrophysics Data System (ADS)

Kim, E.; Safavi-Naini, A.; Hite, D. A.; McKay, K. S.; Pappas, D. P.; Weck, P. F.; Sadeghpour, H. R.

2017-03-01

The decoherence of trapped-ion quantum gates due to heating of their motional modes is a fundamental science and engineering problem. This heating is attributed to electric-field noise arising from the trap-electrode surfaces. In this work, we investigate the source of this noise by focusing on the diffusion of carbon-containing adsorbates on the surface of Au(110). We show by density functional theory, based on detailed scanning probe microscopy, how the carbon adatom diffusion on the gold surface changes the energy landscape and how the adatom dipole moment varies with the diffusive motion. A simple model for the diffusion noise, which varies quadratically with the variation of the dipole moment, predicts a noise spectrum, in accordance with the measured values.

Testing the limits of the Maxwell distribution of velocities for atoms flying nearly parallel to the walls of a thin cell.

PubMed

Todorov, Petko; Bloch, Daniel

2017-11-21

For a gas at thermal equilibrium, it is usually assumed that the velocity distribution follows an isotropic 3-dimensional Maxwell-Boltzmann (M-B) law. This assumption classically implies the assumption of a "cos θ" law for the flux of atoms leaving the surface. Actually, such a law has no grounds in surface physics, and experimental tests of this assumption have remained very few. In a variety of recently developed sub-Doppler laser spectroscopy techniques for gases one-dimensionally confined in a thin cell, the specific contribution of atoms moving nearly parallel to the boundary of the vapor container becomes essential. We report here on the implementation of an experiment to probe effectively the distribution of atomic velocities parallel to the windows for a thin (60 μm) Cs vapor cell. The principle of the setup relies on a spatially separated pump-probe experiment, where the variations of the signal amplitude with the pump-probe separation provide the information on the velocity distribution. The experiment is performed in a sapphire cell on the Cs resonance line, which benefits from a long-lived hyperfine optical pumping. Presently, we can analyze specifically the density of atoms with slow normal velocities ∼5-20 m/s, already corresponding to unusual grazing flight-at ∼85°-88.5° from the normal to the surface-and no deviation from the M-B law is found within the limits of our elementary setup. Finally we suggest tracks to explore more parallel velocities, when surface details-roughness or structure-and the atom-surface interaction should play a key role to restrict the applicability of an M-B-type distribution.

Surface characterization of InP trenches embedded in oxide using scanning probe microscopy

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

Mannarino, Manuel, E-mail: manuel.mannarino@imec.be, E-mail: manuelmannarino@gmail.com; Chintala, Ravi; Vandervorst, Wilfried

2015-12-14

Metrology for structural and electrical analyses at device level has been identified as one of the major challenges to be resolved for the sub-14 nm technology nodes. In these advanced nodes, new high mobility semiconductors, such as III–V compounds, are grown in narrow trenches on a Si substrate. Probing the nature of the defects, the defect density, and the role of processing steps on the surface of such structures are prime metrology requirements. In order to enable defect analysis on a (III–V) surface, a proper sample preparation for oxide removal is of primary importance. In this work, the effectiveness of differentmore » chemical cleanings and thermal annealing procedures is investigated on both blanket InP and oxide embedded InP trenches by means of scanning probe microscopy techniques. It is found that the most effective approach is a combination of an HCl-based chemical cleaning combined with a low-temperature thermal annealing leading to an oxide free surface with atomically flat areas. Scanning tunneling microscopy (STM) has been the preferred method for such investigations on blanket films due to its intrinsic sub-nm spatial resolution. However, its application on oxide embedded structures is non-trivial. To perform STM on the trenches of interest (generally <20 nm wide), we propose a combination of non-contact atomic force microscopy and STM using the same conductive atomic force microscopy tip Our results prove that with these procedures, it is possible to perform STM in narrow InP trenches showing stacking faults and surface reconstruction. Significant differences in terms of roughness and terrace formation are also observed between the blanket and the oxide embedded InP.« less

Density Waves in Saturn's Rings from Cassini Radio Occultations

NASA Astrophysics Data System (ADS)

French, R. G.; Rappaport, N. J.; Marouf, E. A.; McGhee, C. A.

2005-12-01

The Cassini Radio Science Team conducted a set of optimized diametric occultations by Saturn and its rings from May to September 2005, providing 11 separate probes of Saturn's ionosphere and atmosphere, and 12 optical depth profiles of the complete ring system. Each event was observed by the stations of the Deep Space Net (DSN) at three radio frequencies (S, X, Ka bands, with corresponding wavelengths of ? = 13, 3.6, and 0.9 cm). Very accurate pointing by the spacecraft and ground antennas resulted in stable baseline signal levels, and the relatively large ring opening angle (B=19-25°) permitted us to probe even quite dense ring regions with excellent SNR. The RSS occultation technique enables us to recover very fine detailed radial structure by correcting for diffraction effects. Multiple occultation chords, covering a variety of ring longitudes and ring opening angles, reveal the structure of the rings in remarkable detail, including density and bending waves, satellite wakes, and subtle variations at the 100-m radius scale. Janus and Epimetheus are responsible for a particularly rich set of density waves, and their coorbital interactions result in a complex interplay of time-variable ring structure over the 8-year libration period of the two satellites. We compare the first-order 2:1, 4:3, 5:4, and 6:5 coorbital density waves from multiple occultation chords to linear density wave models based on a dynamical model of the orbital exchange between the moons. From the observed dispersion relation of the wave crests, we infer the surface mass density and eccentricity gradient of particle streamlines, and match the detailed shapes of the wave crests using a non-linear analysis. Second-order coorbital features are also evident, and there are even hints of third-order density waves in the high SNR radio occultation data.

The birth and evolution of surface science: child of the union of science and technology.

PubMed

Duke, C B

2003-04-01

This article is an account of the birth and evolution of surface science as an interdisciplinary research area. Surface science emanated from the confluence of concepts and tools in physics and chemistry with technological innovations that made it possible to determine the structure and properties of surfaces and interfaces and the dynamics of chemical reactions at surfaces. The combination in the 1960s and 1970s of ultra-high-vacuum (i.e., P < 10(-7) Pascal or 10(-9) Torr) technology with the recognition that electrons in the energy range from 50 to 500 eV exhibited inelastic collision mean free paths of the order of a few angstroms fostered an explosion of activity. The results were a reformulation of the theory of electron solid scattering, the nearly universal use of electron spectroscopies for surface characterization, the rise of surface science as an independent interdisciplinary research area, and the emergence of the American Vacuum Society (AVS) as a major international scientific society. The rise of microelectronics in the 1970s and 1980s resulted in huge increases in computational power. These increases enabled more complex experiments and the utilization of density functional theory for the quantitative prediction of surface structure and dynamics. Development of scanning-probe microscopies in the 1990s led to atomic-resolution images of macroscopic surfaces and interfaces as well as videos of atoms moving about on surfaces during growth and diffusion. Scanning probes have since brought solid-liquid interfaces into the realm of atomic-level surface science, expanding its scope to more complex systems, including fragile biological materials and processes.

Biofunctionalized silicon nitride platform for sensing applications.

PubMed

Hoi, Hiofan; Rezaie, Salva S; Gong, Lu; Sen, Payel; Zeng, Hongbo; Montemagno, Carlo; Gupta, Manisha

2018-04-15

Silicon nitride (SiN x ) based biosensors have the potential to converge on the technological achievements of semiconductor microfabrication and biotechnology. Development of biofunctionalized SiN x surface and its integration with other devices will allow us to integrate the biosensing capability with probe control, data acquisition and data processing. Here we use the hydrogen plasma generated by inductively coupled plasma-reactive ion etching (ICP-RIE) technique to produce amino-functionality on the surface of SiN x which can then be readily used for biomolecule immobilization. ICP-RIE produces high-density hydrogen ions/radicals at low energy, which produces high-density amino group on the SiN x surface within a short duration of time and with minimal surface damage. In this work, we have demonstrated selective amination of SiN x surface as compared to Si surface. The as-activated SiN x surface can be readily biofunctionalized with both protein and oligonucleotide through covalent immobilization. N-5-azido-2-nitrobenzoyloxysuccinimide, a photoactivable amino reactive bifunctional crosslinker, was used and greater than 90% surface coverage was achieved for protein immobilization. In addition, ssDNA immobilization and hybridization with its complemented strand was shown. Thus, we demonstrate a uniform, reliable, fast and economical technique for creating biofunctionalized SiN x surface that can be used for developing compact high-sensitivity biosensors. Copyright © 2017 Elsevier B.V. All rights reserved.

Surface interaction of polyimide with oxygen ECR plasma

NASA Astrophysics Data System (ADS)

Naddaf, M.; Balasubramanian, C.; Alegaonkar, P. S.; Bhoraskar, V. N.; Mandle, A. B.; Ganeshan, V.; Bhoraskar, S. V.

2004-07-01

Polyimide (Kapton-H), was subjected to atomic oxygen from an electron cyclotron resonance plasma. An optical emission spectrometer was used to characterize the atomic oxygen produced in the reactor chamber. The energy of the ions was measured using a retarding field analyzer, placed near the substrate. The density of atomic oxygen in the plasma was estimated using a nickel catalytic probe. The surface wettability of the polyimide samples monitored by contact angle measurements showed considerable improvement when treated with plasma. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopic studies showed that the atomic oxygen in the plasma is the main specie affecting the surface chemistry and adhesion properties of polyimide. The improvement in the surface wettability is attributed to the high degree of cross-linking and large concentration of polar groups generated in the surface region of polyimide, after plasma treatment. The changes in the surface region of polyimide were observed by atomic force microscopic analysis.

Controlling Reaction Selectivity through the Surface Termination of Perovskite Catalysts

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

Polo-Garzon, Felipe; Yang, Shi-Ze; Fung, Victor

2017-07-19

Although well known in the material science field, surface reconstruction of perovskites has not been implemented in heterogeneous catalysis. In this work, we employ multiple surface sensitive techniques to characterize the surface reconstruction of SrTiO3 (STO) after thermal pretreatment (Sr-enrichment) and chemical etching (Ti-enrichment). We show, using the conversion of 2-propanol as a probe reaction, that the surface reconstruction of STO can be controlled to greatly tune catalytic acid/base properties and consequently the reaction selectivities in a wide range, which are inaccessible using single metal oxides, either SrO or TiO2. Density functional theory (DFT) calculations well explain the selectivity tuningmore » and reaction mechanism on differently reconstructed surfaces of STO. Similar catalytic tunability is also observed on BaZrO3, highlighting the generality of the finding from this work.« less

Surface passivation of (100) GaSb using self-assembled monolayers of long-chain octadecanethiol

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

Papis-Polakowska, E., E-mail: papis@ite.waw.pl; Kaniewski, J.; Jurenczyk, J.

2016-05-15

The passivation of (100) GaSb surface was investigated by means of the long-chain octadecanethiol (ODT) self-assembled monolayer (SAM). The properties of ODT SAM on (100) GaSb were characterized by the atomic force microscopy using Kelvin probe force microscopy mode and X-ray photoelectron spectroscopy. The chemical treatment of 10 mM ODT-C{sub 2}H{sub 5}OH has been applied to the passivation of a type-II superlattice InAs/GaSb photodetector. The electrical measurements indicate that the current density was reduced by one order of magnitude as compared to an unpassivated photodetector.

Fabrication of single/multi-walled hybrid buckypaper composites and their enhancement of electromagnetic interference shielding performance

NASA Astrophysics Data System (ADS)

Lu, Shaowei; Shao, Junyan; Ma, Keming; Wang, Xiaoqiang; Zhang, Lu; Meng, Qingshi

2016-11-01

Multi-walled carbon nanotubes and single-walled carbon nanotubes show great potential for the application as an electromagnetic interference shielding material. In this paper, the electromagnetic interference shielding the effectiveness of a composite surface coated single/multi-walled carbon nanotube hybrid buckypaper was measured, which showed an average shielding effectiveness of ~55 dB with a buckypaper thickness of 50 µm, and bukypaper density of 0.76 g cm-3, it is much higher than other carbon nanotube/resin materials when sample thickness is on the similar order. The structural, specific surface area and conductivity of the buckypapers were examined by field-emission scanning electron microscopy, specific surface area analyzer and four probes resistance tester, respectively.

Radiative energy transfer from MoS2 excitons to surface plasmons

NASA Astrophysics Data System (ADS)

Kang, Yimin; Li, Bowen; Fang, Zheyu

2017-12-01

In this work, we demonstrated the energy transfer process from few-layer MoS2 to gold dimer arrays via ultrafast pump-probe spectroscopy. With the overlap between the MoS2 exciton and the designed plasmon dipolar modes in the frequency domain, the exciton energy can be radiatively transferred to plasmonic structures, excited the localized surface plasmon resonance, and then enhanced the oscillation of coherent acoustic phonons. Power-dependent differential reflection signals and an analytical model based on the rate equation of exciton density were carried out to quantitatively study the energy transfer process. Our finding explores the energy flow between MoS2 excitons and surface plasmons, and can be contributed to the design of exciton-plasmon structures utilizing ultrathin materials.

Investigation of the boundary layer during the transition from volume to surface dominated H- production at the BATMAN test facility

NASA Astrophysics Data System (ADS)

Wimmer, C.; Schiesko, L.; Fantz, U.

2016-02-01

BATMAN (Bavarian Test Machine for Negative ions) is a test facility equipped with a 1/8 scale H- source for the ITER heating neutral beam injection. Several diagnostics in the boundary layer close to the plasma grid (first grid of the accelerator system) followed the transition from volume to surface dominated H- production starting with a Cs-free, cleaned source and subsequent evaporation of caesium, while the source has been operated at ITER relevant pressure of 0.3 Pa: Langmuir probes are used to determine the plasma potential, optical emission spectroscopy is used to follow the caesiation process, and cavity ring-down spectroscopy allows for the measurement of the H- density. The influence on the plasma during the transition from an electron-ion plasma towards an ion-ion plasma, in which negative hydrogen ions become the dominant negatively charged particle species, is seen in a strong increase of the H- density combined with a reduction of the plasma potential. A clear correlation of the extracted current densities (jH-, je) exists with the Cs emission.

Investigation of the boundary layer during the transition from volume to surface dominated H⁻ production at the BATMAN test facility.

PubMed

Wimmer, C; Schiesko, L; Fantz, U

2016-02-01

BATMAN (Bavarian Test Machine for Negative ions) is a test facility equipped with a 18 scale H(-) source for the ITER heating neutral beam injection. Several diagnostics in the boundary layer close to the plasma grid (first grid of the accelerator system) followed the transition from volume to surface dominated H(-) production starting with a Cs-free, cleaned source and subsequent evaporation of caesium, while the source has been operated at ITER relevant pressure of 0.3 Pa: Langmuir probes are used to determine the plasma potential, optical emission spectroscopy is used to follow the caesiation process, and cavity ring-down spectroscopy allows for the measurement of the H(-) density. The influence on the plasma during the transition from an electron-ion plasma towards an ion-ion plasma, in which negative hydrogen ions become the dominant negatively charged particle species, is seen in a strong increase of the H(-) density combined with a reduction of the plasma potential. A clear correlation of the extracted current densities (j(H(-)), j(e)) exists with the Cs emission.

Probing radical kinetics in the afterglow of pulsed discharges by absorption spectroscopy with light emitting diodes: Application to BCl radical

NASA Astrophysics Data System (ADS)

Vempaire, D.; Cunge, G.

2009-01-01

Measuring decay rates of radical densities in the afterglow of pulsed plasmas is a powerful approach to determine their gas phase and surface loss kinetics. We show that this measurement can be achieved by absorption spectroscopy with low cost and simple apparatus by using light emitting diodes as a light source. The feasibility is demonstrated by monitoring BCl radicals in pulsed low pressure high-density BCl3 plasmas. It is shown that BCl is lost both in the gas phase by reacting with Cl2 with a cross section of 9 Å2 and in the chamber walls with a sticking coefficient of about 0.3.

AFM fluid delivery/liquid extraction surface sampling/electrostatic spray cantilever probe

DOEpatents

Van Berkel, Gary J.

2015-06-23

An electrospray system comprises a liquid extraction surface sampling probe. The probe comprises a probe body having a liquid inlet and a liquid outlet, and having a liquid extraction tip. A solvent delivery conduit is provided for receiving solvent liquid from the liquid inlet and delivering the solvent liquid to the liquid extraction tip. An open liquid extraction channel extends across an exterior surface of the probe body from the liquid extraction tip to the liquid outlet. An electrospray emitter tip is in liquid communication with the liquid outlet of the liquid extraction surface sampling probe. A system for analyzing samples, a liquid junction surface sampling system, and a method of analyzing samples are also disclosed.

SU-E-J-205: Monte Carlo Modeling of Ultrasound Probes for Real-Time Ultrasound Image-Guided Radiotherapy

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

Hristov, D; Schlosser, J; Bazalova, M

2014-06-01

Purpose: To quantify the effect of ultrasound (US) probe beam attenuation for radiation therapy delivered under real-time US image guidance by means of Monte Carlo (MC) simulations. Methods: MC models of two Philips US probes, an X6-1 matrix-array transducer and a C5-2 curved-array transducer, were built based on their CT images in the EGSnrc BEAMnrc and DOSXYZnrc codes. Due to the metal parts, the probes were scanned in a Tomotherapy machine with a 3.5 MV beam. Mass densities in the probes were assigned based on an electron density calibration phantom consisting of cylinders with mass densities between 0.2–8.0 g/cm{sup 3}.more » Beam attenuation due to the probes was measured in a solid water phantom for a 6 MV and 15 MV 15x15 cm{sup 2} beam delivered on a Varian Trilogy linear accelerator. The dose was measured with the PTW-729 ionization chamber array at two depths and compared to MC simulations. The extreme case beam attenuation expected in robotic US image guided radiotherapy for probes in upright position was quantified by means of MC simulations. Results: The 3.5 MV CT number to mass density calibration curve was found to be linear with R{sup 2} > 0.99. The maximum mass densities were 4.6 and 4.2 g/cm{sup 3} in the C5-2 and X6-1 probe, respectively. Gamma analysis of the simulated and measured doses revealed that over 98% of measurement points passed the 3%/3mm criteria for both probes and measurement depths. The extreme attenuation for probes in upright position was found to be 25% and 31% for the C5-2 and X6-1 probe, respectively, for both 6 and 15 MV beams at 10 cm depth. Conclusion: MC models of two US probes used for real-time image guidance during radiotherapy have been built. As a Result, radiotherapy treatment planning with the imaging probes in place can now be performed. J Schlosser is an employee of SoniTrack Systems, Inc. D Hristov has financial interest in SoniTrack Systems, Inc.« less

Spatially-Resolved Beam Current and Charge-State Distributions for the NEXT Ion Engine

NASA Technical Reports Server (NTRS)

Pollard, James E.; Diamant, Kevin D.; Crofton, Mark W.; Patterson, Michael J.; Soulas, George C.

2010-01-01

Plume characterization tests with the 36-cm NEXT ion engine are being performed at The Aerospace Corporation using engineering-model and prototype-model thrusters. We have examined the beam current density and xenon charge-state distribution as functions of position on the accel grid. To measure the current density ratio j++/j+, a collimated Eprobe was rotated through the plume with the probe oriented normal to the accel electrode surface at a distance of 82 cm. The beam current density jb versus radial position was measured with a miniature planar probe at 3 cm from the accel. Combining the j++/j+ and jb data yielded the ratio of total Xe+2 current to total Xe+1 current (J++/J+) at forty operating points in the standard throttle table. The production of Xe+2 and Xe+3 was measured as a function of propellant utilization to support performance and lifetime predictions for an extended throttle table. The angular dependence of jb was measured at intermediate and far-field distances to assist with plume modeling and to evaluate the thrust loss due to beam divergence. Thrust correction factors were derived from the total doubles-to-singles current ratio and from the far-field divergence data

Ultra-bright γ-ray flashes and dense attosecond positron bunches from two counter-propagating laser pulses irradiating a micro-wire target.

PubMed

Li, Han-Zhen; Yu, Tong-Pu; Hu, Li-Xiang; Yin, Yan; Zou, De-Bin; Liu, Jian-Xun; Wang, Wei-Quan; Hu, Shun; Shao, Fu-Qiu

2017-09-04

We propose a novel scheme to generate ultra-bright ultra-short γ-ray flashes and high-energy-density attosecond positron bunches by using multi-dimensional particle-in-cell simulations with quantum electrodynamics effects incorporated. By irradiating a 10 PW laser pulse with an intensity of 10 23 W/cm 2 onto a micro-wire target, surface electrons are dragged-out of the micro-wire and are effectively accelerated to several GeV energies by the laser ponderomotive force, forming relativistic attosecond electron bunches. When these electrons interact with the probe pulse from the other side, ultra-short γ-ray flashes are emitted with an ultra-high peak brightness of 1.8 × 10 24 photons s -1 mm -2 mrad -2 per 0.1%BW at 24 MeV. These photons propagate with a low divergence and collide with the probe pulse, triggering the Breit-Wheeler process. Dense attosecond e - e + pair bunches are produced with the positron energy density as high as 10 17 J/m 3 and number of 10 9 . Such ultra-bright ultra-short γ-ray flashes and secondary positron beams may have potential applications in fundamental physics, high-energy-density physics, applied science and laboratory astrophysics.

Triple probe interrogation of spokes in a HiPIMS discharge

NASA Astrophysics Data System (ADS)

Lockwood Estrin, F.; Karkari, S. K.; Bradley, J. W.

2017-07-01

Using a triple probe situated above the racetrack and inside the magnetic trap of a magnetron, rotating spoke-like structures have been clearly identified in a single HiPIMS pulse as periodic modulations of the electron temperature T e, electron density n e, ion saturation current I isat, floating potential V f and plasma potential V p. The spokes rotate in the E  ×  B direction with a velocity of ~8.8 km s-1. Defining the spoke shape from the footprint of the ion current, they deliver to flush-mounted probes embedded in the target, each spoke can be characterised by a dense but cool leading edge (n e ~ 2.0  ×  1019 m-3, T e ~ 2.1 eV) and a relatively hotter but more rarefied trailing edge (n e ~ 1  ×  1019 m-3, T e ~ 3.9 eV). Measurements of V p show a potential hump towards the rear of the spoke, separated from regions of the highest density, with plasma potentials up to 8 V more positive than the inter-spoke regions. Azimuthal electric fields of ~1 kV m-1 associated with these structures are calculated. Transforming the triple probe time-traces to functions of the azimuthal angle θ and assuming a Gaussian radial profile for the plasma parameters, 2D spatial maps of n e, T e and V p have been constructed as well as the target ion current density J p from the embedded probes. The phase relationship between T e, V p and n e can be clearly seen using this representation with n e leading T e and V p with a phase shift between them of ~50°. Regions of maximum ion current to the target, delivered by individual spokes, coincide with the overlap of regions of high n e and T e measured above the target at a height of 15 mm. Ions created at elevated positions above the target in the observed dense region will take several micro-seconds to reach that surface, so contributing to the target ion current in the following spokes.

Ion flux enhancements and oscillations in spatially confined laser produced aluminum plasmas

NASA Astrophysics Data System (ADS)

Singh, S. C.; Fallon, C.; Hayden, P.; Mujawar, M.; Yeates, P.; Costello, J. T.

2014-09-01

Ion signals from laser produced plasmas (LPPs) generated inside aluminum rectangular cavities at a fixed depth d = 2 mm and varying width, x = 1.0, 1.6, and 2.75 mm were obtained by spatially varying the position of a negatively biased Langmuir probe. Damped oscillatory features superimposed on Maxwellian distributed ion signals were observed. Depending on the distance of the probe from the target surface, three to twelve fold enhancements in peak ion density were observed via confinement of the LPP, generated within rectangular cavities of varying width which constrained the plasma plume to near one dimensional expansion in the vertical plane. The effects of lateral spatial confinement on the expansion velocity of the LPP plume front, the temperature, density and expansion velocity of ions, enhancement of ion flux, and ion energy distribution were recorded. The periodic behavior of ion signals was analyzed and found to be related to the electron plasma frequency and electron-ion collision frequency. The effects of confinement and enhancement of various ion parameters and expansion velocities of the LPP ion plume are explained on the basis of shock wave theory.

Probing charge transfer during metal-insulator transitions in graphene-LaAlO3/SrTiO3 systems

NASA Astrophysics Data System (ADS)

Aliaj, I.; Sambri, A.; Miseikis, V.; Stornaiuolo, D.; di Gennaro, E.; Coletti, C.; Pellegrini, V.; Miletto Granozio, F.; Roddaro, S.

2018-06-01

Two-dimensional electron systems (2DESs) at the interface between LaAlO3 (LAO) and SrTiO3 (STO) perovskite oxides display a wide class of tunable phenomena ranging from superconductivity to metal-insulator transitions. Most of these effects are strongly sensitive to surface physics and often involve charge transfer mechanisms, which are, however, hard to detect. In this work, we realize hybrid field-effect devices where graphene is used to modulate the transport properties of the LAO/STO 2DES. Different from a conventional gate, graphene is semimetallic and allows us to probe charge transfer with the oxide structure underneath the field-effect electrode. In LAO/STO samples with a low initial carrier density, graphene-covered regions turn insulating when the temperature is lowered to 3 K, but conduction can be restored in the oxide structure by increasing the temperature or by field effect. The evolution of graphene's electron density is found to be inconsistent with a depletion of LAO/STO, but it rather points to a localization of interfacial carriers in the oxide structure.

Hardware Overview of the Microwave Imaging Reflectometry (MIR) on DIII-D

NASA Astrophysics Data System (ADS)

Hu, Xing; Muscatello, Chirstopher; Domier, Calvin; Luhmann, Neville; Ren, Xiaoxin; Spear, Alexander; Tobias, Benjamin; Yu, Liubing; University of California Davis Collaboration; Princeton Plasma Physics Laboratory Collaboration

2013-10-01

UC Davis in collaboration with PPPL has developed and installed a 12 by 4 (48) channel MIR system on DIII-D to measure 2-D structure of density fluctuations. In the transmitter path, a four-frequency probing beam is generated by mixing the 65 GHz Gunn oscillator signal with two different 0.5 ~ 9 GHz signals. Carefully designed imaging optics shape the beam to ensure the probing beam wavefront matches the cutoff surfaces. In the receiver path, large aperture imaging optics collect the reflected beam and focus it onto the mini lens antenna array, which provides improved LO coupling and antenna performance over earlier imaging systems. The reflected signal is down-converted for the first time on the array and goes into the innovative electronics for a second down-conversion. Low frequency LOs for the IQ mixer are generated by mixing two reference signals from phase-locked circuits. The double down-converted signal is mixed with the low frequency LOs yielding in-phase and quadrature components of the phase and thus density fluctuation information.

Improved analysis techniques for cylindrical and spherical double probes.

PubMed

Beal, Brian; Johnson, Lee; Brown, Daniel; Blakely, Joseph; Bromaghim, Daron

2012-07-01

A versatile double Langmuir probe technique has been developed by incorporating analytical fits to Laframboise's numerical results for ion current collection by biased electrodes of various sizes relative to the local electron Debye length. Application of these fits to the double probe circuit has produced a set of coupled equations that express the potential of each electrode relative to the plasma potential as well as the resulting probe current as a function of applied probe voltage. These equations can be readily solved via standard numerical techniques in order to determine electron temperature and plasma density from probe current and voltage measurements. Because this method self-consistently accounts for the effects of sheath expansion, it can be readily applied to plasmas with a wide range of densities and low ion temperature (T(i)/T(e) ≪ 1) without requiring probe dimensions to be asymptotically large or small with respect to the electron Debye length. The presented approach has been successfully applied to experimental measurements obtained in the plume of a low-power Hall thruster, which produced a quasineutral, flowing xenon plasma during operation at 200 W on xenon. The measured plasma densities and electron temperatures were in the range of 1 × 10(12)-1 × 10(17) m(-3) and 0.5-5.0 eV, respectively. The estimated measurement uncertainty is +6%∕-34% in density and +∕-30% in electron temperature.

A microfluidic brain slice perfusion chamber for multisite recording using penetrating electrodes.

PubMed

Blake, Alexander J; Rodgers, Frank C; Bassuener, Anna; Hippensteel, Joseph A; Pearce, Thomas M; Pearce, Timothy R; Zarnowska, Ewa D; Pearce, Robert A; Williams, Justin C

2010-05-30

To analyze the spatiotemporal dynamics of network activity in a brain tissue slice, it is useful to record simultaneously from multiple locations. When obtained from laminar structures such as the hippocampus or neocortex, multisite recordings also yield information about subcellular current distributions via current source density analysis. Multisite probes developed for in vivo recordings could serve these purposes in vitro, allowing recordings to be obtained from brain slices at sites deeper within the tissue than currently available surface recording methods permit. However, existing recording chambers do not allow for the insertion of lamina-spanning probes that enter through the edges of brain slices. Here, we present a novel brain slice recording chamber design that accomplishes this goal. The device provides a stable microfluidic perfusion environment in which tissue health is optimized by superfusing both surfaces of the slice. Multichannel electrodes can be inserted parallel to the surface of the slice, at any depth relative to the surface. Access is also provided from above for the insertion of additional recording or stimulating electrodes. We illustrate the utility of this recording configuration by measuring current sources and sinks during theta burst stimuli that lead to the induction of long-term potentiation in hippocampal slices. (c) 2010 Elsevier B.V. All rights reserved.

Fibered fluorescence microscopy (FFM) of intra epidermal nerve fibers--translational marker for peripheral neuropathies in preclinical research: processing and analysis of the data

NASA Astrophysics Data System (ADS)

Cornelissen, Frans; De Backer, Steve; Lemeire, Jan; Torfs, Berf; Nuydens, Rony; Meert, Theo; Schelkens, Peter; Scheunders, Paul

2008-08-01

Peripheral neuropathy can be caused by diabetes or AIDS or be a side-effect of chemotherapy. Fibered Fluorescence Microscopy (FFM) is a recently developed imaging modality using a fiber optic probe connected to a laser scanning unit. It allows for in-vivo scanning of small animal subjects by moving the probe along the tissue surface. In preclinical research, FFM enables non-invasive, longitudinal in vivo assessment of intra epidermal nerve fibre density in various models for peripheral neuropathies. By moving the probe, FFM allows visualization of larger surfaces, since, during the movement, images are continuously captured, allowing to acquire an area larger then the field of view of the probe. For analysis purposes, we need to obtain a single static image from the multiple overlapping frames. We introduce a mosaicing procedure for this kind of video sequence. Construction of mosaic images with sub-pixel alignment is indispensable and must be integrated into a global consistent image aligning. An additional motivation for the mosaicing is the use of overlapping redundant information to improve the signal to noise ratio of the acquisition, because the individual frames tend to have both high noise levels and intensity inhomogeneities. For longitudinal analysis, mosaics captured at different times must be aligned as well. For alignment, global correlation-based matching is compared with interest point matching. Use of algorithms working on multiple CPU's (parallel processor/cluster/grid) is imperative for use in a screening model.

Enhanced solid-phase recombinase polymerase amplification and electrochemical detection.

PubMed

Del Río, Jonathan Sabaté; Lobato, Ivan Magriñà; Mayboroda, Olena; Katakis, Ioanis; O'Sullivan, Ciara K

2017-05-01

Recombinase polymerase amplification (RPA) is an elegant method for the rapid, isothermal amplification of nucleic acids. Here, we elucidate the optimal surface chemistry for rapid and efficient solid-phase RPA, which was fine-tuned in order to obtain a maximum signal-to-noise ratio, defining the optimal DNA probe density, probe-to-lateral spacer ratio (1:0, 1:1, 1:10 and 1:100) and length of a vertical spacer of the probe as well as investigating the effect of different types of lateral spacers. The use of different labelling strategies was also examined in order to reduce the number of steps required for the analysis, using biotin or horseradish peroxidase-labelled reverse primers. Optimisation of the amplification temperature used and the use of surface blocking agents were also pursued. The combination of these changes facilitated a significantly more rapid amplification and detection protocol, with a lowered limit of detection (LOD) of 1 · 10 -15 M. The optimised protocol was applied to the detection of Francisella tularensis in real samples from hares and a clear correlation with PCR and qPCR results observed and the solid-phase RPA demonstrated to be capable of detecting 500 fM target DNA in real samples. Graphical abstract Relative size of thiolated lateral spacers tested versus the primer and the uvsx recombinase protein.

A model of heat transfer in sapwood and implications for sap flux density measurements using thermal dissipation probes

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

Wullschleger, Stan D; Childs, Kenneth W; King, Anthony Wayne

2011-01-01

A variety of thermal approaches are used to estimate sap flux density in stems of woody plants. Models have proven valuable tools for interpreting the behavior of heat pulse, heat balance, and heat field deformation techniques, but have seldom been used to describe heat transfer dynamics for the heat dissipation method. Therefore, to better understand the behavior of heat dissipation probes, a model was developed that takes into account the thermal properties of wood, the physical dimensions and thermal characteristics of the probes, and the conductive and convective heat transfer that occurs due to water flow in the sapwood. Probesmore » were simulated as aluminum tubes 20 mm in length and 2 mm in diameter, whereas sapwood, heartwood, and bark each had a density and water fraction that determined their thermal properties. Base simulations assumed a constant sap flux density with sapwood depth and no wounding or physical disruption of xylem beyond the 2 mm diameter hole drilled for probe installation. Simulations across a range of sap flux densities showed that the dimensionless quantity k defined as ( Tm T)/ T where Tm is the temperature differential ( T) between the heated and unheated probe under zero flow conditions was dependent on the thermal conductivity of the sapwood. The relationship between sap flux density and k was also sensitive to radial gradients in sap flux density and to xylem disruption near the probe. Monte Carlo analysis in which 1000 simulations were conducted while simultaneously varying thermal conductivity and wound diameter revealed that sap flux density and k showed considerable departure from the original calibration equation used with this technique. The departure was greatest for abrupt patterns of radial variation typical of ring-porous species. Depending on the specific combination of thermal conductivity and wound diameter, use of the original calibration equation resulted in an 81% under- to 48% over-estimation of sap flux density at modest flux rates. Future studies should verify these simulations and assess their utility in estimating sap flux density for this widely used technique.« less

A beam current density monitor for intense electron beams

NASA Astrophysics Data System (ADS)

Fiorito, R. B.; Raleigh, M.; Seltzer, S. M.

1983-12-01

The authors describe a new type of electric probe for mapping the radial current density profile of high-energy, high current electron beams. The idea of developing an electrically sensitive probe for these conditions was originally suggested to one of the authors during a year's visit to the Lawrence Livermore National Laboratory. The resulting probe is intended for use on the Experimental Test Accelerator (ETA) and the Advanced Test Accelerator at that laboratory. This report discusses in detail: the mechanical design, the electrical response, and temperature effects, as they pertain to the electric probe, and describe the first experimental results obtained using this probe on ETA.

Surface invasive cleavage assay on a maskless light-directed diamond DNA microarray for genome-wide human SNP mapping.

PubMed

Nie, Bei; Yang, Min; Fu, Weiling; Liang, Zhiqing

2015-07-07

The surface invasive cleavage assay, because of its innate accuracy and ability for self-signal amplification, provides a potential route for the mapping of hundreds of thousands of human SNP sites. However, its performance on a high density DNA array has not yet been established, due to the unusual "hairpin" probe design on the microarray and the lack of chemical stability of commercially available substrates. Here we present an applicable method to implement a nanocrystalline diamond thin film as an alternative substrate for fabricating an addressable DNA array using maskless light-directed photochemistry, producing the most chemically stable and biocompatible system for genetic analysis and enzymatic reactions. The surface invasive cleavage reaction, followed by degenerated primer ligation and post-rolling circle amplification is consecutively performed on the addressable diamond DNA array, accurately mapping SNP sites from PCR-amplified human genomic target DNA. Furthermore, a specially-designed DNA array containing dual probes in the same pixel is fabricated by following a reverse light-directed DNA synthesis protocol. This essentially enables us to decipher thousands of SNP alleles in a single-pot reaction by the simple addition of enzyme, target and reaction buffers.

Spatially resolved NMR spectra for the Swiss cheese model in heavy fermion PuCoGa5 superconductor

NASA Astrophysics Data System (ADS)

Das, Tanmoy; Zhu, Jian-Xin; Balatsky, A. V.; Graf, M. J.

2011-03-01

Spatially resolved NMR experiments, which probe the local electronic excitations, play a vital role for studying the pairing symmetry of unconventional superconductors. Here we calculate the spatial modulation of the NMR spin-lattice relaxation rate (1/T1) for the Swiss cheese model as a function of impurity concentration in PuCoGa5 superconductor. The local suppression of the superconducting order parameter due to impurities is related to the number of holes in the Swiss cheese model. Our results indicate that Friedel-like oscillations,as seen in the local-density of states near an impurity, are also present in the behavior of 1/T1 as one moves away from the impurity site. We demonstrate that the gap nodes, which are filled by disorder, can be probed by NMR through the local information encoded in the spectra. The advantage of spatially resolved NMR compared to STM measurements is that the former probe is not sensitive to surface states. Work is supported by US DOE.

Measurement of electron density transients in pulsed RF discharges using a frequency boxcar hairpin probe

NASA Astrophysics Data System (ADS)

Peterson, David; Coumou, David; Shannon, Steven

2015-11-01

Time resolved electron density measurements in pulsed RF discharges are shown using a hairpin resonance probe using low cost electronics, on par with normal Langmuir probe boxcar mode operation. Time resolution of 10 microseconds has been demonstrated. A signal generator produces the applied microwave frequency; the reflected waveform is passed through a directional coupler and filtered to remove the RF component. The signal is heterodyned with a frequency mixer and rectified to produce a DC signal read by an oscilloscope. At certain points during the pulse, the plasma density is such that the applied frequency is the same as the resonance frequency of the probe/plasma system, creating reflected signal dips. The applied microwave frequency is shifted in small increments in a frequency boxcar routine to determine the density as a function of time. A dc sheath correction is applied for the grounded probe, producing low cost, high fidelity, and highly reproducible electron density measurements. The measurements are made in both inductively and capacitively coupled systems, the latter driven by multiple frequencies where a subset of these frequencies are pulsed. Measurements are compared to previous published results, time resolved OES, and in-line measurement of plasma impedance. This work is supported by the NSF DOE partnership on plasma science, the NSF GOALI program, and MKS Instruments.

Effect of the plate surface characteristics and gap height on yield stresses of a magnetorheological fluid

NASA Astrophysics Data System (ADS)

Jonkkari, I.; Kostamo, E.; Kostamo, J.; Syrjala, S.; Pietola, M.

2012-07-01

Effects of the plate material, surface roughness and measuring gap height on static and dynamic yield stresses of a magnetorheological (MR) fluid were investigated with a commercial plate-plate magnetorheometer. Magnetic and non-magnetic plates with smooth (Ra ˜ 0.3 μm) and rough (Ra ˜ 10 μm) surface finishes were used. It was shown by Hall probe measurements and finite element simulations that the use of magnetic plates or higher gap heights increases the level of magnetic flux density and changes the shape of the radial flux density profile. The yield stress increase caused by these factors was determined and subtracted from the measured values in order to examine only the effect of the wall characteristics or the gap height. Roughening of the surfaces offered a significant increase in the yield stresses for non-magnetic plates. With magnetic plates the yield stresses were higher to start with, but roughening did not increase them further. A significant part of the difference in measured stresses between rough non-magnetic and magnetic plates was caused by changes in magnetic flux density rather than by better contact of the particles to the plate surfaces. In a similar manner, an increase in gap height from 0.25 to 1.00 mm can lead to over 20% increase in measured stresses due to changes in the flux density profile. When these changes were compensated the dynamic yield stresses generally remained independent of the gap height, even in the cases where it was obvious that the wall slip was present. This suggests that with MR fluids the wall slip cannot be reliably detected by comparison of flow curves measured at different gap heights.

Superhydrophilic-Superhydrophobic Patterned Surfaces as High-Density Cell Microarrays: Optimization of Reverse Transfection.

