Photocarrier generation mechanisms in anthracene crystals under ultra-high vacuum

1970 ◽  
Vol 23 (8) ◽  
pp. 1571 ◽  
Author(s):  
GR Johnston ◽  
LE Lyons
Keyword(s):  
Incident Light ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Surface Generation ◽  
Generation Process ◽  
Singlet Exciton ◽  
Before And After ◽  
Generation Mechanisms ◽  
Theoretical Considerations ◽  
Hole Generation

A detailed investigation of the transient photocurrents generated in anthracene single crystals has been undertaken. The variations of the measured currents with the wavelength and intensity of the incident light, the applied voltage, and the temperature of the crystal are given for crystals both before, and after, subjection to ultra-high vacuum. Removal of the surface by evaporation is seen to produce large changes in the observed photocurrents. A biphotonic generation process for both hole and electron currents at high light intensities is observed after prolonged evacuation. Theoretical considerations show this biphotonic process to be singlet-exciton/singlet-exciton collision annihilation with a rate constant of 1.8 x 10-18�0.5 m3/s. Surface generation of holes is shown to decrease upon evacuation and to grow on readmission of oxygen. After prolonged evacuation, the bi-excitonic mechanism for hole generation almost completely swamps the "extrinsic" generation at the surface. However, the electron current becomes predominantly monophotonic with evaporation of the surface.

Attractive and repulsive forces between clusters: A STEM study of platinum clusters

1983 ◽  
Vol 41 ◽  
pp. 334-335
Author(s):  
E. G. Chen ◽  
M. Ohtsuki ◽  
A. V. Crewe
Keyword(s):  
High Vacuum ◽  
Carbon Film ◽  
Distribution Functions ◽  
Ultra High Vacuum ◽  
Thin Carbon ◽  
Platinum Clusters ◽  
Before And After ◽  
Thin Carbon Film ◽  
Repulsive Forces ◽  
Theoretical Considerations

Zanghi et al. measured the radial distribution functions of gold clusters on a KC1 substrate before and after annealing, and interpreted their results as indicating that a repulsive force exists between each pair of clusters. However, these results may be insufficient to explain the clustering phenomenon in all cases. For instance if this were the only force involved then coalescence could not occur. However, coalescence always occurs in the forming of thin films.We present experimental results and some theoretical considerations of the interactive forces applied to the clustering of platinum deposited on a thin carbon film of about 20Å thickness. The ultra high vacuum (UHV)-STEM and digital image processor were used for the measurements of the size (d) and edge to edge (r-d) distributions (see Fig. 1).

Exoelectron emission from unexcited metallic glasses Fe78B13Si9 during heat treatment

1992 ◽  
Vol 7 (6) ◽  
pp. 1396-1399 ◽  
Author(s):  
Yoshihisa Watanabe ◽  
Tadayoshi Kubozoe ◽  
Yoshikazu Nakamura
Keyword(s):  
Heat Treatment ◽  
Metallic Glasses ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Exoelectron Emission ◽  
Radiation Chemical ◽  
Temperature Range ◽  
High Vacuum Condition ◽  
Before And After ◽  
Ultra High Vacuum Condition

Exoelectron emission from the surface of unexcited metallic glasses Fe78B13Si9 during heat treatment has been studied under ultra high vacuum condition. In the first heating cycle, exoelectrons are emitted from the as-cast ribbon in the temperature range from approximately 423 K to 773 K (150 °C to 500 °C), although the surface of the specimen is not excited by ionizing radiation, chemical processes, or mechanical treatments prior to measurements. In the second and subsequent heating cycles, however, there is no anomalous emission observed in the same temperature range. In order to elucidate the mechanism of emission, the surface of the specimen is observed by the atomic force microscope (AFM) before and after measurements. In the AFM image, many crystallites in the amorphous matrix can be found in the surface of the heated specimen. These experimental results show that exoelectrons are emitted in the same temperature range as the early stages of crystallization on the surface of metallic glasses. We hypothesize that the two effects are correlated.

