Effects of Potassium on the Adsorption and Reactions of Nitric Oxide on Silicon Surface

1988 ◽  
Vol 131 ◽  
Author(s):  
Z. C. Ying ◽  
W. Ho
Keyword(s):  
High Vacuum ◽  
Ultra High Vacuum ◽  
Thermal Heating ◽  
Photon Irradiation ◽  
Structure Changes ◽  
Function Change ◽  
Resolution Electron ◽  
High K ◽  
Work Function Change ◽  
Electron Energy Loss

ABSTRACTThe adsorption, thermoreactions, and photoreactions of NO coadsorbed with K on Si(111)7×7 at 90 K have been studied and compared with the results obtained from the Kfree surface. The experiments were performed under ultra-high vacuum conditions using high resolution electron energy loss spectroscopy, work function change measurements, and mass spectrometry. NO adsorbs both molecularly and dissociatively on the K-free surface. Two molecular N–O stretching modes are observed at 188 and 225 meV. The concentration of these NO molecules on the surface decreases as the K exposure increases and vanishes at high K exposures. A new N–O stretching mode, attributed to adsorption of NO molecules on K clusters, is observed at 157 meV. After thermal heating or photon irradiation, the surface is covered with atomic O and N. The surface is more oxidized in the presence of K. A steady decrease in the photodesorption cross section is observed as the K exposure increases and is attributed to K-induced band structure changes.

ADSORPTION ON ORDERED BINARY ALLOY SURFACES: HYDROGEN ADSORPTION ON THE CLEAN AND CO-COVERED Cu3Pt(111) SURFACE

1996 ◽  
Vol 03 (05n06) ◽  
pp. 1889-1897 ◽  
Author(s):  
C. BECKER ◽  
U. SCHRÖDER ◽  
R. LINKE ◽  
B. SCHIEFFER ◽  
K. WANDELT
Keyword(s):  
Lattice Gas ◽  
Hydrogen Adsorption ◽  
Thermal Desorption Spectroscopy ◽  
Lateral Interaction ◽  
Function Change ◽  
Resolution Electron ◽  
Work Function Change ◽  
Electron Energy Loss ◽  
Adsorption And Dissociation ◽  
Lateral Segregation

The adsorption of hydrogen, as well as the interaction of adsorbed CO and hydrogen, on the Cu 3 Pt (111) surface have been studied using thermal desorption spectroscopy (TDS), high resolution electron energy loss spectroscopy (HREELS) and work function change measurements (ΔΦ). The results show that hydrogen adsorption and dissociation occur via platinum sites. The process proceeds with second order kinetics with respect to the number of platinum sites available. The desorption spectra are successfully simulated using a lattice gas model. From the simulations the desorption and lateral interaction energies are deduced, showing a weak hydrogen-hydrogen repulsion. The interaction of coadsorbed CO and hydrogen has also been investigated. In contrast to the Pt(111) surface where a lateral segregation of the two adsorbed species takes place, the results presented here suggest a mixed overlayer.

Atomic-level imaging of the surface structure of Ag2O

1984 ◽  
Vol 42 ◽  
pp. 656-657
Author(s):  
William Krakow
Keyword(s):  
High Vacuum ◽  
Atomic Level ◽  
Ultra High Vacuum ◽  
Research Groups ◽  
Resolution Electron ◽  
Surface Reconstructions ◽  
Order Of Magnitude ◽  
High Resolution Electron Microscope ◽  
Saturated Structure ◽  
Transmission And Reflection

In recent years electron microscopy has been used to image surfaces in both the transmission and reflection modes by many research groups. Some of this work has been performed under ultra high vacuum conditions (UHV) and apparent surface reconstructions observed. The level of resolution generally has been at least an order of magnitude worse than is necessary to visualize atoms directly and therefore the detailed atomic rearrangements of the surface are not known. The present author has achieved atomic level resolution under normal vacuum conditions of various Au surfaces. Unfortunately these samples were exposed to atmosphere and could not be cleaned in a standard high resolution electron microscope. The result obtained surfaces which were impurity stabilized and reveal the bulk lattice (1x1) type surface structures also encountered by other surface physics techniques under impure or overlayer contaminant conditions. It was therefore decided to study a system where exposure to air was unimportant by using a oxygen saturated structure, Ag2O, and seeking to find surface reconstructions, which will now be described.