PubMed

Ueda, Erica; Feng, Wenqian; Levkin, Pavel A

2016-10-01

High-density microarrays can screen thousands of genetic and chemical probes at once in a miniaturized and parallelized manner, and thus are a cost-effective alternative to microwell plates. Here, high-density cell microarrays are fabricated by creating superhydrophilic-superhydrophobic micropatterns in thin, nanoporous polymer substrates such that the superhydrophobic barriers confine both aqueous solutions and adherent cells within each superhydrophilic microspot. The superhydrophobic barriers confine and prevent the mixing of larger droplet volumes, and also control the spreading of droplets independent of the volume, minimizing the variability that arises due to different liquid and surface properties. Using a novel liposomal transfection reagent, ScreenFect A, the method of reverse cell transfection is optimized on the patterned substrates and several factors that affect transfection efficiency and cytotoxicity are identified. Higher levels of transfection are achieved on HOOC- versus NH 2 -functionalized superhydrophilic spots, as well as when gelatin and fibronectin are added to the transfection mixture, while minimizing the amount of transfection reagent improves cell viability. Almost no diffusion of the printed transfection mixtures to the neighboring microspots is detected. Thus, superhydrophilic-superhydrophobic patterned surfaces can be used as cell microarrays and for optimizing reverse cell transfection conditions before performing further cell screenings. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Development of a large-area planar surface-wave plasma source with a cavity launcher driven by a 915 MHz UHF wave

NASA Astrophysics Data System (ADS)

Chang, Xijiang; Kunii, Kazuki; Liang, Rongqing; Nagatsu, Masaaki

2013-04-01

A large-area planar surface-wave plasma (SWP) source driven by a 915 MHz ultrahigh frequency (UHF) wave was developed. To avoid using large, thick dielectric plates as vacuum windows, we propose a cavity launcher consisting of a cylindrical cavity with several small quartz discs at the bottom. Three types of launchers with quartz discs located at different positions were tested to compare their plasma production efficiencies and spatial distributions of electron density. With the optimum launcher, large-area plasma discharges with a radial uniformity within ±10% were obtained in a radius of about 25-30 cm in Ar gas at 8 Pa for incident power in the range 0.5-2.5 kW. The maximum electron density and temperature were approximately (0.95-1.1) × 1011 cm-3 and 1.9-2.0 eV, respectively, as measured by a Langmuir probe located 24 cm below the bottom of the cavity launcher. Using an Ar/NH3 SWP with the optimum launcher, we demonstrated large-area amino-group surface modification of polyurethane sheets. Experimental results indicated that a uniform amino-group modification was achieved over a radius of approximately 40 cm, which is slightly larger than the radial uniformity of the electron density distribution.

Pyrene-Labeled Amphiphiles: Dynamic And Structural Probes Of Membranes And Lipoproteins

NASA Astrophysics Data System (ADS)

Pownall, Henry J.; Homan, Reynold; Massey, John B.

1987-01-01

Lipids and proteins are important functional and structural components of living organisms. Although proteins are frequently found as soluble components of plasma or the cell cytoplasm, many lipids are much less soluble and separate into complex assemblies that usually contain proteins. Cell membranes and plasma lipoproteins' are two important macro-molecular assemblies that contain both lipids and proteins. Cell membranes are composed of a variety of lipids and proteins that form an insoluble bilayer array that has relatively little curvature over distances of several nm. Plasma lipoproteins are different in that they are much smaller, water-soluble, and have highly curved surfaces. A model of a high density lipoprotein (HDL) is shown in Figure 1. This model (d - 10 nm) contains a surface of polar lipids and proteins that surrounds a small core of insoluble lipids, mostly triglycerides and cholesteryl esters. The low density (LDL) (d - 25 nm) and very low density (VLDL) (d 90 nm) lipoproteins have similar architectures, except the former has a cholesteryl ester core and the latter a core that is almost exclusively triglyceride (Figure 1). The surface proteins of HDL are amphiphilic and water soluble; the single protein of LDL is insoluble, whereas VLDL contains both soluble and insoluble proteins. The primary structures of all of these proteins are known.

Management of fluid mud in estuaries, bays, and lakes. II: Measurement, modeling, and management

USGS Publications Warehouse

McAnally, W.H.; Teeter, A.; Schoellhamer, David H.; Friedrichs, C.; Hamilton, D.; Hayter, E.; Shrestha, P.; Rodriguez, H.; Sheremet, A.; Kirby, R.

2007-01-01

Techniques for measurement, modeling, and management of fluid mud are available, but research is needed to improve them. Fluid mud can be difficult to detect, measure, or sample, which has led to new instruments and new ways of using existing instruments. Multifrequency acoustic fathometers sense neither density nor viscosity and are, therefore, unreliable in measuring fluid mud. Nuclear density probes, towed sleds, seismic, and drop probes equipped with density meters offer the potential for accurate measurements. Numerical modeling of fluid mud requires solving governing equations for flow velocity, density, pressure, salinity, water surface, plus sediment submodels. A number of such models exist in one-, two-, and three-dimensional form, but they rely on empirical relationships that require substantial site-specific validation to observations. Management of fluid mud techniques can be classified as those that accomplish: Source control, formation control, and removal. Nautical depth, a fourth category, defines the channel bottom as a specific fluid mud density or alternative parameter as safe for navigation. Source control includes watershed management measures to keep fine sediment out of waterways and in-water measures such as structures and traps. Formation control methods include streamlined channels and structures plus other measures to reduce flocculation and structures that train currents. Removal methods include the traditional dredging and transport of dredged material plus agitation that contributes to formation control and/or nautical depth. Conditioning of fluid mud by dredging and aerating offers the possibility of improved navigability. Two examples—the Atchafalaya Bar Channel and Savannah Harbor—illustrate the use of measurements and management of fluid mud.

Probing off-Hugoniot states in Ta, Cu, and Al to 1000 GPa compression with magnetically driven liner implosions

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

Lemke, R. W., E-mail: rwlemke@sandia.gov; Dolan, D. H.; Dalton, D. G.

We report on a new technique for obtaining off-Hugoniot pressure vs. density data for solid metals compressed to extreme pressure by a magnetically driven liner implosion on the Z-machine (Z) at Sandia National Laboratories. In our experiments, the liner comprises inner and outer metal tubes. The inner tube is composed of a sample material (e.g., Ta and Cu) whose compressed state is to be inferred. The outer tube is composed of Al and serves as the current carrying cathode. Another aluminum liner at much larger radius serves as the anode. A shaped current pulse quasi-isentropically compresses the sample as itmore » implodes. The iterative method used to infer pressure vs. density requires two velocity measurements. Photonic Doppler velocimetry probes measure the implosion velocity of the free (inner) surface of the sample material and the explosion velocity of the anode free (outer) surface. These two velocities are used in conjunction with magnetohydrodynamic simulation and mathematical optimization to obtain the current driving the liner implosion, and to infer pressure and density in the sample through maximum compression. This new equation of state calibration technique is illustrated using a simulated experiment with a Cu sample. Monte Carlo uncertainty quantification of synthetic data establishes convergence criteria for experiments. Results are presented from experiments with Al/Ta, Al/Cu, and Al liners. Symmetric liner implosion with quasi-isentropic compression to peak pressure ∼1000 GPa is achieved in all cases. These experiments exhibit unexpectedly softer behavior above 200 GPa, which we conjecture is related to differences in the actual and modeled properties of aluminum.« less

Probing off-Hugoniot states in Ta, Cu, and Al to 1000 GPa compression with magnetically driven liner implosions

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

Lemke, R. W.; Dolan, D. H.; Dalton, D. G.

We report on a new technique for obtaining off-Hugoniot pressure vs. density data for solid metals compressed to extreme pressure by a magnetically driven liner implosion on the Z-machine (Z) at Sandia National Laboratories. In our experiments, the liner comprises inner and outer metal tubes. The inner tube is composed of a sample material (e.g., Ta and Cu) whose compressed state is to be inferred. The outer tube is composed of Al and serves as the current carrying cathode. Another aluminum liner at much larger radius serves as the anode. A shaped current pulse quasi-isentropically compresses the sample as itmore » implodes. The iterative method used to infer pressure vs. density requires two velocity measurements. Photonic Doppler velocimetry probes measure the implosion velocity of the free (inner) surface of the sample material and the explosion velocity of the anode free (outer) surface. These two velocities are used in conjunction with magnetohydrodynamic simulation and mathematical optimization to obtain the current driving the liner implosion, and to infer pressure and density in the sample through maximum compression. This new equation of state calibration technique is illustrated using a simulated experiment with a Cu sample. Monte Carlo uncertainty quantification of synthetic data establishes convergence criteria for experiments. Results are presented from experiments with Al/Ta, Al/Cu, and Al liners. Symmetric liner implosion with quasi-isentropic compression to peak pressure ~1000 GPa is achieved in all cases. Lastly, these experiments exhibit unexpectedly softer behavior above 200 GPa, which we conjecture is related to differences in the actual and modeled properties of aluminum.« less

Probing off-Hugoniot states in Ta, Cu, and Al to 1000 GPa compression with magnetically driven liner implosions

DOE PAGES

Lemke, R. W.; Dolan, D. H.; Dalton, D. G.; ...

2016-01-07

We report on a new technique for obtaining off-Hugoniot pressure vs. density data for solid metals compressed to extreme pressure by a magnetically driven liner implosion on the Z-machine (Z) at Sandia National Laboratories. In our experiments, the liner comprises inner and outer metal tubes. The inner tube is composed of a sample material (e.g., Ta and Cu) whose compressed state is to be inferred. The outer tube is composed of Al and serves as the current carrying cathode. Another aluminum liner at much larger radius serves as the anode. A shaped current pulse quasi-isentropically compresses the sample as itmore » implodes. The iterative method used to infer pressure vs. density requires two velocity measurements. Photonic Doppler velocimetry probes measure the implosion velocity of the free (inner) surface of the sample material and the explosion velocity of the anode free (outer) surface. These two velocities are used in conjunction with magnetohydrodynamic simulation and mathematical optimization to obtain the current driving the liner implosion, and to infer pressure and density in the sample through maximum compression. This new equation of state calibration technique is illustrated using a simulated experiment with a Cu sample. Monte Carlo uncertainty quantification of synthetic data establishes convergence criteria for experiments. Results are presented from experiments with Al/Ta, Al/Cu, and Al liners. Symmetric liner implosion with quasi-isentropic compression to peak pressure ~1000 GPa is achieved in all cases. Lastly, these experiments exhibit unexpectedly softer behavior above 200 GPa, which we conjecture is related to differences in the actual and modeled properties of aluminum.« less

NEBULAR AND STELLAR DUST EXTINCTION ACROSS THE DISK OF EMISSION-LINE GALAXIES ON KILOPARSEC SCALES

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

Hemmati, Shoubaneh; Mobasher, Bahram; Darvish, Behnam

We investigate the resolved kiloparsec-scale stellar and nebular dust distribution in eight star-forming galaxies at z ∼ 0.4 in the Great Observatories Origins Deep Survey fields. This is to get a better understanding of the effect of dust attenuation on measurements of physical properties and its variation with redshift. Constructing the observed spectral energy distributions (SEDs) per pixel, based on seven bands of photometric data from Hubble Space Telescope/Advanced Camera for Surveys and WFC3, we performed pixel-by-pixel SED fits to population synthesis models and estimated the small-scale distribution of stellar dust extinction. We use Hα/Hβ nebular emission line ratios from Keck/DEIMOS high-resolutionmore » spectra at each spatial resolution element to measure the amount of attenuation faced by ionized gas at different radii from the centers of galaxies. We find a good agreement between the integrated and median of resolved color excess measurements in our galaxies. The ratio of integrated nebular to stellar dust extinction is always greater than unity, but does not show any trend with stellar mass or star formation rate (SFR). We find that inclination plays an important role in the variation of the nebular to stellar excess ratio. The stellar color excess profiles are found to have higher values at the center compared to outer parts of the disk. However, for lower mass galaxies, a similar trend is not found for the nebular color excess. We find that the nebular color excess increases with stellar mass surface density. This explains the absence of radial trend in the nebular color excess in lower mass galaxies which lack a large radial variation of stellar mass surface density. Using standard conversions of SFR surface density to gas mass surface density, and the relation between dust mass surface density and color excess, we find no significant variation in the dust-to-gas ratio in regions with high gas mass surface densities over the scales probed in this study.« less

Quantitative assessment of the multivalent protein-carbohydrate interactions on silicon.

PubMed

Yang, Jie; Chazalviel, Jean-Noël; Siriwardena, Aloysius; Boukherroub, Rabah; Ozanam, François; Szunerits, Sabine; Gouget-Laemmel, Anne Chantal

2014-10-21

A key challenge in the development of glycan arrays is that the sensing interface be fabricated reliably so as to ensure the sensitive and accurate analysis of the protein-carbohydrate interaction of interest, reproducibly. These goals are complicated in the case of glycan arrays as surface sugar density can influence dramatically the strength and mode of interaction of the sugar ligand at any interface with lectin partners. In this Article, we describe the preparation of carboxydecyl-terminated crystalline silicon (111) surfaces onto which are grafted either mannosyl moieties or a mixture of mannose and spacer alcohol molecules to provide "diluted" surfaces. The fabrication of the silicon surfaces was achieved efficiently through a strategy implicating a "click" coupling step. The interactions of these newly fabricated glycan interfaces with the lectin, Lens culinaris, have been characterized using quantitative infrared (IR) spectroscopy in the attenuated total geometry (ATR). The density of mannose probes and lectin targets was precisely determined for the first time by the aid of special IR calibration experiments, thus allowing for the interpretation of the distribution of mannose and its multivalent binding with lectins. These experimental findings were accounted for by numerical simulations of lectin adsorption.

Improvement of water management in a vapor feed direct methanol fuel cell

NASA Astrophysics Data System (ADS)

Masdar, M. Shahbudin; Tsujiguchi, Takuya; Nakagawa, Nobuyoshi

Water transport in a vapor feed direct methanol fuel cell was improved by fixing a hydrophobic air filter (HAF) at the cathode. Effects of the HAF properties and the fixed positions, i.e., just on the cathode surface or by providing a certain space from the surface, of the HAF on the water transport as well as the power generation performance were investigated. The water transport was evaluated by measuring the partial pressure of water, PH2O , and methanol, PCH3OH , at the anode gas layer using in situ mass spectrometry with a capillary probe and also the water and methanol fluxes across the electrode structure using a conventional method. The HAF with the highest hydrophobicity and the highest flow resistance had the strongest effect on increasing the water back diffusion from the cathode to the anode through the membrane and increasing the current density. It was noted that the HAF fixation by providing a space from the cathode surface was more effective in increasing JWCO and the current density than that of the direct placement on the cathode surface. There was an optimum distance for the HAF placement depending on the humidity of the outside air.

Friedel oscillation near a van Hove singularity in two-dimensional Dirac materials

NASA Astrophysics Data System (ADS)

Lu, Chi-Ken

2016-02-01

We consider Friedel oscillation in the two-dimensional Dirac materials when the Fermi level is near the van Hove singularity. Twisted graphene bilayer and the surface state of topological crystalline insulator are the representative materials which show low-energy saddle points that are feasible to probe by gating. We approximate the Fermi surface near saddle point with a hyperbola and calculate the static Lindhard response function. Employing a theorem of Lighthill, the induced charge density δ n due to an impurity is obtained and the algebraic decay of δ n is determined by the singularity of the static response function. Although a hyperbolic Fermi surface is rather different from a circular one, the static Lindhard response function in the present case shows a singularity similar with the response function associated with circular Fermi surface, which leads to the δ n\\propto {{R}-2} at large distance R. The dependences of charge density on the Fermi energy are different. Consequently, it is possible to observe in twisted graphene bilayer the evolution that δ n\\propto {{R}-3} near Dirac point changes to δ n\\propto {{R}-2} above the saddle point. Measurements using scanning tunnelling microscopy around the impurity sites could verify the prediction.

Dehydrogenation of methanol to formaldehyde catalyzed by pristine and defective ceria surfaces

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

Beste, Ariana; Overbury, Steven H.

We have explored the dehydrogenation of methoxy on pristine and defective (111), (100), and (110) ceria surfaces with density functional methods. Methanol conversion is used as a probe reaction to understand structure sensitivity of the oxide catalysis. Differences in reaction selectivity have been observed experimentally as a function of crystallographically exposed faces and degree of reduction. We find that the barrier for carbon-hydrogen cleavage in methoxy is similar for the pristine and defective (111), (100), and (110) surfaces. However, there are large differences in the stability of the surface intermediates on the different surfaces. The variations in experimentally observed productmore » selectivities are a consequence of the interplay between barrier controlled bond cleavage and desorption processes. Ultimately, subtle differences in activation energies for carbon-hydrogen cleavage on the different crystallographic faces of ceria could not be correlated with structural or electronic descriptors.« less

Dehydrogenation of methanol to formaldehyde catalyzed by pristine and defective ceria surfaces

DOE PAGES

Beste, Ariana; Overbury, Steven H.

2016-03-09

We have explored the dehydrogenation of methoxy on pristine and defective (111), (100), and (110) ceria surfaces with density functional methods. Methanol conversion is used as a probe reaction to understand structure sensitivity of the oxide catalysis. Differences in reaction selectivity have been observed experimentally as a function of crystallographically exposed faces and degree of reduction. We find that the barrier for carbon-hydrogen cleavage in methoxy is similar for the pristine and defective (111), (100), and (110) surfaces. However, there are large differences in the stability of the surface intermediates on the different surfaces. The variations in experimentally observed productmore » selectivities are a consequence of the interplay between barrier controlled bond cleavage and desorption processes. Ultimately, subtle differences in activation energies for carbon-hydrogen cleavage on the different crystallographic faces of ceria could not be correlated with structural or electronic descriptors.« less

Dehydrogenation of methanol to formaldehyde catalyzed by pristine and defective ceria surfaces.

PubMed

Beste, Ariana; Overbury, Steven H

2016-04-21

We have explored the dehydrogenation of methoxy on pristine and defective (111), (100), and (110) ceria surfaces with density functional methods. Methanol conversion is used as a probe reaction to understand structure sensitivity of the oxide catalysis. Differences in reaction selectivity have been observed experimentally as a function of crystallographically exposed faces and degree of reduction. We find that the barrier for carbon-hydrogen cleavage in methoxy is similar for the pristine and defective (111), (100), and (110) surfaces. However, there are large differences in the stability of the surface intermediates on the different surfaces. The variations in experimentally observed product selectivities are a consequence of the interplay between barrier controlled bond cleavage and desorption processes. Subtle differences in activation energies for carbon-hydrogen cleavage on the different crystallographic faces of ceria could not be correlated with structural or electronic descriptors.

Bridging Zirconia Nodes within a Metal–Organic Framework via Catalytic Ni-Hydroxo Clusters to Form Heterobimetallic Nanowires

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

Platero-Prats, Ana E.; League, Aaron B.; Bernales, Varinia

2017-07-24

Metal-organic frameworks (MOFs), with their well-ordered pore networks and tunable surface chemistries, offer a versatile platform for preparing well-defined nanostructures wherein functionality such as catalysis can be incorporated. We resolved the atomic structure of Ni-oxo species deposited in the MOF NU-1000 through atomic layer deposition using local and long-range structure probes, including X-ray absorption spectroscopy, pair distribution function analysis and difference envelope density analysis, with electron microscopy imaging and computational modeling.

Molecular Velcro constructed from polymer loop brushes showing enhanced adhesion force

NASA Astrophysics Data System (ADS)

Zhou, Tian; Han, Biao; Han, Lin; Li, Christopher; Department of Materials Science; Engineering Team; School of Biomedical Engineering, Science; Health Systems Team

2015-03-01

Molecular Velcro is commonly seen in biological systems as the formation of strong physical entanglement at molecular scale could induce strong adhesion, which is crucial to many biological processes. To mimic this structure, we designed, and fabricated polymer loop brushes using polymer single crystals with desired surface functionality and controlled chain folding. Compared with reported loop brushes fabricated using triblock copolymers, the present loop bushes have precise loop sizes, loop grafting density, and well controlled tethering locations on the solid surface. Atomic force microscopy-based force spectroscopy measurements using a polymer chain coated probe reveal that the adhesion force are significantly enhanced on the loop brush surface as compared with its single-strand counterpart. This study directly shows the effect of polymer brush conformation on their properties, and suggests a promising strategy for advanced polymer surface design.

A microscopic study investigating the structure of SnSe surfaces

NASA Astrophysics Data System (ADS)

Kim, Sang-ui; Duong, Anh-Tuan; Cho, Sunglae; Rhim, S. H.; Kim, Jungdae

2016-09-01

SnSe has been widely studied due to its many potential applications that take advantage of its excellent thermoelectric, photovoltaic, and optoelectronic properties. However, experimental investigations into the microscopic structure of SnSe remain largely unexplored. Herein, for the first time, the atomic and electronic structures of SnSe surfaces are studied by a home-built low temperature scanning tunneling microscope (STM) and density functional theory (DFT) calculations. The cleaved surface of SnSe is comprised of covalently bonded Se and Sn atoms in zigzag patterns. However, rectangular periodicity was observed in the atomic images of SnSe surfaces for filled and empty state probing. Detailed atomic structures are analyzed by DFT calculations, indicating that the bright extrusions of both filled and empty state images are mostly located at the positions of Sn atoms.

Polarity compensation mechanisms on the perovskite surface KTaO 3(001)

DOE PAGES

Setvin, Martin; Reticcioli, Michele; Poelzleitner, Flora; ...

2018-02-02

The stacking of alternating charged planes in ionic crystals creates a diverging electrostatic energy—a “polar catastrophe”—that must be compensated at the surface. We used scanning probe microscopies and density functional theory to study compensation mechanisms at the perovskite potassium tantalate (KTaO 3) (001) surface as increasing degrees of freedom were enabled. The as-cleaved surface in vacuum is frozen in place but immediately responds with an insulator-to-metal transition and possibly ferroelectric lattice distortions. Annealing in vacuum allows the formation of isolated oxygen vacancies, followed by a complete rearrangement of the top layers into an ordered pattern of KO and TaO 2more » stripes. The optimal solution is found after exposure to water vapor through the formation of a hydroxylated overlayer with ideal geometry and charge.« less

Langmuir Probe Distortions and Probe Compensation in an Inductively Coupled Plasma

NASA Technical Reports Server (NTRS)

Ji, J. S.; Cappelli, M. A.; Kim, J. S.; Rao, M. V. V. S.; Sharma, S. P.

1999-01-01

In many RF discharges, Langmuir probe measurements are usually made against a background of sinusoidal (and not so sinusoidal) fluctuations in the plasma parameters such as the plasma potential (Vp), the electron number density (ne), and the electron temperature (Te). The compensation of sinusoidal fluctuations in Vp has been extensively studied and is relatively well understood. Less attention has been paid to the possible distortions introduced by small fluctuations in plasma density and/or plasma temperature, which may arise in the sheath and pre-sheath regions of RF discharges. Here, we present the results of a model simulation of probe characteristics subject to fluctuations in both Vp and ne. The modeling of probe distortion due to possible fluctuations in Te is less straightforward. A comparison is presented of calculations with experimental measurements using a compensated and uncompensated Langmuir probe in an inductively coupled GEC reference cell plasma, operating on Ar and Ar/CF4 mixtures. The plasma parameters determined from the compensated probe characteristics are compared to previous measurements of others made in similar discharges, and to our own measurements of the average electron density derived from electrical impedance measurements.

Characterisation of SOL density fluctuations in front of the LHCD PAM launcher in Tore

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

Oosako, T.; Ekedahl, A.; Goniche, M.

2011-12-23

The density fluctuations, modified by Lower Hybrid Wave (LHW), is analyzed in Tore Supra with reference to the injected LHW power, density and the gap between LCFS (Last Closed Flux Surface) and the PAM (passive-active-multijunction) launcher. The density fluctuations are measured with RF probes installed at the PAM launcher front. A density scan at nominal toroidal field (3.8 T) shows that the fluctuations rate stays nearly constant ({approx}50%) for <3.5x10{sup 19}m{sup -3} and with LHW power up to 2MW. However, when increasing the density above <{approx}4.2x10{sup 19}m{sup -3}, using strong gas puffing, the fluctuation rate increases to >70%more » and is characterized by strong negative spikes, with typical frequency >100kHz. These are most likely originating from acceleration of electrons in the LHW near field due to parasitic absorption, as evidenced on the IR images, showing hot spots on the side limiters.« less

Gravitational lens effects of a cosmological density of compact objects

NASA Technical Reports Server (NTRS)

Canizares, C. R.

1983-01-01

Amplification of quasar light by a cosmological density of compact objects causes significant effects on many quasars in magnitude-limited samples. For lens masses solar mass less than 100,000 solar mass the continuum would be amplified by a magnitude or more but the line emission would not. Examination of the UV selected sample of Marshall et al. (1983) gives limits to more than 90 percent statistical confidence of Omega(c) less than 0.1 for a mass between 200 and 100,000 solar mass, where Omega(c) is the mean density of objects of mass M relative to the closure density. Preliminary results from an X-ray selected sample may probe to more than 0.1 solar mass and give a value for Omega(c) of less than one. These limits indicate that the remnants of an early population of massive stars cannot make a cosmologically significant contribution to the mass density of the universe. On a separate topic, recent work on the enhanced surface density of quasars near galaxies due to lensing by stars in the galaxy halos is reviewed.

Reversible chemical tuning of charge carriers for enhanced photoelectrochemical conversion and probing of living cells.

PubMed

Wang, Yongcheng; Tang, Jing; Zhou, Tong; Da, Peimei; Li, Jun; Kong, Biao; Yang, Zhongqin; Zheng, Gengfeng

2014-12-10

A facile, solution method for reversible tuning of oxygen vacancies inside TiO2 nanowires, in which the reducing treatment of TiO2 by NaBH4 leads to 2.4-fold increase of photocurrent density, compared to pristine TiO2 nanowires, is reported. Subsequent oxidizing treatment using KMnO4 or annealing in air can reset the photocurrent density to the original values. The incident photo-to-current conversion efficiency measurement exhibits that the reduced TiO2 nanowires present both enhanced photoactivity in both UV and visible regions. Density functional theory calculations reveal that the oxygen vacancies in the reduced TiO2 cause defect states in the band structure and result in enhanced carrier density and conductivity. In addition, the enhanced solar energy-driven photoelectrochemical conversion allows real-time, sensitive chemical probing of living cells that are directly grown on the TiO2 nanowire photoanodes. As proofs-of-concept, after functionalized with horseradish peroxidase (HRP) on the surface, the reduced TiO2 NWs demonstrate sensitive, real-time monitoring of the H2O2 levels in several distinctive living cell lines, with the lowest detectable H2O2 concentration of 7.7 nM. This reversible tuning of oxygen vacancies suggests a facile means for transition metal oxides, with enhanced photoconversion activity and electrochemical sensitivity. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Research progress on ionic plasmas generated in an intense hydrogen negative ion source

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

Takeiri, Y., E-mail: takeiri@nifs.ac.jp; Tsumori, K.; Nagaoka, K.

2015-04-08

Characteristics of ionic plasmas, observed in a high-density hydrogen negative ion source, are investigated with a multi-diagnostics system. The ionic plasma, which consists of hydrogen positive- and negative-ions with a significantly low-density of electrons, is generated in the ion extraction region, from which the negative ions are extracted through the plasma grid. The negative ion density, i.e., the ionic plasma density, as high as the order of 1×10{sup 17}m{sup −3}, is measured with cavity ring-down spectroscopy, while the electron density is lower than 1×10{sup 16}m{sup −3}, which is confirmed with millimeter-wave interferometer. Reduction of the negative ion density is observedmore » at the negative ion extraction, and at that time the electron flow into the ionic plasma region is observed to conserve the charge neutrality. Distribution of the plasma potential is measured in the extraction region in the direction normal to the plasma grid surface with a Langmuir probe, and the results suggest that the sheath is formed at the plasma boundary to the plasma grid to which the bias voltage is applied. The beam extraction should drive the negative ion transport in the ionic plasma across the sheath formed on the extraction surface. Larger reduction of the negative ions at the beam extraction is observed in a region above the extraction aperture on the plasma grid, which is confirmed with 2D image measurement of the Hα emission and cavity ring-down spectroscopy. The electron distribution is also measured near the plasma grid surface. These various properties observed in the ionic plasma are discussed.« less

In-Situ F2-Region Plasma Density and Temperature Measurements from the International Space Station

NASA Technical Reports Server (NTRS)

Coffey, Victoria; Wright, Kenneth; Minow, Joseph

2008-01-01

The International Space Station orbit provides an ideal platform for in-situ studies of space weather effects on the mid and low latitude F-2 region ionosphere. The Floating Potential Measurement Unit (FPMU) operating on the ISS since Aug 2006. is a suite of plasma instruments: a Floating Potential Probe (FPP), a Plasma Impedance Probe (PIP), a Wide-sweep langmuir Probe (WLP), and a Narrow-sweep Langmuir Probe (NLP). This instrument package provides a new opportunity lor collaborative multi-instrument studies of the F-region ionosphere during both quiet and disturbed periods. This presentation first describes the operational parameters for each of the FPMU probes and shOWS examples of an intra-instrument validation. We then show comparisons with the plasma density and temperature measurements derived from the TIMED GUVI ultraviolet imager, the Millstone Hill ground based incoherent scatter radar, and DIAS digisondes, Finally we show one of several observations of night-time equatorial density holes demonstrating the capabilities of the probes lor monitoring mid and low latitude plasma processes.

The birth and evolution of surface science: Child of the union of science and technology

PubMed Central

Duke, C. B.

2003-01-01

This article is an account of the birth and evolution of surface science as an interdisciplinary research area. Surface science emanated from the confluence of concepts and tools in physics and chemistry with technological innovations that made it possible to determine the structure and properties of surfaces and interfaces and the dynamics of chemical reactions at surfaces. The combination in the 1960s and 1970s of ultra-high-vacuum (i.e., P < 10−7 Pascal or 10−9 Torr) technology with the recognition that electrons in the energy range from 50 to 500 eV exhibited inelastic collision mean free paths of the order of a few angstroms fostered an explosion of activity. The results were a reformulation of the theory of electron solid scattering, the nearly universal use of electron spectroscopies for surface characterization, the rise of surface science as an independent interdisciplinary research area, and the emergence of the American Vacuum Society (AVS) as a major international scientific society. The rise of microelectronics in the 1970s and 1980s resulted in huge increases in computational power. These increases enabled more complex experiments and the utilization of density functional theory for the quantitative prediction of surface structure and dynamics. Development of scanning-probe microscopies in the 1990s led to atomic-resolution images of macroscopic surfaces and interfaces as well as videos of atoms moving about on surfaces during growth and diffusion. Scanning probes have since brought solid–liquid interfaces into the realm of atomic-level surface science, expanding its scope to more complex systems, including fragile biological materials and processes. PMID:12651946

Overestimation of Mach number due to probe shadow

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

Gosselin, J. J.; Thakur, S. C.; Tynan, G. R.

2016-07-15

Comparisons of the plasma ion flow speed measurements from Mach probes and laser induced fluorescence were performed in the Controlled Shear Decorrelation Experiment. We show the presence of the probe causes a low density geometric shadow downstream of the probe that affects the current density collected by the probe in collisional plasmas if the ion-neutral mean free path is shorter than the probe shadow length, L{sub g} = w{sup 2} V{sub drift}/D{sub ⊥}, resulting in erroneous Mach numbers. We then present a simple correction term that provides the corrected Mach number from probe data when the sound speed, ion-neutral mean free path,more » and perpendicular diffusion coefficient of the plasma are known. The probe shadow effect must be taken into account whenever the ion-neutral mean free path is on the order of the probe shadow length in linear devices and the open-field line region of fusion devices.« less

Method for making a hot wire anemometer and product thereof

NASA Technical Reports Server (NTRS)

Milkulla, V. (Inventor)

1977-01-01

A hot wire anemometer probe is described that includes a ceramic body supporting two conductive rods parallel to each other. The body has a narrow edge surface from which the rods protrude. A probe wire is welded to the rods and extends along the edge surface. A ceramic adhesive is used to secure the probe wire to the surface so that the probe wire is rigid. A method for fabricating the probe is also described in which the body is molded and precisely shaped by machining techniques before the probe wires are installed.

Testing the limits of the Maxwell distribution of velocities for atoms flying nearly parallel to the walls of a thin cell

NASA Astrophysics Data System (ADS)

Todorov, Petko; Bloch, Daniel

2017-11-01

For a gas at thermal equilibrium, it is usually assumed that the velocity distribution follows an isotropic 3-dimensional Maxwell-Boltzmann (M-B) law. This assumption classically implies the assumption of a "cos θ" law for the flux of atoms leaving the surface. Actually, such a law has no grounds in surface physics, and experimental tests of this assumption have remained very few. In a variety of recently developed sub-Doppler laser spectroscopy techniques for gases one-dimensionally confined in a thin cell, the specific contribution of atoms moving nearly parallel to the boundary of the vapor container becomes essential. We report here on the implementation of an experiment to probe effectively the distribution of atomic velocities parallel to the windows for a thin (60 μm) Cs vapor cell. The principle of the setup relies on a spatially separated pump-probe experiment, where the variations of the signal amplitude with the pump-probe separation provide the information on the velocity distribution. The experiment is performed in a sapphire cell on the Cs resonance line, which benefits from a long-lived hyperfine optical pumping. Presently, we can analyze specifically the density of atoms with slow normal velocities ˜5-20 m/s, already corresponding to unusual grazing flight—at ˜85°-88.5° from the normal to the surface—and no deviation from the M-B law is found within the limits of our elementary setup. Finally we suggest tracks to explore more parallel velocities, when surface details—roughness or structure—and the atom-surface interaction should play a key role to restrict the applicability of an M-B-type distribution.

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

Setvin, Martin; Reticcioli, Michele; Poelzleitner, Flora

The stacking of alternating charged planes in ionic crystals creates a diverging electrostatic energy—a “polar catastrophe”—that must be compensated at the surface. We used scanning probe microscopies and density functional theory to study compensation mechanisms at the perovskite potassium tantalate (KTaO 3) (001) surface as increasing degrees of freedom were enabled. The as-cleaved surface in vacuum is frozen in place but immediately responds with an insulator-to-metal transition and possibly ferroelectric lattice distortions. Annealing in vacuum allows the formation of isolated oxygen vacancies, followed by a complete rearrangement of the top layers into an ordered pattern of KO and TaO 2more » stripes. The optimal solution is found after exposure to water vapor through the formation of a hydroxylated overlayer with ideal geometry and charge.« less

Magnetically Filtered Faraday Probe for Measuring the Ion Current Density Profile of a Hall Thruster

DTIC Science & Technology

2006-01-01

Hall thruster is investigated. The MFFP is designed to eliminate the collection of low-energy, charge-exchange (CEX) ions by using a variable magnetic field as an ion filter. In this study, a MFFP, Faraday probe with a reduced acceptance angle (BFP), and nude Faraday probe are used to measure the ion current density profile of a 5 kW Hall thruster operating over the range of 300-500 V and 5-10 mg/s. The probes are evaluated on a xenon propellant Hall thruster in the University of Michigan Large Vacuum Test Facility at operating

Spectroscopic Infrared Extinction Mapping as a Probe of Grain Growth in IRDCs

NASA Astrophysics Data System (ADS)

Lim, Wanggi; Carey, Sean J.; Tan, Jonathan C.

2015-11-01

We present spectroscopic tests of MIR to FIR extinction laws in IRDC G028.36+00.07, a potential site of massive star and star cluster formation. Lim & Tan developed methods of FIR extinction mapping of this source using Spitzer-MIPS 24 μm and Herschel-PACS 70 μm images, and by comparing to MIR Spitzer-IRAC 3-8 μm extinction maps, found tentative evidence for grain growth in the highest mass surface density regions. Here we present results of spectroscopic infrared extinction mapping using Spitzer-IRS (14-38 μm) data of the same Infrared dark cloud (IRDC). These methods allow us to first measure the SED of the diffuse Galactic interstellar medium that is in the foreground of the IRDC. We then carry out our primary investigation of measuring the MIR to FIR opacity law and searching for potential variations as a function of mass surface density within the IRDC. We find relatively flat, featureless MIR-FIR opacity laws that lack the ˜12 and ˜35 μm features associated with the thick water ice mantle models of Ossenkopf & Henning. Their thin ice mantle models and the coagulating aggregate dust models of Ormel et al. are a generally better match to the observed opacity laws. We also find evidence for generally flatter MIR to FIR extinction laws as mass surface density increases, strengthening the evidence for grain and ice mantle growth in higher density regions.

SPECTROSCOPIC INFRARED EXTINCTION MAPPING AS A PROBE OF GRAIN GROWTH IN IRDCs

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

Lim, Wanggi; Carey, Sean J.; Tan, Jonathan C.

We present spectroscopic tests of MIR to FIR extinction laws in IRDC G028.36+00.07, a potential site of massive star and star cluster formation. Lim and Tan developed methods of FIR extinction mapping of this source using Spitzer-MIPS 24 μm and Herschel-PACS 70 μm images, and by comparing to MIR Spitzer-IRAC 3–8 μm extinction maps, found tentative evidence for grain growth in the highest mass surface density regions. Here we present results of spectroscopic infrared extinction mapping using Spitzer-IRS (14–38 μm) data of the same Infrared dark cloud (IRDC). These methods allow us to first measure the SED of the diffusemore » Galactic interstellar medium that is in the foreground of the IRDC. We then carry out our primary investigation of measuring the MIR to FIR opacity law and searching for potential variations as a function of mass surface density within the IRDC. We find relatively flat, featureless MIR–FIR opacity laws that lack the ∼12 and ∼35 μm features associated with the thick water ice mantle models of Ossenkopf and Henning. Their thin ice mantle models and the coagulating aggregate dust models of Ormel et al. are a generally better match to the observed opacity laws. We also find evidence for generally flatter MIR to FIR extinction laws as mass surface density increases, strengthening the evidence for grain and ice mantle growth in higher density regions.« less

An in vitro bacterial adhesion assessment of surface-modified medical-grade PVC.

PubMed

Asadinezhad, Ahmad; Novák, Igor; Lehocký, Marián; Sedlarík, Vladimir; Vesel, Alenka; Junkar, Ita; Sáha, Petr; Chodák, Ivan

2010-06-01

Medical-grade polyvinyl chloride was surface modified by a multistep physicochemical approach to improve bacterial adhesion prevention properties. This was fulfilled via surface activation by diffuse coplanar surface barrier discharge plasma followed by radical graft copolymerization of acrylic acid through surface-initiated pathway to render a structured high density brush. Three known antibacterial agents, bronopol, benzalkonium chloride, and chlorhexidine, were then individually coated onto functionalized surface to induce biological properties. Various modern surface probe techniques were employed to explore the effects of the modification steps. In vitro bacterial adhesion and biofilm formation assay was performed. Escherichia coli strain was found to be more susceptible to modifications rather than Staphylococcus aureus as up to 85% reduction in adherence degree of the former was observed upon treating with above antibacterial agents, while only chlorhexidine could retard the adhesion of the latter by 50%. Also, plasma treated and graft copolymerized samples were remarkably effective to diminish the adherence of E. coli. Copyright 2010 Elsevier B.V. All rights reserved.

High-resolution measurements of the spatial and temporal evolution of megagauss magnetic fields created in intense short-pulse laser-plasma interactions

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

Chatterjee, Gourab, E-mail: gourab@tifr.res.in; Singh, Prashant Kumar; Adak, Amitava

A pump-probe polarimetric technique is demonstrated, which provides a complete, temporally and spatially resolved mapping of the megagauss magnetic fields generated in intense short-pulse laser-plasma interactions. A normally incident time-delayed probe pulse reflected from its critical surface undergoes a change in its ellipticity according to the magneto-optic Cotton-Mouton effect due to the azimuthal nature of the ambient self-generated megagauss magnetic fields. The temporal resolution of the magnetic field mapping is typically of the order of the pulsewidth, limited by the laser intensity contrast, whereas a spatial resolution of a few μm is achieved by this optical technique. High-harmonics of themore » probe can be employed to penetrate deeper into the plasma to even near-solid densities. The spatial and temporal evolution of the megagauss magnetic fields at the target front as well as at the target rear are presented. The μm-scale resolution of the magnetic field mapping provides valuable information on the filamentary instabilities at the target front, whereas probing the target rear mirrors the highly complex fast electron transport in intense laser-plasma interactions.« less

Experimental plasma studies

NASA Technical Reports Server (NTRS)

Dunn, M. G.

