Finite-Rate Oxidation Model for Carbon Surfaces from Molecular Beam Experiments

Molecular beam-surface scattering experiments have been used to study the effect of N atoms on the reactivity of O atoms with a high-temperature carbon surface to produce CO. The CO flux produced from bombardment of a vitreous carbon surface by a beam containing N and O atoms was compared with the CO flux produced from bombardment by beams containing either N or O atoms. The presence of small mole fractions of N atoms of 0.02-0.08 enhanced the reactivity of O atoms by a factor of 1.4-1.6 in the range of surface temperatures from 1100 to 1700 K. A detailed explanation of the observed results requires more study, but it appears that N atoms can act as a catalyst to increase the reactivity of O with carbon and that a relatively low flux of N atoms may be sufficient to saturate the catalytic effect. This catalytic effect seems to be fairly insensitive to the surface temperature, at least over the temperature range used in this study. This observation is important in the development of finite-rate models of air-carbon ablation during hypersonic flight.

Download Full-text

Construction of Finite Rate Surface Chemistry Models From Molecular Beam Experimental Data

47th AIAA Thermophysics Conference ◽

10.2514/6.2017-4347 ◽

2017 ◽

Cited By ~ 2

Author(s):

Krishnan Swaminathan Gopalan ◽

Kelly A. Stephani

Keyword(s):

Experimental Data ◽

Surface Chemistry ◽

Molecular Beam ◽

Finite Rate

Download Full-text

Effect of N atoms on O-Atom Reactivity with Carbon

10.26434/chemrxiv.12510716.v1 ◽

2020 ◽

Author(s):

Chenbiao Xu ◽

Timothy Minton

Keyword(s):

High Temperature ◽

Surface Temperature ◽

Molecular Beam ◽

Catalytic Effect ◽

Surface Scattering ◽

Carbon Surface ◽

Vitreous Carbon ◽

Finite Rate ◽

Detailed Explanation ◽

Beam Surface

Molecular beam-surface scattering experiments have been used to study the effect of N atoms on the reactivity of O atoms with a high-temperature carbon surface to produce CO. The CO flux produced from bombardment of a vitreous carbon surface by a beam containing N and O atoms was compared with the CO flux produced from bombardment by beams containing either N or O atoms. The presence of small mole fractions of N atoms of 0.02-0.08 enhanced the reactivity of O atoms by a factor of 1.4-1.6 in the range of surface temperatures from 1100 to 1700 K. A detailed explanation of the observed results requires more study, but it appears that N atoms can act as a catalyst to increase the reactivity of O with carbon and that a relatively low flux of N atoms may be sufficient to saturate the catalytic effect. This catalytic effect seems to be fairly insensitive to the surface temperature, at least over the temperature range used in this study. This observation is important in the development of finite-rate models of air-carbon ablation during hypersonic flight.

Download Full-text

Defects in Heavily-Doped MBE GaAs

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100054704 ◽

1982 ◽

Vol 40 ◽

pp. 442-445

Author(s):

C.B. Carter ◽

D.M. DeSimone ◽

T. Griem ◽

C.E.C. Wood

Keyword(s):

Molecular Beam Epitaxy ◽

Molecular Beam ◽

Heavily Doped

Molecular-beam epitaxy (MBE) is potentially an extremely valuable tool for growing III-V compounds. The value of the technique results partly from the ease with which controlled layers of precisely determined composition can be grown, and partly from the ability that it provides for growing accurately doped layers.

Download Full-text

STM studies of crystal growth

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100086179 ◽

1991 ◽

Vol 49 ◽

pp. 374-375

Author(s):

M. G. Lagally

Keyword(s):

Crystal Growth ◽

Molecular Beam ◽

Chemical Vapor ◽

Sputter Deposition ◽

Field Of View ◽

Scanning Tunneling ◽

Wide Field ◽

Tunneling Microscopy ◽

Wide Field Of View ◽

The One

It has been recognized since the earliest days of crystal growth that kinetic processes of all Kinds control the nature of the growth. As the technology of crystal growth has become ever more refined, with the advent of such atomistic processes as molecular beam epitaxy, chemical vapor deposition, sputter deposition, and plasma enhanced techniques for the creation of “crystals” as little as one or a few atomic layers thick, multilayer structures, and novel materials combinations, the need to understand the mechanisms controlling the growth process is becoming more critical. Unfortunately, available techniques have not lent themselves well to obtaining a truly microscopic picture of such processes. Because of its atomic resolution on the one hand, and the achievable wide field of view on the other (of the order of micrometers) scanning tunneling microscopy (STM) gives us this opportunity. In this talk, we briefly review the types of growth kinetics measurements that can be made using STM. The use of STM for studies of kinetics is one of the more recent applications of what is itself still a very young field.

Download Full-text

An in situ and ex situ TEM study of the formation of thin cobalt silicide films by molecular beam epitaxy on the silicon (100) surface

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010010648x ◽

1988 ◽

Vol 46 ◽

pp. 884-885

Author(s):

D. Loretto ◽

J. M. Gibson ◽

S. M. Yalisove ◽

R. T. Tung

Keyword(s):

Molecular Beam Epitaxy ◽

Molecular Beam ◽

Defect Density ◽

High Vacuum ◽

Ultra High Vacuum ◽

Ex Situ ◽

Metal Base ◽

In Situ Experiments ◽

Potential Applications

The cobalt disilicide/silicon system has potential applications as a metal-base and as a permeable-base transistor. Although thin, low defect density, films of CoSi2 on Si(111) have been successfully grown, there are reasons to believe that Si(100)/CoSi2 may be better suited to the transmission of electrons at the silicon/silicide interface than Si(111)/CoSi2. A TEM study of the formation of CoSi2 on Si(100) is therefore being conducted. We have previously reported TEM observations on Si(111)/CoSi2 grown both in situ, in an ultra high vacuum (UHV) TEM and ex situ, in a conventional Molecular Beam Epitaxy system.The procedures used for the MBE growth have been described elsewhere. In situ experiments were performed in a JEOL 200CX electron microscope, extensively modified to give a vacuum of better than 10-9 T in the specimen region and the capacity to do in situ sample heating and deposition. Cobalt was deposited onto clean Si(100) samples by thermal evaporation from cobalt-coated Ta filaments.

Download Full-text

Near-Surface Aggregation of Sn In Heavily Sn-Doped GaAs Films Grown By Molecular Beam Epitaxy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100118710 ◽

1985 ◽

Vol 43 ◽

pp. 368-369

Author(s):

S. H. Chen

Keyword(s):

Molecular Beam Epitaxy ◽

Cross Section ◽

Electron Spectroscopy ◽

Molecular Beam ◽

Surface Segregation ◽

Secondary Ion Mass Spectrometry ◽

Specimen Preparation ◽

Near Surface ◽

Gaas Films ◽

Secondary Ion

Sn has been used extensively as an n-type dopant in GaAs grown by molecular-beam epitaxy (MBE). The surface accumulation of Sn during the growth of Sn-doped GaAs has been observed by several investigators. It is still not clear whether the accumulation of Sn is a kinetically hindered process, as proposed first by Wood and Joyce, or surface segregation due to thermodynamic factors. The proposed donor-incorporation mechanisms were based on experimental results from such techniques as secondary ion mass spectrometry, Auger electron spectroscopy, and C-V measurements. In the present study, electron microscopy was used in combination with cross-section specimen preparation. The information on the morphology and microstructure of the surface accumulation can be obtained in a fine scale and may confirm several suggestions from indirect experimental evidence in the previous studies.

Download Full-text