Observation of GaAs/Si Epitaxial Interfaces by Atomic Resolution Electron Microscopy

1986 ◽  
Vol 67 ◽  
Author(s):  
N. Otsuka ◽  
C. Choi ◽  
Y. Nakamura ◽  
S. Nagakura ◽  
R. Fischer ◽  
...  
Keyword(s):  
Substrate Surface ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Threading Dislocations ◽  
Misfit Dislocations ◽  
Si Substrates ◽  
Voltage Electron ◽  
Resolution Electron ◽  
Gaas Films ◽  
Substrate Surfaces

ABSTRACTRecent studies have shown that high quality GaAs films can be grown by MBE on Si substrates whose surfaces are slightly tilted from the (100) plane. In order to investigate the effect of the tilting of substrate surfaces on the formation of threading dislocations, the GaAs/Si epitaxial interfaces have been observed with a 1 MB ultra-high vacuum, high voltage electron microscope. Two types of misfit dislocations, one with Burgers vectors parallel to the interface and the other with Burgers vectors inclined from the interface, were found in these epitaxial interfaces. The observation of crosssectional samples perpendicular to each other has shown that the tilting of the substrate surface directly influences the generation of these two types of misfit dislocations. The mechanism of the reduction of threading dislocations by the tilting of the substrate surface is discussed based on these observations.

Hrem Study of Ultra Thin Titanium Films

1997 ◽  
Vol 472 ◽  
Author(s):  
T. Braisaz ◽  
P. Ruterana ◽  
G. Nouet ◽  
Ph. Komninou ◽  
Th. Kehagias ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
High Vacuum ◽  
High Resolution Electron Microscopy ◽  
Zone Axis ◽  
Ultra High Vacuum ◽  
Electron Gun ◽  
Mirror Plane ◽  
Planar Defects ◽  
Resolution Electron ◽  
Order Of Magnitude

ABSTRACTHigh resolution electron microscopy has been used to characterize the structure of ultra thin films of titanium deposited on KBr substrate by Ultra High Vacuum (UHV) electron-gun evaporation. The size of the grains has an order of magnitude of 10 nm whatever the substrate temperature. The observations have been carried out along <1123> zone axis. Some of the grains contain planar defects which were identified as the twin {1011}. The atomic structure of this twin is characterized by a mirror plane similar to that observed in polycrystalline titanium. Additionaly, this structure can be modified by a b2/2 twinning dislocation.

A Field Emission Electron Microscope

1971 ◽  
Vol 29 ◽  
pp. 6-7
Author(s):  
A. Tonomura ◽  
T. Komoda
Keyword(s):  
Electron Microscope ◽  
Field Emission ◽  
High Vacuum ◽  
High Resolution Electron Microscopy ◽  
Ultra High Vacuum ◽  
Electron Optics ◽  
Ion Pumps ◽  
High Brightness ◽  
Emission Electron ◽  
Resolution Electron

We have developed a field emission electron microscope. Although field emission gun requires ultra high vacuum and skillful technique, it brings about the favorable characteristics of high brightness and small energy spread. This characteristics will enable a significant progress in coherent electron optics and high resolution electron microscopy, especially in electron beam holography.Its column is Hitachi HU-11C Electron Microscope modified for ultra high vacuum operation, and it is evacuated with five ion pumps. Field emission gun is divided into two parts and is evacuated differentially with two ion pumps and a sublimation pump. The final pressures in these rooms are 5x10-10 Torr and 5x10-8 Torr respectively.

Electron energy loss spectroscopy in glancing reflection and other recent EELS developments

1983 ◽  
Vol 41 ◽  
pp. 386-387
Author(s):  
O.L. Krivanek ◽  
Y. Tanishiro ◽  
K. Yagi ◽  
R.P. Burgner
Keyword(s):  
Energy Loss ◽  
Electron Energy ◽  
Large Fraction ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
X Rays ◽  
Reconstruction Process ◽  
Surface Reflection ◽  
Surface Steps ◽  
Electron Energy Loss