1972-01-01

The rate coefficients for the reactions C(+) + e(-) + e(-) yields C + e(-) and CO(+) + e(-) yields C + O were measured over the electron temperature range of approximately 1500 deg K to 7000 deg K. The measurements were performed in CO that had expanded from equilibrium reservoir conditions of 7060 deg K at 17.3 atm pressure and from 6260 deg K at 10.0 atm pressure. Two RAM flight probes were used to measure electron density and electron temperature in the expanding flow of a shock tunnel. Experiments were performed in the inviscid flow with both probes and in the nozzle-wall boundary layer with the constant bias-voltage probe. The distributions of electron density and electron temperature were independently measured using voltage-swept thin-wire probes. Thin-wire Langmuir probes were also used to measure the electron-density and electron-temperature distributions in the boundary layer of a sharp flat plate located on the nozzle centerline. Admittance measurements were performed with the RAM C and RAM C-C S-band antennas in the presence of an ionized boundary layer.

Experimentally Determined Plasma Parameters in a 30 cm Ion Engine

NASA Technical Reports Server (NTRS)

Sengupta, Anita; Goebel, Dan; Fitzgerald, Dennis; Owens, Al; Tynan, George; Dorner, Russ

2004-01-01

Single planar Langmuir probes and fiber optic probes are used to concurrently measure the plasma properties and neutral density variation in a 30cm diameter ion engine discharge chamber, from the immediate vicinity of the keeper to the near grid plasma region. The fiber optic probe consists of a collimated optical fiber recessed into a double bore ceramic tube fitted with a stainless steel light-limiting window. The optical fiber probe is used to measure the emission intensity of excited neutral xenon for a small volume of plasma, at various radial and axial locations. The single Langmuir probes, are used to generate current-voltage characteristics at a total of 140 spatial locations inside the discharge chamber. Assuming a maxwellian distribution for the electron population, the Langmuir probe traces provide spatially resolved measurements of plasma potential, electron temperature, and plasma density. Data reduction for the NSTAR TH8 and TH15 throttle points indicates an electron temperature range of 1 to 7.9 eV and an electron density range of 4e10 to le13 cm(sup -3), throughout the discharge chamber, consistent with the results in the literature. Plasma potential estimates, computed from the first derivative of the probe characteristic, indicate potential from 0.5V to 11V above the discharge voltage along the thruster centerline. These values are believed to be excessively high due to the sampling of the primary electron population along the thruster centerline. Relative neutral density profiles are also obtained with a fiber optic probe sampling photon flux from the 823.1 nm excited to ground state transition. Plasma parameter measurements and neutral density profiles will be presented as a function of probe location and engine discharge conditions. A discussion of the measured electron energy distribution function will also be presented, with regards to variation from pure maxwellian. It has been found that there is a distinct primary population found along the thruster centerline, which causes estimates of electron temperature, electron density, and plasma potential, to err on the high side, due this energetic population. Computation of the energy distribution fimction of the plasma clearly indicates the presence of primaries, whose presence become less obvious with radial distance from the main discharge plume.

How does a probe inserted into the discharge influence the plasma structure?

NASA Astrophysics Data System (ADS)

Yordanov, D.; Lishev, St.; Shivarova, A.

2016-05-01

Shielding the bias applied to the probe by the sheath formed around it and determination of parameters of unperturbed plasmas are in the basis of the probe diagnostics. The results from a two-dimensional model of a discharge with a probe inserted in it show that the probe influences the spatial distribution of the plasma parameters in the entire discharge. The increase (although slight) in the electron temperature, due to the increased losses of charged particles on the additional wall in the discharge (mainly the probe holder), leads to redistribution of the plasma density and plasma potential, as shown by the results obtained at the floating potential of the probe. The deviations due to the bias applied to the probe tip are stronger in the ion saturation region of the probe characteristics. The pattern of the spatial redistribution of the plasma parameters advances together with the movement of the probe deeper in the discharge. Although probe sheaths and probe characteristics resulting from the model are shown, the study does not aim at discussions on the theories for determination of the plasma density from the ion saturation current. Regardless of the modifications in the plasma behavior in the entire discharge, the deviations of the plasma parameters at the position of the probe tip and, respectively, the uncertainty which should be added as an error when the accuracy of the probe diagnostics is estimated do not exceed 10%. Consequently, the electron density and temperature obtained, respectively, at the position of the plasma potential on the probe characteristics and from its transition region are in reasonable agreement with the results from the model of the discharge without a probe. Being in the scope of research on a source of negative hydrogen ions with the design of a matrix of small radius inductive discharges, the model is specified for a low-pressure hydrogen discharge sustained in a small-radius tube.

Art By Don Davis Artist's concept of one of the probes on the hot surface of Venus. Although the

NASA Technical Reports Server (NTRS)

1977-01-01

Art By Don Davis Artist's concept of one of the probes on the hot surface of Venus. Although the probes were not designed to withstand impact, there was a chance that one might survive and transmit some data from the surface. A small probe did survive and transmitted data for 67 minutes.

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

Yamashita, G.; Nagai, M., E-mail: mnagai@mp.es.osaka-u.ac.jp, E-mail: ashida@mp.es.osaka-u.ac.jp; Ashida, M., E-mail: mnagai@mp.es.osaka-u.ac.jp, E-mail: ashida@mp.es.osaka-u.ac.jp

We estimated the carrier multiplication efficiency in the most common solar-cell material, Si, by using optical-pump/terahertz-probe spectroscopy. Through close analysis of time-resolved data, we extracted the exact number of photoexcited carriers from the sheet carrier density 10 ps after photoexcitation, excluding the influences of spatial diffusion and surface recombination in the time domain. For incident photon energies greater than 4.0 eV, we observed enhanced internal quantum efficiency due to carrier multiplication. The evaluated value of internal quantum efficiency agrees well with the results of photocurrent measurements. This optical method allows us to estimate the carrier multiplication and surface recombination of carriersmore » quantitatively, which are crucial for the design of the solar cells.« less

Simultaneous surface and depth neural activity recording with graphene transistor-based dual-modality probes.

PubMed

Du, Mingde; Xu, Xianchen; Yang, Long; Guo, Yichuan; Guan, Shouliang; Shi, Jidong; Wang, Jinfen; Fang, Ying

2018-05-15

Subdural surface and penetrating depth probes are widely applied to record neural activities from the cortical surface and intracortical locations of the brain, respectively. Simultaneous surface and depth neural activity recording is essential to understand the linkage between the two modalities. Here, we develop flexible dual-modality neural probes based on graphene transistors. The neural probes exhibit stable electrical performance even under 90° bending because of the excellent mechanical properties of graphene, and thus allow multi-site recording from the subdural surface of rat cortex. In addition, finite element analysis was carried out to investigate the mechanical interactions between probe and cortex tissue during intracortical implantation. Based on the simulation results, a sharp tip angle of π/6 was chosen to facilitate tissue penetration of the neural probes. Accordingly, the graphene transistor-based dual-modality neural probes have been successfully applied for simultaneous surface and depth recording of epileptiform activity of rat brain in vivo. Our results show that graphene transistor-based dual-modality neural probes can serve as a facile and versatile tool to study tempo-spatial patterns of neural activities. Copyright © 2018 Elsevier B.V. All rights reserved.

Scanning electrochemical microscopy of graphene/polymer hybrid thin films as supercapacitors: Physical-chemical interfacial processes

NASA Astrophysics Data System (ADS)

Gupta, Sanju; Price, Carson

2015-10-01

Hybrid electrode comprising an electric double-layer capacitor of graphene nanosheets and a pseudocapacitor of the electrically conducting polymers namely, polyaniline; PAni and polypyrrole; PPy are constructed that exhibited synergistic effect with excellent electrochemical performance as thin film supercapacitors for alternative energy. The hybrid supercapacitors were prepared by layer-by-layer (LbL) assembly based on controlled electrochemical polymerization followed by reduction of graphene oxide electrochemically producing ErGO, for establishing intimate electronic contact through nanoscale architecture and chemical stability, producing a single bilayer of (PAni/ErGO)1, (PPy/ErGO)1, (PAni/GO)1 and (PPy/GO)1. The rationale design is to create thin films that possess interconnected graphene nanosheets (GNS) with polymer nanostructures forming well-defined tailored interfaces allowing sufficient surface adsorption and faster ion transport due to short diffusion distances. We investigated their electrochemical properties and performance in terms of gravimetric specific capacitance, Cs, from cyclic voltammograms. The LbL-assembled bilayer films exhibited an excellent Cs of ≥350 F g-1 as compared with constituents (˜70 F g-1) at discharge current density of 0.3 A g-1 that outperformed many other hybrid supercapacitors. To gain deeper insights into the physical-chemical interfacial processes occurring at the electrode/electrolyte interface that govern their operation, we have used scanning electrochemical microscopy (SECM) technique in feedback and probe approach modes. We present our findings from viewpoint of reinforcing the role played by heterogeneous electrode surface composed of nanoscale graphene sheets (conducting) and conducting polymers (semiconducting) backbone with ordered polymer chains via higher/lower probe current distribution maps. Also targeted is SECM imaging that allowed to determine electrochemical (re)activity of surface ion adsorption sites density at solid/liquid interface.

Eddy-Current Inspection of Ball Bearings

NASA Technical Reports Server (NTRS)

Bankston, B.

1985-01-01

Custom eddy-current probe locates surface anomalies. Low friction air cushion within cone allows ball to roll easily. Eddy current probe reliably detects surface and near-surface cracks, voids, and material anomalies in bearing balls or other spherical objects. Defects in ball surface detected by probe displayed on CRT and recorded on strip-chart recorder.

Small-scale cosmic microwave background anisotropies as probe of the geometry of the universe

NASA Technical Reports Server (NTRS)

Kamionkowski, Marc; Spergel, David N.; Sugiyama, Naoshi

1994-01-01

We perform detailed calculations of cosmic microwave background (CMB) anisotropies in a cold dark matter (CDM)-dominated open universe with primordial adiabatic density perturbations for a variety of reionization histories. The CMB anisotropies depend primarily on the geometry of the universe, which in a matter-dominated universe is determined by Omega and the optical depth to the surface of last scattering. In particular, the location on the primary Doppler peak depends primarily on Omega and is fairly insensitive to the other unknown parameters, such as Omega(sub b), h, Lambda, and the shape of the power spectrum. Therefore, if the primordial density perturbations are adiabatic, measurements of CMB anisotropies on small scales may be used to determine Omega.

Photoemission and Photoabsorption Investigation of the Electronic Structure of Ytterbium Doped Strontium Fluoroapatite

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

Nelson, A J; van Buuren, T; Bostedt, C

X-ray photoemission and x-ray photoabsorption were used to study the composition and the electronic structure of ytterbium doped strontium fluoroapatite (Yb:S-FAP). High resolution photoemission measurements on the valence band electronic structure was used to evaluate the density of occupied states of this fluoroapatite. Element specific density of unoccupied electronic states in Yb:S-FAP were probed by x-ray absorption spectroscopy (XAS) at the Yb 4d (N{sub 4,5}-edge), Sr 3d (M{sub 4,5}-edge), P 2p (L{sub 2,3}-edge), F 1s and O 1s (K-edges) absorption edges. These results provide the first measurements of the electronic structure and surface chemistry of this material.

Nanoscale Electrostructural Characterization of Compositionally Graded Al(x)Ga(1-x)N Heterostructures on GaN/Sapphire (0001) Substrate.

PubMed

Kuchuk, Andrian V; Lytvyn, Petro M; Li, Chen; Stanchu, Hryhorii V; Mazur, Yuriy I; Ware, Morgan E; Benamara, Mourad; Ratajczak, Renata; Dorogan, Vitaliy; Kladko, Vasyl P; Belyaev, Alexander E; Salamo, Gregory G

2015-10-21

We report on AlxGa1-xN heterostructures resulting from the coherent growth of a positive then a negative gradient of the Al concentration on a [0001]-oriented GaN substrate. These polarization-doped p-n junction structures were characterized at the nanoscale by a combination of averaging as well as depth-resolved experimental techniques including: cross-sectional transmission electron microscopy, high-resolution X-ray diffraction, Rutherford backscattering spectrometry, and scanning probe microscopy. We observed that a small miscut in the substrate orientation along with the accumulated strain during growth led to a change in the mosaic structure of the AlxGa1-xN film, resulting in the formation of macrosteps on the surface. Moreover, we found a lateral modulation of charge carriers on the surface which were directly correlated with these steps. Finally, using nanoscale probes of the charge density in cross sections of the samples, we have directly measured, semiquantitatively, both n- and p-type polarization doping resulting from the gradient concentration of the AlxGa1-xN layers.

Effects of isoconcentration surface threshold values on the characteristics of needle-shaped precipitates in atom probe tomography data from an aged Al-Mg-Si alloy.

PubMed

Aruga, Yasuhiro; Kozuka, Masaya

2016-04-01

Needle-shaped precipitates in an aged Al-0.62Mg-0.93Si (mass%) alloy were identified using a compositional threshold method, an isoconcentration surface, in atom probe tomography (APT). The influence of thresholds on the morphological and compositional characteristics of the precipitates was investigated. Utilizing optimum parameters for the concentration space, a reliable number density of the precipitates is obtained without dependence on the elemental concentration threshold in comparison with evaluation by transmission electron microscopy (TEM). It is suggested that careful selection of the concentration space in APT can lead to a reasonable average Mg/Si ratio for the precipitates. It was found that the maximum length and maximum diameter of the precipitates are affected by the elemental concentration threshold. Adjustment of the concentration threshold gives better agreement with the precipitate dimensions measured by TEM. © The Author 2015. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Near-Field Microwave Detection of Corrosion Precursor Pitting under Thin Dielectric Coatings in Metallic Substrate

NASA Astrophysics Data System (ADS)

Hughes, D.; Zoughi, R.; Austin, R.; Wood, N.; Engelbart, R.

2003-03-01

Detection of corrosion precursor pitting on metallic surfaces under various coatings and on bare metal is of keen interest in evaluation of aircraft fuselage. Near-field microwave nondestructive testing methods, utilizing open-ended rectangular waveguides and coaxial probes, have been used extensively for detection of surface flaws in metals, both on bare metal and under a dielectric coating. This paper presents the preliminary results of using microwave techniques to detect corrosion precursor pitting under paint and primer, applique and on bare metal. Machined pits of 500 μm diameter were detected using open-ended rectangular waveguides at V-Band under paint and primer and applique, and on bare metal. Using coaxial probes, machined pits with diameters down to 150 μm on bare metal were also detected. Relative pit size and density were shown on a corrosion-pitted sample using open-ended rectangular waveguides at frequencies of 35 GHz to 70 GHz. The use of Boeing's MAUS™ scanning systems provided improved results by alleviating standoff variation and scanning artifact. Typical results of this investigation are also presented.

Carbon Nanotube Tip Probes: Stability and Lateral Resolution in Scanning Probe Microscopy and Application to Surface Science to Semiconductors

NASA Technical Reports Server (NTRS)

Nguyen, Cattien V.; Chao, Kuo-Jen; Stevens, Ramsey M. D.; Delzeit, Lance; Cassell, Alan; Han, Jie; Meyyappan, M.; Arnold, James (Technical Monitor)

2001-01-01

In this paper we present results on the stability and lateral resolution capability of carbon nanotube (CNT) scanning probes as applied to atomic force microscopy (AFM). Surface topography images of ultra-thin films (2-5 nm thickness) obtained with AFM are used to illustrate the lateral resolution capability of single-walled carbon nanotube probes. Images of metal films prepared by ion beam sputtering exhibit grain sizes ranging from greater than 10 nm to as small as approximately 2 nm for gold and iridium respectively. In addition, imaging stability and lifetime of multi-walled carbon nanotube scanning probes are studied on a relatively hard surface of silicon nitride (Si3N4). AFM images Of Si3N4 surface collected after more than 15 hrs of continuous scanning show no detectable degradation in lateral resolution. These results indicate the general feasibility of CNT tips and scanning probe microscopy for examining nanometer-scale surface features of deposited metals as well as non-conductive thin films. AFM coupled with CNT tips offers a simple and nondestructive technique for probing a variety of surfaces, and has immense potential as a surface characterization tool in integrated circuit manufacturing.

Anisotropic high-harmonic generation in bulk crystals

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

You, Yong Sing; Reis, David A.; Ghimire, Shambhu

2016-11-21

The microscopic valence electron density determines the optical, electronic, structural and thermal properties of materials. However, current techniques for measuring this electron charge density are limited: for example, scanning tunnelling microscopy is confined to investigations at the surface, and electron diffraction requires very thin samples to avoid multiple scattering. Therefore, an optical method is desirable for measuring the valence charge density of bulk materials. Since the discovery of high-harmonic generation (HHG) in solids, there has been growing interest in using HHG to probe the electronic structure of solids. Here, using single-crystal MgO, we demonstrate that high-harmonic generation in solids ismore » sensitive to interatomic bonding. We find that harmonic efficiency is enhanced (diminished) for semi-classical electron trajectories that connect (avoid) neighbouring atomic sites in the crystal. Finally, these results indicate the possibility of using materials’ own electrons for retrieving the interatomic potential and thus the valence electron density, and perhaps even wavefunctions, in an all-optical setting.« less

Highly Sensitive Detection of Target Biomolecules on Cell Surface Using Gold Nanoparticle Conjugated with Aptamer Probe

NASA Astrophysics Data System (ADS)

Kim, Hyonchol; Terazono, Hideyuki; Hayashi, Masahito; Takei, Hiroyuki; Yasuda, Kenji

2012-06-01

A method of gold nanoparticle (Au NP) labeling with backscattered electron (BE) imaging of field emission scanning electron microscopy (FE-SEM) was applied for specific detection of target biomolecules on a cell surface. A single-stranded DNA aptamer, which specifically binds to the target molecule on a human acute lymphoblastic leukemia cell, was conjugated with a 20 nm Au NP and used as a probe to label its target molecule on the cell. The Au NP probe was incubated with the cell, and the interaction was confirmed using BE imaging of FE-SEM through direct counting of the number of Au NPs attached on the target cell surface. Specific Au NP-aptamer probes were observed on a single cell surface and their spatial distributions including submicron-order localizations were also clearly visualized, whereas the nonspecific aptamer probes were not observed on it. The aptamer probe can be potentially dislodged from the cell surface with treatment of nucleases, indicating that Au NP-conjugated aptamer probes can be used as sensitive and reversible probes to label target biomolecules on cells.

Suppression of surface charge accumulation on Al{sub 2}O{sub 3}-filled epoxy resin insulator under dc voltage by direct fluorination

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

Zhang, Boya; Zhang, Guixin, E-mail: guixin@mail.tsinghua.edu.cn; Li, Chuanyang

2015-12-15

Surface charge accumulation on insulators under high dc voltage is a major factor that may lead to the reduction of insulation levels in gas insulated devices. In this paper, disc insulators made of Al{sub 2}O{sub 3}-filled epoxy resin were surface fluorinated using a F{sub 2}/N{sub 2} mixture (12.5% F{sub 2}) at 50 °C and 0.1 MPa for different durations of 15 min, 30 min and 60 min. A dc voltage was applied to the insulator for 30 min and the charge density on its surface was measured by an electrostatic probe. The results revealed significant lower surface charge densities on themore » fluorinated insulators in comparison with the original one. Surface conductivity measurements indicated a higher surface conductivity by over three orders of magnitude after fluorination, which would allow the charges to transfer along the surface and thus may suppress their accumulation. Further, attenuated total reflection infrared analysis and surface morphology observations of the samples revealed that the introduction of fluoride groups altered the surface physicochemical properties. These structure changes, especially the physical defects reduced the depth of charge traps in the surface layer, which was verified by the measurement of energy distributions of the electron and hole traps based on the isothermal current theory. The results in this paper demonstrate that fluorination can be a promising and effective method to suppress surface charge accumulation on epoxy insulators in gas insulated devices.« less

Substrate preparation effects on defect density in molecular beam epitaxial growth of CdTe on CdTe (100) and (211)B

DOE PAGES

Burton, George L.; Diercks, David R.; Perkins, Craig L.; ...

2017-07-01

Recent studies have demonstrated that growth of CdTe on CdTe (100) and (211)B substrates via molecular beam epitaxy (MBE) results in planar defect densities 2 and 3 orders of magnitude higher than growth on InSb (100) substrates, respectively. To understand this shortcoming, MBE growth on CdTe substrates with a variety of substrate preparation methods is studied by scanning electron microscopy, secondary ion mass spectrometry, x-ray photoelectron spectroscopy, cross sectional transmission electron microscopy, and atom probe tomography (APT). Prior to growth, carbon is shown to remain on substrate surfaces even after atomic hydrogen cleaning. APT revealed that following the growth ofmore » films, trace amounts of carbon remained at the substrate/film interface. This residual carbon may lead to structural degradation, which was determined as the main cause of higher defect density.« less

Probing electron density across Ar{sup +} irradiation-induced self-organized TiO{sub 2−x} nanochannels for memory application

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

Barman, A.; Saini, C. P.; Ghosh, S. K.

2016-06-13

The variation of electron density in TiO{sub 2−x} nanochannels, exhibiting resistive switching phenomenon, produced by Ar{sup +} ion-irradiation at the threshold fluence of 5 × 10{sup 16} ions/cm{sup 2} is demonstrated by X-ray reflectivity (XRR). The transmission electron microscopy reveals the formation of nanochannels, while the energy dispersive X-ray spectroscopy confirms Ti enrichment near the surface due to ion-irradiation, in consistent with the increase in electron density by XRR measurements. Such a variation in Ti concentration indicates the evolution of oxygen vacancies (OVs) along the TiO{sub 2−x} nanochannels, and thus paves the way to explain the operation and performance of the Pt/TiO{sub 2−x}/Pt-basedmore » memory devices via OV migration.« less

Improvement of ion thruster design

NASA Technical Reports Server (NTRS)

Carpenter, R. T.

1986-01-01

Two types of measurements were performed on ion thrustors equipped with SmCo magnets in either ring cusp or line cusp arrangements. Langmuir probes were used to measure plasma potential, electron density, and electron temperture in all regions inside the thruster. Loss fluxes to various surfaces were determined by measuring the currents to foils attached to or imbedded in the surface. Data were obtained for several sets of discharge voltages and currents. The loss currents were determined from current vs voltage characteristics observed on a transistor curve tracer oscilloscope. Both ion and electron currents were measured to all parts of the walls and to all parts of the cathode assembly using collecting plates. These measurement were also made for various parameter sets. In line cusp configuration the plasma density is essentially as predicted by existing calculations. In the ring cusp arrangement the interior of the plasma contains an inhomogeneous and relatively large magnetic field so the geometry is decidely two-dimensional and the models of Self (1967) and of Kino and Sham (1966) do not agree.

Influence of lead ions on the macromorphology of electrodeposited zinc

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

Tsuda, Tetsuaki; Tobias, Charles W.

1981-09-01

The morphology of zinc as it is electrodeposited from acid solutions demonstrates a remarkable imprint of electrolyte flow conditions. The development of macromorphology of zinc deposits has been investigated under galvanostatic conditions on a rotating plantinum disk electrode by use of photomacrography, scanning electron microscopy, electron probe microanalysis and Auger microprobe analysis. Logarithmic spiral markings, which reflect the hydrodynamic flow on a rotating disk, appear in a certain region of current density well below the limiting current density. Morphological observations revealed the major influence of trace lead ions on the amplifications of surface roughness through coalescence and preferred growth ofmore » initial protrusions. Results obtained from ultra-pure electrolyte suggest preferred crystal growth towards well-mixed orientation in the concentration field caused by slight differences in crystallization overpotential. A qualitative model involving a coupling mechanism between the evolving surface roughness and instability phenomena in the boundary layer is advanced to explain the formation of spiral patterns.« less

Dual path mechanism in the thermal reduction of graphene oxide.

PubMed

Larciprete, Rosanna; Fabris, Stefano; Sun, Tao; Lacovig, Paolo; Baraldi, Alessandro; Lizzit, Silvano

2011-11-02

Graphene is easily produced by thermally reducing graphene oxide. However, defect formation in the C network during deoxygenation compromises the charge carrier mobility in the reduced material. Understanding the mechanisms of the thermal reactions is essential for defining alternative routes able to limit the density of defects generated by carbon evolution. Here, we identify a dual path mechanism in the thermal reduction of graphene oxide driven by the oxygen coverage: at low surface density, the O atoms adsorbed as epoxy groups evolve as O(2) leaving the C network unmodified. At higher coverage, the formation of other O-containing species opens competing reaction channels, which consume the C backbone. We combined spectroscopic tools and ab initio calculations to probe the species residing on the surface and those released in the gas phase during heating and to identify reaction pathways and rate-limiting steps. Our results illuminate the current puzzling scenario of the low temperature gasification of graphene oxide.

Continuum Lowering and Fermi-Surface Rising in Strongly Coupled and Degenerate Plasmas

NASA Astrophysics Data System (ADS)

Hu, S. X.

2017-08-01

Continuum lowering is a well known and important physics concept that describes the ionization potential depression (IPD) in plasmas caused by thermal- or pressure-induced ionization of outer-shell electrons. The existing IPD models are often used to characterize plasma conditions and to gauge opacity calculations. Recent precision measurements have revealed deficits in our understanding of continuum lowering in dense hot plasmas. However, these investigations have so far been limited to IPD in strongly coupled but nondegenerate plasmas. Here, we report a first-principles study of the K -edge shifting in both strongly coupled and fully degenerate carbon plasmas, with quantum molecular dynamics calculations based on the all-electron density-functional theory. The resulting K -edge shifting versus plasma density, as a probe to the continuum lowering and the Fermi-surface rising, is found to be significantly different from predictions of existing IPD models. In contrast, a simple model of "single-atom-in-box," developed in this work, accurately predicts K -edge locations as ab initio calculations provide.

Cluster-lensing: A Python Package for Galaxy Clusters and Miscentering

NASA Astrophysics Data System (ADS)

Ford, Jes; VanderPlas, Jake

2016-12-01

We describe a new open source package for calculating properties of galaxy clusters, including Navarro, Frenk, and White halo profiles with and without the effects of cluster miscentering. This pure-Python package, cluster-lensing, provides well-documented and easy-to-use classes and functions for calculating cluster scaling relations, including mass-richness and mass-concentration relations from the literature, as well as the surface mass density {{Σ }}(R) and differential surface mass density {{Δ }}{{Σ }}(R) profiles, probed by weak lensing magnification and shear. Galaxy cluster miscentering is especially a concern for stacked weak lensing shear studies of galaxy clusters, where offsets between the assumed and the true underlying matter distribution can lead to a significant bias in the mass estimates if not accounted for. This software has been developed and released in a public GitHub repository, and is licensed under the permissive MIT license. The cluster-lensing package is archived on Zenodo. Full documentation, source code, and installation instructions are available at http://jesford.github.io/cluster-lensing/.

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

Yordanov, D., E-mail: yordanov@phys.uni-sofia.bg; Lishev, St.; Shivarova, A.

Shielding the bias applied to the probe by the sheath formed around it and determination of parameters of unperturbed plasmas are in the basis of the probe diagnostics. The results from a two-dimensional model of a discharge with a probe inserted in it show that the probe influences the spatial distribution of the plasma parameters in the entire discharge. The increase (although slight) in the electron temperature, due to the increased losses of charged particles on the additional wall in the discharge (mainly the probe holder), leads to redistribution of the plasma density and plasma potential, as shown by themore » results obtained at the floating potential of the probe. The deviations due to the bias applied to the probe tip are stronger in the ion saturation region of the probe characteristics. The pattern of the spatial redistribution of the plasma parameters advances together with the movement of the probe deeper in the discharge. Although probe sheaths and probe characteristics resulting from the model are shown, the study does not aim at discussions on the theories for determination of the plasma density from the ion saturation current. Regardless of the modifications in the plasma behavior in the entire discharge, the deviations of the plasma parameters at the position of the probe tip and, respectively, the uncertainty which should be added as an error when the accuracy of the probe diagnostics is estimated do not exceed 10%. Consequently, the electron density and temperature obtained, respectively, at the position of the plasma potential on the probe characteristics and from its transition region are in reasonable agreement with the results from the model of the discharge without a probe. Being in the scope of research on a source of negative hydrogen ions with the design of a matrix of small radius inductive discharges, the model is specified for a low-pressure hydrogen discharge sustained in a small-radius tube.« less

Electro-Optic Surface Field Imaging System

DTIC Science & Technology

1989-06-01

ELECTRO - OPTIC SURFACE FIELD IMAGING SYSTEM L. E. Kingsley and W. R. Donaldson LABORATORY FOR LASER ENERGETICS University of Rochester 250 East...surface electric fields present during switch operation. The electro - optic , or Pockel’s effect, provides an extremely useful probe of surface electric...fields. Using the electro - optic effect, surface fields can be measured with an optical probe. This paper describes an electro - optic probe which is

Monte Carlo modeling of ultrasound probes for image guided radiotherapy

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

Bazalova-Carter, Magdalena, E-mail: bazalova@uvic.ca; Schlosser, Jeffrey; Chen, Josephine

2015-10-15

Purpose: To build Monte Carlo (MC) models of two ultrasound (US) probes and to quantify the effect of beam attenuation due to the US probes for radiation therapy delivered under real-time US image guidance. Methods: MC models of two Philips US probes, an X6-1 matrix-array transducer and a C5-2 curved-array transducer, were built based on their megavoltage (MV) CT images acquired in a Tomotherapy machine with a 3.5 MV beam in the EGSnrc, BEAMnrc, and DOSXYZnrc codes. Mass densities in the probes were assigned based on an electron density calibration phantom consisting of cylinders with mass densities between 0.2 andmore » 8.0 g/cm{sup 3}. Beam attenuation due to the US probes in horizontal (for both probes) and vertical (for the X6-1 probe) orientation was measured in a solid water phantom for 6 and 15 MV (15 × 15) cm{sup 2} beams with a 2D ionization chamber array and radiographic films at 5 cm depth. The MC models of the US probes were validated by comparison of the measured dose distributions and dose distributions predicted by MC. Attenuation of depth dose in the (15 × 15) cm{sup 2} beams and small circular beams due to the presence of the probes was assessed by means of MC simulations. Results: The 3.5 MV CT number to mass density calibration curve was found to be linear with R{sup 2} > 0.99. The maximum mass densities in the X6-1 and C5-2 probes were found to be 4.8 and 5.2 g/cm{sup 3}, respectively. Dose profile differences between MC simulations and measurements of less than 3% for US probes in horizontal orientation were found, with the exception of the penumbra region. The largest 6% dose difference was observed in dose profiles of the X6-1 probe placed in vertical orientation, which was attributed to inadequate modeling of the probe cable. Gamma analysis of the simulated and measured doses showed that over 96% of measurement points passed the 3%/3 mm criteria for both probes placed in horizontal orientation and for the X6-1 probe in vertical orientation. The X6-1 probe in vertical orientation caused the highest attenuation of the 6 and 15 MV beams, which at 10 cm depth accounted for 33% and 43% decrease compared to the respective (15 × 15) cm{sup 2} open fields. The C5-2 probe in horizontal orientation, on the other hand, caused a dose increase of 10% and 53% for the 6 and 15 MV beams, respectively, in the buildup region at 0.5 cm depth. For the X6-1 probe in vertical orientation, the dose at 5 cm depth for the 3-cm diameter 6 MV and 5-cm diameter 15 MV beams was attenuated compared to the corresponding open fields to a greater degree by 65% and 43%, respectively. Conclusions: MC models of two US probes used for real-time image guidance during radiotherapy have been built. Due to the high beam attenuation of the US probes, the authors generally recommend avoiding delivery of treatment beams that intersect the probe. However, the presented MC models can be effectively integrated into US-guided radiotherapy treatment planning in cases for which beam avoidance is not practical due to anatomy geometry.« less

Surface-enhanced Raman scattering (SERS) dosimeter and probe

DOEpatents

Vo-Dinh, Tuan

1995-01-01

A dosimeter and probe for measuring exposure to chemical and biological compounds is disclosed. The dosimeter or probe includes a collector which may be analyzed by surface-enhanced Raman spectroscopy. The collector comprises a surface-enhanced Raman scattering-active material having a coating applied thereto to improve the adsorption properties of the collector. The collector may also be used in automated sequential devises, in probe array devices.

3D electron density distributions in the solar corona during solar minima: assessment for more realistic solar wind modeling

NASA Astrophysics Data System (ADS)

de Patoul, J.; Foullon, C.; Riley, P.

2015-12-01

Knowledge of the electron density distribution in the solar corona put constraints on the magnetic field configurations for coronal modeling, and on initial conditions for solar wind modeling. We work with polarized SOHO/LASCO-C2 images from the last two recent minima of solar activity (1996-1997 and 2008-2010), devoid of coronal mass ejections. We derive the 4D electron density distributions in the corona by applying a newly developed time-dependent tomographic reconstruction method. First we compare the density distributions obtained from tomography with magnetohydrodynamic (MHD) solutions. The tomography provides more accurate distributions of electron densities in the polar regions, and we find that the observed density varies with the solar cycle in both polar and equatorial regions. Second, we find that the highest-density structures do not always correspond to the predicted large-scale heliospheric current sheet or its helmet streamer but can follow the locations of pseudo-streamers. We conclude that tomography offers reliable density distribution in the corona, reproducing the slow time evolution of coronal structures, without prior knowledge of the coronal magnetic field over a full rotation. Finally, we suggest that the highest-density structures show a differential rotation well above the surface depending on how it is magnetically connected to the surface. Such valuable information on the rotation of large-scale structures could help to connect the sources of the solar wind to their in-situ counterparts in future missions such as Solar Orbiter and Solar Probe Plus. This research combined with the MHD coronal modeling efforts has the potential to increase the reliability for future space weather forecasting.

Interfacial dynamic surface traps of lead sulfide (PbS) nanocrystals: test-platform for interfacial charge carrier traps at the organic/inorganic functional interface

NASA Astrophysics Data System (ADS)

Kim, Youngjun; Ko, Hyungduk; Park, Byoungnam

2018-04-01

Nanocrystal (NC) size and ligand dependent dynamic trap formation of lead sulfide (PbS) NCs in contact with an organic semiconductor were investigated using a pentacene/PbS field effect transistor (FET). We used a bilayer pentacene/PbS FET to extract information of the surface traps of PbS NCs at the pentacene/PbS interface through the field effect-induced charge carrier density measurement in the threshold and subthreshold regions. PbS size and ligand dependent trap properties were elucidated by the time domain and threshold voltage measurements in which threshold voltage shift occurs by carrier charging and discharging in the trap states of PbS NCs. The observed threshold voltage shift is interpreted in context of electron trapping through dynamic trap formation associated with PbS NCs. To the best of our knowledge, this is the first demonstration of the presence of interfacial dynamic trap density of PbS NC in contact with an organic semiconductor (pentacene). We found that the dynamic trap density of the PbS NC is size dependent and the carrier residence time in the specific trap sites is more sensitive to NC size variation than to NC ligand exchange. The probing method presented in the study offers a means to investigate the interfacial surface traps at the organic-inorganic hetero-junction, otherwise understanding of the buried surface traps at the functional interface would be elusive.

Structure analysis of the single-domain Si(111)4 × 1-In surface by μ-probe Auger electron diffraction and μ-probe reflection high energy electron diffraction

NASA Astrophysics Data System (ADS)

Nakamura, N.; Anno, K.; Kono, S.

1991-10-01

A single-domain Si(111)4 × 1-In surface has been studied by μ-probe reflection high-energy electron diffraction (RHEED) to elucidate the symmetry of the 4 × 1 surface. Azimuthal diffraction patterns of In MNN Auger electron have been obtained by a μ-probe Auger electron diffraction (AED) apparatus from the single-domain Si(111)4 × 1-In surface. On the basis of information from scanning tunneling microscopy [J. Microsc. 152 (1988) 727] and under the assumption that the 4 × 1 surface is composed of In-overlayers, the μ-probe AED patterns were kinematically analyzed to reach a concrete model of indium arrangement.

Capacitance-level/density monitor for fluidized-bed combustor

DOEpatents

Fasching, George E.; Utt, Carroll E.

1982-01-01

A multiple segment three-terminal type capacitance probe with segment selection, capacitance detection and compensation circuitry and read-out control for level/density measurements in a fluidized-bed vessel is provided. The probe is driven at a high excitation frequency of up to 50 kHz to sense quadrature (capacitive) current related to probe/vessel capacitance while being relatively insensitive to the resistance current component. Compensation circuitry is provided for generating a negative current of equal magnitude to cancel out only the resistive component current. Clock-operated control circuitry separately selects the probe segments in a predetermined order for detecting and storing this capacitance measurement. The selected segment acts as a guarded electrode and is connected to the read-out circuitry while all unselected segments are connected to the probe body, which together form the probe guard electrode. The selected probe segment capacitance component signal is directed to a corresponding segment channel sample and hold circuit dedicated to that segment to store the signal derived from that segment. This provides parallel outputs for display, computer input, etc., for the detected capacitance values. The rate of segment sampling may be varied to either monitor the dynamic density profile of the bed (high sampling rate) or monitor average bed characteristics (slower sampling rate).

All-optical switching in GaAs microdisk resonators by a femtosecond pump-probe technique through tapered-fiber coupling.

PubMed

Lin, Yen-Chih; Mao, Ming-Hua; Lin, You-Ru; Lin, Hao-Hsiung; Lin, Che-An; Wang, Lon A

2014-09-01

We demonstrate ultrafast all-optical switching in GaAs microdisk resonators using a femtosecond pump-probe technique through tapered-fiber coupling. The temporal tuning of the resonant modes resulted from the refractive index change due to photoexcited carrier density variation inside the GaAs microdisk resonator. Transmission through the GaAs microdisk resonator can be modulated by more than 10 dB with a switching time window of 8 ps in the switch-off operation using pumping pulses with energies as low as 17.5 pJ. The carrier lifetime was fitted to be 42 ps, much shorter than that of the bulk GaAs, typically of the order of nanoseconds. The above observation indicates that the surface recombination plays an important role in increasing the switching speed.

Design of a Miniaturized Langmuir Plasma Probe for the QuadSat/PnP

NASA Astrophysics Data System (ADS)

Landavazo, M.; Jorgensen, A. M.; Del Barga, C.; Ferguson, D.; Guillette, D.; Huynh, A.; Klepper, J.; Kuker, J.; Lyke, J. C.; Marohn, B.; Mason, J.; Quiroga, J.; Ravindran, V.; Yelton, C.; Zagrai, A. N.; Zufelt, B.

2011-12-01

We have developed a miniaturized Langmuir plasma probe for measuring plasma density in low-earth orbit. Measuring plasma density in the upper ionosphere is important as a diagnostic for the rest of the ionosphere and as an input to space weather forecasting models. Developing miniaturized instrumentation allows easier deployment of a large number of small satellites for monitoring space weather. Our instrument was designed for the Swedish QuadSat/PnP, with the following constraints: A volume constraint of 5x5x1.25cm for the electronics enclosure, a mass budget 100 g, and a power budget of 0.5 W. We met the volume and mass constraints and where able to use less power than budgeted, only 0.25 W. We designed the probe for a bias range of +/-15V and current measurements in the 1 nA to 1 mA range (6 orders of magnitude). Necessary voltage of +/- 15 V and 3.3 V were generated on-board from a single 5 V supply. The electronics suite is based off carefully selected yet affordable commercial components that exhibit low noise, low leakage currents and low power consumption. Size constraints, low noise and low leakage requirements called for a carefully designed four layer PCB with a properly guarded current path using surface mount components on both sides. An ultra-low power microcontroller handles instrument functionality and is fully controllable over i2c using SPA-1 space plug and play. We elected for a probe launched deployed, which required careful design to survive launch vibrations while staying within the mass budget. The QuadSat/PnP has not been launched at the time of writing. We will present details of the instrument design and initial calibration data.

