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.

Elektronische Wechselwirkung zwischen Kohlenmonoxyd und aufgedampften Ge-Filmen mit reiner oder mit Sauerstoff vorbelegter Oberfläche

1963 ◽  
Vol 18 (5) ◽  
pp. 633-638
Author(s):  
R. Suhrmann ◽  
M. Kruel ◽  
G. Wedler
Keyword(s):  
Room Temperature ◽  
High Vacuum ◽  
Electron Donors ◽  
Band Model ◽  
Electronic Interaction ◽  
Electric Resistance ◽  
Before And After ◽  
Adsorption Of Co ◽  
Higher Temperature ◽  
Ordered State

Ge-films are evaporated under 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 carbon monoxide. R is plotted as a function of time and coverage n, Φ as a function of n. At 77°K an electronic interaction between the CO molecules and the Ge-film follows from an observed irreversible and reversible increase in R; Φ is not altered. The discussion by means of a band model shows that the CO molecules act as electron donors. At room temperature no interaction is found. Films precovered with oxygen show two simultaneous reactions during the adsorption of CO: a stronger adsorption on the spots precovered with oxygen and a weaker one on the bare Ge surface.

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.

Hydridization and catalysis by lanthanide films

1984 ◽  
Vol 393 (1805) ◽  
pp. 257-276 ◽  
Keyword(s):  
Activation Energy ◽  
High Vacuum ◽  
Deuterium Atom ◽  
Ultra High Vacuum ◽  
Gas Uptake ◽  
Metal Sublattice ◽  
Hydrogen Deuterium ◽  
Higher Temperature ◽  
Temperature Programmed ◽  
Interstitial Hydrogen

Hydrogen absorption to give the dihydrides MH 2+1 containing interstitial hydrogen H i has been studied for the metals Gd, Dy, Er, Yb and Lu in the form of films deposited in ultra-high vacuum on glass. Film areas were determined by Kr adsorption, and hydrogen content, in particular inter­stitial hydrogen H i , characterized by gas uptake, temperature programmed desorption, electrical conductivity and work function measurements by the diode method. The catalytic activity of the dihydride films for the H 2 + D 2 → 2HD reaction was studied at a pressure of 1.1 Torr over 175-579 K, and at 273 K over 0.19-6.2 Torr. Arrhenius plots for the rate con­stant show a low temperature low activation energy region changing over at a temperature T c to a higher temperature higher activation energy régime, with T c on average for the five metals about 50 K below the tem­perature T max at which the interstitial hydrogen H i has disappeared. The suggested mechanisms are T < T c : D 2 + H i □ s → (D 2 H i )□ s → □ s D i + HD, (1) T > T c : D 2 + H 2 + 4□ s → 2(D i □ s ) (H i □ s ) → 4□ s + 2HD, (2) where H i □ s , D i □ s , denotes a hydrogen, deuterium, atom held on a surface octahedral site in the f. c. c. metal sublattice. These mechanisms agree with the observed approximate first-order pressure dependency down to 77 K. The rate constants at both 273 K (under T c ) and 573 K (over T c ) decrease over Gd, Dy, Er, to Yb, and rise again to Lu, and this is discussed in terms of the metal-hydrogen, H i □ s or D i □ s bond strength.

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.

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).

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.

A Note on the Effect of Surface Finish on the Thrust of a Supersonic Conical Nozzle

1958 ◽  
Vol 62 (575) ◽  
pp. 829-829
Author(s):  
P. N. Rowe
Keyword(s):  
Boundary Layer ◽  
Layer Thickness ◽  
Surface Finish ◽  
Boundary Layer Thickness ◽  
Conical Nozzle ◽  
Polishing Process ◽  
Interior Surface ◽  
Before And After ◽  
Usual Process ◽  
Effect Of Surface

The Propelling Nozzles tested are turned from brass and the interior surface finish shows a centre line average of about 15 micro inches when examined on a Taylor Hobson machine. This is fairly rough compared with the estimated boundary layer thickness and it was required to know whether this in fact affected the thrust. The thrust of a nozzle manufactured by the usual process was measured before and after a polishing process. An improvement of one half per cent was recorded.

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.

Sign in / Sign up

Export Citation Format

Share Document