Surface reflection images have recently revealed surface steps, surface- intersecting dislocations, and even the nature of a surface reconstruction process. While a large fraction of electrons incident on a crystal at a low angle penetrate into the bulk where they excite X-rays thus rendering glancing reflection EDXS surface insensitive, the electrons which emerge eventually penetrate typically only 10 to 30Å into the crystal, and should thus be highly sensitive as a surface probe. We have therefore investigated the suitability of glancing reflection EELS as a surface-sensitive chemical analysis technique complementary to glancing reflection imaging.The experiments were performed in a JEM 100B electron microscope modified for ultra-high vacuum (UHV) performance by the addition of liquid He cryo- pumping around the specimen, using a Gatan 607 electron energy loss spectrometer. Fig. 1 shows a series of spectra recorded for various glancing reflection conditions on clean (111) Si. It is clear that most electrons with which REM images are formed have been scattered inelastically at least once.

In situ quantitative analysis of GeXSi1-X alloys during growth by reflection EELS

1991 ◽  
Vol 49 ◽  
pp. 878-879
Author(s):  
Shouleh Nikzad ◽  
Channing C. Ahn ◽  
Harry A. Atwater
Keyword(s):  
Energy Loss ◽  
Electron Energy ◽  
Film Growth ◽  
High Vacuum ◽  
High Energy ◽  
Ultra High Vacuum ◽  
Mbe Growth ◽  
Electron Microscopes ◽  
Electron Energy Loss

The universality of reflection high energy electron diffraction (RHEED) as a structural tool during film growth by molecular beam epitaxy (MBE) brings with it the possibility for in situ surface chemical analysis via spectroscopy of the accompanying inelastically scattered electrons. We have modified a serial electron energy loss spectrometer typically used on an electron microscope to work with a 30 keV RHEED-equipped MBE growth chamber in order to determine the composition of GexSi1-x alloys by reflection electron energy loss (REELS) experiments. Similar work done in transmission electron microscopes has emphasized the surface sensitivity of this technique even though these experiments have never been done under ultra-high vacuum conditions. In this work, we are primarily concerned with the accuracy with which core losses can be used to determine composition during MBE growth.

Photoreactions of Mo(CO)6 on Potassium Precovered Silicon Surface with UV to IR Radiation

1988 ◽  
Vol 129 ◽  
Author(s):  
Z. C. Ying ◽  
W. Ho
Keyword(s):  
Uv Radiation ◽  
Wavelength Range ◽  
Silicon Surface ◽  
High Vacuum ◽  
Dissociative Adsorption ◽  
Charge Carriers ◽  
Ultra High Vacuum ◽  
Ir Radiation ◽  
Photon Irradiation ◽  
Wide Wavelength Range

ABSTRACTThe adsorption and photoreactions of Mo(CO)6 coadsorbed with K on Si(111)7×7 at 90 K have been studied under ultra-high vacuum conditions. It is found that dissociative adsorption of Mo(CO)6 on the K preadsorbed surface occurs for coverages below a monolayer. A multilayer of physisorbed Mo(CO)6 molecules is formed on top of the monolayer. Under photon irradiation physisorbed Mo(CO)6 molecules are dissociated and CO desorption is observed. The photoreactions of Mo(CO)6 occur over a wide wavelength range from the UV to IR. In contrast, only UV radiation induces photoreactions of Mo(CO)6 on the K-free Si(111)7×7 surface. Evidently K opens a new channel for the photoreactions of Mo(CO)6 on the surface. A mechanism involving interactions between photogenerated charge carriers and the substrate-adsorbate complex is proposed.

A Computer Controlled Vidicon System For High Resolution Microscopy

1973 ◽  
Vol 31 ◽  
pp. 264-265
Author(s):  
William Goldfarb ◽  
Benjamin M. Siegel
Keyword(s):  
High Resolution ◽  
High Vacuum ◽  
High Energy ◽  
Ultra High Vacuum ◽  
Energy Beam ◽  
Resolution Electron ◽  
Light Coupling ◽  
Optical Magnification ◽  
High Resolution Electron Microscope ◽  
Computer Controlled

The image collecting system of the experimental high resolution electron microscope being developed in this laboratory must be compatible with the ultra-high vacuum (10−10Torr) maintained in the total column. The characteristics of an SEC porous KCl target used to record directly the primary high energy beam has been previously reported. It was also noted that a phosphor transducer could be used with an external recording medium without loss of information if adequate electron optical magnification and sufficient light coupling are utilized.

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