Eddy current probe response to open and closed surface flaws

NASA Technical Reports Server (NTRS)

Auld, B. A.; Muennemann, F.; Winslow, D. K.

1981-01-01

A general analysis of eddy current response to certain types of open and closed surface flaws is presented for both standard low-frequency and ferromagnetic-resonance (FMR) probes. It is shown analytically that for two-dimensional and three-dimensional surface flaws interrogated by a uniform probe field, the crack opening sensitivity increases with the operating frequency of the probe, this behavior being due to the Faraday induction effect. Experiments with low-frequency probes operating at or below 1 MHz and with the FMR probe operating at approximately 1000 MHz confirm this increase of the crack mouth opening displacement for practical situations where the probe field is not uniform in the vicinity of the flaw.

The role of probe oxide in local surface conductivity measurements

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

Barnett, C. J.; Kryvchenkova, O.; Wilson, L. S. J.

2015-05-07

Local probe methods can be used to measure nanoscale surface conductivity, but some techniques including nanoscale four point probe rely on at least two of the probes forming the same low resistivity non-rectifying contact to the sample. Here, the role of probe shank oxide has been examined by carrying out contact and non-contact I V measurements on GaAs when the probe oxide has been controllably reduced, both experimentally and in simulation. In contact, the barrier height is pinned but the barrier shape changes with probe shank oxide dimensions. In non-contact measurements, the oxide modifies the electrostatic interaction inducing a quantummore » dot that alters the tunneling behavior. For both, the contact resistance change is dependent on polarity, which violates the assumption required for four point probe to remove probe contact resistance from the measured conductivity. This has implications for all nanoscale surface probe measurements and macroscopic four point probe, both in air and vacuum, where the role of probe oxide contamination is not well understood.« less

Ion-gel-gating-induced oxygen vacancy formation in epitaxial L a0.5S r0.5Co O3 -δ films from in operando x-ray and neutron scattering

NASA Astrophysics Data System (ADS)

Walter, Jeff; Yu, Guichuan; Yu, Biqiong; Grutter, Alexander; Kirby, Brian; Borchers, Julie; Zhang, Zhan; Zhou, Hua; Birol, Turan; Greven, Martin; Leighton, Chris

2017-12-01

Ionic-liquid/gel-based transistors have emerged as a potentially ideal means to accumulate high charge-carrier densities at the surfaces of materials such as oxides, enabling control over electronic phase transitions. Substantial gaps remain in the understanding of gating mechanisms, however, particularly with respect to charge carrier vs oxygen defect creation, one contributing factor being the dearth of experimental probes beyond electronic transport. Here we demonstrate the use of synchrotron hard x-ray diffraction and polarized neutron reflectometry as in operando probes of ion-gel transistors based on ferromagnetic L a0.5S r0.5Co O3 -δ . An asymmetric gate-bias response is confirmed to derive from electrostatic hole accumulation at negative gate bias vs oxygen vacancy formation at positive bias. The latter is detected via a large gate-induced lattice expansion (up to 1%), complementary bulk measurements and density functional calculations enabling quantification of the bias-dependent oxygen vacancy density. Remarkably, the gate-induced oxygen vacancies proliferate through the entire thickness of 30-40-unit-cell-thick films, quantitatively accounting for changes in the magnetization depth profile. These results directly elucidate the issue of electrostatic vs redox-based response in electrolyte-gated oxides, also demonstrating powerful approaches to their in operando investigation.

Dual-probe near-field fiber head with gap servo control for data storage applications.

PubMed

Fang, Jen-Yu; Tien, Chung-Hao; Shieh, Han-Ping D

2007-10-29

We present a novel fiber-based near-field optical head consisting of a straw-shaped writing probe and a flat gap sensing probe. The straw-shaped probe with a C-aperture on the end face exhibits enhanced transmission by a factor of 3 orders of magnitude over a conventional fiber probe due to a hybrid effect that excites both propagation modes and surface plasmon waves. In the gap sensing probe, the spacing between the probe and the disk surface functions as an external cavity. The high sensitivity of the output power to the change in the gap width is used as a feedback control signal. We characterize and design the straw-shaped writing probe and the flat gap sensing probe. The dual-probe system is installed on a conventional biaxial actuator to demonstrate the capability of flying over a disk surface with nanometer position precision.

Cell-mediated fibre recruitment drives extracellular matrix mechanosensing in engineered fibrillar microenvironments

NASA Astrophysics Data System (ADS)

Baker, Brendon M.; Trappmann, Britta; Wang, William Y.; Sakar, Mahmut S.; Kim, Iris L.; Shenoy, Vivek B.; Burdick, Jason A.; Chen, Christopher S.

2015-12-01

To investigate how cells sense stiffness in settings structurally similar to native extracellular matrices, we designed a synthetic fibrous material with tunable mechanics and user-defined architecture. In contrast to flat hydrogel surfaces, these fibrous materials recapitulated cell-matrix interactions observed with collagen matrices including stellate cell morphologies, cell-mediated realignment of fibres, and bulk contraction of the material. Increasing the stiffness of flat hydrogel surfaces induced mesenchymal stem cell spreading and proliferation; however, increasing fibre stiffness instead suppressed spreading and proliferation for certain network architectures. Lower fibre stiffness permitted active cellular forces to recruit nearby fibres, dynamically increasing ligand density at the cell surface and promoting the formation of focal adhesions and related signalling. These studies demonstrate a departure from the well-described relationship between material stiffness and spreading established with hydrogel surfaces, and introduce fibre recruitment as a previously undescribed mechanism by which cells probe and respond to mechanics in fibrillar matrices.

Four-probe measurements with a three-probe scanning tunneling microscope.

PubMed

Salomons, Mark; Martins, Bruno V C; Zikovsky, Janik; Wolkow, Robert A

2014-04-01

We present an ultrahigh vacuum (UHV) three-probe scanning tunneling microscope in which each probe is capable of atomic resolution. A UHV JEOL scanning electron microscope aids in the placement of the probes on the sample. The machine also has a field ion microscope to clean, atomically image, and shape the probe tips. The machine uses bare conductive samples and tips with a homebuilt set of pliers for heating and loading. Automated feedback controlled tip-surface contacts allow for electrical stability and reproducibility while also greatly reducing tip and surface damage due to contact formation. The ability to register inter-tip position by imaging of a single surface feature by multiple tips is demonstrated. Four-probe material characterization is achieved by deploying two tips as fixed current probes and the third tip as a movable voltage probe.

Probing the Active Surface Sites for CO Reduction on Oxide-Derived Copper Electrocatalysts

DOE PAGES

Verdaguer-Casadevall, Arnau; Li, Christina W.; Johansson, Tobias P.; ...

2015-07-30

CO electroreduction activity on oxide-derived Cu (OD-Cu) was found to correlate with metastable surface features that bind CO strongly. OD-Cu electrodes prepared by H 2 reduction of Cu 2O precursors reduce CO to acetate and ethanol with nearly 50% Faradaic efficiency at moderate overpotential. Temperature-programmed desorption of CO on OD-Cu revealed the presence of surface sites with strong CO binding that are distinct from the terraces and stepped sites found on polycrystalline Cu foil. After annealing at 350 °C, the surface-area corrected current density for CO reduction is 44-fold lower and the Faradaic efficiency is less than 5%. These changesmore » are accompanied by a reduction in the proportion of strong CO binding sites. Here, we propose that the active sites for CO reduction on OD-Cu surfaces are strong CO binding sites that are supported by grain boundaries. Uncovering these sites is a first step toward understanding the surface chemistry necessary for efficient CO electroreduction.« less

Electrodeposition of gold nanoparticles on aryl diazonium monolayer functionalized HOPG surfaces.

PubMed

González, M C R; Orive, A G; Salvarezza, R C; Creus, A H

2016-01-21

Gold nanoparticle electrodeposition on a modified HOPG surface with a monolayer organic film based on aryl diazonium chemistry has been studied. This organic monolayer is electrochemically grown with the use of 2,2-diphenyl-1-picrylhydrazyl (DPPH), a radical scavenger. The electrodeposition of gold on this modified surface is highly favored resulting in an AuNP surface density comparable to that found on glassy carbon. AuNPs grow only in the areas covered by the organic monolayer leaving free clean HOPG zones. A progressive mechanism for the nucleation and growth is followed giving hemispherical AuNPs, homogeneously distributed on the surface and their sizes can be well controlled by the applied electrodeposition potential. By using AFM, C-AFM and electrochemical measurements with the aid of two redox probes, namely Fe(CN)6(4-)/Fe(CN)6(3-) and dopamine, relevant results about the electrochemical modified surface as well as the gold nanoparticles electrodeposited on them are obtained.

Tunable SERS signals of Rhodamine B molecules on Fe3O4@Au nanocomposite substrates controlled by magnetic field

NASA Astrophysics Data System (ADS)

Song, Hao; Fang, Rui Yang; Li, Ling

2018-02-01

In this work, we experimentally synthesized the Fe3O4@Au nanocomposites and used them as surface-enhanced Raman scattering (SERS) substrates. The Fe3O4@Au nanocomposites retained the metallic plasmon resonant effect and possessed the magnetic field controllable characteristics. The Raman spectra of Rhodamine B (RhB) probe molecules were studied under different external magnetic field. The magnitude of external magnetic field varied from 0 Gs to 700 Gs (1 Gs = 10-4 T) with intervals of 100 Gs. When the magnetic field magnitude increased, the Raman intensity of RhB probe molecules at 1356 cm-1 increased linearly. The slope of the linear fitting curves for the Raman intensity and area were 0.118/Gs and 3.700/Gs. The Raman enhancement could raise up to 7 times for RhB probe molecules when the magnetic field magnitude increased to 700 Gs. After removing the external magnetic field, the Raman peaks returned to its original intensity in several minutes. Under the external magnetic field, the Fe3O4@Au nanocomposites were concentrated, leading to the increase number of SERS "hot spots" and the surface Au density. The results show that the magnetic field controlled Fe3O4@Au nanocomposites can realize the enhanced and controllable SERS effect, which can be used in the reversible optical sensing and bio-medical applications.

Optical Antenna Arrays on a Fiber Facet for In Situ Surface Enhanced Raman Scattering Detection

PubMed Central

Smythe, Elizabeth J.; Dickey, Michael D.; Bao, Jiming; Whitesides, George M.

2009-01-01

This paper reports a bidirectional fiber optic probe for the detection of surface enhanced Raman scattering (SERS). One facet of the probe features an array of gold optical antennas designed to enhance Raman signal, while the other facet of the fiber is used for the input and collection of light. Simultaneous detection of benzenethiol and 2-[(E)-2-pyridin-4-ylethenyl]pyridine is demonstrated through a 35 cm long fiber. The array of nanoscale optical antennas was first defined by electron-beam lithography on a silicon wafer. The array was subsequently stripped from the wafer and then transferred to the facet of a fiber. Lithographic definition of the antennas provides a method for producing two-dimensional arrays with well-defined geometry, which allows (i) the optical response of the probe to be tuned and (ii) the density of ‘hot spots’ generating the enhanced Raman signal to be controlled. It is difficult to determine the Raman signal enhancement factor (EF) of most fiber optic Raman sensors featuring ‘hot spots’ because the geometry of the Raman enhancing nanostructures is poorly defined. The ability to control the size and spacing of the antennas enables the EF of the transferred array to be estimated. EF values estimated after focusing a laser directly onto the transferred array ranged from 2.6 × 105 to 5.1 × 105. PMID:19236032

Electrochemical current rectification-a novel signal amplification strategy for highly sensitive and selective aptamer-based biosensor.

PubMed

Feng, Lingyan; Sivanesan, Arumugam; Lyu, Zhaozi; Offenhäusser, Andreas; Mayer, Dirk

2015-04-15

Electrochemical aptamer-based (E-AB) sensors represent an emerging class of recently developed sensors. However, numerous of these sensors are limited by a low surface density of electrode-bound redox-oligonucleotides which are used as probe. Here we propose to use the concept of electrochemical current rectification (ECR) for the enhancement of the redox signal of E-AB sensors. Commonly, the probe-DNA performs a change in conformation during target binding and enables a nonrecurring charge transfer between redox-tag and electrode. In our system, the redox-tag of the probe-DNA is continuously replenished by solution-phase redox molecules. A unidirectional electron transfer from electrode via surface-linked redox-tag to the solution-phase redox molecules arises that efficiently amplifies the current response. Using this robust and straight-forward strategy, the developed sensor showed a substantial signal amplification and consequently improved sensitivity with a calculated detection limit of 114nM for ATP, which was improved by one order of magnitude compared with the amplification-free detection and superior to other previous detection results using enzymes or nanomaterials-based signal amplification. To the best of our knowledge, this is the first demonstration of an aptamer-based electrochemical biosensor involving electrochemical rectification, which can be presumably transferred to other biomedical sensor systems. Copyright © 2014 Elsevier B.V. All rights reserved.

Comparison of Langmuir probe and multipole resonance probe measurements in argon, hydrogen, nitrogen, and oxygen mixtures in a double ICP discharge

NASA Astrophysics Data System (ADS)

Fiebrandt, Marcel; Oberberg, Moritz; Awakowicz, Peter

2017-07-01

The results of a Multipole Resonance Probe (MRP) are compared to a Langmuir probe in measuring the electron density in Ar, H2, N2, and O2 mixtures. The MRP was designed for measurements in industry processes, i.e., coating or etching. To evaluate a possible influence on the MRP measurement due to molecular gases, different plasmas with increasing molecular gas content in a double inductively coupled plasma at 5 Pa and 10 Pa at 500 W are used. The determined electron densities from the MRP and the Langmuir probe slightly differ in H2 and N2 diluted argon plasmas, but diverge significantly with oxygen. In pure molecular gas plasmas, electron densities measured with the MRP are always higher than those measured with the Langmuir Probe, in particular, in oxygen containing mixtures. The differences can be attributed to etching of the tungsten wire in the Ar:O2 mixtures and rf distortion in the pure molecular discharges. The influence of a non-Maxwellian electron energy distribution function, negative ions or secondary electron emission seems to be of no or only minor importance.

Surface-enhanced Raman scattering (SERS) dosimeter and probe

DOEpatents

Vo-Dinh, T.

1995-03-21

A dosimeter and probe for measuring exposure to chemical and biological compounds is disclosed. The dosimeter or probe includes a collector which may be analyzed by surface-enhanced Raman spectroscopy. The collector comprises a surface-enhanced Raman scattering-active material having a coating applied thereto to improve the adsorption properties of the collector. The collector may also be used in automated sequential devices, in probe array devices. 10 figures.

Surface-enhanced Raman scattering based nonfluorescent probe for multiplex DNA detection.

PubMed

Sun, Lan; Yu, Chenxu; Irudayaraj, Joseph

2007-06-01

To provide rapid and accurate detection of DNA markers in a straightforward, inexpensive, and multiplex format, an alternative surface-enhanced Raman scattering based probe was designed and fabricated to covalently attach both DNA probing sequence and nonfluorescent Raman tags to the surface of gold nanoparticles (DNA-AuP-RTag). The intensity of Raman signal of the probes could be controlled through the surface coverage of the nonfluorescent Raman tags (RTags). Detection sensitivity of these probes could be optimized by fine-tuning the amount of DNA molecules and RTags on the probes. Long-term stability of the DNA-AuP-RTag probes was found to be good (over 3 months). Excellent multiplexing capability of the DNA-AuP-RTag scheme was demonstrated by simultaneous identification of up to eight probes in a mixture. Detection of hybridization of single-stranded DNA to its complementary targets was successfully accomplished with a long-term goal to use nonfluorescent RTags in a Raman-based DNA microarray platform.

Surface-Enhanced Raman Scattering Based Nonfluorescent Probe for Multiplex DNA Detection

PubMed Central

Sun, Lan; Yu, Chenxu; Irudayaraj, Joseph

2008-01-01

To provide rapid and accurate detection of DNA markers in a straightforward, inexpensive and multiplex format, an alternative surface enhanced Raman scattering (SERS) based probe was designed and fabricated to covalently attach both DNA probing sequence and non-fluorescent Raman tags to the surface of gold nanoparticles (DNA-AuP-RTag). The intensity of Raman signal of the probes could be controlled through the surface coverage of the non-fluorescent Raman tags (RTags). Detection sensitivity of these probes could be optimized by fine-tuning the amount of DNA molecules and RTags on the probes. Long-term stability of the DNA-AuP-RTag probes was found to be good (over 3 months). Excellent multiplexing capability of the DNA-AuP-RTag scheme was demonstrated by simultaneous identification of up to eight probes in a mixture. Detection of hybridization of single-stranded DNA (ssDNA) to its complementary targets was successfully accomplished with a long-term goal to use non-fluorescent RTags in a Raman-based DNA microarray platform. PMID:17465531

Hydrogen-related defects in hydrogenated amorphous semiconductors

NASA Astrophysics Data System (ADS)

Jin, Shu; Ley, Lothar

1991-07-01

One of the key steps in the formation of glow-discharge-deposited (GD) a-Si:H or a-Ge:H films by plasma deposition from the gas phase is the elimination of excess hydrogen from the growth surface which is necessary for the cross linking of the Si or Ge network and the reduction of the defect density associated with the hydrogen-rich surface layer. The high defect density (~1018 cm-3) in a growing surface layer can, depending on preparation conditions, be either reduced (to ~1016 cm-3) or be trapped in the bulk upon subsequent growth, as evidenced by a great deal of data. However, little is known about its origin and implication. We have investigated the change in electronic structure related with this process using UHV-evaporated a-Ge as a model system, subjected to thermal hydrogenation, plasma hydrogenation, and various annealing cycles. The density of occupied states in the pseudogap of the a-Ge(:H) surface (probing depth ~50 Å) was determined with total-yield photoelectron spectroscopy. In this way, effects of thermal annealing, hydrogenation, and ion bombarding on the near-surface defect density could be studied. We identify in room-temperature (RT) hydrogenated a-Ge:H another defect at about Ev+0.45 eV in addition to the dangling-bond defect. This defect exists at the initial stage of hydrogen incorporation, decreases upon ~250 °C annealing, and is restored upon RT rehydrogenation. Therefore we suspect that this defect is hydrogen induced and concomitant with the formation of unexpected bondings [both multiply bonded XHx (X=Si or Ge and x=2 and 3) and polyhydride (XH2)n configurations] favored at RT hydrogenation. As a possible candidate we suggest the Ge-H-Ge three-center bond in which one electron is placed in a nonbonding orbital that gives rise to the paramagnetic state in the gap of a-Ge:H observed here. This defect also accounts for the large defect density at the growing surface in the optimized plasma chemical-vapor-deposition process, where the special bonding configurations mentioned above are the predominant species. The formation and annealing of this defect will be discussed.

Functionalization of poly(methyl methacrylate) (PMMA) as a substrate for DNA microarrays

PubMed Central

Fixe, F.; Dufva, M.; Telleman, P.; Christensen, C. B. V.

2004-01-01

A chemical procedure was developed to functionalize poly(methyl methacrylate) (PMMA) substrates. PMMA is reacted with hexamethylene diamine to yield an aminated surface for immobilizing DNA in microarrays. The density of primary NH2 groups was 0.29 nmol/cm2. The availability of these primary amines was confirmed by the immobilization of DNA probes and hybridization with a complementary DNA strand. The hybridization signal and the hybridization efficiency of the chemically aminated PMMA slides were comparable to the hybridization signal and the hybridization efficiency obtained from differently chemically modified PMMA slides, silanized glass, commercial silylated glass and commercial plastic Euray™ slides. Immobilized and hybridized densities of 10 and 0.75 pmol/cm2, respectively, were observed for microarrays on chemically aminated PMMA. The immobilized probes were heat stable since the hybridization performance of microarrays subjected to 20 PCR heat cycles was only reduced by 4%. In conclusion, this new strategy to modify PMMA provides a robust procedure to immobilize DNA, which is a very useful substrate for fabricating single use diagnostics devices with integrated functions, like sample preparation, treatment and detection using microfabrication and microelectronic techniques. PMID:14718554

Plasma Potential and Langmuir Probe Measurements in the Near-field Plume of the NASA-457Mv2 Hall Thruster

NASA Technical Reports Server (NTRS)

Shastry, Rohit; Huang, Wensheng; Herman, Daniel A.; Soulas, George C.; Kamhawi, Hani

2012-01-01

In order to further the design of future high-power Hall thrusters and provide experimental validation for ongoing modeling efforts, plasma potential and Langmuir probe measurements were performed on the 50-kW NASA-457Mv2. An electrostatic probe array comprised of a near-field Faraday probe, single Langmuir probe, and emissive probe was used to interrogate the near-field plume from approximately 0.1 - 2.0 mean thruster diameters downstream of the thruster exit plane at the following operating conditions: 300 V, 400 V and 500 V at 30 kW and 500 V at 50 kW. Results have shown that the acceleration zone is limited to within 0.4 mean thruster diameters of the exit plane while the high-temperature region is limited to 0.25 mean thruster diameters from the exit plane at all four operating conditions. Maximum plasma potentials in the near-field at 300 and 400 V were approximately 50 V with respect to cathode potential, while maximum electron temperatures varied from 24 - 32 eV, depending on operating condition. Isothermal lines at all operating conditions were found to strongly resemble the magnetic field topology in the high-temperature regions. This distribution was found to create regions of high temperature and low density near the magnetic poles, indicating strong, thick sheath formation along these surfaces. The data taken from this study are considered valuable for future design as well as modeling validation.

Protein sensing by nanofluidic crystal and its signal enhancement

PubMed Central

Sang, Jianming; Du, Hongtan; Wang, Wei; Chu, Ming; Wang, Yuedan; Li, Haichao; Alice Zhang, Haixia; Wu, Wengang; Li, Zhihong

2013-01-01

Nanofluidics has a unique property that ionic conductance across a nanometer-sized confined space is strongly affected by the space surface charge density, which can be utilized to construct electrical read-out biosensor. Based on this principle, this work demonstrated a novel protein sensor along with a sandwich signal enhancement approach. Nanoparticles with designed aptamer onside are assembled in a suspended micropore to form a 3-dimensional network of nanometer-sized interstices, named as nanofluidic crystal hereafter, as the basic sensing unit. Proteins captured by aptamers will change the surface charge density of nanoparticles and thereby can be detected by monitoring the ionic conductance across this nanofluidic crystal. Another aptamer can further enlarge the variations of the surface charge density by forming a sandwich structure (capturing aptamer/protein/signal enhancement aptamer) and the read-out conductance as well. The preliminary experimental results indicated that human α-thrombin was successfully detected by the corresponding aptamer modified nanofluidic crystal with the limit of detection of 5 nM (0.18 μg/ml) and the read-out signal was enhanced up to 3 folds by using another thrombin aptamer. Being easy to graft probe, facile and low-cost to prepare the nano-device, and having an electrical read-out, the present nanofluidic crystal scheme is a promising and universal strategy for protein sensing. PMID:24404017

STAR FORMATION AT Z = 2.481 IN THE LENSED GALAXY SDSS J1110+6459: STAR FORMATION DOWN TO 30 PARSEC SCALES.

PubMed

Johnson, Traci L; Rigby, Jane R; Sharon, Keren; Gladders, Michael D; Florian, Michael; Bayliss, Matthew B; Wuyts, Eva; Whitaker, Katherine E; Livermore, Rachael; Murray, Katherine T

2017-07-10

We present measurements of the surface density of star formation, the star-forming clump luminosity function, and the clump size distribution function, for the lensed galaxy SGAS J111020.0+645950.8 at a redshift of z =2.481. The physical size scales that we probe, radii r = 30-50 pc, are considerably smaller scales than have yet been studied at these redshifts. The star formation surface density we find within these small clumps is consistent with surface densities measured previously for other lensed galaxies at similar redshift. Twenty-two percent of the rest-frame ultraviolet light in this lensed galaxy arises from small clumps, with r <100 pc. Within the range of overlap, the clump luminosity function measured for this lensed galaxy is remarkably similar to those of z ∼ 0 galaxies. In this galaxy, star-forming regions smaller than 100 pc-physical scales not usually resolved at these redshifts by current telescopes-are important locations of star formation in the distant universe. If this galaxy is representative, this may contradict the theoretical picture in which the critical size scale for star formation in the distant universe is of order 1 kiloparsec. Instead, our results suggest that current telescopes have not yet resolved the critical size scales of star-forming activity in galaxies over most of cosmic time.

Characterizing ISS Charging Environments with On-Board Ionospheric Plasma Measurements

NASA Technical Reports Server (NTRS)

Minow, Jospeh I.; Craven, Paul D.; Coffey, Victoria N.; Schneider, Todd A.; Vaughn, Jason A.; Wright Jr, Kenneth; Parker, Paul D.; Mikatarian, Ronald R.; Kramer, Leonard; Hartman, William A.;

What We Learned From the Venus Surface in-situ Exploration And What Looks Promising to do Next

NASA Astrophysics Data System (ADS)

Basilevsky, A. T.; Head, J. W.

2005-12-01

The in-situ study of Venus surface started on Dec 15, 1970 with the landing of the Soviet Venera 7 probe, which sent back to Earth data on the surface temperature and atmosphere pressure. Then, since 1972 till 1985 there were successful landings of the Soviet Venera 9 to 14 and Vega 1-2 probes. The Day probe, part of the US Pioneer Venus Multiprobe (1978), also sent the data from the Venus surface. Gained by these missions we have the results of gamma-spectrometry measurements of K, U, and Th contents in the surface material in five sites and the X-ray fluorescence measurements of major elements contents in three sites as well as TV panoramas of four landing sites. In addition, in some of these sites there have been measured the surface material density, bearing capacity and electro conductivity as well as albedo and color. The results of the geochemical measurements, all characterizing Venusian plains, are consistent with basaltic composition of the surface material in all seven sampled sites. Recent comparisons of the Venusian compositions with those of the extended database of terrestrial magmatic rocks from different geodynamic environments within the oceanic crust showed that except one (Venera 14) all other measurements suggest enrichment in LIL elements and differ from N-MORB compositions. The surface in the imaged landing sites was found to consist of very dark finely layered and mechanically weak rock and even darker soil. Recent joint analysis of the Veneras' and Magellan data showed that the layered rock most likely is thermally sintered airborn sediment of fine debris derived from ejecta of impact craters. This sediment, although of small thickness, seems to be widespread on the Venus surface that should be taken into account in planning new missions. The future landings have to provide more compositional knowledge on Venus surface by significantly improving the analyses accuracies and detection limits and extending sampled geologic formations beyond the already sampled plains. Determination of mineralogic composition of the surface material as well as the redox-controlling components of the atmosphere are of a key value. Seismic and other geophysical sounding of Venus interior should be also planned. Sample return mission(s) as distant but necessary step in Venus studies should be considered too.

Using a short-pulse diffraction-limited laser beam to probe filamentation of a random phase plate smoothed beam.

PubMed

Kline, J L; Montgomery, D S; Flippo, K A; Johnson, R P; Rose, H A; Shimada, T; Williams, E A

2008-10-01

A short pulse (few picoseconds) laser probe provides high temporal resolution measurements to elucidate details of fast dynamic phenomena not observable with typical longer laser pulse probes and gated diagnostics. Such a short pulse laser probe (SPLP) has been used to measure filamentation of a random phase plate (RPP) smoothed laser beam in a gas-jet plasma. The plasma index of refraction due to driven density and temperature fluctuations by the RPP beam perturbs the phase front of a SPLP propagating at a 90 degree angle with respect to the RPP interaction beam. The density and temperature fluctuations are quasistatic on the time scale of the SPLP (approximately 2 ps). The transmitted near-field intensity distribution from the SPLP provides a measure of the phase front perturbation. At low plasma densities, the transmitted intensity pattern is asymmetric with striations across the entire probe beam in the direction of the RPP smoothed beam. As the plasma density increases, the striations break up into smaller sizes along the direction of the RPP beam propagation. The breakup of the intensity pattern is consistent with self-focusing of the RPP smoothed interaction beam. Simulations of the experiment using the wave propagation code, PF3D, are in qualitative agreement demonstrating that the asymmetric striations can be attributed to the RPP driven density fluctuations. Quantification of the beam breakup measured by the transmitted SPLP could lead to a new method for measuring self-focusing of lasers in underdense plasmas.

Colloidal silica films for high-capacity DNA arrays

NASA Astrophysics Data System (ADS)

Glazer, Marc Irving

The human genome project has greatly expanded the amount of genetic information available to researchers, but before this vast new source of data can be fully utilized, techniques for rapid, large-scale analysis of DNA and RNA must continue to develop. DNA arrays have emerged as a powerful new technology for analyzing genomic samples in a highly parallel format. The detection sensitivity of these arrays is dependent on the quantity and density of immobilized probe molecules. We have investigated substrates with a porous, "three-dimensional" surface layer as a means of increasing the surface area available for the synthesis of oligonucleotide probes, thereby increasing the number of available probes and the amount of detectable bound target. Porous colloidal silica films were created by two techniques. In the first approach, films were deposited by spin-coating silica colloid suspensions onto flat glass substrates, with the pores being formed by the natural voids between the solid particles (typically 23nm pores, 35% porosity). In the second approach, latex particles were co-deposited with the silica and then pyrolyzed, creating films with larger pores (36 nm), higher porosity (65%), and higher surface area. For 0.3 mum films, enhancements of eight to ten-fold and 12- to 14-fold were achieved with the pure silica films and the films "templated" with polymer latex, respectively. In gene expression assays for up to 7,000 genes using complex biological samples, the high-capacity films provided enhanced signals and performed equivalently or better than planar glass on all other functional measures, confirming that colloidal silica films are a promising platform for high-capacity DNA arrays. We have also investigated the kinetics of hybridization on planar glass and high-capacity substrates. Adsorption on planar arrays is similar to ideal Langmuir-type adsorption, although with an "overshoot" at high solution concentration. Hybridization on high-capacity films is controlled by traditional adsorption (ka) and desorption (kd) coefficients, as well as morphology factors and transient binding interactions between the target and probes. The strength of the transient probe/target binding interactions are on the order of 5--7 DNA base pairs, which suggests the formation of nucleation or other metastable complexes, rather than fully-zippered duplexes.

Systems and methods for laser assisted sample transfer to solution for chemical analysis

DOEpatents

Van Berkel, Gary J.; Kertesz, Vilmos; Ovchinnikova, Olga S.

2014-06-03

Systems and methods are described for laser ablation of an analyte from a specimen and capturing of the analyte in a dispensed solvent to form a testing solution. A solvent dispensing and extraction system can form a liquid microjunction with the specimen. The solvent dispensing and extraction system can include a surface sampling probe. The laser beam can be directed through the surface sampling probe. The surface sampling probe can also serve as an atomic force microscopy probe. The surface sampling probe can form a seal with the specimen. The testing solution including the analyte can then be analyzed using an analytical instrument or undergo further processing.

Systems and methods for laser assisted sample transfer to solution for chemical analysis

DOEpatents

Van Berkel, Gary J.; Kertesz, Vilmos; Ovchinnikova, Olga S.

2015-09-29

Systems and methods are described for laser ablation of an analyte from a specimen and capturing of the analyte in a dispensed solvent to form a testing solution. A solvent dispensing and extraction system can form a liquid microjunction with the specimen. The solvent dispensing and extraction system can include a surface sampling probe. The laser beam can be directed through the surface sampling probe. The surface sampling probe can also serve as an atomic force microscopy probe. The surface sampling probe can form a seal with the specimen. The testing solution including the analyte can then be analyzed using an analytical instrument or undergo further processing.

Systems and methods for laser assisted sample transfer to solution for chemical analysis

DOEpatents

Van Berkel, Gary J; Kertesz, Vilmos; Ovchinnikova, Olga S

2013-08-27

Systems and methods are described for laser ablation of an analyte from a specimen and capturing of the analyte in a dispensed solvent to form a testing solution. A solvent dispensing and extraction system can form a liquid microjunction with the specimen. The solvent dispensing and extraction system can include a surface sampling probe. The laser beam can be directed through the surface sampling probe. The surface sampling probe can also serve as an atomic force microscopy probe. The surface sampling probe can form a seal with the specimen. The testing solution including the analyte can then be analyzed using an analytical instrument or undergo further processing.

Four-probe measurements with a three-probe scanning tunneling microscope

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

Salomons, Mark; Martins, Bruno V. C.; Zikovsky, Janik

2014-04-15

We present an ultrahigh vacuum (UHV) three-probe scanning tunneling microscope in which each probe is capable of atomic resolution. A UHV JEOL scanning electron microscope aids in the placement of the probes on the sample. The machine also has a field ion microscope to clean, atomically image, and shape the probe tips. The machine uses bare conductive samples and tips with a homebuilt set of pliers for heating and loading. Automated feedback controlled tip-surface contacts allow for electrical stability and reproducibility while also greatly reducing tip and surface damage due to contact formation. The ability to register inter-tip position bymore » imaging of a single surface feature by multiple tips is demonstrated. Four-probe material characterization is achieved by deploying two tips as fixed current probes and the third tip as a movable voltage probe.« less

Superposition of \\sqrt{13}\\times \\sqrt{13} and 3 × 3 supermodulations in TaS2 probed by scanning tunneling microscopy

NASA Astrophysics Data System (ADS)

Fujisawa, Y.; Iwasaki, T.; Fujii, D.; Ohta, S.; Iwashita, J.; Fujita, T.; Nakata, M.; Kishimoto, K.; Demura, S.; Sakata, H.

2018-03-01

We report on a scanning tunnelling microscopy study of TaS2 at 4.2 K. A surface prepared by cleavage showed a superimposed pattern of two types of charge density waves with 3a 0 × 3a 0 and \\sqrt{13}{a}0× \\sqrt{13}{a}0 periodicity, which had never been observed previously. We attribute the superposition to regular stacking of 4H b polytypes or irregular stacking of 2H and 4H b layers.

3D ELECTRON DENSITY DISTRIBUTIONS IN THE SOLAR CORONA DURING SOLAR MINIMA: ASSESSMENT FOR MORE REALISTIC SOLAR WIND MODELING

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

Patoul, Judith de; Foullon, Claire; Riley, Pete, E-mail: j.depatoul@exeter.ac.uk, E-mail: c.foullon@exeter.ac.uk, E-mail: rileype@saic.com

Knowledge of the electron density distribution in the solar corona put constraints on the magnetic field configurations for coronal modeling and on initial conditions for solar wind modeling. We work with polarized SOHO/LASCO-C2 images from the last two recent minima of solar activity (1996–1997 and 2008–2010), devoid of coronal mass ejections. The goals are to derive the 4D electron density distributions in the corona by applying a newly developed time-dependent tomographic reconstruction method and to compare the results between the two solar minima and with two magnetohydrodynamic models. First, we confirm that the values of the density distribution in thermodynamic models aremore » more realistic than in polytropic ones. The tomography provides more accurate distributions in the polar regions, and we find that the density in tomographic and thermodynamic solutions varies with the solar cycle in both polar and equatorial regions. Second, we find that the highest-density structures do not always correspond to the predicted large-scale heliospheric current sheet or its helmet streamer but can follow the locations of pseudo-streamers. We deduce that tomography offers reliable density distributions in the corona, reproducing the slow time evolution of coronal structures, without prior knowledge of the coronal magnetic field over a full rotation. Finally, we suggest that the highest-density structures show a differential rotation well above the surface depending on how they are magnetically connected to the surface. Such valuable information on the rotation of large-scale structures could help to connect the sources of the solar wind to their in situ counterparts in future missions such as Solar Orbiter and Solar Probe Plus.« less

Investigating the interfacial dynamics of thin films

NASA Astrophysics Data System (ADS)

Rosenbaum, Aaron W.

This thesis probes the interfacial dynamics and associated phenomena of thin films. Surface specific tools were used to study the self-assembly of alkanethiols, the mono- and bilayer dynamics of SF6, and the surface motion of poly(methyl methacrylate). Non-pertubative helium atom scattering was the principal technique used to investigate these systems. A variety of other complementary tools, including scanning tunneling microscopy, electron diffraction, Auger spectroscopy, atomic force microscopy, and ellipsometry were used in tandem with the neutral atom scattering studies. Controlling the spontaneous assembly of alkanethiols on Au(111) requires a better fundamental understanding of the adsorbate-adsorbate and substrate-adsorbate interactions. Our characterization focused on two key components, the surface structure and adsorbate vibrations. The study indicates that the Au(111) reconstruction plays a larger role than anticipated in the low-density phase of alkanethiol monolayers. A new structure is proposed for the 1-decanethiol monolayer that impacts the low-energy vibrational mode. Varying the alkane chain lengths imparts insight into the assembly process via characterization of a dispersionless phonon mode. Studies of SF6 physisorbed on Au(111) bridge surface research on rare gas adsorbates with complicated dynamical organic thin films. Mono- and bilayer coverages of SF6/Au(111) were studied at cryogenic temperatures. Our experiments probed the surface properties of SF6 yielding insights into substrate and coverage effects. The study discovered a dispersionless Einstein oscillation with multiple harmonic overtones. A second layer of SF6 softened the mode, but did not show any indications of bulk or cooperative interactions. The vibrational properties of SF 6 showed both striking similarities and differences when compared with physisorbed rare gases. Lastly, this thesis will discuss studies of thin film poly(methyl methacrylate) on Si. The non-pertubative and surface specific nature of helium atom scattering allows for a deft study of the relationship between surface motion and the glass transition temperature. An added parameter in this complex organic system is the film thickness. The confinement effects and enhanced surface displacement were examined as a function of the thermal attenuation of both inelastic and elastic helium atom scattering. The Debye-Waller factor for these thin films of PMMA is similar to the low-density alkanethiol self-assembled monolayers discussed earlier.

Nanoscale laminin coating modulates cortical scarring response around implanted silicon microelectrode arrays

NASA Astrophysics Data System (ADS)

He, Wei; McConnell, George C.; Bellamkonda, Ravi V.

2006-12-01

Neural electrodes could significantly enhance the quality of life for patients with sensory and/or motor deficits as well as improve our understanding of brain functions. However, long-term electrical connectivity between neural tissue and recording sites is compromised by the development of astroglial scar around the recording probes. In this study we investigate the effect of a nanoscale laminin (LN) coating on Si-based neural probes on chronic cortical tissue reaction in a rat model. Tissue reaction was evaluated after 1 day, 1 week, and 4 weeks post-implant for coated and uncoated probes using immunohistochemical techniques to evaluate activated microglia/macrophages (ED-1), astrocytes (GFAP) and neurons (NeuN). The coating did not have an observable effect on neuronal density or proximity to the electrode surface. However, the response of microglia/macrophages and astrocytes was altered by the coating. One day post-implant, we observed an ~60% increase in ED-1 expression near LN-coated probe sites compared with control uncoated probe sites. Four weeks post-implant, we observed an ~20% reduction in ED-1 expression along with an ~50% reduction in GFAP expression at coated relative to uncoated probe sites. These results suggest that LN has a stimulatory effect on early microglia activation, accelerating the phagocytic function of these cells. This hypothesis is further supported by the increased mRNA expression of several pro-inflammatory cytokines (TNF-α, IL-1 and IL-6) in cultured microglia on LN-bound Si substrates. LN immunostaining of coated probes immediately after insertion and retrieval demonstrates that the coating integrity is not compromised by the shear force during insertion. We speculate, based on these encouraging results, that LN coating of Si neural probes could potentially improve chronic neural recordings through dispersion of the astroglial scar.

Lessons Learned from Previous Space-Borne Sounders as a Guide to Future Sounder Development

NASA Technical Reports Server (NTRS)

Benson, Robert F.; Deshpande, Manohar D.; Farrell,William M.; Fung, Shing F.; Osherovich, Vladimir A.; Pfaff, Rovert E.; Rowland, Douglas E.; Adrian, Mark L.