The Origins of High Spatial Resolution Secondary Electron Microscopy

1992 ◽  
Vol 295 ◽  
Author(s):  
M. R. Scheinfein ◽  
J. S. Drucker ◽  
J. Liu ◽  
J. K. Weiss ◽  
G. G. Hembree ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Spatial Resolution ◽  
Secondary Electron ◽  
High Spatial Resolution ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Generation Process ◽  
Secondary Electrons ◽  
Electron Generation ◽  
Secondary Electron Generation

AbstractThe secondary electron generation process is studied in an ultra-high vacuum scanning transmission electron microscope using electron coincidence spectroscopy. Production pathways for secondary electrons are determined by analyzing coincidences between secondary electrons and individual excitation events. The ultimate spatial resolution available in scanning electron microscopy is limited by the delocalization of the secondary electron generation process. This delocalization is studied using momentum resolved coincidence electron spectroscopy. The fraction of secondary electrons resulting from localized excitations can explain the high spatial resolution observed in secondary electron microscopy images.

scholarly journals Elektronische Wechselwirkung zwischen aufgedampften Germaniumfilmen und Sauerstoff

1963 ◽  
Vol 18 (2) ◽  
pp. 119-125 ◽  
Author(s):  
R. Suhrmann ◽  
M. Kruel ◽  
G. Wedler
Keyword(s):  
Boundary Layer ◽  
Electron Acceptor ◽  
Boundary Layer Thickness ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Band Model ◽  
Electric Resistance ◽  
Before And After ◽  
Higher Temperature ◽  
Ordered State

Ge films of thicknesses within the p-boundary layer thickness are precipitated under ultra high vacuum conditions, at 77°K. They are investigated either in the disordered state (before annealing at a higher temperature) or in the ordered state (after annealing). The electric resistance R and the photoelectric work function Φ are measured before and after the influence of known amounts of oxygen. R is plotted as a function of time and coverage n, Φ as a function of n. Small amounts of oxygen cause R to increase without changing Φ, large amounts result in a succeeding decrease of R and cause Φ to increase by 0.1 to 0.2 V. The results are discussed by means of a band model. At small coverages oxygen acts as an electron donator, at higher coverages as an electron acceptor.

Deuterium Out-Diffusion Kinetics in Magnesium-Doped GaN

2007 ◽  
Vol 994 ◽  
Author(s):  
Jacques Chevallier ◽  
François Jomard ◽  
Norbert H. Nickel ◽  
Philippe de Mierry ◽  
Sébastien Chenot ◽  
...  
Keyword(s):  
High Vacuum ◽  
Ultra High Vacuum ◽  
Diffusion Kinetics ◽  
First Order ◽  
Annealing Step ◽  
Before And After ◽  
Sims Analysis ◽  
Kinetics Of ◽  
Annealing Experiments ◽  
Mg Doped

AbstractA series of isothermal annealing experiments have been performed in the range 790–920°C under N2 flow in order to study the deuterium out-diffusion kinetics of Mg-doped GaN grown on sapphire under deuterated ammonia. The deuterium concentration was measured by SIMS analysis before and after each annealing step. The kinetics closely follow a first-order law. The activation energy related to the deuterium out-diffusion process is 3.1 eV. In addition, deuterium effusion measurements were performed measuring the molecular HD flux while the specimens were annealed in ultra high vacuum with a linear heating rate. In contrast to SIMS, this method detects the species that migrated out of the sample. Effusion peaks of the HD flux at 360 and 490°C are attributed to the fragmentation of adsorbed CHxDy complexes. The molecular HD flux starts increasing at 800°C which is the onset of the GaN decomposition and has its maximum at 920°C. This HD flux is accompanied by the desorption of H and D containing radicals and molecules desorbing above 900°C.

Surface Composition of TiO2-Zn Nanotubes by NanoSIMS

MRS Advances ◽  
2016 ◽  
Vol 1 (46) ◽  
pp. 3151-3156
Author(s):  
Indu B Mishra ◽  
Diana Khusnutdinova ◽  
William T Petuskey
Keyword(s):  
Secondary Electron ◽  
High Spatial Resolution ◽  
Surface Composition ◽  
High Vacuum ◽  
Isotopic Analysis ◽  
Ultra High Vacuum ◽  
Actual Content ◽  
Before And After ◽  
Sims Analysis

ABSTRACTTitania nanotubes were prepared by anodic oxidation of Ti. The titania surfaces were partially coated with Zn by reacting zinc acetate with the nanotubes and then annealed. [1] An annealed nanotube cluster was placed carefully on a silicon wafer using tweezers. Secondary electron images were acquired by bombarding with Cs+ and observing the ejected OZn- and OTi- respectively. The SIMS analysis was done in ultra-high vacuum (∼ 10-10 Torr). The location of before and after the SIMS analysis was confirmed by scanning electron microscopy (SEM). Specific areas with various orientations (vertical and horizontal orientations) of the nanotubes were selected for the NanoSIMS 50L analysis. The NanoSIMS 50L is made by Ametek Cameca, Gennevillieres, France and is capable of doing in situ isotopic analysis of surfaces at high spatial resolution (25 nm2). The average ZnO/TiO was ∼1.8%, confirming the actual content of Zn used during synthesis of the nanotubes. Qualitatively, the TiO/ZnO ratio increased with increasing depth implying that ZnO concentration was decreasing as we probed into the nanotubes.