2008-01-01

Space-borne radio sounding is considered to be the gold standard for electron-density (N(sub e)) measurements compared to other techniques even under low-density conditions, such as N(sub e) < 1/cu cm, when other techniques are known to experience difficulties. These reliable measurements are not restricted to in-situ N(sub e) determinations since a spaceborne sounder can provide vertical N(sub e) profiles (N(sub e)(h)) from the spacecraft altitude to the altitude of maximum N(sub e). Near-conjunction studies involving the International Satellites for Ionospheric Studies (ISIS) satellites in the topside ionosphere and Dynamics Explorer 2 (DE 2) near the altitude of the F-region peak density have verified that, even at the greatest distance from the sounder, the ISIS-derived N(sub e)(h) profiles agree with the DE-2 Langmuir-probe measurements to within about 30% over a density range of more than two decades. Space-borne sounders can also provide N(sub e) profiles along the magnetic-field B, by inverting echoes that are ducted along field-aligned irregularities (FAI), and can provide information about the terrain beneath the satellite by examining surface reflections in the frequency range above the ionospheric penetration frequency. Many nations have launched rocket and satellite radio sounders in geospace over more than 4 decades and there have been sounders on space-probes and in orbit around other planets. Here we will summarize some of the lessons learned from these accomplishments by analyzing data from radio sounders on the Alouette and ISIS satellites and the OEDIPUS and other rockets in the terrestrial ionosphere, the IMAGE satellite in the terrestrial magnetosphere, the Ulysses space probe in Jupiter's 10 plasma torus and the MARSIS satellite in orbit around Mars. The emphasis will be on information deduced concerning (1) fundamental plasma processes and gradients in N, and B in the vicinity of the sounders from sounder-stimulated plasma resonances and short-range echoes involving ion as well as electron motions, (2) the importance of the antenna orientation relative to B for the detection of different plasma resonances, (3) sounder-stimulated plasma phenomena, including FAI, when special plasma conditions are satisfied, (4) the minimum power required for long-range echoes, as indicated by echoes from frequency components of the transmitted pulse and by multiple ducted echoes, and (5) the terrain beneath the satellite from surface reflections. Knowledge of these results should enable the optimum design of a future sounder to satisfy specific science requirements with minimal spacecraft resources.

An in situ probe for on-line monitoring of cell density and viability on the basis of dark field microscopy in conjunction with image processing and supervised machine learning.

PubMed

Wei, Ning; You, Jia; Friehs, Karl; Flaschel, Erwin; Nattkemper, Tim Wilhelm

2007-08-15

Fermentation industries would benefit from on-line monitoring of important parameters describing cell growth such as cell density and viability during fermentation processes. For this purpose, an in situ probe has been developed, which utilizes a dark field illumination unit to obtain high contrast images with an integrated CCD camera. To test the probe, brewer's yeast Saccharomyces cerevisiae is chosen as the target microorganism. Images of the yeast cells in the bioreactors are captured, processed, and analyzed automatically by means of mechatronics, image processing, and machine learning. Two support vector machine based classifiers are used for separating cells from background, and for distinguishing live from dead cells afterwards. The evaluation of the in situ experiments showed strong correlation between results obtained by the probe and those by widely accepted standard methods. Thus, the in situ probe has been proved to be a feasible device for on-line monitoring of both cell density and viability with high accuracy and stability. (c) 2007 Wiley Periodicals, Inc.

Investigation of the Arcjet near Field Plume Using Electrostatic Probes

NASA Technical Reports Server (NTRS)

Sankovic, John M.

1990-01-01

The near field plume of a 1 kW class arcjet thruster was investigated using electrostatic probes of various geometries. The electron number densities and temperatures were determined in a simulated hydrazine plume at axial distances between 3 cm (1.2 in.) and 15 cm (5.9 in.) and radial distances extending to 10 cm (3.9 in.) off centerline. Values of electron number densities obtained using cylindrical and spherical probes of different geometries agreed very well. The electron density on centerline followed a source flow approximation for axial distances as near as 3 cm (1.2 in.) from the nozzle exit plane. The model agreed well with previously obtained data in the far field. The effects of propellant mass flow rate and input power level were also studied. Cylindrical probes were used to obtain ion streamlines by changing the probe orientation with respect to the flow. The effects of electrical configuration on the plasma characteristics of the plume were also investigated by using a segmented anode/nozzle thruster. The results showed that the electrical configuration in the nozzle affected the distribution of electrons in the plume.

Investigation of the arcjet plume near field using electrostatic probes

NASA Technical Reports Server (NTRS)

Sankovic, John M.

1990-01-01

The near field plum of a 1 kW class arcjet thruster was investigated using electrostatic probes of various geometries. The electron number densities and temperatures were determined in a simulated hydrazine plume at axial distances between 3 cm (1.2 in) and 15 cm (5.9 in) and radial distances extending to 10 cm (3.9 in) off centerline. Values of electron number densities obtained using cylindrical and spherical probes of different geometries agreed very well. The electron density on centerline followed a source flow approximation for axial distances as near as 3 cm (1.2 in) from the nozzle exit plane. The model agreed well with previously obtained data in the far field. The effects of propellant mass flow rate and input power level were also studied. Cylindrical probes were used to obtain ion streamlines by changing the probe orientation with respect to the flow. The effects of electrical configuration on the plasma characteristics of the plume were also investigated by using a segmented anode/nozzle thruster. The results showed that the electrical configuration in the nozzle affected the distribution of electrons in the plume.

An analytical model for floating probes in AC plasma and its application to double probes for high density, high power RF discharges

NASA Astrophysics Data System (ADS)

Caneses, Juan Francisco; Blackwell, Boyd; Plasma Research Laboratory Team

2013-10-01

In this work we provide an analytical model that allows one to quantitatively assess the RF compensation performance and suitability of the double probe technique for use in RF generated plasma. The model is based in the theory of the self-bias effect as described in Braithwaite's work, which we extend to include the time resolved behavior of floating probes. We provide experimental verification for this model and show that the theory of transient RF self-bias probes and harmonic current detection probes are limiting cases of this extended model. Furthermore, the model shows that the RF compensation is solely dependent on the sheath impedance, the probe's stray capacitance to ground and RF frequency. In addition, we use these results to implement a double probe system for use in high density helicon plasma where heat loads could potentially damage the intricate components in an RF compensating circuit. Finally we use this model to (1) recommend ways to extend the operational regime of double probes where the plasma conditions would render them unsuitable and to (2) comment on the use of this model to aid design of RF compensated Langmuir probes.

Surface plasmon resonance spectroscopy sensor and methods for using same

DOEpatents

Anderson, Brian Benjamin; Nave, Stanley Eugene

2002-01-01

A surface plasmon resonance ("SPR") probe with a detachable sensor head and system and methods for using the same in various applications is described. The SPR probe couples fiber optic cables directly to an SPR substrate that has a generally planar input surface and a generally curved reflecting surface, such as a substrate formed as a hemisphere. Forming the SPR probe in this manner allows the probe to be miniaturized and operate without the need for high precision, expensive and bulky collimating or focusing optics. Additionally, the curved reflecting surface of the substrate can be coated with one or multiple patches of sensing medium to allow the probe to detect for multiple analytes of interest or to provide multiple readings for comparison and higher precision. Specific applications for the probe are disclosed, including extremely high sensitive relative humidity and dewpoint detection for, e.g., moisture-sensitive environment such as volatile chemical reactions. The SPR probe disclosed operates with a large dynamic range and provides extremely high quality spectra despite being robust enough for field deployment and readily manufacturable.

Detection of an electron beam in a high density plasma via an electrostatic probe

NASA Astrophysics Data System (ADS)

Majeski, Stephen; Yoo, Jongsoo; Zweben, Stewart; Yamada, Masaaki

2018-07-01

An electron beam is detected by a 1D floating potential probe array in a relatively high density (1012–1013 cm‑3) and low temperature (∼5 eV) plasma of the Magnetic Reconnection Experiment. Clear perturbations in the floating potential profile by the electron beam are observed. Based on the floating potential profile and a current balance equation to the probe array tips, the effective width of the electron beam is determined, from which we determine the radial and toroidal beam current density profiles. After the profile of the electron beam is specified from the measured beam current, we demonstrate the consistency of the current balance equation and the location of the perturbation is also in agreement with field line mapping. No significant broadening of the electron beam is observed after the beam propagates for tens of centimeters through the high density plasma. These results prove that the field line mapping is, in principle, possible in high density plasmas.

Detection of an electron beam in a high density plasma via an electrostatic probe

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

Majeski, Stephen; Yoo, Jongsoo; Zweben, Stewart

Here, an electron beam is detected by a 1D floating potential probe array in a relatively high density (10 12–10 13 cm -3) and low temperature (~5 eV) plasma of the Magnetic Reconnection Experiment. Clear perturbations in the floating potential profile by the electron beam are observed. Based on the floating potential profile and a current balance equation to the probe array tips, the effective width of the electron beam is determined, from which we determine the radial and toroidal beam current density profiles. After the profile of the electron beam is specified from the measured beam current, we demonstratemore » the consistency of the current balance equation and the location of the perturbation is also in agreement with field line mapping. No significant broadening of the electron beam is observed after the beam propagates for tens of centimeters through the high density plasma. These results prove that the field line mapping is, in principle, possible in high density plasmas.« less

Detection of an electron beam in a high density plasma via an electrostatic probe

DOE PAGES

Majeski, Stephen; Yoo, Jongsoo; Zweben, Stewart; ...

2018-05-08

Here, an electron beam is detected by a 1D floating potential probe array in a relatively high density (10 12–10 13 cm -3) and low temperature (~5 eV) plasma of the Magnetic Reconnection Experiment. Clear perturbations in the floating potential profile by the electron beam are observed. Based on the floating potential profile and a current balance equation to the probe array tips, the effective width of the electron beam is determined, from which we determine the radial and toroidal beam current density profiles. After the profile of the electron beam is specified from the measured beam current, we demonstratemore » the consistency of the current balance equation and the location of the perturbation is also in agreement with field line mapping. No significant broadening of the electron beam is observed after the beam propagates for tens of centimeters through the high density plasma. These results prove that the field line mapping is, in principle, possible in high density plasmas.« less

Influence of irradiation conditions on plasma evolution in laser-surface interaction

NASA Astrophysics Data System (ADS)

Hermann, J.; Boulmer-Leborgne, C.; Dubreuil, B.; Mihailescu, I. N.

1993-09-01

The plasma plume induced by pulsed CO2 laser irradiation of a Ti target at power densities up to 4×108 W cm-2 was studied by emission spectroscopy. Time- and space-resolved measurements were performed by varying laser intensity, laser temporal pulse shape, ambient gas pressure, and the nature of the ambient gas. Experimental results are discussed by comparison with usual models. We show that shock wave and plasma propagation depend critically on the ratio Ivap/Ii, Ivap being the intensity threshold for surface vaporization and Ii the plasma ignition threshold of the ambient gas. Spectroscopic diagnostics of the helium breakdown plasma show maximum values of electron temperature and electron density in the order of kTe˜10 eV and ne=1018 cm-3, respectively. The plasma cannot be described by local thermodynamic equilibrium modeling. Nevertheless, excited metal atoms appear to be in equilibrium with electrons, hence, they can be used like a probe to measure the electron temperature. In order to get information on the role of the plasma in the laser-surface interaction, Ti surfaces were investigated by microscopy after irradiation. Thus an enhanced momentum transfer from the plasma to the target due to the recoil pressure of the breakdown plasma could be evidenced.

Direct Laser Ice Penetrator for Exploring Icy Ocean Worlds: Design, Modeling and Test Results of a Proof-of-Concept Prototype

NASA Astrophysics Data System (ADS)

Hogan, B.; Stone, W.; Bramall, N. E.; Siegel, V.; Lelievre, S.; Rothhammer, B.; Richmond, K.; Flesher, C.

2016-12-01

Subsurface exploration of icy ocean worlds requires an efficient method of penetrating ice to significant depths under extreme environment conditions. Searching for extant life dictates descent to a depth which is habitable or where biomarkers can survive and allow detection. It's anticipated that several meters to 10s of meters of shielding is required to prevent cosmic background radiation and other energetic particles from destroying biomarker evidence. We have devised, developed and demonstrated an entirely novel ice penetrating technology utilizing laser light carried by an optical fiber tether and emitted from a probe's optical nose cone and radiated directly into the volume of ice preceding the penetrator. We have termed it a "Direct Laser Penetrator" or DLP. We present design details, modeling, and test data from preliminary proof-of-concept experiments conducted at Stone Aerospace with results exceeding expectations and achieving the fastest reported thermal probe descent rate to date (> 12 m / hr). DLP has critical benefits over conventional "hot point" melt probes, which must generate large temperature gradients to force heat by conduction through the nose cone, and layers of ice and water. Additionally, hot point melt probes tested under vacuum have shown extreme difficulty initiating penetration, as virtually no thermal contact exists between the probe nose and rough ice surface. The ice simply sublimates and any transferred heat is quickly dissipated due to the low power density and extreme cold. DLP requires NO thermal contact between the probe nose and the ice surface since the laser energy is radiated directly into the volume (vs. surface) of ice preceding the penetrator. A proposed key element of the DLP is the fiber optic tether, coupled with a dedicated sensor fiber, enables "optical access" to the subsurface environment by a lander's shared or DLP dedicated on-board instruments (Raman / Fluorescence / fiber / UV / VIS / NIR spectroscopy, etc). These sensors can search for extant life by detecting biomarkers as well as characterizing the radiation / light environment for subsurface habitability. The combination of a laser penetrator w/ integrated fiber coupled instruments could be an important tool for an icy ocean worlds lander. (Supported by NASA funded SAS projects VALKYRIE and SPINDLE)

Probing the energetics of organic–nanoparticle interactions of ethanol on calcite

PubMed Central

Wu, Di; Navrotsky, Alexandra

2015-01-01

Knowing the nature of interactions between small organic molecules and surfaces of nanoparticles (NP) is crucial for fundamental understanding of natural phenomena and engineering processes. Herein, we report direct adsorption enthalpy measurement of ethanol on a series of calcite nanocrystals, with the aim of mimicking organic–NP interactions in various environments. The energetics suggests a spectrum of adsorption events as a function of coverage: strongest initial chemisorption on active sites on fresh calcite surfaces, followed by major chemical binding to form an ethanol monolayer and, subsequently, very weak, near-zero energy, physisorption. These thermochemical observations directly support a structure where the ethanol monolayer is bonded to the calcite surface through its polar hydroxyl group, leaving the hydrophobic ends of the ethanol molecules to interact only weakly with the next layer of adsorbing ethanol and resulting in a spatial gap with low ethanol density between the monolayer and subsequent added ethanol molecules, as predicted by molecular dynamics and density functional calculations. Such an ordered assembly of ethanol on calcite NP is analogous to, although less strongly bonded than, a capping layer of organics intentionally introduced during NP synthesis, and suggests a continuous variation of surface structure depending on molecular chemistry, ranging from largely disordered surface layers to ordered layers that nevertheless are mobile and can rearrange or be displaced by other molecules to strongly bonded immobile organic capping layers. These differences in surface structure will affect chemical reactions, including the further nucleation and growth of nanocrystals on organic ligand-capped surfaces. PMID:25870281

Multiple charge density wave states at the surface of TbT e 3

DOE PAGES

Fu, Ling; Kraft, Aaron M.; Sharma, Bishnu; ...

2016-11-01

We studied TbTe 3 using scanning tunneling microscopy (STM) in the temperature range of 298–355 K. Our measurements detect a unidirectional charge density wave (CDW) state in the surface Te layer with a wave vector consistent with that of the bulk q CDW = 0.30 ± 0.01c*. However, unlike previous STM measurements, and differing from measurements probing the bulk, we detect two perpendicular orientations for the unidirectional CDW with no directional preference for the in-plane crystal axes (a or c axis) and no noticeable difference in wave vector magnitude. In addition, we find regions in which the bidirectional CDW statesmore » coexist. We propose that observation of two unidirectional CDW states indicates a decoupling of the surface Te layer from the rare-earth block layer below, and that strain variations in the Te surface layer drive the local CDW direction to the specific unidirectional or, in rare occurrences, bidirectional CDW orders observed. This indicates that similar driving mechanisms for CDW formation in the bulk, where anisotropic lattice strain energy is important, are at play at the surface. Furthermore, the wave vectors for the bidirectional order we observe differ from those theoretically predicted for checkerboard order competing with stripe order in a Fermi-surface nesting scenario, suggesting that factors beyond Fermi-surface nesting drive CDW order in TbTe 3. As a result, our temperature-dependent measurements provide evidence for localized CDW formation above the bulk transition temperature T CDW.« less

Unsteady loads due to propulsive lift configurations. Part C: Development of experimental techniques for investigation of unsteady pressures behind a cold model jet

NASA Technical Reports Server (NTRS)

Haviland, J. K.; Schroeder, J. C.

1978-01-01

As part of an overall study of the scaling laws for the fluctuating pressures induced on the wings and flaps of STOL aircraft by jet engine impingement, an experimental investigation was made of the near field fluctuating pressures behind a cold circular jet, both when it was free and when it was impinging on a flat plate. Miniature static pressure probes were developed for measurements in the free jet and on the flat plate which were connected by plastic tubing to 1/8 inch microphones and acted as pressure transducers. Using a digital correlator together with an FFT program on the CDC 6400 computer, spectral densities, relative amplitudes, phase lags, and coherences were also obtained for the signals from pairs of these probes, and were used to calibrate these probes directly against microphones. This system of instrumentation was employed to obtain single point rms and third octave surveys of the static pressures in the free jet and on the surface of the plate.

Sampling probe for microarray read out using electrospray mass spectrometry

DOEpatents

Van Berkel, Gary J.

2004-10-12

An automated electrospray based sampling system and method for analysis obtains samples from surface array spots having analytes. The system includes at least one probe, the probe including an inlet for flowing at least one eluting solvent to respective ones of a plurality of spots and an outlet for directing the analyte away from the spots. An automatic positioning system is provided for translating the probe relative to the spots to permit sampling of any spot. An electrospray ion source having an input fluidicly connected to the probe receives the analyte and generates ions from the analyte. The ion source provides the generated ions to a structure for analysis to identify the analyte, preferably being a mass spectrometer. The probe can be a surface contact probe, where the probe forms an enclosing seal along the periphery of the array spot surface.

Direct observations of L-I-H and H-I-L transitions with the X-point reciprocating probe in ASDEX Upgrade

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

Müller, S. H.; Conway, G. D.; Birkenmeier, G.

A reciprocating Langmuir probe was used to directly measure the behavior of turbulence and flows in the X-point region during transitions between low-(L) and high-confinement (H) mode in ASDEX Upgrade. The probe traverses the divertor horizontally in 140 ms, typically 2–5 cm below the X-point. Toroidal Mach number, density, floating potential (ϕ{sub f}), and electron temperature (T{sub e}) are measured. In the regime accessible to the probe (P{sub inj}<1.5 MW, line-integrated core density <4×10{sup 19} m{sup −2}), the L-H transition features an intermediate phase (I-phase), characterized by limit-cycle oscillations at 0.5–3 kHz [Conway et al., Phys. Rev. Lett. 106, 065001 (2011)]. The probe measurements revealmore » that this pulsing affects both the density and the toroidal Mach number. It is present in both the low-(LFS) and high-field sides (HFS) of the scrape-off layer, while high-amplitude broadband turbulence usually dominates the private-flux region. Profile comparisons between L-mode and I-phase show lower density in pulsing regions and small shifts in T{sub e}, directed oppositely on LFS and HFS, which are compensated by shifts in ϕ{sub f} to yield a surprisingly unchanged plasma potential profile. Directly observed L-I-phase transitions reveal that the onset of the pulsing is preceded by a fast 50% density drop in the HFS X-point region. Back transitions to L-mode occur essentially symmetrically, with the pulsing stopping first, followed by a fast recovery to L-mode density levels in the divertor.« less

16 CFR 1505.51 - Hot surfaces.

Code of Federal Regulations, 2011 CFR

2011-01-01

... CHILDREN Policies and Interpretations § 1505.51 Hot surfaces. (a) Test probe. Section 1505.6(g)(2) defines... inches long. To test for accessibility using this test probe, it shall be inserted no more than 3 inches into any opening in the toy. Unless the probe contacts a surface within 3 inches of the plane of the...

16 CFR 1505.51 - Hot surfaces.

Code of Federal Regulations, 2014 CFR

2014-01-01

... CHILDREN Policies and Interpretations § 1505.51 Hot surfaces. (a) Test probe. Section 1505.6(g)(2) defines... inches long. To test for accessibility using this test probe, it shall be inserted no more than 3 inches into any opening in the toy. Unless the probe contacts a surface within 3 inches of the plane of the...

16 CFR 1505.51 - Hot surfaces.

Code of Federal Regulations, 2012 CFR

2012-01-01

... CHILDREN Policies and Interpretations § 1505.51 Hot surfaces. (a) Test probe. Section 1505.6(g)(2) defines... inches long. To test for accessibility using this test probe, it shall be inserted no more than 3 inches into any opening in the toy. Unless the probe contacts a surface within 3 inches of the plane of the...

An Investigation of the Mechanical Properties of Some Martian Regolith Simulants with Respect to the Surface Properties at the InSight Mission Landing Site

NASA Astrophysics Data System (ADS)

Delage, Pierre; Karakostas, Foivos; Dhemaied, Amine; Belmokhtar, Malik; Lognonné, Philippe; Golombek, Matt; De Laure, Emmanuel; Hurst, Ken; Dupla, Jean-Claude; Kedar, Sharon; Cui, Yu Jun; Banerdt, Bruce

2017-10-01

In support of the InSight mission in which two instruments (the SEIS seismometer and the HP3 heat flow probe) will interact directly with the regolith on the surface of Mars, a series of mechanical tests were conducted on three different regolith simulants to better understand the observations of the physical and mechanical parameters that will be derived from InSight. The mechanical data obtained were also compared to data on terrestrial sands. The density of the regolith strongly influences its mechanical properties, as determined from the data on terrestrial sands. The elastoplastic compression volume changes were investigated through oedometer tests that also provided estimates of possible changes in density with depth. The results of direct shear tests provided values of friction angles that were compared with that of a terrestrial sand, and an extrapolation to lower density provided a friction angle compatible with that estimated from previous observations on the surface of Mars. The importance of the contracting/dilating shear volume changes of sands on the dynamic penetration of the mole was determined, with penetration facilitated by the ˜1.3 Mg/m3 density estimated at the landing site. Seismic velocities, measured by means of piezoelectric bender elements in triaxial specimens submitted to various isotropic confining stresses, show the importance of the confining stress, with lesser influence of density changes under compression. A power law relation of velocity as a function of confining stress with an exponent of 0.3 was identified from the tests, allowing an estimate of the surface seismic velocity of 150 m/s. The effect on the seismic velocity of a 10% proportion of rock in the regolith was also studied. These data will be compared with in situ data measured by InSight after landing.

Experimental investigation of density behaviors in front of the lower hybrid launcher in experimental advanced superconducting tokamak

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

Zhang, L.; Ding, B. J.; Li, M. H.

2013-06-15

A triple Langmuir probe is mounted on the top of the Lower Hybrid (LH) antenna to measure the electron density near the LH grills in Experimental Advanced Superconducting Tokamak. In this work, the LH power density ranges from 2.3 MWm{sup −2} to 10.3 MWm{sup −2} and the rate of puffing gas varies from 1.7 × 10{sup 20} el/s to 14 × 10{sup 20} el/s. The relation between the edge density (from 0.3 × n{sub e-cutoff} to 20 × n{sub e-cutoff}, where n{sub e-cutoff} is the cutoff density, n{sub e-cutoff} = 0.74 × 10{sup 17} m{sup −3} for 2.45 GHz lowermore » hybrid current drive) near the LH grill and the LH power reflection coefficients is investigated. The factors, including the gap between the LH grills and the last closed magnetic flux surface, line-averaged density, LH power, edge safety factor, and gas puffing, are analyzed. The experiments show that injection of LH power is beneficial for increasing edge density. Gas puffing is beneficial for increasing grill density but excess gas puffing is unfavorable for coupling and current drive.« less

Asymmetries in the spectral density of an interaction-quenched Luttinger liquid

NASA Astrophysics Data System (ADS)

Calzona, A.; Gambetta, F. M.; Carrega, M.; Cavaliere, F.; Sassetti, M.

2018-03-01

The spectral density of an interaction-quenched one-dimensional system is investigated. Both direct and inverse quench protocols are considered and it is found that the former leads to stronger effects on the spectral density with respect to the latter. Such asymmetry is directly reflected on transport properties of the system, namely the charge and energy current flowing to the system from a tunnel coupled biased probe. In particular, the injection of particles from the probe to the right-moving channel of the system is considered. The resulting fractionalization phenomena are strongly affected by the quench protocol and display asymmetries in the case of direct and inverse quench. Transport properties therefore emerge as natural probes for the observation of this quench-induced behavior.

Development of 3D microwave imaging reflectometry in LHD (invited).

PubMed

Nagayama, Y; Kuwahara, D; Yoshinaga, T; Hamada, Y; Kogi, Y; Mase, A; Tsuchiya, H; Tsuji-Iio, S; Yamaguchi, S

2012-10-01

Three-dimensional (3D) microwave imaging reflectometry has been developed in the large helical device to visualize fluctuating reflection surface which is caused by the density fluctuations. The plasma is illuminated by the probe wave with four frequencies, which correspond to four radial positions. The imaging optics makes the image of cut-off surface onto the 2D (7 × 7 channels) horn antenna mixer arrays. Multi-channel receivers have been also developed using micro-strip-line technology to handle many channels at reasonable cost. This system is first applied to observe the edge harmonic oscillation (EHO), which is an MHD mode with many harmonics that appears in the edge plasma. A narrow structure along field lines is observed during EHO.

Development of 3D microwave imaging reflectometry in LHD (invited)a)

NASA Astrophysics Data System (ADS)

Nagayama, Y.; Kuwahara, D.; Yoshinaga, T.; Hamada, Y.; Kogi, Y.; Mase, A.; Tsuchiya, H.; Tsuji-Iio, S.; Yamaguchi, S.

2012-10-01

Three-dimensional (3D) microwave imaging reflectometry has been developed in the large helical device to visualize fluctuating reflection surface which is caused by the density fluctuations. The plasma is illuminated by the probe wave with four frequencies, which correspond to four radial positions. The imaging optics makes the image of cut-off surface onto the 2D (7 × 7 channels) horn antenna mixer arrays. Multi-channel receivers have been also developed using micro-strip-line technology to handle many channels at reasonable cost. This system is first applied to observe the edge harmonic oscillation (EHO), which is an MHD mode with many harmonics that appears in the edge plasma. A narrow structure along field lines is observed during EHO.

Resolving phase information of the optical local density of state with scattering near-field probes

NASA Astrophysics Data System (ADS)

Prasad, R.; Vincent, R.

2016-10-01

We theoretically discuss the link between the phase measured using a scattering optical scanning near-field microscopy (s-SNOM) and the local density of optical states (LDOS). A remarkable result is that the LDOS information is directly included in the phase of the probe. Therefore by monitoring the spatial variation of the trans-scattering phase, we locally measure the phase modulation associated with the probe and the optical paths. We demonstrate numerically that a technique involving two-phase imaging of a sample with two different sized tips should allow to obtain the image the pLDOS. For this imaging method, numerical comparison with extinction probe measurement shows crucial qualitative and quantitative improvement.

Fabrication and characterization of a real-time optical fiber dosimeter probe

NASA Astrophysics Data System (ADS)

Croteau, André; Caron, Serge; Rink, Alexandra; Jaffray, David; Mermut, Ozzy

2011-07-01

There is a pressing need for a low cost, passive optical fiber dosimeter probe for use in real-time monitoring of radiation dose delivered to clinical radiation therapy patients. An optical fiber probe using radiochromic material has been designed and fabricated based on the deposition of a radiochromic thin film on a dielectric mirror. Measurements of the net optical density vs. time before, during, and after irradiation at a rate of 500 cGy/minute to a total dose of 5 Gy were performed. Net optical densities increased from 0.2 to 2.0 for radiochromic thin film thicknesses of 2 to 20 μm, respectively. An improved optical fiber probe fabrication method is presented.

2D electron density profile measurement in tokamak by laser-accelerated ion-beam probe.

PubMed

Chen, Y H; Yang, X Y; Lin, C; Wang, L; Xu, M; Wang, X G; Xiao, C J

2014-11-01

A new concept of Heavy Ion Beam Probe (HIBP) diagnostic has been proposed, of which the key is to replace the electrostatic accelerator of traditional HIBP by a laser-driven ion accelerator. Due to the large energy spread of ions, the laser-accelerated HIBP can measure the two-dimensional (2D) electron density profile of tokamak plasma. In a preliminary simulation, a 2D density profile was reconstructed with a spatial resolution of about 2 cm, and with the error below 15% in the core region. Diagnostics of 2D density fluctuation is also discussed.

Evaluation of Plume Divergence and Facility Effects on Far-Field Faraday Probe Current Density Profiles

DTIC Science & Technology

2009-09-01

elevated background pressure, compared nude Faraday probe designs, and evaluated design modifications to minimize uncertainty due to charge exchange...evaluated Faraday probe design and facility background pressure on collected ion current. A comparison of two nude Faraday probe designs concluded...140.5 Plasma potential in the region surrounding a nude Faraday probe has been measured to study the possibility of probe bias voltage acting as a

An adaptive technique for estimating the atmospheric density profile during the AE mission

NASA Technical Reports Server (NTRS)

Argentiero, P.

1973-01-01

A technique is presented for processing accelerometer data obtained during the AE missions in order to estimate the atmospheric density profile. A minimum variance, adaptive filter is utilized. The trajectory of the probe and probe parameters are in a consider mode where their estimates are unimproved but their associated uncertainties are permitted an impact on filter behavior. Simulations indicate that the technique is effective in estimating a density profile to within a few percentage points.

Active radiometer for self-calibrated furnace temperature measurements

DOEpatents

Woskov, Paul P.; Cohn, Daniel R.; Titus, Charles H.; Wittle, J. Kenneth; Surma, Jeffrey E.

1996-01-01

Radiometer with a probe beam superimposed on its field-of-view for furnace temperature measurements. The radiometer includes a heterodyne millimeter/submillimeter-wave receiver including a millimeter/submillimeter-wave source for probing. The receiver is adapted to receive radiation from a surface whose temperature is to be measured. The radiation includes a surface emission portion and a surface reflection portion which includes the probe beam energy reflected from the surface. The surface emission portion is related to the surface temperature and the surface reflection portion is related to the emissivity of the surface. The simultaneous measurement of surface emissivity serves as a real time calibration of the temperature measurement.

Atomic Layer Deposition Alumina-Passivated Silicon Nanowires: Probing the Transition from Electrochemical Double-Layer Capacitor to Electrolytic Capacitor.

PubMed

Gaboriau, Dorian; Boniface, Maxime; Valero, Anthony; Aldakov, Dmitry; Brousse, Thierry; Gentile, Pascal; Sadki, Said

2017-04-19

Silicon nanowires were coated by a 1-5 nm thin alumina layer by atomic layer deposition (ALD) in order to replace poorly reproducible and unstable native silicon oxide by a highly conformal passivating alumina layer. The surface coating enabled probing the behavior of symmetric devices using such electrodes in the EMI-TFSI electrolyte, allowing us to attain a large cell voltage up to 6 V in ionic liquid, together with very high cyclability with less than 4% capacitance fade after 10 6 charge/discharge cycles. These results yielded fruitful insights into the transition between an electrochemical double-layer capacitor behavior and an electrolytic capacitor behavior. Ultimately, thin ALD dielectric coatings can be used to obtain hybrid devices exhibiting large cell voltage and excellent cycle life of dielectric capacitors, while retaining energy and power densities close to the ones displayed by supercapacitors.

Electron temperature and heat load measurements in the COMPASS divertor using the new system of probes

NASA Astrophysics Data System (ADS)

Adamek, J.; Seidl, J.; Horacek, J.; Komm, M.; Eich, T.; Panek, R.; Cavalier, J.; Devitre, A.; Peterka, M.; Vondracek, P.; Stöckel, J.; Sestak, D.; Grover, O.; Bilkova, P.; Böhm, P.; Varju, J.; Havranek, A.; Weinzettl, V.; Lovell, J.; Dimitrova, M.; Mitosinkova, K.; Dejarnac, R.; Hron, M.; The COMPASS Team; The EUROfusion MST1 Team

2017-11-01

A new system of probes was recently installed in the divertor of tokamak COMPASS in order to investigate the ELM energy density with high spatial and temporal resolution. The new system consists of two arrays of rooftop-shaped Langmuir probes (LPs) used to measure the floating potential or the ion saturation current density and one array of Ball-pen probes (BPPs) used to measure the plasma potential with a spatial resolution of ~3.5 mm. The combination of floating BPPs and LPs yields the electron temperature with microsecond temporal resolution. We report on the design of the new divertor probe arrays and first results of electron temperature profile measurements in ELMy H-mode and L-mode. We also present comparative measurements of the parallel heat flux using the new probe arrays and fast infrared termography (IR) data during L-mode with excellent agreement between both techniques using a heat power transmission coefficient γ  =  7. The ELM energy density {{\\varepsilon }\\parallel } was measured during a set of NBI assisted ELMy H-mode discharges. The peak values of {{\\varepsilon }\\parallel } were compared with those predicted by model and with experimental data from JET, AUG and MAST with a good agreement.

Thermal probe design for Europa sample acquisition

NASA Astrophysics Data System (ADS)

Horne, Mera F.

2018-01-01

The planned lander missions to the surface of Europa will access samples from the subsurface of the ice in a search for signs of life. A small thermal drill (probe) is proposed to meet the sample requirement of the Science Definition Team's (SDT) report for the Europa mission. The probe is 2 cm in diameter and 16 cm in length and is designed to access the subsurface to 10 cm deep and to collect five ice samples of 7 cm3 each, approximately. The energy required to penetrate the top 10 cm of ice in a vacuum is 26 Wh, approximately, and to melt 7 cm3 of ice is 1.2 Wh, approximately. The requirement stated in the SDT report of collecting samples from five different sites can be accommodated with repeated use of the same thermal drill. For smaller sample sizes, a smaller probe of 1.0 cm in diameter with the same length of 16 cm could be utilized that would require approximately 6.4 Wh to penetrate the top 10 cm of ice, and 0.02 Wh to collect 0.1 g of sample. The thermal drill has the advantage of simplicity of design and operations and the ability to penetrate ice over a range of densities and hardness while maintaining sample integrity.

16 CFR § 1505.51 - Hot surfaces.

Code of Federal Regulations, 2013 CFR

2013-01-01

... CHILDREN Policies and Interpretations § 1505.51 Hot surfaces. (a) Test probe. Section 1505.6(g)(2) defines... inches long. To test for accessibility using this test probe, it shall be inserted no more than 3 inches into any opening in the toy. Unless the probe contacts a surface within 3 inches of the plane of the...

Development of Simple Designs of Multitip Probe Diagnostic Systems for RF Plasma Characterization

PubMed Central

Naz, M. Y.; Shukrullah, S.; Ghaffar, A.; Rehman, N. U.

2014-01-01

Multitip probes are very useful diagnostics for analyzing and controlling the physical phenomena occurring in low temperature discharge plasmas. However, DC biased probes often fail to perform well in processing plasmas. The objective of the work was to deduce simple designs of DC biased multitip probes for parametric study of radio frequency plasmas. For this purpose, symmetric double probe, asymmetric double probe, and symmetric triple probe diagnostic systems and their driving circuits were designed and tested in an inductively coupled plasma (ICP) generated by a 13.56 MHz radio frequency (RF) source. Using I-V characteristics of these probes, electron temperature, electron number density, and ion saturation current was measured as a function of input power and filling gas pressure. An increasing trend was noticed in electron temperature and electron number density for increasing input RF power whilst a decreasing trend was evident in these parameters when measured against filling gas pressure. In addition, the electron energy probability function (EEPF) was also studied by using an asymmetric double probe. These studies confirmed the non-Maxwellian nature of the EEPF and the presence of two groups of the energetic electrons at low filling gas pressures. PMID:24683326

Optic probe for semiconductor characterization

DOEpatents

Sopori, Bhushan L [Denver, CO; Hambarian, Artak [Yerevan, AM

2008-09-02

Described herein is an optical probe (120) for use in characterizing surface defects in wafers, such as semiconductor wafers. The optical probe (120) detects laser light reflected from the surface (124) of the wafer (106) within various ranges of angles. Characteristics of defects in the surface (124) of the wafer (106) are determined based on the amount of reflected laser light detected in each of the ranges of angles. Additionally, a wafer characterization system (100) is described that includes the described optical probe (120).

Acid–base catalysis over perovskites: a review

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

Polo-Garzon, Felipe; Wu, Zili

We present that perovskite catalysts have been extensively studied for reduction–oxidation (redox) reactions; however, their acid–base catalytic properties are still under-explored. This review collects work aiming to study the acid–base catalytic properties of perovskites. Reports regarding combined acid–base/redox catalysis over perovskites lie beyond the scope of the present review. For the characterization of acid–base properties, researchers have studied the interaction of probe molecules with perovskite surfaces by means of multiple techniques that provide information about the density, strength and type of adsorption sites. The top-surface composition of perovskites, which relates to the abundance of the acid–base sites, has been studiedmore » by means of low energy ion scattering (LEIS), and, the less surface sensitive, conventional X-ray photoelectron spectroscopy (XPS). Probe reactions, with the conversion of 2-propanol as the common choice, have also been employed for characterizing the acid–base catalytic properties of perovskites. The complex nature of perovskite surfaces, which explains the still absent fundamental relations between the structure of the catalyst and reaction rates/selectivity, encounters a great challenge due to the surface reconstruction of these materials. In this review, we devote a special section to highlight recent publications that report the impact of surface reconstruction and particle shape on acid–base catalysis over perovskites. In addition, we review promising catalytic performances of perovskite catalysts for other reactions of interest. Challenges in acid–base catalysis over perovskites focus on the development of time-resolved monolayer-sensitive characterization of surfaces under operando conditions and the discernment of combined acid–base/redox reaction mechanisms. Finally, opportunities lay on tuning the acid–base characteristics of perovskites with computation-based catalytic descriptors to achieve desired selectivities and enhanced rates.« less

Acid–base catalysis over perovskites: a review

DOE PAGES

Polo-Garzon, Felipe; Wu, Zili

2018-01-15

We present that perovskite catalysts have been extensively studied for reduction–oxidation (redox) reactions; however, their acid–base catalytic properties are still under-explored. This review collects work aiming to study the acid–base catalytic properties of perovskites. Reports regarding combined acid–base/redox catalysis over perovskites lie beyond the scope of the present review. For the characterization of acid–base properties, researchers have studied the interaction of probe molecules with perovskite surfaces by means of multiple techniques that provide information about the density, strength and type of adsorption sites. The top-surface composition of perovskites, which relates to the abundance of the acid–base sites, has been studiedmore » by means of low energy ion scattering (LEIS), and, the less surface sensitive, conventional X-ray photoelectron spectroscopy (XPS). Probe reactions, with the conversion of 2-propanol as the common choice, have also been employed for characterizing the acid–base catalytic properties of perovskites. The complex nature of perovskite surfaces, which explains the still absent fundamental relations between the structure of the catalyst and reaction rates/selectivity, encounters a great challenge due to the surface reconstruction of these materials. In this review, we devote a special section to highlight recent publications that report the impact of surface reconstruction and particle shape on acid–base catalysis over perovskites. In addition, we review promising catalytic performances of perovskite catalysts for other reactions of interest. Challenges in acid–base catalysis over perovskites focus on the development of time-resolved monolayer-sensitive characterization of surfaces under operando conditions and the discernment of combined acid–base/redox reaction mechanisms. Finally, opportunities lay on tuning the acid–base characteristics of perovskites with computation-based catalytic descriptors to achieve desired selectivities and enhanced rates.« less

Reconnection-Driven Solar Polar Jets to be Encountered by Solar Probe Plus: Simulated In Situ Measurements and Data Analysis

NASA Astrophysics Data System (ADS)

Uritsky, V. M.; Roberts, M. A.; Karpen, J. T.; DeVore, C. R.

2015-12-01

Solar polar jets are observed to originate in regions within the open field of solar coronal holes. These so called "anemone" regions are associated with an embedded dipole topology, consisting of a fan-separatrix and a spine line emanating from a null point occurring at the top of the dome shaped fan surface (Antiochos 1996). In this study, we analyze simulations using the Adaptively Refined MHD Solver (ARMS) that take into account gravity, solar wind, and spherical geometry to generate polar jets by reconnection between a twisted embedded bipole and the surrounding open field (Karpen et al. 2015). These simulations confirm and extend previous Cartesian studies of polar jets based on this mechanism (Pariat et al. 2009, 2010, 2015), as well as extending the analyses from our previous work (Roberts et al. 2014,2015) out to radial distances that will be sampled by Solar Probe Plus. Focusing on the plasma density, velocity, magnetic field, and current density, we interpolate the adaptively gridded simulation data onto a regular grid, and analyze the signatures that the jet produces as it propagates outward from the solar surface into the inner heliosphere. We also conduct simulated spacecraft fly-throughs of the jet in several different velocity regimes, illustrating the signatures that Solar Probe Plus may encounter in situ as the jet propagates into the heliosphere. The trans-Alfvénic nature of the jet front is confirmed by temporally differencing the plasma mass density and comparing the result with the local Alfvén speed. Our analysis confirms the presence of a reconnection driven magnetic turbulence in the simulated plasma jet, finding spatial correlations of magnetic fluctuations inside the jet to be in agreement with the scaling model of MHD turbulence. The turbulence cascade is supported by multiscale current sheets combined with filamentary structures representing fluid vorticies. The spatial orientation of these current sheets, combined with the anisotropy of the magnetic fluctuations, is indicative of torsional Alfvén wave packets, consistent with the helical geometry of the jet. This research was supported by NASA grant NNG11PL10A 670.036 to CUA/IACS (M.A.R. and V.M.U.) and NASA's Living With a Star Targeted Research and Technology (J.T.K. and C.R.D.) program.

Applications of functional polymer brushes for nanoparticle uptake and prevention of protein adsorption

NASA Astrophysics Data System (ADS)

Arifuzzaman, Shafi M.

The central theme of this Ph.D. dissertation is to develop novel multifunctional polymer coatings for understanding partition of proteins and nanoparticles on polymers grafted to flat surfaces (so-called brushes). Systematic investigation of the adsorption phenomena is accomplished by utilizing surface-anchored assemblies comprising grafted polymers with variation in physical properties (i.e., length or/and grafting density) and chemical functionality. The chemical composition of the brush is tailored by either "chemical coloring" of a parent homopolymer brush with selective chemical moieties or by sequential growth of two chemically dissimilar polymer blocks. We present preparation of two types of tailor-made, surface-grafted copolymers: (1) those composed of hydrophilic and hydrophobic blocks (so-called amphiphilic polymer brushes), and (2) those comprising of anionic and cationic polymer segments (so-called polyampholyte brushes). We describe the organization of functionality in the grafted polymer brushes and the partitioning of proteins and nanoparticles using a battery of complementary analytical probes. Specifically, we address how varying the molecular weight, grafting density, and chemical composition of the brush affects adsorbtion and desorbtion of model proteins and gold nanoparticles. Our observations indicate densely-populated responsive amphiphilic polymers are very efficient in suppressing protein adsorption. In addition, we have established that the length of poly(ethylene glycol) spacers attached to a parent homopolymer brush is a key factor governing uptake of gold nanoparticles. Both grafting density and molecular weight of the coating are important in controlling the kinetics and thermodynamics of protein adsorption on surfaces. Our findings and methodologies can lead to the development of next generation environmentally friendly antifouling surfaces and will find application in medical devices, antifouling coatings and anti reflection finishes.

Surface interaction forces of cellulose nanocrystals grafted with thermoresponsive polymer brushes.

PubMed

Zoppe, Justin O; Osterberg, Monika; Venditti, Richard A; Laine, Janne; Rojas, Orlando J

2011-07-11

The colloidal stability and thermoresponsive behavior of poly(N-isopropylacrylamide) brushes grafted from cellulose nanocrystals (CNCs) of varying graft densities and molecular weights was investigated. Indication of the grafted polymer brushes was obtained after AFM imaging of CNCs adsorbed on silica. Also, aggregation of the nanoparticles carrying grafts of high degree of polymerization was observed. The responsiveness of grafted CNCs in aqueous dispersions and as an ultrathin film was evaluated by using light scattering, viscosimetry, and colloidal probe microscopy (CPM). Light transmittance measurements showed temperature-dependent aggregation originating from the different graft densities and molecular weights. The lower critical solution temperature (LCST) of grafted poly(NiPAAm) brushes was found to decrease with the ionic strength, as is the case for free poly(NiPAAm) in aqueous solution. Thermal responsive behavior of grafted CNCs in aqueous dispersions was observed by a sharp increase in dispersion viscosity as the temperature approached the LCST. CPM in liquid media for asymmetric systems consisting of ultrathin films of CNCs and a colloidal silica probe showed the distinctive effects of the grafted polymer brushes on interaction and adhesive forces. The origin of such forces was found to be mainly electrostatic and steric in the case of bare and grafted CNCs, respectively. A decrease in the onset of attractive and adhesion forces of grafted CNCs films were observed with the ionic strength of the aqueous solution. The decreased mobility of polymer brushes upon partial collapse and decreased availability of hydrogen bonding sites with higher electrolyte concentration were hypothesized as the main reasons for the less prominent polymer bridging between interacting surfaces.

A scanning probe mounted on a field-effect transistor: Characterization of ion damage in Si.

PubMed

Shin, Kumjae; Lee, Hoontaek; Sung, Min; Lee, Sang Hoon; Shin, Hyunjung; Moon, Wonkyu

2017-10-01

We have examined the capabilities of a Tip-On-Gate of Field-Effect Transistor (ToGoFET) probe for characterization of FIB-induced damage in Si surface. A ToGoFET probe is the SPM probe which the Field Effect Transistor(FET) is embedded at the end of a cantilever and a Pt tip was mounted at the gate of FET. The ToGoFET probe can detect the surface electrical properties by measuring source-drain current directly modulated by the charge on the tip. In this study, a Si specimen whose surface was processed with Ga+ ion beam was prepared. Irradiation and implantation with Ga+ ions induce highly localized modifications to the contact potential. The FET embedded on ToGoFET probe detected the surface electric field profile generated by schottky contact between the Pt tip and the sample surface. Experimentally, it was shown that significant differences of electric field due to the contact potential barrier in differently processed specimens were observed using ToGOFET probe. This result shows the potential that the local contact potential difference can be measured by simple working principle with high sensitivity. Copyright © 2017 Elsevier Ltd. All rights reserved.

Fundamentals of Nanoscale Polymer–Protein Interactions and Potential Contributions to Solid-State Nanobioarrays

PubMed Central

2015-01-01

Protein adsorption onto polymer surfaces is a very complex, ubiquitous, and integrated process, impacting essential areas of food processing and packaging, health devices, diagnostic tools, and medical products. The nature of protein–surface interactions is becoming much more complicated with continuous efforts toward miniaturization, especially for the development of highly compact protein detection and diagnostic devices. A large body of literature reports on protein adsorption from the perspective of ensemble-averaged behavior on macroscopic, chemically homogeneous, polymeric surfaces. However, protein–surface interactions governing the nanoscale size regime may not be effectively inferred from their macroscopic and microscopic characteristics. Recently, research efforts have been made to produce periodically arranged, nanoscopic protein patterns on diblock copolymer surfaces solely through self-assembly. Intriguing protein adsorption phenomena are directly probed on the individual biomolecule level for a fundamental understanding of protein adsorption on nanoscale surfaces exhibiting varying degrees of chemical heterogeneity. Insight gained from protein assembly on diblock copolymers can be effectively used to control the surface density, conformation, orientation, and biofunctionality of prebound proteins in highly miniaturized applications, now approaching the nanoscale. This feature article will highlight recent experimental and theoretical advances made on these fronts while focusing on single-biomolecule-level investigations of protein adsorption behavior combined with surface chemical heterogeneity on the length scale commensurate with a single protein. This article will also address advantages and challenges of the self-assembly-driven patterning technology used to produce protein nanoarrays and its implications for ultrahigh density, functional, and quantifiable protein detection in a highly miniaturized format. PMID:24456577

Fundamentals of nanoscale polymer-protein interactions and potential contributions to solid-state nanobioarrays.

PubMed

Hahm, Jong-in

2014-08-26

Protein adsorption onto polymer surfaces is a very complex, ubiquitous, and integrated process, impacting essential areas of food processing and packaging, health devices, diagnostic tools, and medical products. The nature of protein-surface interactions is becoming much more complicated with continuous efforts toward miniaturization, especially for the development of highly compact protein detection and diagnostic devices. A large body of literature reports on protein adsorption from the perspective of ensemble-averaged behavior on macroscopic, chemically homogeneous, polymeric surfaces. However, protein-surface interactions governing the nanoscale size regime may not be effectively inferred from their macroscopic and microscopic characteristics. Recently, research efforts have been made to produce periodically arranged, nanoscopic protein patterns on diblock copolymer surfaces solely through self-assembly. Intriguing protein adsorption phenomena are directly probed on the individual biomolecule level for a fundamental understanding of protein adsorption on nanoscale surfaces exhibiting varying degrees of chemical heterogeneity. Insight gained from protein assembly on diblock copolymers can be effectively used to control the surface density, conformation, orientation, and biofunctionality of prebound proteins in highly miniaturized applications, now approaching the nanoscale. This feature article will highlight recent experimental and theoretical advances made on these fronts while focusing on single-biomolecule-level investigations of protein adsorption behavior combined with surface chemical heterogeneity on the length scale commensurate with a single protein. This article will also address advantages and challenges of the self-assembly-driven patterning technology used to produce protein nanoarrays and its implications for ultrahigh density, functional, and quantifiable protein detection in a highly miniaturized format.

Critical evaluation of dipolar, acid-base and charge interactions I. Electron displacement within and between molecules, liquids and semiconductors.

PubMed

Rosenholm, Jarl B

2017-09-01

Specific dipolar, acid-base and charge interactions involve electron displacements. For atoms, single bonds and molecules electron displacement is characterized by electronic potential, absolute hardness, electronegativity and electron gap. In addition, dissociation, bonding, atomization, formation, ionization, affinity and lattice enthalpies are required to quantify the electron displacement in solids. Semiconductors are characterized by valence and conduction band energies, electron gaps and average Fermi energies which in turn determine Galvani potentials of the bulk, space charge layer and surface states. Electron displacement due to interaction between (probe) molecules, liquids and solids are characterized by parameters such as Hamaker constant, solubility parameter, exchange energy density, surface tension, work of adhesion and immersion. They are determined from permittivity, refractive index, enthalpy of vaporization, molar volume, surface pressure and contact angle. Moreover, acidic and basic probes may form adducts which are adsorbed on target substrates in order to establish an indirect measure of polarity, acidity, basicity or hydrogen bonding. Acidic acceptor numbers (AN), basic donor numbers (DN), acidic and basic "electrostatic" (E) and "covalent" (C) parameters determined by enthalpy of adduct formation are considered as general acid-base scales. However, the formal grounds for assignments as dispersive, Lifshitz-van der Waals, polar, acid, base and hydrogen bond interactions are inconsistent. Although correlations are found no of the parameters are mutually fully compatible and moreover the enthalpies of acid-base interaction do not correspond to free energies. In this review the foundations of different acid-base parameters relating to electron displacement within and between (probe) molecules, liquids and (semiconducting) solids are thoroughly investigated and their mutual relationships are evaluated. Copyright © 2017 Elsevier B.V. All rights reserved.

New Results on Titan’s Atmosphere and Surface from Huygens Probe Measurements

NASA Astrophysics Data System (ADS)

Lorenz, Ralph

2013-10-01

The global Titan perspective afforded by ongoing Cassini observations, and prospects for future in-situ exploration, have prompted a re-examination of Huygens data, yielding new results in several areas. Gravity waves have been detected (Lorenz, Ferri and Young, submitted) in the HASI descent temperature data, with 2K amplitude. These waves are seen above about 60km, and analysis suggests they may therefore be controlled by interaction of upward-propagating waves with the zonal wind field. A curious cessation of detection of sound pulses by a Surface Science Package ultrasound instrument about 15 minutes after the probe landed appears to be best explained (Lorenz et al., submitted) by an accumulation of polyatomic vapors such as ethane, sweated out of the ground by the warm probe. Such gases have high acoustic attenuation, and were independently measured by the probe GCMS. A new integrated timeline product, which arranges second-by-second measurements from several Huygens sensors on a convenient, common tabulation, has been archived on the PDS Atmospheres node. Also archived is an independent retrieval of Doppler information from VLBI receivers that has a higher time resolution than the DWE archive product, and an expanded event summary product that documents when key observations, system events and anomalies occurred. Finally, a troubling discrepancy exists between radio occultation and infrared soundings from Cassini, and the lower stratospheric temperature retrieved from the HASI accelerometer record. Two factors may contribute to this discrepancy - the assumed probe mass history, and the assumed zonal wind profile. The sensitivity of the recovered temperature profile to these factors is examined : in particular it is noted that the speed relative to the atmosphere in the late part of entry, when the hypersonic entry speed has been largely bled away by drag, is particularly sensitive to assumed winds, and it is in this altitude region where the recovered density (or temperature) profile discrepancy may be highest.

Liquid Microjunction Surface Sampling Probe Fluid Dynamics: Computational and Experimental Analysis of Coaxial Intercapillary Positioning Effects on Sample Manipulation

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

ElNaggar, Mariam S; Barbier, Charlotte N; Van Berkel, Gary J

A coaxial geometry liquid microjunction surface sampling probe (LMJ-SSP) enables direct extraction of analytes from surfaces for subsequent analysis by techniques like mass spectrometry. Solution dynamics at the probe-to-sample surface interface in the LMJ-SSP has been suspected to influence sampling efficiency and dispersion but has not been rigorously investigated. The effect on flow dynamics and analyte transport to the mass spectrometer caused by coaxial retraction of the inner and outer capillaries from each other and the surface during sampling with a LMJ-SSP was investigated using computational fluid dynamics and experimentation. A transparent LMJ-SSP was constructed to provide the means formore » visual observation of the dynamics of the surface sampling process. Visual observation, computational fluid dynamics (CFD) analysis, and experimental results revealed that inner capillary axial retraction from the flush position relative to the outer capillary transitioned the probe from a continuous sampling and injection mode through an intermediate regime to sample plug formationmode caused by eddy currents at the sampling end of the probe. The potential for analytical implementation of these newly discovered probe operational modes is discussed.« less

Effect of nonparallel placement of in-circle bipolar radiofrequency ablation probes on volume of tissue ablated with heat sink.

PubMed

Pillai, Krishna; Al-Alem, Ihssan; Akhter, Javed; Chua, Terence C; Shehata, Mena; Morris, David L

2015-06-01

Percutaneous bipolar radiofrequency ablation (RFA) is a minimally invasive technique for treating liver tumors. It is not always possible to insert the bipolar probes parallel to each other on either side of tumor, since it restricts maneuverability away from vital structures or ablate certain tumor shape. Therefore, we investigated how nonparallel placement of probes affected ablation. Bipolar RFA in parallel and in divergent positions were submerged in tissue model (800 mL egg white) at 37°C and ablated. Temperature probes, T1 and T2 were placed 8.00 mm below the tip of the probes, T3 in between the probe coil elements and T4 and T5 at water inlet and outlet, respectively. Both models with heat sink (+HS) and without (-HS) were investigated. The mean ablated tissue volume, mass, density and height increased linearly with unit angle increase for -HS model. With +HS, a smaller increase in mean volume and mass, a slightly greater increase in mean density but a reduction in height of tissue was seen. The mean ablation time and duration of maximum temperature with +HS was slightly larger, compared with -HS, while -HS ablated at a slightly higher temperature. The heat sink present was minimal for probes in parallel position compared to nonparallel positions. Divergence from parallel insertion of bipolar RFA probes increased the mean volume, mass, and density of tissue ablated. However, the presence of large heat sinks may limit the application of this technique, when tumors border on larger vessels. © The Author(s) 2014.

Active radiometer for self-calibrated furnace temperature measurements

DOEpatents

Woskov, P.P.; Cohn, D.R.; Titus, C.H.; Wittle, J.K.; Surma, J.E.

1996-11-12

A radiometer is described with a probe beam superimposed on its field-of-view for furnace temperature measurements. The radiometer includes a heterodyne millimeter/submillimeter-wave receiver including a millimeter/submillimeter-wave source for probing. The receiver is adapted to receive radiation from a surface whose temperature is to be measured. The radiation includes a surface emission portion and a surface reflection portion which includes the probe beam energy reflected from the surface. The surface emission portion is related to the surface temperature and the surface reflection portion is related to the emissivity of the surface. The simultaneous measurement of surface emissivity serves as a real time calibration of the temperature measurement. 5 figs.

Planar Multipol-Resonance-Probe: A Spectral Kinetic Approach

NASA Astrophysics Data System (ADS)

Friedrichs, Michael; Gong, Junbo; Brinkmann, Ralf Peter; Oberrath, Jens; Wilczek, Sebastian

2016-09-01

Measuring plasma parameters, e.g. electron density and electron temperature, is an important procedure to verify the stability and behavior of a plasma process. For this purpose the multipole resonance probe (MRP) represents a satisfying solution to measure the electron density. However the influence of the probe on the plasma through its physical presence makes it unattractive for some processes in industrial application. A solution to combine the benefits of the spherical MRP with the ability to integrate the probe into the plasma reactor is introduced by the planar model of the MRP (pMRP). Introducing the spectral kinetic formalism leads to a reduced simulation-circle compared to particle-in-cell simulations. The model of the pMRP is implemented and first simulation results are presented.

Laboratory measurements of ice tensile strength dependence on density and concentration of silicate and polymer impurities at low temperatures

NASA Astrophysics Data System (ADS)

Litwin, K. L.; Beyeler, J. D.; Polito, P. J.; Zygielbaum, B. R.; Sklar, L. S.; Collins, G. C.

2009-12-01

The tensile strength of ice bedrock on Titan should strongly influence the effectiveness of the erosional processes responsible for carving the extensive fluvial drainage networks and other surface features visible in images returned by the Cassini and Huygens probes. Recent measurements of the effect of temperature on the tensile strength of low-porosity, polycrystalline ice, without impurities, suggest that ice bedrock at the Titan surface temperature of 93 K may be as much as five times stronger than ice at terrestrial surface temperatures. However, ice bedrock on Titan and other outer solar system bodies may have significant porosity, and impurities such silicates or polymers are possible in such ices. In this laboratory investigation we are exploring the dependence of tensile strength on the density and concentration of impurities, for polycrystalline ice across a wide range of temperatures. We use the Brazilian tensile splitting test to measure strength, and control temperature with dry ice and liquid nitrogen. The 50 mm diameter ice cores are made from a log-normally distributed seed crystal mixture with a median size of 1.4 mm. To control ice density and porosity we vary the packing density of the seed grains in core molds and vary the degree of saturation of the matrix with added near-freezing distilled water. We also vary ice density by blending in a similarly-sized mixture of angular fragments of two types of impurities, a fine-grained volcanic rock and a polyethylene polymer. Because both types of impurities have greater tensile strength than ice at Earth surface temperatures, we expect higher concentrations of impurities to correlate with increased strength for ice-rock and ice-polymer mixtures. However, at the ultra-cold temperatures of the outer planets, we expect significant divergence in the temperature dependence of ice tensile strength for the various mixtures and resulting densities. These measurements will help constrain the range of possible ice tensile strengths that might occur on Titan and other solar system bodies.

Chemically stable Au nanorods as probes for sensitive surface enhanced scattering (SERS) analysis of blue BIC ballpoint pens

NASA Astrophysics Data System (ADS)

Alyami, Abeer; Saviello, Daniela; McAuliffe, Micheal A. P.; Cucciniello, Raffaele; Mirabile, Antonio; Proto, Antonio; Lewis, Liam; Iacopino, Daniela

2017-08-01

Au nanorods were used as an alternative to commonly used Ag nanoparticles as Surface Enhanced Raman Scattering (SERS) probes for identification of dye composition of blue BIC ballpoint pens. When used in combination with Thin Layer Chromatography (TLC), Au nanorod colloids allowed identification of the major dye components of the BIC pen ink, otherwise not identifiable by normal Raman spectroscopy. Thanks to their enhanced chemical stability compared to Ag colloids, Au nanorods provided stable and reproducible SERS signals and allowed easy identification of phthalocyanine and triarylene dyes in the pen ink mixture. These findings were supported by FTIR and MALDI analyses, also performed on the pen ink. Furthermore, the self-assembly of Au nanorods into large area ordered superstructures allowed identification of BIC pen traces. SERS spectra of good intensity and high reproducibility were obtained using Au nanorod vertical arrays, due to the high density of hot spots and morphological reproducibility of these superstructures. These results open the way to the employment of SERS for fast screening analysis and for quantitative analysis of pens and faded pens which are relevant for the fields of forensic and art conservation sciences.

Nanoscale electrical and structural modification induced by rapid thermal oxidation of AlGaN/GaN heterostructures.

PubMed

Greco, Giuseppe; Fiorenza, Patrick; Giannazzo, Filippo; Alberti, Alessandra; Roccaforte, Fabrizio

2014-01-17

In this paper, the structural and electrical modifications induced, in the nanoscale, by a rapid thermal oxidation process on AlGaN/GaN heterostructures, are investigated. A local rapid oxidation (900 ° C in O2, 10 min) localized under the anode region of an AlGaN/GaN diode enabled a reduction of the leakage current with respect to a standard Schottky contact. The insulating properties of the near-surface oxidized layer were probed by a nanoscale electrical characterization using scanning probe microscopy techniques. The structural characterization indicated the formation of a thin uniform oxide layer on the surface, with preferential oxidation paths along V-shaped defects penetrating through the AlGaN/GaN interface. The oxidation process resulted in an expansion of the lattice parameters due to the incorporation of oxygen atoms, accompanied by an increase of the crystal mosaicity. As a consequence, a decrease of the sheet carrier density of the two-dimensional electron gas and a positive shift of the threshold voltage are observed. The results provide useful insights for a possible future integration of rapid oxidation processes during GaN device fabrication.

Analysis of a tungsten sputtering experiment in DIII-D and code/data validation of high redeposition/reduced erosion

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

Wampler, William R.; Brooks, J. N.; Elder, J. D.

2015-03-29

We analyze a DIII-D tokamak experiment where two tungsten spots on the removable DiMES divertor probe were exposed to 12 s of attached plasma conditions, with moderate strike point temperature and density (~20 eV, ~4.5 × 10 19 m –3), and 3% carbon impurity content. Both very small (1 mm diameter) and small (1 cm diameter) deposited samples were used for assessing gross and net tungsten sputtering erosion. The analysis uses a 3-D erosion/redeposition code package (REDEP/WBC), with input from a diagnostic-calibrated near-surface plasma code (OEDGE), and with focus on charge state resolved impinging carbon ion flux and energy. Themore » tungsten surfaces are primarily sputtered by the carbon, in charge states +1 to +4. We predict high redeposition (~75%) of sputtered tungsten on the 1 cm spot—with consequent reduced net erosion—and this agrees well with post-exposure DiMES probe RBS analysis data. As a result, this study and recent related work is encouraging for erosion lifetime and non-contamination performance of tokamak reactor high-Z plasma facing components.« less

Insights into electrode/electrolyte interfacial processes and the effect of nanostructured cobalt oxides loading on graphene-based hybrids by scanning electrochemical microscopy

NASA Astrophysics Data System (ADS)

Gupta, Sanju; Carrizosa, Sara B.

2016-12-01

Nanostructured cobalt oxide polymorphs (CoO and Co3O4) deposited via electrodeposition allowed optimal loading on supercapacitive graphene nanosheets producing a set of graphene-based hybrids namely, CoO/GO, CoO/ErGO, Co3O4/GO, Co3O4/rGO, and Co3O4/ErGO, as pseudocapacitive electrochemical electrodes. We gained fundamental insights into the complex physicochemical interfacial processes at electrode surfaces and electrode/electrolyte (or solid/liquid) interfaces by scanning electrochemical microscopy operating in the feedback probe approach and imaging modes while monitoring and mapping the redox probe (re)activity behavior. We determined the various experimental descriptors including diffusion coefficient, electron transfer rate, and electroactive site distribution on electrodes. We emphasize the interplay of (1) heterogeneous basal and edge plane active sites, (2) graphene surface functional moieties (conducting/semiconducting), and (3) crystalline spinel cobalt oxides (semiconducting/insulating) coated graphene, reinforcing the available electron density of states in the vicinity of the Fermi level contributing to higher electroactivity, faster interfacial diffusion, and shorter distances for electron transfer, facilitated through molecular and chemical bridges obtained by electrodeposition as compared with the physical deposition.

Simultaneous use of camera and probe diagnostics to unambiguously identify and study the dynamics of multiple underlying instabilities during the route to plasma turbulence.

PubMed

Thakur, S C; Brandt, C; Light, A; Cui, L; Gosselin, J J; Tynan, G R

2014-11-01

We use multiple-tip Langmuir probes and fast imaging to unambiguously identify and study the dynamics of underlying instabilities during the controlled route to fully-developed plasma turbulence in a linear magnetized helicon plasma device. Langmuir probes measure radial profiles of electron temperature, plasma density and potential; from which we compute linear growth rates of instabilities, cross-phase between density and potential fluctuations, Reynold's stress, particle flux, vorticity, time-delay estimated velocity, etc. Fast imaging complements the 1D probe measurements by providing temporally and spatially resolved 2D details of plasma structures associated with the instabilities. We find that three radially separated plasma instabilities exist simultaneously. Density gradient driven resistive drift waves propagating in the electron diamagnetic drift direction separate the plasma into an edge region dominated by strong, velocity shear driven Kelvin-Helmholtz instabilities and a central core region which shows coherent Rayleigh-Taylor modes propagating in the ion diamagnetic drift direction. The simultaneous, complementary use of both probes and camera was crucial to identify the instabilities and understand the details of the very rich plasma dynamics.

Experimental testing of four correction algorithms for the forward scattering spectrometer probe

NASA Technical Reports Server (NTRS)

Hovenac, Edward A.; Oldenburg, John R.; Lock, James A.

1992-01-01

Three number density correction algorithms and one size distribution correction algorithm for the Forward Scattering Spectrometer Probe (FSSP) were compared with data taken by the Phase Doppler Particle Analyzer (PDPA) and an optical number density measuring instrument (NDMI). Of the three number density correction algorithms, the one that compared best to the PDPA and NDMI data was the algorithm developed by Baumgardner, Strapp, and Dye (1985). The algorithm that corrects sizing errors in the FSSP that was developed by Lock and Hovenac (1989) was shown to be within 25 percent of the Phase Doppler measurements at number densities as high as 3000/cc.

Validation of a new device to quantify groundwater-surface water exchange

NASA Astrophysics Data System (ADS)

Cremeans, Mackenzie M.; Devlin, J. F.

2017-11-01

Distributions of flow across the groundwater-surface water interface should be expected to be as complex as the geologic deposits associated with stream or lake beds and their underlying aquifers. In these environments, the conventional Darcy-based method of characterizing flow systems (near streams) has significant limitations, including reliance on parameters with high uncertainties (e.g., hydraulic conductivity), the common use of drilled wells in the case of streambank investigations, and potentially lengthy measurement times for aquifer characterization and water level measurements. Less logistically demanding tools for quantifying exchanges across streambeds have been developed and include drive-point mini-piezometers, seepage meters, and temperature profiling tools. This project adds to that toolbox by introducing the Streambed Point Velocity Probe (SBPVP), a reusable tool designed to quantify groundwater-surface water interactions (GWSWI) at the interface with high density sampling, which can effectively, rapidly, and accurately complement conventional methods. The SBPVP is a direct push device that measures in situ water velocities at the GWSWI with a small-scale tracer test on the probe surface. Tracer tests do not rely on hydraulic conductivity or gradient information, nor do they require long equilibration times. Laboratory testing indicated that the SBPVP has an average accuracy of ± 3% and an average precision of ± 2%. Preliminary field testing, conducted in the Grindsted Å in Jutland, Denmark, yielded promising agreement between groundwater fluxes determined by conventional methods and those estimated from the SBPVP tests executed at similar scales. These results suggest the SBPVP is a viable tool to quantify groundwater-surface water interactions in high definition in sandy streambeds.

Validation of Ionospheric Measurements from the International Space Station (ISS)

NASA Technical Reports Server (NTRS)

Coffey, Victoria; Minow, Joseph; Wright, Kenneth

2009-01-01

The International Space Station orbit provides an ideal platform for in-situ studies of space weather effects on the mid and low-latitude F-2 region ionosphere. The Floating Potential Measurement Unit (FPMU) operating on the ISS since Aug 2006, is a suite of plasma instruments: a Floating Potential Probe (FPP), a Plasma Impedance Probe (PIP), a Wide-sweep Langmuir Probe (WLP), and a Narrow-Sweep Langmuir Probe. This instrument package provides a new opportunity for collaborative multi-instrument studies of the F-region ionosphere during both quiet and disturbed periods. This presentation first describes the operational parameters for each of the FPMU probes and shows examples of an intra-instrument validation. We then show comparisons with the plasma density and temperature measurements derived from the TIMED GUVI ultraviolet imager, the Millstone Hill ground based incoherent scatter radar, and DIAS digisondes, Finally we show one of several observations of night-time equatorial density holes demonstrating the capabilities of the probes for monitoring mid and low latitude plasma processes.

In-situ Observations of the Ionospheric F2-Region from the International Space Station

NASA Technical Reports Server (NTRS)

Coffey, Victoria N.; Wright, Kenneth H.; Minow, Joseph I.; Chandler, Michael O.; Parker, Linda N.

2008-01-01

The International Space Station orbit provides an ideal platform for in-situ studies of space weather effects on the mid and low latitude F-2 region ionosphere. The Floating Potential Measurement Unit (FPMU) operating on the ISS since Aug 2006, is a suite of plasma instruments: a Floating Potential Probe (FPP), a Plasma Impedance Probe (PIP), a Wide-sweep Langmuir Probe (WLP), and a Narrow-sweep Langmuir Probe (NLP). This instrument package provides a new opportunity for collaborative multi-instrument studies of the F-region ionosphere during both quiet and disturbed periods. This presentation first describes the operational parameters for each of the FPMU probes and shows examples of an intra-instrument validation. We then show comparisons with the plasma density and temperature measurements derived from the TIMED GUVI ultraviolet imager, the Millstone Hill ground based incoherent scatter radar, and DIAS digisondes, Finally we show one of several observations of night-time equatorial density holes demonstrating the capabilities of the probes for monitoring mid and low latitude plasma processes.

Investigating the topological structure of quenched lattice QCD with overlap fermions using a multi-probing approximation

NASA Astrophysics Data System (ADS)

Zou, You-Hao; Zhang, Jian-Bo; Xiong, Guang-Yi; Chen, Ying; Liu, Chuan; Liu, Yu-Bin; Ma, Jian-Ping

2017-10-01

The topological charge density and topological susceptibility are determined by a multi-probing approximation using overlap fermions in quenched SU(3) gauge theory. Then we investigate the topological structure of the quenched QCD vacuum, and compare it with results from the all-scale topological density. The results are consistent. Random permuted topological charge density is used to check whether these structures represent underlying ordered properties. The pseudoscalar glueball mass is extracted from the two-point correlation function of the topological charge density. We study 3 ensembles of different lattice spacing a with the same lattice volume 163×32. The results are compatible with the results of all-scale topological charge density, and the topological structures revealed by multi-probing are much closer to all-scale topological charge density than those from eigenmode expansion. Supported by National Natural Science Foundation of China (NSFC) (11335001, 11275169, 11075167), It is also supported in part by the DFG and the NSFC (11261130311) through funds provided to the Sino-German CRC 110 "Symmetries and the Emergence of Structure in QCD". This work was also funded in part by National Basic Research Program of China (973 Program) (2015CB856700)

Guided self-assembly of lateral InAs/GaAs quantum-dot molecules for single molecule spectroscopy

PubMed Central

Wang, L; Kiravittaya, S; Songmuang, R; Schmidt, OG; Krause, B; Metzger, TH

2006-01-01

We report on the growth and characterization of lateral InAs/GaAs (001) quantum-dot molecules (QDMs) suitable for single QDM optical spectroscopy. The QDMs, forming by depositing InAs on GaAs surfaces with self-assembled nanoholes, are aligned along the [] direction. The relative number of isolated single quantum dots (QDs) is substantially reduced by performing the growth on GaAs surfaces containing stepped mounds. Surface morphology and X-ray measurements suggest that the strain produced by InGaAs-filled nanoholes superimposed to the strain relaxation at the step edges are responsible for the improved QDM properties. QDMs are Ga-richer compared to single QDs, consistent with strain- enhanced intermixing. The high optical quality of single QDMs is probed by micro-photoluminescence spectroscopy in samples with QDM densities lower than 108 cm−2.

Direct observation of the oxygenated species during oxygen reduction on a platinum fuel cell cathode

NASA Astrophysics Data System (ADS)

Casalongue, Hernan Sanchez; Kaya, Sarp; Viswanathan, Venkatasubramanian; Miller, Daniel J.; Friebel, Daniel; Hansen, Heine A.; Nørskov, Jens K.; Nilsson, Anders; Ogasawara, Hirohito

2013-12-01

The performance of polymer electrolyte membrane fuel cells is limited by the reduction at the cathode of various oxygenated intermediates in the four-electron pathway of the oxygen reduction reaction. Here we use ambient pressure X-ray photoelectron spectroscopy, and directly probe the correlation between the adsorbed species on the surface and the electrochemical potential. We demonstrate that, during the oxygen reduction reaction, hydroxyl intermediates on the cathode surface occur in several configurations with significantly different structures and reactivities. In particular, we find that near the open-circuit potential, non-hydrated hydroxyl is the dominant surface species. On the basis of density functional theory calculations, we show that the removal of hydration enhances the reactivity of oxygen species. Tuning the hydration of hydroxyl near the triple phase boundary will be crucial for designing more active fuel cell cathodes.

Crystallographic Fragment Based Drug Discovery: Use of a Brominated Fragment Library Targeting HIV Protease

PubMed Central

Tiefenbrunn, Theresa; Forli, Stefano; Happer, Meaghan; Gonzalez, Ana; Tsai, Yingssu; Soltis, Michael; Elder, John H.; Olson, Arthur J.; Stout, C. David

2013-01-01

A library of 68 brominated fragments was screened against a new crystal form of inhibited HIV-1 protease in order to probe surface sites in soaking experiments. Often fragments are weak binders with partial occupancy, resulting in weak, difficult-to-fit electron density. The use of a brominated fragment library addresses this challenge, as bromine can be located unequivocally via anomalous scattering. Data collection was carried out in an automated fashion using AutoDrug at SSRL. Novel hits were identified in the known surface sites: 3-bromo-2,6-dimethoxybenzoic acid (Br6) in the flap site, and 1-bromo-2-naphthoic acid (Br27) in the exosite, expanding the chemistry of known fragments for development of higher affinity potential allosteric inhibitors. At the same time, mapping the binding sites of a number of weaker binding Br-fragments provides further insight into the nature of these surface pockets. PMID:23998903

Electronic Structure of Ytterbium-Doped Strontium Fluoroapatite: Photoemission and Photoabsorption Investigation

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

Nelson, Art J.; Van Buuren, Tony W.; Bostedt, C

X-ray photoemission and x-ray photoabsorption were used to study the composition and the electronic structure of ytterbium-doped strontium fluoroapatite (Yb:S-FAP). High resolution photoemission measurements on the valence band electronic structure and Sr 3d, P 2p and 2s, Yb 4d and 4p, F 1s and O 1s core lines were used to evaluate the surface and near surface chemistry of this fluoroapatite. Element specific density of unoccupied electronic states in Yb:S-FAP were probed by x-ray absorption spectroscopy (XAS) at the Yb 4d (N4,5-edge), Sr 3d (M4,5-edge), P 2p (L2,3-edge), F 1s and O 1s (K-edges) absorption edges. These results provide themore » first measurements of the electronic structure and surface chemistry of this material.« less

Stretchable ultrasonic transducer arrays for three-dimensional imaging on complex surfaces

PubMed Central

Zhu, Xuan; Li, Xiaoshi; Chen, Zeyu; Chen, Yimu; Lei, Yusheng; Li, Yang; Nomoto, Akihiro; Zhou, Qifa; di Scalea, Francesco Lanza

2018-01-01

Ultrasonic imaging has been implemented as a powerful tool for noninvasive subsurface inspections of both structural and biological media. Current ultrasound probes are rigid and bulky and cannot readily image through nonplanar three-dimensional (3D) surfaces. However, imaging through these complicated surfaces is vital because stress concentrations at geometrical discontinuities render these surfaces highly prone to defects. This study reports a stretchable ultrasound probe that can conform to and detect nonplanar complex surfaces. The probe consists of a 10 × 10 array of piezoelectric transducers that exploit an “island-bridge” layout with multilayer electrodes, encapsulated by thin and compliant silicone elastomers. The stretchable probe shows excellent electromechanical coupling, minimal cross-talk, and more than 50% stretchability. Its performance is demonstrated by reconstructing defects in 3D space with high spatial resolution through flat, concave, and convex surfaces. The results hold great implications for applications of ultrasound that require imaging through complex surfaces. PMID:29740603

Laser-based ultrasonics by dual-probe interferometer detection and narrow-band ultrasound generation

NASA Astrophysics Data System (ADS)

Huang, Jin

1993-01-01

Despite the advantages of laser-based ultrasonic (LBU) systems, the overall sensitivity of LBU systems needs to be improved for practical applications. Progress is reported to achieve better LBU detection accuracy and sensitivity for applications with surface waves and Lamb waves. A novel dual-probe laser interferometer has been developed to measure the same signal at two points. The dual-probe interferometer is a modification of a conventional single-probe interferometer in that the reference beam is guided to a second detecting point on the specimen surface to form a differential measurement mode, which measure the difference of the displacements at the two points. This dual-probe interferometer is particularly useful for accurate measurements of the speed and attenuation of surface waves and Lamb waves. The dual-probe interferometer has been applied to obtain accurate measurements of the surface wave speed and attenuation on surfaces of increasing surface roughness. It has also been demonstrated that with an appropriate signal processing method, namely, the power cepstrum method, the dual-probe interferometer is applicable to measure the local surface wave speed even when the probe separation is so small that the two waveforms in the interferometer output signal overlap in the time domain. Narrow-band signal generation and detection improve the sensitivity of LBU systems. It is proposed to use a diffraction grating to form an array of illuminating strips which form a source of narrowband surface and Lamb waves. The line-array of thermoelastic sources generates narrow-band signals whose frequency and bandwidth can be easily controlled. The optimum line-array parameters, such as width, spacing and the number of lines in the array have been derived theoretically and verified experimentally. Narrow-band signal generation with optimum parameters has been demonstrated. The enhanced LBU system with dual-probe detection and narrowband signal generation has been successfully applied to the detection of cracks emanating from rivet holes in aircraft fuselage panel samples. A compact fiber-optic dual-probe interferometer has also been developed and applied to the above mentioned problem of crack detection. Results agree well with those obtained with a bulk LBU system.

Simulation of Mach Probes in Non-Uniform Magnetized Plasmas: the Influence of a Background Density Gradient

NASA Astrophysics Data System (ADS)

Haakonsen, Christian Bernt; Hutchinson, Ian H.

2013-10-01

Mach probes can be used to measure transverse flow in magnetized plasmas, but what they actually measure in strongly non-uniform plasmas has not been definitively established. A fluid treatment in previous work has suggested that the diamagnetic drifts associated with background density and temperature gradients affect transverse flow measurements, but detailed computational study is required to validate and elaborate on those results; it is really a kinetic problem, since the probe deforms and introduces voids in the ion and electron distribution functions. A new code, the Plasma-Object Simulator with Iterated Trajectories (POSIT) has been developed to self-consistently compute the steady-state six-dimensional ion and electron distribution functions in the perturbed plasma. Particle trajectories are integrated backwards in time to the domain boundary, where arbitrary background distribution functions can be specified. This allows POSIT to compute the ion and electron density at each node of its unstructured mesh, update the potential based on those densities, and then iterate until convergence. POSIT is used to study the impact of a background density gradient on transverse Mach probe measurements, and the results compared to the previous fluid theory. C.B. Haakonsen was supported in part by NSF/DOE Grant No. DE-FG02-06ER54512, and in part by an SCGF award administered by ORISE under DOE Contract No. DE-AC05-06OR23100.