Carbon Nanotube Modification Using BaF2 Vapor in Ultra-High Vacuum Environment

2003 ◽  
Vol 782 ◽  
Author(s):  
Francisco Santiago ◽  
Victor H. Gehman ◽  
Karen Long ◽  
Kevin A. Boulais
Keyword(s):  
Carbon Nanotubes ◽  
Carbon Nanotube ◽  
Photoelectron Spectroscopy ◽  
High Vacuum ◽  
Heat Exposure ◽  
Major Change ◽  
Ultra High Vacuum ◽  
Force Microscopy ◽  
Before And After ◽  
Potential Applications

ABSTRACTCarbon nanotubes have attracted significant attention in the scientific community due to their unique properties and potential applications. One of the most promising applications is a carbon-nanotube transistor. The motivation of this work is to find ways to connect carbon nanotubes directly to silicon using Ba as a chemical link. We studied chemical interactions between carbon nanotubes and BaF2 vapors using x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Surfaces of silicon wafers were chemically modified to allow the epitaxial growth of BaF2 using molecular beam epitaxy (MBE). Samples containing 2D single crystal islands of BaF2 were covered with carbon nanotubes with an average coverage of 10 nanotubes per um2. The samples were transferred to an outgasing station inside the MBE system and heated to 900°C for two hours in a pressure of 10-9 mbar. XPS C1s data before and after heat show a major change in the nature of the carbon nanotube electronic states. In addition XPS shows formation of a Ba-C “carbide like” bond and no presence of fluorine. AFM images of the same region taken before and after heat exposure show remarkable changes in the surface morphology of the carbon-nanotube wall.

Thin Pyrolytic Graphite Films for Electron Microscope Substrates

1971 ◽  
Vol 29 ◽  
pp. 226-227 ◽  
Author(s):  
George H. N. Riddle ◽  
Benjamin M. Siegel
Keyword(s):  
Vacuum Chamber ◽  
Pyrolytic Graphite ◽  
High Vacuum ◽  
Dark Field ◽  
Ultra High Vacuum ◽  
Graphite Substrate ◽  
Nickel Substrate ◽  
Routine Procedure ◽  
Field Electron Microscopy ◽  
Dark Field Electron

A routine procedure for growing very thin graphite substrate films has been developed. The films are grown pyrolytically in an ultra-high vacuum chamber by exposing (111) epitaxial nickel films to carbon monoxide gas. The nickel serves as a catalyst for the disproportionation of CO through the reaction 2C0 → C + CO2. The nickel catalyst is prepared by evaporation onto artificial mica at 400°C and annealing for 1/2 hour at 600°C in vacuum. Exposure of the annealed nickel to 1 torr CO for 3 hours at 500°C results in the growth of very thin continuous graphite films. The graphite is stripped from its nickel substrate in acid and mounted on holey formvar support films for use as specimen substrates.The graphite films, self-supporting over formvar holes up to five microns in diameter, have been studied by bright and dark field electron microscopy, by electron diffraction, and have been shadowed to reveal their topography and thickness. The films consist of individual crystallites typically a micron across with their basal planes parallel to the surface but oriented in different, apparently random directions about the normal to the basal plane.

A High Voltage Electron Microscopy Study of Sub-Oxide Formation in Vanadium

1971 ◽  
Vol 29 ◽  
pp. 212-213
Author(s):  
R. H. Geiss ◽  
R. L. Ladd ◽  
K. R. Lawless
Keyword(s):  
High Vacuum ◽  
Microscopy Study ◽  
Electron Microscopy Study ◽  
Ultra High Vacuum ◽  
Pure Oxygen ◽  
Pressure Oxidation ◽  
High Voltage Electron Microscopy ◽  
Oxidation Study ◽  
Voltage Electron ◽  
Good Agreement

Detailed electron microscope and diffraction studies of the sub-oxides of vanadium have been reported by Cambini and co-workers, and an oxidation study, possibly complicated by carbon and/or nitrogen, has been published by Edington and Smallman. The results reported by these different authors are not in good agreement. For this study, high purity polycrystalline vanadium samples were electrochemically thinned in a dual jet polisher using a solution of 20% H2SO4, 80% CH3OH, and then oxidized in an ion-pumped ultra-high vacuum reactor system using spectroscopically pure oxygen. Samples were oxidized at 350°C and 100μ oxygen pressure for periods of 30,60,90 and 160 minutes. Since our primary interest is in the mechanism of the low pressure oxidation process, the oxidized samples were cooled rapidly and not homogenized. The specimens were then examined in the HVEM at voltages up to 500 kV, the higher voltages being necessary to examine thick sections for which the oxidation behavior was more characteristic of the bulk.

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