Real-time optical fiber dosimeter probe

NASA Astrophysics Data System (ADS)

Croteau, André; Caron, Serge; Rink, Alexandra; Jaffray, David; Mermut, Ozzy

2011-03-01

There is a pressing need for a passive optical fiber dosimeter probe for use in real-time monitoring of radiation dose delivered to clinical radiation therapy patients. An optical fiber probe using radiochromic material has been designed and fabricated based on a thin film of the radiochromic material on a dielectric mirror. Measurements of the net optical density vs. time before, during, and after irradiation at a rate of 500cGy/minute to a total dose of 5 Gy were performed. Net optical densities increased from 0.2 to 2.0 for radiochromic thin film thicknesses of 2 to 20 μm, respectively.

The levels and kinetics of oxygen tension detectable at the surface of human dermal fibroblast cultures.

PubMed

Tokuda, Y; Crane, S; Yamaguchi, Y; Zhou, L; Falanga, V

2000-03-01

Low oxygen tension has recently been shown to stimulate cell growth and clonal expansion, as well as synthesis and transcription of certain growth factors and extracellular matrix components. These results have been obtained by exposing cell cultures to a hypoxic environment. Using an oxygen probe, we have now studied how experimental conditions affect the oxygen tension detectable at the cell surface. Dissolved oxygen tension was directly related to the height of the medium above the cell surface (r = 0.8793, P = 0.021), but was constant when no cells were present in the flask (r = -0. 9732, P = 0.001). In both human dermal fibroblasts and NIH/3T3 cultures, oxygen tension decreased linearly as cell density increased (r = -0.835, P < 0.0001; r = -0.916, P < 0.0001, respectively). When human dermal fibroblasts were exposed to 2% O(2), maximum hypoxic levels (0 mmHg) were achieved within approximately 15 min, and the recovery time was within a similar time frame. The addition of rotenone, an inhibitor of cellular respiration, blocked this decrease in oxygen tension at the cell surface, suggesting that cellular consumption of oxygen is responsible for the decline. Finally, we examined the cell-surface oxygen tension in control and acutely wounded human skin equivalents (HSE), consisting of a keratinocyte layer over a type I collagen matrix containing fibroblasts. We found that oxygen tension dropped significantly (P < 0.0001) in acutely wounded areas of HSE as compared to unwounded areas of HSE and that this drop was prevented by the addition of mitomycin C. These results indicate that cell-surface oxygen tension is indirectly related to cell density, and that the amount of detectable oxygen at the cell surface is a function of cell density, the oxygen tension in the incubator, and increased cellular activity, as occurs after injury. Copyright 2000 Wiley-Liss, Inc.

Fe-Impregnated Mineral Colloids for Peroxide Activation: Effects of Mineral Substrate and Fe Precursor.

PubMed

Li, Yue; Machala, Libor; Yan, Weile

2016-02-02

Heterogeneous iron species at the mineral/water interface are important catalysts for the generation of reactive oxygen species at circumneutral pH. One significant pathway leading to the formation of such species arises from deposition of dissolved iron onto mineral colloids due to changes in redox conditions. This study investigates the catalytic properties of Fe impregnated on silica, alumina, and titania nanoparticles (as prototypical mineral colloids). Fe impregnation was carried out by immersing the mineral nanoparticles in dilute Fe(II) or Fe(III) solutions at pH 6 and 3, respectively, in an aerobic environment. The uptake of iron per unit surface area follows the order of nTiO2 > nAl2O3 > nSiO2 for both types of Fe precursors. Impregnation of mineral particles in Fe(II) solutions results in predominantly Fe(III) species due to efficient surface-mediated oxidation. The catalytic activity of the impregnated solids to produce hydroxyl radical (·OH) from H2O2 decomposition was evaluated using benzoic acid as a probe compound under dark conditions. Invariably, the rates of benzoic acid oxidation with different Fe-laden particles increase with the surface density of Fe until a critical density above which the catalytic activity approaches a plateau, suggesting active Fe species are formed predominantly at low surface loadings. The critical surface density of Fe varies with the mineral substrate as well as the aqueous Fe precursor. Fe impregnated on TiO2 exhibits markedly higher activity than its Al2O3 and SiO2 counterparts. The speciation of interfacial Fe is analyzed with diffuse reflectance UV-vis analysis and interpretation of the data in the context of benzoic oxidation rates suggests that the surface activity of the solids for ·OH generation correlates strongly with the isolated (i.e., mononuclear) Fe species. Therefore, iron dispersed on mineral colloids is a significant form of reactive iron surfaces in the aquatic environment.

The Harp probe - An in situ Bragg scattering sensor

NASA Technical Reports Server (NTRS)

Mollo-Christensen, E.; Huang, N. E.; Long, S. R.; Bliven, L. F.

1984-01-01

A wave sensor, consisting of parallel, evenly spaced capacitance wires, whose output is the sum of the water surface deflections at the wires, has been built and tested in a wave tank. The probe output simulates Bragg scattering of electromagnetic waves from a water surface with waves; it can be used to simulate electromagnetic probing of the sea surface by radar. The study establishes that the wave probe, called the 'Harp' for short, will simulate Bragg scattering and that it can also be used to study nonlinear wave processes.

Spatial Variations of Turbulent Properties of Neutral Hydrogen Gas in the Small Magellanic Cloud Using Structure-function Analysis

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

Nestingen-Palm, David; Stanimirović, Snežana; González-Casanova, Diego F.

2017-08-10

We investigate spatial variations of turbulent properties in the Small Magellanic Cloud (SMC) by using neutral hydrogen (H i) observations. With the goal of testing the importance of stellar feedback on H i turbulence, we define central and outer SMC regions based on the star formation rate (SFR) surface density, as well as the H i integrated intensity. We use the structure function and the velocity channel analysis to calculate the power-law index ( γ ) for both underlying density and velocity fields in these regions. In all cases, our results show essentially no difference in γ between the centralmore » and outer regions. This suggests that H i turbulent properties are surprisingly homogeneous across the SMC when probed at a resolution of 30 pc. Contrary to recent suggestions from numerical simulations, we do not find a significant change in γ due to stellar feedback as traced by the SFR surface density. This could be due to the stellar feedback being widespread over the whole of the SMC, but more likely due to a large-scale gravitational driving of turbulence. We show that the lack of difference between central and outer SMC regions cannot be explained by the high optical depth H I.« less

Atom probe tomography characterization of neutron irradiated surveillance samples from the R. E. Ginna reactor pressure vessel

DOE PAGES

Edmondson, Philip D.; Miller, Michael K.; Powers, Kathy A.; ...

2015-12-29

Surveillance samples of a low copper (nominally 0.05 wt.% Cu) forging and a higher copper (0.23 wt.% Cu) submerged arc weld from the R. E. Ginna reactor pressure vessel have been characterized by atom probe tomography (APT) after exposure to three levels of neutron irradiation, i.e., fluences of 1.7, 3.6 and 5.8 × 10 23 n.m –2 (E > 1 MeV), and inlet temperatures of ~289 °C (~552 °F). As no copper-enriched precipitates were observed in the low copper forging, and the measured copper content in the ferrite matrix was 0.04± <0.01 at.% Cu, after neutron irradiation to a fluencemore » of 1.7 × 10 23 n.m –3, this copper level was below the solubility limit. A number density of 2 × 10 22 m –3 of Ni–, Mn– Si-enriched precipitates with an equivalent radius of gyration of 1.7 ± 0.4 nm were detected in the sample. However, Cu-, Ni-, Mn-enriched precipitates were observed in specimens cut from different surveillance specimens from the same forging material in which the overall measured copper level was 0.08± <0.01 at.% (fluence of 3.6 × 10 23 n.m –3) and 0.09± <0.01 at.% Cu (fluence of 5.8 × 10 23 n.m –3). Therefore, these slightly higher copper contents were above the solubility limit of Cu under these irradiation conditions. A best fit of all the composition data indicated that the size and number density of the Cu-enriched precipitates increased slightly in both size and number density by additional exposure to neutron irradiation. High number densities of Cu-enriched precipitates were observed in the higher Cu submerged arc weld for all irradiated conditions. The size and number density of the precipitates in the welds were higher than in the same fluence forgings. Some Cu-enriched precipitates were found to have Ni-, Mn- Si-, and P-enriched regions on their surfaces suggesting a preferential nucleation site. Furthermore, atom maps revealed P, Ni, and Mn segregation to, and preferential precipitation of, Cu-enriched precipitates over the surface of a grain boundary in the low fluence weld.« less

Atom probe tomography characterization of neutron irradiated surveillance samples from the R. E. Ginna reactor pressure vessel

NASA Astrophysics Data System (ADS)

Edmondson, P. D.; Miller, M. K.; Powers, K. A.; Nanstad, R. K.

2016-03-01

Surveillance samples of a low copper (nominally 0.05 wt.% Cu) forging and a higher copper (0.23 wt.% Cu) submerged arc weld from the R. E. Ginna reactor pressure vessel have been characterized by atom probe tomography (APT) after exposure to three levels of neutron irradiation, i.e., fluences of 1.7, 3.6 and 5.8 × 1023 n.m-2 (E > 1 MeV), and inlet temperatures of ∼289 °C (∼552 °F). As no copper-enriched precipitates were observed in the low copper forging, and the measured copper content in the ferrite matrix was 0.04± <0.01 at.% Cu, after neutron irradiation to a fluence of 1.7 × 1023 n.m-3, this copper level was below the solubility limit. A number density of 2 × 1022 m-3 of Ni-, Mn- Si-enriched precipitates with an equivalent radius of gyration of 1.7 ± 0.4 nm were detected in the sample. However, Cu-, Ni-, Mn-enriched precipitates were observed in specimens cut from different surveillance specimens from the same forging material in which the overall measured copper level was 0.08± <0.01 at.% (fluence of 3.6 × 1023 n.m-3) and 0.09± <0.01 at.% Cu (fluence of 5.8 × 1023 n.m-3). Therefore, these slightly higher copper contents were above the solubility limit of Cu under these irradiation conditions. A best fit of all the composition data indicated that the size and number density of the Cu-enriched precipitates increased slightly in both size and number density by additional exposure to neutron irradiation. High number densities of Cu-enriched precipitates were observed in the higher Cu submerged arc weld for all irradiated conditions. The size and number density of the precipitates in the welds were higher than in the same fluence forgings. Some Cu-enriched precipitates were found to have Ni-, Mn- Si-, and P-enriched regions on their surfaces suggesting a preferential nucleation site. Atom maps revealed P, Ni, and Mn segregation to, and preferential precipitation of, Cu-enriched precipitates over the surface of a grain boundary in the low fluence weld.

Atom probe tomography characterization of neutron irradiated surveillance samples from the R. E. Ginna reactor pressure vessel

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

Edmondson, Philip D.; Miller, Michael K.; Powers, Kathy A.

Surveillance samples of a low copper (nominally 0.05 wt.% Cu) forging and a higher copper (0.23 wt.% Cu) submerged arc weld from the R. E. Ginna reactor pressure vessel have been characterized by atom probe tomography (APT) after exposure to three levels of neutron irradiation, i.e., fluences of 1.7, 3.6 and 5.8 × 10 23 n.m –2 (E > 1 MeV), and inlet temperatures of ~289 °C (~552 °F). As no copper-enriched precipitates were observed in the low copper forging, and the measured copper content in the ferrite matrix was 0.04± <0.01 at.% Cu, after neutron irradiation to a fluencemore » of 1.7 × 10 23 n.m –3, this copper level was below the solubility limit. A number density of 2 × 10 22 m –3 of Ni–, Mn– Si-enriched precipitates with an equivalent radius of gyration of 1.7 ± 0.4 nm were detected in the sample. However, Cu-, Ni-, Mn-enriched precipitates were observed in specimens cut from different surveillance specimens from the same forging material in which the overall measured copper level was 0.08± <0.01 at.% (fluence of 3.6 × 10 23 n.m –3) and 0.09± <0.01 at.% Cu (fluence of 5.8 × 10 23 n.m –3). Therefore, these slightly higher copper contents were above the solubility limit of Cu under these irradiation conditions. A best fit of all the composition data indicated that the size and number density of the Cu-enriched precipitates increased slightly in both size and number density by additional exposure to neutron irradiation. High number densities of Cu-enriched precipitates were observed in the higher Cu submerged arc weld for all irradiated conditions. The size and number density of the precipitates in the welds were higher than in the same fluence forgings. Some Cu-enriched precipitates were found to have Ni-, Mn- Si-, and P-enriched regions on their surfaces suggesting a preferential nucleation site. Furthermore, atom maps revealed P, Ni, and Mn segregation to, and preferential precipitation of, Cu-enriched precipitates over the surface of a grain boundary in the low fluence weld.« less

Continuum Lowering and Fermi-Surface Rising in Strongly Coupled and Degenerate Plasmas

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

Hu, S. X.

Here, continuum lowering is a well-known and important physics concept that describes the ionization potential depression (IPD) in plasmas caused by thermal-/pressure-induced ionization of outer-shell electrons. The existing IPD models are often used to characterize plasma conditions and to gauge opacity calculations. Recent precision measurements have revealed deficits in our understanding of continuum lowering in dense hot plasmas. However, these investigations have so far been limited to IPD in strongly coupled but nondegenerate plasmas. Here, we report a first-principles study of the K-edge shifting in both strongly coupled and fully degenerate carbon plasmas, with quantum molecular dynamics (QMD) calculations basedmore » on the all-electron density-functional theory (DFT). The resulted K-edge shifting versus plasma density, as a probe to the continuum lowering and the Fermi-surface rising, is found to be significantly different from predictions of existing IPD models. In contrast, a simple model of “single atom in box” (SAIB), developed in this work, accurately predicts K-edge locations as what ab-initio calculations provide.« less

Rare isotopes and the sound of dilute nuclear matter

NASA Astrophysics Data System (ADS)

Papakonstantinou, P.

2018-04-01

Dilute baryonic matter, at densities below the normal saturation density of symmetric matter, is found on the crust of neutron stars and in collapsing supernova matter, its properties determining the evolution of those stellar objects. It is also readily found on the surface of ordinary and exotic atomic nuclei and lives fleetingly in the form of space-extended resonances of excited nucleons. Liminal states of nuclear matter, between saturation and full evaporation or clusterization, are manifest in the structure of symmetric nuclei through clustering and of very asymmetric rare species in haloes and the neutron skin; they stand literally at the threshold of a nucleus's response to hadronic probes, including processes which hinder or enable fusion. In this contribution I focus on excited states, and in particular exotic or not-so-exotic dipole excitation modes of N = Z nuclei and neutron-rich species, including new theoretical results on threshold strength. Modes of special interest are vibrations of and within diffuse surface layers and alpha-cluster oscillations. The modeling of such processes is relevant, directly or indirectly, for the description of reactions at astrophysical energies.

Continuum Lowering and Fermi-Surface Rising in Strongly Coupled and Degenerate Plasmas

DOE PAGES

Hu, S. X.

2017-08-10

Here, continuum lowering is a well-known and important physics concept that describes the ionization potential depression (IPD) in plasmas caused by thermal-/pressure-induced ionization of outer-shell electrons. The existing IPD models are often used to characterize plasma conditions and to gauge opacity calculations. Recent precision measurements have revealed deficits in our understanding of continuum lowering in dense hot plasmas. However, these investigations have so far been limited to IPD in strongly coupled but nondegenerate plasmas. Here, we report a first-principles study of the K-edge shifting in both strongly coupled and fully degenerate carbon plasmas, with quantum molecular dynamics (QMD) calculations basedmore » on the all-electron density-functional theory (DFT). The resulted K-edge shifting versus plasma density, as a probe to the continuum lowering and the Fermi-surface rising, is found to be significantly different from predictions of existing IPD models. In contrast, a simple model of “single atom in box” (SAIB), developed in this work, accurately predicts K-edge locations as what ab-initio calculations provide.« less

Capacitive coupling in hybrid graphene/GaAs nanostructures

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

Simonet, Pauline, E-mail: psimonet@phys.ethz.ch; Rössler, Clemens; Krähenmann, Tobias

2015-07-13

Coupled hybrid nanostructures are demonstrated using the combination of lithographically patterned graphene on top of a two-dimensional electron gas (2DEG) buried in a GaAs/AlGaAs heterostructure. The graphene forms Schottky barriers at the surface of the heterostructure and therefore allows tuning the electronic density of the 2DEG. Conversely, the 2DEG potential can tune the graphene Fermi energy. Graphene-defined quantum point contacts in the 2DEG show half-plateaus of quantized conductance in finite bias spectroscopy and display the 0.7 anomaly for a large range of densities in the constriction, testifying to their good electronic properties. Finally, we demonstrate that the GaAs nanostructure canmore » detect charges in the vicinity of the heterostructure's surface. This confirms the strong coupling of the hybrid device: localized states in the graphene ribbon could, in principle, be probed by the underlying confined channel. The present hybrid graphene/GaAs nanostructures are promising for the investigation of strong interactions and coherent coupling between the two fundamentally different materials.« less

Langmuir probe analysis in electronegative plasmas

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

Bredin, Jerome, E-mail: jerome.bredin@lpp.polytechnique.fr; Chabert, Pascal; Aanesland, Ane

2014-12-15

This paper compares two methods to analyze Langmuir probe data obtained in electronegative plasmas. The techniques are developed to allow investigations in plasmas, where the electronegativity α{sub 0} = n{sub –}/n{sub e} (the ratio between the negative ion and electron densities) varies strongly. The first technique uses an analytical model to express the Langmuir probe current-voltage (I-V) characteristic and its second derivative as a function of the electron and ion densities (n{sub e}, n{sub +}, n{sub –}), temperatures (T{sub e}, T{sub +}, T{sub –}), and masses (m{sub e}, m{sub +}, m{sub –}). The analytical curves are fitted to the experimental data bymore » adjusting these variables and parameters. To reduce the number of fitted parameters, the ion masses are assumed constant within the source volume, and quasi-neutrality is assumed everywhere. In this theory, Maxwellian distributions are assumed for all charged species. We show that this data analysis can predict the various plasma parameters within 5–10%, including the ion temperatures when α{sub 0} > 100. However, the method is tedious, time consuming, and requires a precise measurement of the energy distribution function. A second technique is therefore developed for easier access to the electron and ion densities, but does not give access to the ion temperatures. Here, only the measured I-V characteristic is needed. The electron density, temperature, and ion saturation current for positive ions are determined by classical probe techniques. The electronegativity α{sub 0} and the ion densities are deduced via an iterative method since these variables are coupled via the modified Bohm velocity. For both techniques, a Child-Law sheath model for cylindrical probes has been developed and is presented to emphasize the importance of this model for small cylindrical Langmuir probes.« less

Barium-strontium-titanate etching characteristics in chlorinated discharges

NASA Astrophysics Data System (ADS)

Stafford, Luc; Margot, Joëlle; Langlois, Olivier; Chaker, Mohamed

2003-07-01

The etching characteristics of barium-strontium-titanate (BST) were investigated using a high-density plasma sustained by surface waves at 190 MHz in Ar/Cl2 gas mixtures. The etch rate was examined as a function of both the total gas pressure and the Cl2 fraction in Ar/Cl2 using a wafer temperature of 10 °C. The results were correlated to positive ion density and plasma composition obtained from Langmuir probes and mass spectrometry. The BST etch rate was found to increase linearly with the positive ion density and to decrease with increasing chlorine atom concentration. This result indicates that for the temperature conditions used, the interaction between chlorine and BST yields compounds having a volatility that is lower than the original material. As a consequence, the contribution of neutral atomic Cl atoms to the etch mechanism is detrimental, thereby reducing the etch rate. As the wafer temperature increases, the role of chemistry in the etching process is enhanced.

Nanoscale morphogenesis of nylon-sputtered plasma polymer particles

NASA Astrophysics Data System (ADS)

Choukourov, Andrei; Shelemin, Artem; Pleskunov, Pavel; Nikitin, Daniil; Khalakhan, Ivan; Hanuš, Jan

2018-05-01

Sub-micron polymer particles are highly important in various fields including astrophysics, thermonuclear fusion and nanomedicine. Plasma polymerization offers the possibility to produce particles with tailor-made size, crosslink density and chemical composition to meet the requirements of a particular application. However, the mechanism of nucleation and growth of plasma polymer particles as well as diversity of their morphology remain far from being clear. Here, we prepared nitrogen-containing plasma polymer particles by rf magnetron sputtering of nylon in a gas aggregation cluster source with variable length. The method allowed the production of particles with roughly constant chemical composition and number density but with the mean size changing from 80 to 320 nm. Atomic Force Microscopy with super-sharp probes was applied to study the evolution of the particle surface topography as they grow in size. Height–height correlation and power spectral density functions were obtained to quantify the roughness exponent α  =  0.78, the growth exponent β  =  0.35, and the dynamic exponent 1/z  =  0.50. The set of critical exponents indicates that the particle surface evolves in a self-affine mode and the overall particle growth is caused by the accretion of polymer-forming species from the gas phase and not by coagulation. Redistribution of the incoming material over the surface coupled with the inhomogeneous distribution of inner stress is suggested as the main factor that determines the morphogenesis of the plasma polymer particles.

Scanning micro-Hall probe mapping of magnetic flux distributions and current densities in YBa2Cu3O7 thin films

NASA Technical Reports Server (NTRS)

Xing, W.; Heinrich, B.; Zhou, HU; Fife, A. A.; Cragg, A. R.; Grant, P. D.

1995-01-01

Mapping of the magnetic flux density B(sub z) (perpendicular to the film plane) for a YBa2Cu3O7 thin-film sample was carried out using a scanning micro-Hall probe. The sheet magnetization and sheet current densities were calculated from the B(sub z) distributions. From the known sheet magnetization, the tangential (B(sub x,y)) and normal components of the flux density B were calculated in the vicinity of the film. It was found that the sheet current density was mostly determined by 2B(sub x,y)/d, where d is the film thickness. The evolution of flux penetration as a function of applied field will be shown.

Mediated Electron Transfer at Vertically Aligned Single-Walled Carbon Nanotube Electrodes During Detection of DNA Hybridization.

PubMed

Wallen, Rachel; Gokarn, Nirmal; Bercea, Priscila; Grzincic, Elissa; Bandyopadhyay, Krisanu

2015-12-01

Vertically aligned single-walled carbon nanotube (VASWCNT) assemblies are generated on cysteamine and 2-mercaptoethanol (2-ME)-functionalized gold surfaces through amide bond formation between carboxylic groups generated at the end of acid-shortened single-walled carbon nanotubes (SWCNTs) and amine groups present on the gold surfaces. Atomic force microscopy (AFM) imaging confirms the vertical alignment mode of SWCNT attachment through significant changes in surface roughness compared to bare gold surfaces and the lack of any horizontally aligned SWCNTs present. These SWCNT assemblies are further modified with an amine-terminated single-stranded probe-DNA. Subsequent hybridization of the surface-bound probe-DNA in the presence of complementary strands in solution is followed using impedance measurements in the presence of Fe(CN)6 (3-/4-) as the redox probe in solution, which show changes in the interfacial electrochemical properties, specifically the charge-transfer resistance, due to hybridization. In addition, hybridization of the probe-DNA is also compared when it is attached directly to the gold surfaces without any intermediary SWCNTs. Contrary to our expectations, impedance measurements show a decrease in charge-transfer resistance with time due to hybridization with 300 nM complementary DNA in solution with the probe-DNA attached to SWCNTs. In contrast, an increase in charge-transfer resistance is observed with time during hybridization when the probe-DNA is attached directly to the gold surfaces. The decrease in charge-transfer resistance during hybridization in the presence of VASWCNTs indicates an enhancement in the electron transfer process of the redox probe at the VASWCNT-modified electrode. The results suggest that VASWCNTs are acting as mediators of electron transfer, which facilitate the charge transfer of the redox probe at the electrode-solution interface.

Mediated Electron Transfer at Vertically Aligned Single-Walled Carbon Nanotube Electrodes During Detection of DNA Hybridization

NASA Astrophysics Data System (ADS)

Wallen, Rachel; Gokarn, Nirmal; Bercea, Priscila; Grzincic, Elissa; Bandyopadhyay, Krisanu

2015-06-01

Vertically aligned single-walled carbon nanotube (VASWCNT) assemblies are generated on cysteamine and 2-mercaptoethanol (2-ME)-functionalized gold surfaces through amide bond formation between carboxylic groups generated at the end of acid-shortened single-walled carbon nanotubes (SWCNTs) and amine groups present on the gold surfaces. Atomic force microscopy (AFM) imaging confirms the vertical alignment mode of SWCNT attachment through significant changes in surface roughness compared to bare gold surfaces and the lack of any horizontally aligned SWCNTs present. These SWCNT assemblies are further modified with an amine-terminated single-stranded probe-DNA. Subsequent hybridization of the surface-bound probe-DNA in the presence of complementary strands in solution is followed using impedance measurements in the presence of Fe(CN)6 3-/4- as the redox probe in solution, which show changes in the interfacial electrochemical properties, specifically the charge-transfer resistance, due to hybridization. In addition, hybridization of the probe-DNA is also compared when it is attached directly to the gold surfaces without any intermediary SWCNTs. Contrary to our expectations, impedance measurements show a decrease in charge-transfer resistance with time due to hybridization with 300 nM complementary DNA in solution with the probe-DNA attached to SWCNTs. In contrast, an increase in charge-transfer resistance is observed with time during hybridization when the probe-DNA is attached directly to the gold surfaces. The decrease in charge-transfer resistance during hybridization in the presence of VASWCNTs indicates an enhancement in the electron transfer process of the redox probe at the VASWCNT-modified electrode. The results suggest that VASWCNTs are acting as mediators of electron transfer, which facilitate the charge transfer of the redox probe at the electrode-solution interface.

Inductively-coupled plasmas in pure chlorine: comparison experiments/HPEM

NASA Astrophysics Data System (ADS)

Booth, Jean-Paul; Sirse, Nishant; Azamoum, Yasmina; Chabert, Pascal

2012-10-01

Inductively-coupled plasmas in chlorine-based gas mixtures are widely used for etching of nanometric features in silicon for CMOS device manufacture. This system is also of considerable fundamental interest as an archetype of strongly electronegative plasmas in a simple gas, for which reliable techniques exist to measure the densities of all key species. As such, it is an ideal test-bed for comparison of simulations to experiment. We have developed a technique based on two-photon Laser-Induced Fluorescence to determine the absolute Cl atom density. The Cl surface recombination coefficient was determined from time-resolved measurements in the afterglow. Electron densities were determined by microwave hairpin resonator and EEDF's were measured by Langmuir probe. Whereas the HPEM results were in good agreement at lower pressures (below 10mTorr), electron densities are increasingly underestimated at higher pressures. The gas temperature was measured by Doppler-resolved Infra-red Laser Absorption spectroscopy of Ar metastable atoms (with a small fraction Ar added). At higher pressures the gas temperature was considerably underestimated by the model. The concomitant overestimation of the gas density is a major reason for the disagreement between model and experiment.

Tailored Rh surface facilitates, enhancement of Raman scattering in trimetallic AuPt core/Rh shell composites: Experimental and theoretical evidences

NASA Astrophysics Data System (ADS)

Loganathan, B.; Chandraboss, V. L.; Senthilvelan, S.; Karthikeyan, B.

2016-01-01

We present a detailed analysis of surface-enhanced Raman scattering of 7-azaindole and L-cysteine adsorbed on a tailored Rh surface by using experimental and density functional theoretical (DFT) calculations. DFT with the B3LYP/Lanl2DZ basis set was used for the optimization of the ground state geometries and simulation of the surface-enhanced Raman spectrum of probe molecules adsorbed on Rh6 cluster. 7-azaindole and L-cysteine adsorption at the shell interface was ascertained from first-principles. In addition, characterization of synthesized trimetallic AuPt core/Rh shell colloidal nanocomposites has been analyzed by UV-visible spectroscopy, high-resolution transmission and scanning electron microscopy, selected area electron diffraction pattern analysis, energy-dispersive X-ray spectroscopy, atomic force, confocal Raman microscopy, FT-Raman and surface-enhanced Raman spectroscopic analysis. This analysis serves as the first step in gaining an accurate understanding of specific interactions at the interface of organic and biomolecules and to gain knowledge on the surface composition of trimetallic Au/Pt/Rh colloidal nanocomposites.

Ligand-surface interactions and surface oxidation of colloidal PbSe quantum dots revealed by thin-film positron annihilation methods

NASA Astrophysics Data System (ADS)

Shi, Wenqin; Eijt, Stephan W. H.; Suchand Sandeep, C. S.; Siebbeles, Laurens D. A.; Houtepen, Arjan J.; Kinge, Sachin; Brück, Ekkes; Barbiellini, Bernardo; Bansil, Arun

2016-02-01

Positron Two Dimensional Angular Correlation of Annihilation Radiation (2D-ACAR) measurements reveal modifications of the electronic structure and composition at the surfaces of PbSe quantum dots (QDs), deposited as thin films, produced by various ligands containing either oxygen or nitrogen atoms. In particular, the 2D-ACAR measurements on thin films of colloidal PbSe QDs capped with oleic acid ligands yield an increased intensity in the electron momentum density (EMD) at high momenta compared to PbSe quantum dots capped with oleylamine. Moreover, the EMD of PbSe QDs is strongly affected by the small ethylenediamine ligands, since these molecules lead to small distances between QDs and favor neck formation between near neighbor QDs, inducing electronic coupling between neighboring QDs. The high sensitivity to the presence of oxygen atoms at the surface can be also exploited to monitor the surface oxidation of PbSe QDs upon exposure to air. Our study clearly demonstrates that positron annihilation spectroscopy applied to thin films can probe surface transformations of colloidal semiconductor QDs embedded in functional layers.

Cassini Radio Occultation by Enceladus Plume

NASA Astrophysics Data System (ADS)

Kliore, A.; Armstrong, J.; Flasar, F.; French, R.; Marouf, E.; Nagy, A.; Rappaport, N.; McGhee, C.; Schinder, P.; Anabtawi, A.; Asmar, S.; Barbinis, E.; Fleischman, D.; Goltz, G.; Aguilar, R.; Rochblatt, D.

2006-12-01

A fortuitous Cassini radio occultation by Enceladus plume occurs on September 15, 2006. The occultation track (the spacecraft trajectory in the plane of the sky as viewed from the Earth) has been designed to pass behind the plume (to pass above the south polar region of Enceladus) in a roughly symmetrical geometry centered on a minimum altitude above the surface of about 20 km. The minimum altitude was selected primarily to ensure probing much of the plume with good confidence given the uncertainty in the spacecraft trajectory. Three nearly-pure sinusoidal signals of 0.94, 3.6, and 13 cm-wavelength (Ka-, X-, and S-band, respectively) are simultaneously transmitted from Cassini and are monitored at two 34-m Earth receiving stations of the Deep Space Network (DSN) in Madrid, Spain (DSS-55 and DSS-65). The occultation of the visible plume is extremely fast, lasting less than about two minutes. The actual observation time extends over a much longer time interval, however, to provide a good reference baseline for potential detection of signal perturbations introduced by the tenuous neutral and ionized plume environment. Given the likely very small fraction of optical depth due to neutral particles of sizes larger than about 1 mm, detectable changes in signal intensity is perhaps unlikely. Detection of plume plasma along the radio path as perturbations in the signals frequency/phase is more likely and the magnitude will depend on the electron columnar density probed. The occultation time occurs not far from solar conjunction time (Sun-Earth-probe angle of about 33 degrees), causing phase scintillations due to the solar wind to be the primary limiting noise source. We estimate a delectability limit of about 1 to 3E16 electrons per square meter columnar density assuming about 100 seconds integration time. Potential measurement of the profile of electron columnar density along the occultation track is an exciting prospect at this time.

Hybridization behavior of mixed DNA/alkylthiol monolayers on gold: characterization by surface plasmon resonance and 32P radiometric assay.

PubMed

Gong, Ping; Lee, Chi-Ying; Gamble, Lara J; Castner, David G; Grainger, David W

2006-05-15

Nucleic acid assay from a complex biological milieu is attractive but currently difficult and far from routine. In this study, DNA hybridization from serum dilutions into mixed DNA/mercaptoundecanol (MCU) adlayers on gold was monitored by surface plasmon resonance (SPR). Immobilized DNA probe and hybridized target densities on these surfaces were quantified using 32P-radiometric assays as a function of MCU diluent exposure. SPR surface capture results correlated with radiometric analysis for hybridization performance, demonstrating a maximum DNA hybridization on DNA/MCU mixed adlayers. The maximum target surface capture produced by MCU addition to the DNA probe layer correlates with structural and conformational data on identical mixed DNA/MCU adlayers on gold derived from XPS, NEXAFS, and fluorescence intensity measurements reported in a related study (Lee, C.-Y.; Gong, P.; Harbers, G. M.; Grainger, D. W.; Castner, D. G.; Gamble, L. J. Anal. Chem. 2006, 78, 3316-3325.). MCU addition into the DNA adlayer on gold also improved surface resistance to both nonspecific DNA and serum protein adsorption. Target DNA hybridization from serum dilutions was monitored with SPR on the optimally mixed DNA/MCU adlayers. Both hybridization kinetics and efficiency were strongly affected by nonspecific protein adsorption from a complex milieu even at a minimal serum concentration (e.g., 1%). No target hybridization was detected in SPR assays from serum concentrations above 30%, indicating nonspecific protein adsorption interference of DNA capture and hybridization from complex milieu. Removal of nonsignal proteins from nucleic acid targets prior to assay represents a significant issue for direct sample-to-assay nucleic acid diagnostics from food, blood, tissue, PCR mixtures, and many other biologically complex sample formats.

Probing the energetics of organic–nanoparticle interactions of ethanol on calcite

DOE PAGES

Wu, Di; Navrotsky, Alexandra

2015-04-13

Knowing the nature of interactions between small organic molecules and surfaces of nanoparticles (NP) is crucial for fundamental understanding of natural phenomena and engineering processes. In this paper, we report direct adsorption enthalpy measurement of ethanol on a series of calcite nanocrystals, with the aim of mimicking organic–NP interactions in various environments. The energetics suggests a spectrum of adsorption events as a function of coverage: strongest initial chemisorption on active sites on fresh calcite surfaces, followed by major chemical binding to form an ethanol monolayer and, subsequently, very weak, near-zero energy, physisorption. Furthermore, these thermochemical observations directly support a structuremore » where the ethanol monolayer is bonded to the calcite surface through its polar hydroxyl group, leaving the hydrophobic ends of the ethanol molecules to interact only weakly with the next layer of adsorbing ethanol and resulting in a spatial gap with low ethanol density between the monolayer and subsequent added ethanol molecules, as predicted by molecular dynamics and density functional calculations. Such an ordered assembly of ethanol on calcite NP is analogous to, although less strongly bonded than, a capping layer of organics intentionally introduced during NP synthesis, and suggests a continuous variation of surface structure depending on molecular chemistry, ranging from largely disordered surface layers to ordered layers that nevertheless are mobile and can rearrange or be displaced by other molecules to strongly bonded immobile organic capping layers. Finally, these differences in surface structure will affect chemical reactions, including the further nucleation and growth of nanocrystals on organic ligand-capped surfaces.« less

Atomically manufactured nickel-silicon quantum dots displaying robust resonant tunneling and negative differential resistance

NASA Astrophysics Data System (ADS)

Cheng, Jian-Yih; Fisher, Brandon L.; Guisinger, Nathan P.; Lilley, Carmen M.

2017-12-01

Providing a spin-free host material in the development of quantum information technology has made silicon a very interesting and desirable material for qubit design. Much of the work and experimental progress has focused on isolated phosphorous atoms. In this article, we report on the exploration of Ni-Si clusters that are atomically manufactured via self-assembly from the bottom-up and behave as isolated quantum dots. These small quantum dot structures are probed at the atomic-scale with scanning tunneling microscopy and spectroscopy, revealing robust resonance through discrete quantized energy levels within the Ni-Si clusters. The resonance energy is reproducible and the peak spacing of the quantum dot structures increases as the number of atoms in the cluster decrease. Probing these quantum dot structures on degenerately doped silicon results in the observation of negative differential resistance in both I-V and dI/dV spectra. At higher surface coverage of nickel, a well-known √19 surface modification is observed and is essentially a tightly packed array of the clusters. Spatial conductance maps reveal variations in the local density of states that suggest the clusters are influencing the electronic properties of their neighbors. All of these results are extremely encouraging towards the utilization of metal modified silicon surfaces to advance or complement existing quantum information technology.

Atomically manufactured nickel–silicon quantum dots displaying robust resonant tunneling and negative differential resistance

DOE PAGES

Cheng, Jian -Yih; Fisher, Brandon L.; Guisinger, Nathan P.; ...

2017-05-22

Providing a spin-free host material in the development of quantum information technology has made silicon a very interesting and desirable material for qubit design. Much of the work and experimental progress has focused on isolated phosphorous atoms. In this article, we report on the exploration of Ni–Si clusters that are atomically manufactured via self-assembly from the bottom-up and behave as isolated quantum dots. These small quantum dot structures are probed at the atomic-scale with scanning tunneling microscopy and spectroscopy, revealing robust resonance through discrete quantized energy levels within the Ni–Si clusters. The resonance energy is reproducible and the peak spacingmore » of the quantum dot structures increases as the number of atoms in the cluster decrease. Probing these quantum dot structures on degenerately doped silicon results in the observation of negative differential resistance in both I–V and dI/dV spectra. At higher surface coverage of nickel, a well-known √19 surface modification is observed and is essentially a tightly packed array of the clusters. Spatial conductance maps reveal variations in the local density of states that suggest the clusters are influencing the electronic properties of their neighbors. Furthermore, all of these results are extremely encouraging towards the utilization of metal modified silicon surfaces to advance or complement existing quantum information technology.« less

Atomically manufactured nickel–silicon quantum dots displaying robust resonant tunneling and negative differential resistance

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

Cheng, Jian -Yih; Fisher, Brandon L.; Guisinger, Nathan P.

Providing a spin-free host material in the development of quantum information technology has made silicon a very interesting and desirable material for qubit design. Much of the work and experimental progress has focused on isolated phosphorous atoms. In this article, we report on the exploration of Ni–Si clusters that are atomically manufactured via self-assembly from the bottom-up and behave as isolated quantum dots. These small quantum dot structures are probed at the atomic-scale with scanning tunneling microscopy and spectroscopy, revealing robust resonance through discrete quantized energy levels within the Ni–Si clusters. The resonance energy is reproducible and the peak spacingmore » of the quantum dot structures increases as the number of atoms in the cluster decrease. Probing these quantum dot structures on degenerately doped silicon results in the observation of negative differential resistance in both I–V and dI/dV spectra. At higher surface coverage of nickel, a well-known √19 surface modification is observed and is essentially a tightly packed array of the clusters. Spatial conductance maps reveal variations in the local density of states that suggest the clusters are influencing the electronic properties of their neighbors. Furthermore, all of these results are extremely encouraging towards the utilization of metal modified silicon surfaces to advance or complement existing quantum information technology.« less

Multiplexed, High Density Electrophysiology with Nanofabricated Neural Probes

PubMed Central

Du, Jiangang; Blanche, Timothy J.; Harrison, Reid R.; Lester, Henry A.; Masmanidis, Sotiris C.

2011-01-01

Extracellular electrode arrays can reveal the neuronal network correlates of behavior with single-cell, single-spike, and sub-millisecond resolution. However, implantable electrodes are inherently invasive, and efforts to scale up the number and density of recording sites must compromise on device size in order to connect the electrodes. Here, we report on silicon-based neural probes employing nanofabricated, high-density electrical leads. Furthermore, we address the challenge of reading out multichannel data with an application-specific integrated circuit (ASIC) performing signal amplification, band-pass filtering, and multiplexing functions. We demonstrate high spatial resolution extracellular measurements with a fully integrated, low noise 64-channel system weighing just 330 mg. The on-chip multiplexers make possible recordings with substantially fewer external wires than the number of input channels. By combining nanofabricated probes with ASICs we have implemented a system for performing large-scale, high-density electrophysiology in small, freely behaving animals that is both minimally invasive and highly scalable. PMID:22022568

Probing Extreme-density Matter with Gravitational-wave Observations of Binary Neutron Star Merger Remnants

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

Radice, David; Bernuzzi, Sebastiano; Pozzo, Walter Del

We present a proof-of-concept study, based on numerical-relativity simulations, of how gravitational waves (GWs) from neutron star merger remnants can probe the nature of matter at extreme densities. Phase transitions and extra degrees of freedom can emerge at densities beyond those reached during the inspiral, and typically result in a softening of the equation of state (EOS). We show that such physical effects change the qualitative dynamics of the remnant evolution, but they are not identifiable as a signature in the GW frequency, with the exception of possible black hole formation effects. The EOS softening is, instead, encoded in themore » GW luminosity and phase and is in principle detectable up to distances of the order of several megaparsecs with advanced detectors and up to hundreds of megaparsecs with third-generation detectors. Probing extreme-density matter will require going beyond the current paradigm and developing a more holistic strategy for modeling and analyzing postmerger GW signals.« less

Measurements of electron density and temperature profiles in plasma produced by Nike KrF laser for laser plasma instability research

NASA Astrophysics Data System (ADS)

Oh, Jaechul; Weaver, J. L.; Karasik, M.; Chan, L. Y.

2015-08-01

A grid image refractometer (GIR) has been implemented at the Nike krypton fluoride laser facility of the Naval Research Laboratory. This instrument simultaneously measures propagation angles and transmissions of UV probe rays (λ = 263 nm, Δt = 10 ps) refracted through plasma. We report results of the first Nike-GIR measurement on a CH plasma produced by the Nike laser pulse (˜1 ns FWHM) with the intensity of 1.1 × 1015 W/cm2. The measured angles and transmissions were processed to construct spatial profiles of electron density (ne) and temperature (Te) in the underdense coronal region of the plasma. Using an inversion algorithm developed for the strongly refracted rays, the deployed GIR system probed electron densities up to 4 × 1021 cm-3 with the density scale length of 120 μm along the plasma symmetry axis. The resulting ne and Te profiles are verified to be self-consistent with the measured quantities of the refracted probe light.

Using tobacco mosaic virus to probe enhanced surface diffusion of molecular glasses.

PubMed

Zhang, Yue; Potter, Richard; Zhang, William; Fakhraai, Zahra

2016-11-09

Recent studies have shown that diffusion on the surface of organic glasses can be many orders of magnitude faster than bulk diffusion. Developing new probes that can readily measure surface diffusion can help study the effect of parameters such as chemical structure, intermolecular interaction, molecules' shape and size on the enhanced surface diffusion. In this study, we develop a novel probe that significantly simplifies these types of studies. Tobacco mosaic virus (TMV) is used as probe particle to measure surface diffusion coefficient of molecular glass N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD). The evolution of the meniscus formed around TMV is probed as a function of time at various temperatures. TMV has a well-defined, mono-dispersed, cylindrical shape, with a large aspect-ratio (average diameter of 16.6 nm, length of 300 nm). As such, the shape of the meniscus around the center of TMV is semi-two dimensional, which compared to using a nanosphere as probe, increases the driving force for meniscus formation and simplifies the analysis of surface diffusion. We show that under these conditions, after a short transient time the shape of the meniscus is self-similar, allowing accurate determination of the surface diffusion coefficient. Measurements at various temperatures are then performed to investigate the temperature dependence of the surface diffusion coefficient. It is found that surface diffusion is greatly enhanced in TPD and has a lower activation barrier compared to the bulk counterpart. These observations are consistent with previous studies of surface diffusion on molecular glasses, demonstrating the accuracy of this method.

Controlled Immobilization Strategies to Probe Short Hyaluronan-Protein Interactions

NASA Astrophysics Data System (ADS)

Minsky, Burcu Baykal; Antoni, Christiane H.; Boehm, Heike

2016-02-01

Well-controlled grafting of small hyaluronan oligosaccharides (sHA) enables novel approaches to investigate biological processes such as angiogenesis, immune reactions and cancer metastasis. We develop two strategies for covalent attachment of sHA, a fast high-density adsorption and a two-layer system that allows tuning the density and mode of immobilization. We monitored the sHA adlayer formation and subsequent macromolecular interactions by label-free quartz crystal microbalance with dissipation (QCM-D). The modified surfaces are inert to unspecific protein adsorption, and yet retain the specific binding capacity of sHA. Thus they are an ideal tool to study the interactions of hyaluronan-binding proteins and short hyaluronan molecules as demonstrated by the specific recognition of LYVE-1 and aggrecan. Both hyaladherins recognize sHA and the binding is independent to the presence of the reducing end.

Pump-probe Kelvin-probe force microscopy: Principle of operation and resolution limits

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

Murawski, J.; Graupner, T.; Milde, P., E-mail: peter.milde@tu-dresden.de

Knowledge on surface potential dynamics is crucial for understanding the performance of modern-type nanoscale devices. We describe an electrical pump-probe approach in Kelvin-probe force microscopy that enables a quantitative measurement of dynamic surface potentials at nanosecond-time and nanometer-length scales. Also, we investigate the performance of pump-probe Kelvin-probe force microscopy with respect to the relevant experimental parameters. We exemplify a measurement on an organic field effect transistor that verifies the undisturbed functionality of our pump-probe approach in terms of simultaneous and quantitative mapping of topographic and electronic information at a high lateral and temporal resolution.

Fission of Multielectron Bubbles in Liquid Helium Under Electric Fields

NASA Astrophysics Data System (ADS)

Vadakkumbatt, V.; Ghosh, A.

2017-06-01

Multielectron bubbles (MEBs) are cavities in liquid helium which contain a layer of electrons trapped within few nanometres from their inner surfaces. These bubbles are promising candidates to probe a system of interacting electrons in curved geometries, but have been subjected to limited experimental investigation. Here, we report on the observation of fission of MEBs under strong electric fields, which arises due to fast rearrangement of electrons inside the bubbles, leading to their deformation and eventually instability. We measured the electrons to be distributed unequally between the daughter bubbles which could be used to control the charge density inside MEBs.

Identifying passivated dynamic force microscopy tips on H:Si(100)

NASA Astrophysics Data System (ADS)

Sharp, Peter; Jarvis, Sam; Woolley, Richard; Sweetman, Adam; Kantorovich, Lev; Pakes, Chris; Moriarty, Philip

2012-06-01

The chemical reactivity of the tip plays a central role in image formation in dynamic force microscopy, but in very many cases the state of the probe is a key experimental unknown. We show here that an H-terminated and thus chemically unreactive tip can be readily identified via characteristic imaging and spectroscopic (F(z)) signatures, including, in particular, contrast inversion, on hydrogen-passivated Si(100). We determine the tip apex termination by comparing site-specific difference force curves with the results of density functional theory, providing a clear protocol for the identification of chemically unreactive tips on silicon surfaces.

Direct Observations of Nucleation in a Nondilute Multicomponent Alloy

NASA Technical Reports Server (NTRS)

Sudbrack, Chantal K.; Noebe, Ronald D.; Seidman, David N.

2006-01-01

The chemical pathways leading to gamma'(L1(sub 2)) nucleation from nondilute Ni-5.2 Al-14.2 Cr at. %, gama(fcc), at 873 K are followed with radial distribution functions and isoconcentration surface analyses of direct-space atom-probe tomographic images. Although Cr atoms initially are randomly distributed, a distribution of congruent Ni3Al short-range-order domains (SRO), [R] approx. equals 0.6 nm, results from Al diffusion during quenching. Domain site occupancy develops as their number density increases leading to Al-rich phase separation by gamma'-nucleation, [R]=0.75 nm, after SRO occurs.

Advancements in non-contact metrology of asphere and diffractive optics

NASA Astrophysics Data System (ADS)

DeFisher, Scott

2017-11-01

Advancements in optical manufacturing technology allow optical designers to implement steep aspheric or high departure surfaces into their systems. Measuring these surfaces with profilometers or CMMs can be difficult due to large surface slopes or sharp steps in the surface. OptiPro has developed UltraSurf to qualify the form and figure of steep aspheric and diffractive optics. UltraSurf is a computer controlled, non-contact coordinate measuring machine. It incorporates five air-bearing axes, linear motors, high-resolution feedback, and a non-contact probe. The measuring probe is scanned over the optical surface while maintaining perpendicularity and a constant focal offset. Multiple probe technologies are available on UltraSurf. Each probe has strengths and weaknesses relative to the material properties, surface finish, and figure error of an optical component. The measuring probes utilize absolute distance to resolve step heights and diffractive surface patterns. The non-contact scanning method avoids common pitfalls with stylus contact instruments. Advancements in measuring speed and precision has enabled fast and accurate non-contact metrology of diffractive and steep aspheric surfaces. The benefits of data sampling with twodimensional profiles and three-dimensional topography maps will be presented. In addition, accuracy, repeatability, and machine qualification will be discussed with regards to aspheres and diffractive surfaces.

ERRATUM: In vivo evaluation of a neural stem cell-seeded prosthesis In vivo evaluation of a neural stem cell-seeded prosthesis

NASA Astrophysics Data System (ADS)

Purcell, E. K.; Seymour, J. P.; Yandamuri, S.; Kipke, D. R.

2009-08-01

In the published article, an error was made in figure 5. Specifically, the three-month, NSC-seeded image is a duplicate of the six-week image, and the one-day, probe alone image is a duplicate of the three-month image. The corrected figure is reproduced below. Figure 5 Figure 5. Glial encapsulation of each probe condition over the 3 month time course. Ox-42 labeled microglia and GFAP labeled astrocytes are shown. Images are taken from probes implanted in the same animal at each time point. NSC seeding was associated with reduced non-neuronal density at 1 day post-implantation in comparison to alginate coated probes and at the 1 week time point in comparison to untreated probes (P < 0.001). Glial activation is at its overall peak 1 week after insertion. A thin encapsulation layer surrounds probes at the 6 week and 3 month time points, with NSC-seeded probes having the greatest surrounding non-neuronal density P < 0.001). Interestingly, microglia appeared to have a ramified, or `surveilling', morphology surrounding a neural stem cell-alginate probe initially, whereas activated cells with an amoeboid structure were found near an alginate probe in the same hemisphere of one animal (left panels).

Eddy current probe with foil sensor mounted on flexible probe tip and method of use

DOEpatents

Viertl, John R. M.; Lee, Martin K.

2001-01-01

A pair of copper coils are embedded in the foil strip. A first coil of the pair generates an electromagnetic field that induces eddy currents on the surface, and the second coil carries a current influenced by the eddy currents on the surface. The currents in the second coil are analyzed to obtain information on the surface eddy currents. An eddy current probe has a metal housing having a tip that is covered by a flexible conductive foil strip. The foil strip is mounted on a deformable nose at the probe tip so that the strip and coils will conform to the surface to which they are applied.

Probing nuclear symmetry energy at high densities using pion, kaon, eta and photon productions in heavy-ion collisions

NASA Astrophysics Data System (ADS)

Xiao, Zhi-Gang; Yong, Gao-Chan; Chen, Lie-Wen; Li, Bao-An; Zhang, Ming; Xiao, Guo-Qing; Xu, Nu

2014-02-01

The high-density behavior of nuclear symmetry energy is among the most uncertain properties of dense neutron-rich matter. Its accurate determination has significant ramifications in understanding not only the reaction dynamics of heavy-ion reactions, especially those induced by radioactive beams, but also many interesting phenomena in astrophysics, such as the explosion mechanism of supernova and the properties of neutron stars. The heavy-ion physics community has devoted much effort during the last few years to constrain the high-density symmetry using various probes. In particular, the / ratio has been most extensively studied both theoretically and experimentally. All models have consistently predicted qualitatively that the / ratio is a sensitive probe of the high-density symmetry energy especially with beam energies near the pion production threshold. However, the predicted values of the / ratio are still quite model dependent mostly because of the complexity of modeling pion production and reabsorption dynamics in heavy-ion collisions, leading to currently still controversial conclusions regarding the high-density behavior of nuclear symmetry energy from comparing various model calculations with available experimental data. As more / data become available and a deeper understanding about the pion dynamics in heavy-ion reactions is obtained, more penetrating probes, such as the K +/ K 0 ratio, meson and high-energy photons are also being investigated or planned at several facilities. Here, we review some of our recent contributions to the community effort of constraining the high-density behavior of nuclear symmetry energy in heavy-ion collisions. In addition, the status of some worldwide experiments for studying the high-density symmetry energy, including the HIRFL-CSR external target experiment (CEE) are briefly introduced.

Complexation of lysozyme with adsorbed PtBS-b-SCPI block polyelectrolyte micelles on silver surface.

PubMed

Papagiannopoulos, Aristeidis; Christoulaki, Anastasia; Spiliopoulos, Nikolaos; Vradis, Alexandros; Toprakcioglu, Chris; Pispas, Stergios

2015-01-20

We present a study of the interaction of the positively charged model protein lysozyme with the negatively charged amphiphilic diblock polyelectrolyte micelles of poly(tert-butylstyrene-b-sodium (sulfamate/carboxylate)isoprene) (PtBS-b-SCPI) on the silver/water interface. The adsorption kinetics are monitored by surface plasmon resonance, and the surface morphology is probed by atomic force microscopy. The micellar adsorption is described by stretched-exponential kinetics, and the micellar layer morphology shows that the micelles do not lose their integrity upon adsorption. The complexation of lysozyme with the adsorbed micellar layers depends on the micelles arrangement and density in the underlying layer, and lysozyme follows the local morphology of the underlying roughness. When the micellar adsorbed amount is small, the layers show low capacity in protein complexation and low resistance in loading. When the micellar adsorbed amount is high, the situation is reversed. The adsorbed layers both with or without added protein are found to be irreversibly adsorbed on the Ag surface.

Effect of secondary electron emission on the plasma sheath

NASA Astrophysics Data System (ADS)

Langendorf, S.; Walker, M.

2015-03-01

In this experiment, plasma sheath potential profiles are measured over boron nitride walls in argon plasma and the effect of secondary electron emission is observed. Results are compared to a kinetic model. Plasmas are generated with a number density of 3 × 1012 m-3 at a pressure of 10-4 Torr-Ar, with a 1%-16% fraction of energetic primary electrons. The sheath potential profile at the surface of each sample is measured with emissive probes. The electron number densities and temperatures are measured in the bulk plasma with a planar Langmuir probe. The plasma is non-Maxwellian, with isotropic and directed energetic electron populations from 50 to 200 eV and hot and cold Maxwellian populations from 3.6 to 6.4 eV and 0.3 to 1.3 eV, respectively. Plasma Debye lengths range from 4 to 7 mm and the ion-neutral mean free path is 0.8 m. Sheath thicknesses range from 20 to 50 mm, with the smaller thickness occurring near the critical secondary electron emission yield of the wall material. Measured floating potentials are within 16% of model predictions. Measured sheath potential profiles agree with model predictions within 5 V (˜1 Te), and in four out of six cases deviate less than the measurement uncertainty of 1 V.

Single-molecule analysis of the major glycopolymers of pathogenic and non-pathogenic yeast cells

NASA Astrophysics Data System (ADS)

El-Kirat-Chatel, Sofiane; Beaussart, Audrey; Alsteens, David; Sarazin, Aurore; Jouault, Thierry; Dufrêne, Yves F.

2013-05-01

Most microbes are coated with carbohydrates that show remarkable structural variability and play a crucial role in mediating microbial-host interactions. Understanding the functions of cell wall glycoconjugates requires detailed knowledge of their molecular organization, diversity and heterogeneity. Here we use atomic force microscopy (AFM) with tips bearing specific probes (lectins, antibodies) to analyze the major glycopolymers of pathogenic and non-pathogenic yeast cells at molecular resolution. We show that non-ubiquitous β-1,2-mannans are largely exposed on the surface of native cells from pathogenic Candida albicans and C. glabrata, the former species displaying the highest glycopolymer density and extensions. We also find that chitin, a major component of the inner layer of the yeast cell wall, is much more abundant in C. albicans. These differences in molecular properties, further supported by flow cytometry measurements, may play an important role in strengthening cell wall mechanics and immune interactions. This study demonstrates that single-molecule AFM, combined with immunological and fluorescence methods, is a powerful platform in fungal glycobiology for probing the density, distribution and extension of specific cell wall glycoconjugates. In nanomedicine, we anticipate that this new form of AFM-based nanoglycobiology will contribute to the development of sugar-based drugs, immunotherapeutics, vaccines and diagnostics.

Computation of the influence of scanning probe microscope (SPM) on quantum dot eigenstates and 2DEG potential

NASA Astrophysics Data System (ADS)

Stopa, Michael

2005-03-01

We calculate the electronic structure of GaAs-AlGaAs two-dimensional electron gas (2DEG) devices, such as quantum dots and quantum point contacts (QPCs) in the presence of a tip of a scanning probe microscope at some distance above the surface. The calculation employs standard density functional theory with exchange and correlation treated in the local density approximation. The position and voltage on the tip are varied and the conditions for depletion of the 2DEG are shown to compare favorably to experiment [1]. We show that the size of the depletion region created (by a negative tip voltage) is unexpectedly small due to focusing of the potential lines by the higher dielectric. We study the interaction of the tip with an isolated quantum dot that contains one or two electrons. The raster pattern of the difference between single particle energies reveals that the tip distorts the shape of the confining potential and suggests that excited state properties, if they can be measured experimentally, can contribute to the resolution of spatial information. [1] M.A. Topinka, R.M. Westervelt, E.J. Heller, ``http://meso.deas.harvard.edu/papers/Topinka, PT 56 12 (2003)'' (Imaging Electron Flow), Physics Today 56, 12 (2003).

Graphene Field-Effect Transistors for the Sensitive and Selective Detection of Escherichia coli Using Pyrene-Tagged DNA Aptamer.

PubMed

Wu, Guangfu; Dai, Ziwen; Tang, Xin; Lin, Zihong; Lo, Pik Kwan; Meyyappan, M; Lai, King Wai Chiu

2017-10-01

This study reports biosensing using graphene field-effect transistors with the aid of pyrene-tagged DNA aptamers, which exhibit excellent selectivity, affinity, and stability for Escherichia coli (E. coli) detection. The aptamer is employed as the sensing probe due to its advantages such as high stability and high affinity toward small molecules and even whole cells. The change of the carrier density in the probe-modified graphene due to the attachment of E. coli is discussed theoretically for the first time and also verified experimentally. The conformational change of the aptamer due to the binding of E. coli brings the negatively charged E. coli close to the graphene surface, increasing the hole carrier density efficiently in graphene and achieving electrical detection. The binding of negatively charged E. coli induces holes in graphene, which are pumped into the graphene channel from the contact electrodes. The carrier mobility, which correlates the gate voltage to the electrical signal of the APG-FETs, is analyzed and optimized here. The excellent sensing performance such as low detection limit, high sensitivity, outstanding selectivity and stability of the graphene biosensor for E. coli detection paves the way to develop graphene biosensors for bacterial detection. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Noise and Ionic Conductivity in Glass Nanochannels

NASA Astrophysics Data System (ADS)

Wiener, Benjamin; Siria, Alessandro; Bocquet, Lydéric; Stein, Derek

2015-03-01

Ion transport in nanochannels is relevant to processes in biology and has technological applications like batteries, fuel cells, and water desalination. We report experimental studies of the ionic conductance and noise characteristics of pulled glass capillaries with openings on the order of 200 nanometers. We employed an AC measurement technique to probe very low frequency fluctuations in the conductivity and to test a theory attributing these to chemical fluctuations in the surface charge density of the glass. We also investigate Hooge's empirical description of the noise power spectrum and its relationship to current rectification observed in nanochannels in the surface dominated ``Dukhin'' regime. Finally, we test the effects of anion and cation mobility on the direction and magnitude of the observed rectification. Research supported by NSF Grant DMR-1409577 and Oxford Nanopore Technologies.

Laminar Boundary Layer Stability Measurements at Mach 7 Including Wall Temperature Effects

DTIC Science & Technology

1977-11-01

Diagnostics were done by a four-probe rake bearing a pitot tube, a To probe and two hot films - a boundary layer hot film probe (BLHF) and a freestream hot...tunnel. Inset shows hot film probe close to the surface with second probe positioned higher to sample simultaneously the frcestream turbulence ( pitot ... rake away from the surface by small increments and taking readings at each stop. The readings were simultaneously recorded and reduced by the Tunnel B

Test probe for surface mounted leadless chip carrier

DOEpatents

Meyer, Kerry L.; Topolewski, John

1989-05-23

A test probe for a surface mounted leadless chip carrier is disclosed. The probed includes specially designed connector pins which allow size reductions in the probe. A thermoplastic housing provides spring action to ensure good mechanical and electrical contact between the pins and the contact strips of a leadless chip carrier. Other features include flexible wires molded into the housing and two different types of pins alternately placed in the housing. These features allow fabrication of a smaller and simpler test probe.

Test probe for surface mounted leadless chip carrier

DOEpatents

Meyer, K.L.; Topolewski, J.

1987-10-02

A test probe for a surface mounted leadless chip carrier is disclosed. The probe includes specially designed connector pins which allow size reductions in the probe. A thermoplastic housing provides spring action to ensure good mechanical and electrical contact between the pins and the contact strips of a leadless chip carrier. Other features include flexible wires molded into the housing and two different types of pins alternately placed in the housing. These features allow fabrication of a smaller and simpler test probe. 1 fig.

Melting probes revisited - Ice penetration experiments under Mars surface pressure conditions

NASA Astrophysics Data System (ADS)

Kömle, Norbert I.; Tiefenbacher, Patrick; Weiss, Peter; Bendiukova, Anastasiia

2018-07-01

Melting probes as vehicles to explore terrestrial ice sheets have been designed and applied successfully since the early 1960's. Later on, in the 1990's, various proposals were made to apply such probes also as a means to explore ice sheets on other bodies of the solar system, e.g. Jupiter's icy satellite Europa or the ice caps of Mars. For this type of subsurface probes the name cryobot has become common. We review both early developments and more recent efforts to develop probes for application in planetary environments, i.e. under low pressures and low temperatures. The current state of art as well as the pros and cons of the different concepts hitherto considered are described. While many tests with various probes have been done in terrestrial environments, experiments under low surface pressure conditions are rare. Therefore, we report here on lab tests with a simple melting probe under the range of pressure and temperature conditions that would be encountered on the surface of Mars and compare them with corresponding tests under a much lower gas pressure, possibly representative for icy satellites. The contribution of evaporation during the melting and its variation with surface pressure is also considered. All surface pressure measurements that have been performed on Mars up to now indicate a surface pressure above the water triple point pressure (612 Pa). This means that water ice always transforms into the liquid phase when warmed up to 0°C, before it evaporates into the ambient atmosphere. The temporary existence of the liquid phase around the heated tip of the cryobot allows good thermal conductance between probe and surrounding ice, which is an important pre-requisite for efficient melt penetration. Our experiments indicate that under all possible Mars surface pressures the liquid phase is present when the probe is heated up. This finding confirms experimentally that a probe as it was proposed by Paige (1992) for in situ exploration of the Mars north polar layers would work in the expected way, although the penetration velocity must be expected be lower than under Earth pressure conditions. A test with the same probe, but under an almost two orders of magnitude lower gas pressure than on Mars, still indicates the temporary existence of the liquid phase in the contact region between the probe and the surrounding ice.

Neutron reflectivity measurement of protein A-antibody complex at the solid-liquid interface.

PubMed

Mazzer, Alice R; Clifton, Luke A; Perevozchikova, Tatiana; Butler, Paul D; Roberts, Christopher J; Bracewell, Daniel G

2017-05-26

Chromatography is a ubiquitous unit operation in the purification of biopharmaceuticals yet few studies have addressed the biophysical characterisation of proteins at the solution-resin interface. Chromatography and other adsorption and desorption processes have been shown to induce protein aggregation which is undesirable in biopharmaceutical products. In order to advance understanding of how adsorption processes might impact protein stability, neutron reflectivity was used to characterise the structure of adsorbed immunoglobulin G (IgG) on model surfaces. In the first model system, IgG was adsorbed directly to silica and demonstrated a side-on orientation with high surface contact. A maximum dimension of 60Å in the surface normal direction and high density surface coverage were observed under pH 4.1 conditions. In chromatography buffers, pH was found to influence IgG packing density and orientation at the solid-liquid interface. In the second model system, which was designed to mimic an affinity chromatography surface, protein A was attached to a silica surface to produce a configuration representative of a porous glass chromatography resin. Interfacial structure was probed during sequential stages from ligand attachment, through to IgG binding and elution. Adsorbed IgG structures extended up to 250Å away from the surface and showed dependence on surface blocking strategies. The data was suggestive of two IgG molecules bound to protein A with a somewhat skewed orientation and close proximity to the silica surface. The findings provide insight into the orientation of adsorbed antibody structures under conditions encountered during chromatographic separations. Copyright © 2017 The Author(s). Published by Elsevier B.V. All rights reserved.

Langmuir Probe Diagnostics of Pulsed Plasma Doping System

NASA Astrophysics Data System (ADS)

Lei, Yu; Overzet, Lawrence J.; Felch, Susan B.; Fang, Ziwei; Koo, Bon-Woong; Goeckner, Matthew J.

2002-10-01

Pulsed plasma doping (P2LAD) is a potential solution to implement ultra-shallow junctions. In this study, Langmuir probe diagnostics techniques were investigated thoroughly for its application to P2LAD system, and the current sensing scheme using batteries and a 'downstairs' load resistor turned out to be the most reliable. Severe limitations of current transformers were found in diagnostics of pulsed plasma. A floating probe was proven to be good at monitoring the disturbances of the Langmuir probe and the cathode voltage. With the above technique, time-resolved Langmuir probe measurements have been carried out in a P2LAD system. The Langmuir probe data in Ar plasma indicate that during a 20 microns long implant pulse the plasma density ranges from 1E9 1E10 cm-3 and the electron temperature ranges from 0.4 to 14 eV. Between the pulses, the density keeps at the high level for 30 ms and then decays exponentially until reaching the range of 3E8 1E9 cm-3, which demonstrates the presence of residual plasma between pulses. A non-zero plasma density during the afterglow is also observed for BF3 plasma. Significant amounts of primary electron and electron beams are present during the ignition and ensuing steady region in both Ar and BF3 plasmas while they are much stronger in BF3 plasma. Plasma density is observed to increase with cathode voltage and pressure while the electron temperature is mainly influenced by the pressure. An overshoot of the cathode voltage during the afterglow region was found, and it significantly influences the plasma potential during the afterglow.

Tribological behavior of micro/nano-patterned surfaces in contact with AFM colloidal probe

NASA Astrophysics Data System (ADS)

Zhang, Xiaoliang; Wang, Xiu; Kong, Wen; Yi, Gewen; Jia, Junhong

2011-10-01

In effort to investigate the influence of the micro/nano-patterning or surface texturing on the nanotribological properties of patterned surfaces, the patterned polydimethylsiloxane (PDMS) surfaces with pillars were fabricated by replica molding technique. The surface morphologies of patterned PDMS surfaces with varying pillar sizes and spacing between pillars were characterized by atomic force microscope (AFM) and scanning electron microscope (SEM). The AFM/FFM was used to acquire the friction force images of micro/nano-patterned surfaces using a colloidal probe. A difference in friction force produced a contrast on the friction force images when the colloidal probe slid over different regions of the patterned polymer surfaces. The average friction force of patterned surface was related to the spacing between the pillars and their size. It decreased with the decreasing of spacing between the pillars and the increasing of pillar size. A reduction in friction force was attributed to the reduced area of contact between patterned surface and colloidal probe. Additionally, the average friction force increased with increasing applied load and sliding velocity.

Effect of working power and pressure on plasma properties during the deposition of TiN films in reactive magnetron sputtering plasma measured using Langmuir probe measurement

NASA Astrophysics Data System (ADS)

How, Soo Ren; Nayan, Nafarizal; Khairul Ahmad, Mohd; Fhong Soon, Chin; Zainizan Sahdan, Mohd; Lias, Jais; Shuhaimi Abu Bakar, Ahmad; Arshad, Mohd Khairuddin Md; Hashim, Uda; Yazid Ahmad, Mohd

2018-04-01

The ion, electron density and electron temperature during formation of TiN films in reactive magnetron sputtering system have been investigated for various settings of radio frequency (RF) power and working pressure by using Langmuir probe measurements. The RF power and working pressure able to affect the densities and plasma properties during the deposition process. In this work, a working pressure (100 and 20 mTorr) and RF power (100, 150 and 200 W) have been used for data acquisition of probe measurement. Fundamental of studied on sputter deposition is very important for improvement of film quality and deposition rate. Higher working pressure and RF power able to produce a higher ion density and reduction of electron temperature.

Probing electron acceleration and x-ray emission in laser-plasma accelerators

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

Thaury, C.; Ta Phuoc, K.; Corde, S.

2013-06-15

While laser-plasma accelerators have demonstrated a strong potential in the acceleration of electrons up to giga-electronvolt energies, few experimental tools for studying the acceleration physics have been developed. In this paper, we demonstrate a method for probing the acceleration process. A second laser beam, propagating perpendicular to the main beam, is focused on the gas jet few nanosecond before the main beam creates the accelerating plasma wave. This second beam is intense enough to ionize the gas and form a density depletion, which will locally inhibit the acceleration. The position of the density depletion is scanned along the interaction lengthmore » to probe the electron injection and acceleration, and the betatron X-ray emission. To illustrate the potential of the method, the variation of the injection position with the plasma density is studied.« less

Predicting In-Situ X-ray Diffraction for the SrTiO3/Liquid Interface from First Principles

NASA Astrophysics Data System (ADS)

Letchworth-Weaver, Kendra; Gunceler, Deniz; Sundararaman, Ravishankar; Huang, Xin; Brock, Joel; Arias, T. A.

2013-03-01

Recent advances in experimental techniques, such as in-situ x-ray diffraction, allow researchers to probe the solid-liquid interface in electrochemical systems under operating conditions. These advances offer an unprecedented opportunity for theory to predict properties of electrode materials in aqueous environments and inform the design of energy conversion and storage devices. To compare with experiment, these theoretical studies require microscopic details of both the liquid and the electrode surface. Joint Density Functional Theory (JDFT), a computationally efficient alternative to molecular dynamics, couples a classical density-functional, which captures molecular structure of the liquid, to a quantum-mechanical functional for the electrode surface. We present a JDFT exploration of SrTiO3, which can catalyze solar-driven water splitting, in an electrochemical environment. We determine the geometry of the polar SrTiO3 surface and the equilibrium structure of the contacting liquid, as well as the influence of the liquid upon the electronic structure of the surface. We then predict the effect of the fluid environment on x-ray diffraction patterns and compare our predictions to in-situ measurements performed at the Cornell High Energy Synchrotron Source (CHESS). This material is based upon work supported by the Energy Materials Center at Cornell (EMC2), an Energy Frontier Research Center funded by the U.S. Department of Energy.

Nanostructured optical fibre arrays for high-density biochemical sensing and remote imaging.

PubMed

Deiss, F; Sojic, N; White, D J; Stoddart, P R

2010-01-01

Optical fibre bundles usually comprise a few thousand to tens of thousands of individually clad glass optical fibres. The ordered arrangement of the fibres enables coherent transmission of an image through the bundle and therefore enables analysis and viewing in remote locations. In fused bundles, this architecture has also been used to fabricate arrays of various micro to nano-scale surface structures (micro/nanowells, nanotips, triangles, etc.) over relatively large areas. These surface structures have been used to obtain new optical and analytical capabilities. Indeed, the imaging bundle can be thought of as a "starting material" that can be sculpted by a combination of fibre drawing and selective wet-chemical etching processes. A large variety of bioanalytical applications have thus been developed, ranging from nano-optics to DNA nanoarrays. For instance, nanostructured optical surfaces with intrinsic light-guiding properties have been exploited as surface-enhanced Raman scattering (SERS) platforms and as near-field probe arrays. They have also been productively associated with electrochemistry to fabricate arrays of transparent nanoelectrodes with electrochemiluminescent imaging properties. The confined geometry of the wells has been loaded with biosensing materials and used as femtolitre-sized vessels to detect single molecules. This review describes the fabrication of high-density nanostructured optical fibre arrays and summarizes the large range of optical and bioanalytical applications that have been developed, reflecting the versatility of this ordered light-guiding platform.

Hybrid catadioptric system for advanced optical cavity velocimetry

DOEpatents

Frayer, Daniel K.

2018-02-06

A probe including reflector is disclosed to measure the velocity distribution of a moving surface along many lines of sight. Laser light, directed to the surface by the probe and then reflected back from the surface, is Doppler shifted by the moving surface, collected into probe, and then directed to detection equipment through optic fibers. The received light is mixed with reference laser light and using photonic Doppler velocimetry, a continuous time record of the surface movement is obtained. An array of single-mode optical fibers provides an optic signal to one or more lens groups and a reflector, such as a parabolic reflector having a mirrored interior surface.

Reversible electrochemical modification of the surface of a semiconductor by an atomic-force microscope probe

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

Kozhukhov, A. S., E-mail: antonkozhukhov@yandex.ru; Sheglov, D. V.; Latyshev, A. V.

A technique for reversible surface modification with an atomic-force-microscope (AFM) probe is suggested. In this method, no significant mechanical or topographic changes occur upon a local variation in the surface potential of a sample under the AFM probe. The method allows a controlled relative change in the ohmic resistance of a channel in a Hall bridge within the range 20–25%.

Eliminating Size-Associated Diffusion Constraints for Rapid On-Surface Bioassays with Nanoparticle Probes.

PubMed

Li, Junwei; Zrazhevskiy, Pavel; Gao, Xiaohu

2016-02-24

Nanoparticle probes enable implementation of advanced on-surface assay formats, but impose often underappreciated size-associated constraints, in particular on assay kinetics and sensitivity. The present study highlights substantially slower diffusion-limited assay kinetics due to the rapid development of a nanoprobe depletion layer next to the surface, which static incubation and mixing of bulk solution employed in conventional assay setups often fail to disrupt. In contrast, cyclic solution draining and replenishing yields reaction-limited assay kinetics irrespective of the probe size. Using common surface bioassays, enzyme-linked immunosorbent assays and immunofluorescence, this study shows that this conceptually distinct approach effectively "erases" size-dependent diffusion constraints, providing a straightforward route to rapid on-surface bioassays employing bulky probes and procedures involving multiple labeling cycles, such as multicycle single-cell molecular profiling. For proof-of-concept, the study demonstrates that the assay time can be shortened from hours to minutes with the same probe concentration and, at a typical incubation time, comparable target labeling can be achieved with up to eight times lower nanoprobe concentration. The findings are expected to enable realization of novel assay formats and stimulate development of rapid on-surface bioassays with nanoparticle probes. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Some experiments with the tunnel probe in a low temperature magnetized plasma

NASA Astrophysics Data System (ADS)

Kovačič, J.; Gyergyek, T.; Kavaš, B.; Vodnik, M.; Kavčič, J.; Gunn, J. P.

2018-02-01

Experiments were performed using a Tunnel Probe (TP) inside the weakly-ionised plasma of the Linear Magnetized Plasma Device (LMPD). The TP is designed as a concave probe, which should annihilate the problem of sheath expansion in the ion branch of the I-V characteristic. As the ion saturation current is consequently well defined, the ion parallel current and plasma density can be more accurately calculated. Furthermore the ratio between the ion saturation currents on the two collectors (tunnel ring and the back-plate) can be used to derive the electron temperature. The TP has been repeatedly used with success on the former Castor and Tore-Supra tokamaks and will be used on the upgraded version of Tore-supra, namely the WEST tokamak, as well [1, 2]. It was however never used successfully in a low-temperature plasma. We studied the feasibility of the TP use in a low-temperature plasma for direct measurements of plasma temperature and density. The various probe characteristic dimensions, such as the distance between the two collectors, the aperture size and the probe radius were varied to see influence of the individual probe feature. We also varied the level of magnetization of the charged particle species, the background gas pressure (which influences the electron energy distribution function), the plasma density (important for the ratio between the λ D and the ion Larmor radius). The sensitivity of the probe alignment to the magnetic field lines was also studied. We found, that the ion saturation current does not necessarily saturate and that the probe works according to expectations only in a limited amount of regimes.

Scanning electrochemical microscopy of graphene/polymer hybrid thin films as supercapacitors: Physical-chemical interfacial processes

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

Gupta, Sanju, E-mail: sanju.gupta@wku.edu; Price, Carson

2015-10-15

Hybrid electrode comprising an electric double-layer capacitor of graphene nanosheets and a pseudocapacitor of the electrically conducting polymers namely, polyaniline; PAni and polypyrrole; PPy are constructed that exhibited synergistic effect with excellent electrochemical performance as thin film supercapacitors for alternative energy. The hybrid supercapacitors were prepared by layer-by-layer (LbL) assembly based on controlled electrochemical polymerization followed by reduction of graphene oxide electrochemically producing ErGO, for establishing intimate electronic contact through nanoscale architecture and chemical stability, producing a single bilayer of (PAni/ErGO){sub 1}, (PPy/ErGO){sub 1}, (PAni/GO){sub 1} and (PPy/GO){sub 1}. The rationale design is to create thin films that possess interconnectedmore » graphene nanosheets (GNS) with polymer nanostructures forming well-defined tailored interfaces allowing sufficient surface adsorption and faster ion transport due to short diffusion distances. We investigated their electrochemical properties and performance in terms of gravimetric specific capacitance, C{sub s}, from cyclic voltammograms. The LbL-assembled bilayer films exhibited an excellent C{sub s} of ≥350 F g{sup −1} as compared with constituents (∼70 F g{sup −1}) at discharge current density of 0.3 A g{sup −1} that outperformed many other hybrid supercapacitors. To gain deeper insights into the physical-chemical interfacial processes occurring at the electrode/electrolyte interface that govern their operation, we have used scanning electrochemical microscopy (SECM) technique in feedback and probe approach modes. We present our findings from viewpoint of reinforcing the role played by heterogeneous electrode surface composed of nanoscale graphene sheets (conducting) and conducting polymers (semiconducting) backbone with ordered polymer chains via higher/lower probe current distribution maps. Also targeted is SECM imaging that allowed to determine electrochemical (re)activity of surface ion adsorption sites density at solid/liquid interface.« less

Surface enhanced Raman gene probe and methods thereof

DOEpatents

Vo-Dinh, T.

1998-09-29

The subject invention disclosed herein is a new gene probe biosensor and methods based on surface enhanced Raman scattering (SERS) label detection. The SER gene probe biosensor comprises a support means, a SER gene probe having at least one oligonucleotide strand labeled with at least one SERS label, and a SERS active substrate disposed on the support means and having at least one of the SER gene probes adsorbed thereon. Biotargets such as bacterial and viral DNA, RNA and PNA are detected using a SER gene probe via hybridization to oligonucleotide strands complementary to the SER gene probe. The support means supporting the SERS active substrate includes a fiberoptic probe, an array of fiberoptic probes for performance of multiple assays and a waveguide microsensor array with charge-coupled devices or photodiode arrays. 18 figs.

Surface enhanced Raman gene probe and methods thereof

DOEpatents

Vo-Dinh, Tuan

1998-01-01

The subject invention disclosed herein is a new gene probe biosensor and methods thereof based on surface enhanced Raman scattering (SERS) label detection. The SER gene probe biosensor comprises a support means, a SER gene probe having at least one oligonucleotide strand labeled with at least one SERS label, and a SERS active substrate disposed on the support means and having at least one of the SER gene probes adsorbed thereon. Biotargets such as bacterial and viral DNA, RNA and PNA are detected using a SER gene probe via hybridization to oligonucleotide strands complementary to the SER gene probe. The support means supporting the SERS active substrate includes a fiberoptic probe, an array of fiberoptic probes for performance of multiple assays and a waveguide microsensor array with charge-coupled devices or photodiode arrays.