Atomic oxygen atoms are routed to a material through a sufficiently tortuous path so that vacuum ultraviolet radiation is obstructed from arriving at the surface of the material. However, the material surface continues to be exposed to the atomic oxygen

Banks, Bruce A.

Rutledge, Sharon K.

English

NASA Technical Reports Server

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USOO5280174A 
United States Patent [191 [ i i ]  Patent Number: 5,280,174 
Banks et al. 1451 Date of Patent: Jan. 18, 1994 
METHOD AND APPARATUS FOR 
PRODUCING A THERMAL ATOMIC 
OXYGEN BEAM 
Inventors: Bruce A. Banks, Olmsted Township, 
Cuyahoga County; Sharon K. 
Rutledge, Bedford, both of Ohio 
The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
Assignee: 
Appl. No.: 8,026 
Filed: Jan. 25,1993 
Int. C l . 5  ............................................... HOSH 3/00 
U.S. Cl. .................................................... 250/251 
Field of Search ......................................... 250/251 
References Cited 
U.S. PATENT DOCUMENTS 
4,209,704 6/1980 Krimmel ......................... 250/423 R 
4,434,131 2/1984 Dagenhart et ai. ................. 376/130 
4,649,273 3/1987 Chutjian .............................. 250/251 
4,828,817 5/1989 Outlaw ................................ 250/251 
4,886,964 12/1989 Pritchard et al. ................... 250/251 
4,914,305 4/1990 Benveniste et al. .............. 250/492.3 
4,921,327 5/1990 Zit0 .................................. 350/96.32 
5,126,575 6/1942 White ............................... 250/492.3 
5,146,098 911992 Stack ................................ 250/492.2 
OTHER PUBLICATIONS 
Brink et al., Rev. Sci. Instr., vol. 39, No. 8, Aug. 1968, 
Primary Examiner-Jack I. Berman 
Attorney, Agent, or Firm-Gene E. Shook; James A. 
Mackin; Guy M. Miller 
V I  ABSTRACT 
Atomic oxygen atoms are routed to a material through 
a sufficiently tortuous path so that vacuum ultraviolet 
radiation is obstructed from arriving at the surface of 
the material. However, the material surface continues 
to be exposed to the atomic oxygen. 
pp. 1171-1172. 
19 Claims, 2 Drawing Sheets 
https://ntrs.nasa.gov/search.jsp?R=19940019352 2020-06-17T23:39:01+00:00Z
U.S. Patent Jan. 18, 1994 Sheet 1 of 2 
I 18 
5,280,174 
FIG. 1 
US,  Patent Jan. 18, 1994 Sheet 2 of 2 5,280,174 
i 1 I !  1 
22 J -  
28 
P 8  
FIG. 2 
1 
5,280,174 
2 
A still further object of the invention is to use glass 
surfaces to absorb VUV radiation to prevent it from 
arriving on the materials being tested. 
Still another object of the invention is to use geomet- 
5 ric configurations which permit high fluxes of atomic 
oxygen to arrive on the surfaces of the materials being 
faces. 
METHOD AND APPARATUS FOR PRODUCING A 
THERMAL ATOMIC OXYGEN BEAM 
ORIGIN O F  THE INVENTION 
The invention described herein was made by employ- - of the U.S, Government and may be manufactured tested preventing vuv exposure of these sur- 
and used by Or for the Government for governmental 
Another object qf the invention is to use glass sur- purposes without the payment of royalties thereon or 
therefor. 
TECHNICAL FIELD 
10 faces to eliminate ion and metastable species by their 
Still another object of the invention is to use shaped 
conversion to ground state atomic oxygen. 
glass surfaces which allow controlled and optional 
WV radiation exposure of test surfaces while prevcnt- 
ing undesirable radiation exposure from the oxygen 
plasma source. 
Yet another object of the invention is to provide an 
beam exposure of samples which is necessary for pro- 
power SOurce and 2o ducing test samples large enough for optical or mechan- 
ical evaluation. 
This invention is concerned with the production of 
thermal atomic oxygen beams. The invention is particu- 15 
larly directed to a high flux, broad atomic oxygen beam 
which is to be impinged upon materials during testing. 
oxygen beams comprise exposing samples directly to a 
plasma produced by a 
oxygen gas. Typically, an electron cyclotron resonant 
source is used to produce a mixture of atomic oxygen, 
oxygen ions, and metastable states. Ion beams also have 
been produced using bombardment ion U.S. Pat. No. 4,209,704 relates to a means of separat- 
sources, as well as gridless or end hall ion sources. 25 ing ions which are being accelerated to a set of targets. 
vacuum ultraviolet radiation produced by the plasma redirects the ions and the charge prior to 
associated with production of atomic oxygen. TYP~- 3o reaching a divider portion used to separate ions by 
cally, oxygen plasmas produce very intense vacuum mass. 
ultraviolet radiation at 130 nm as a result of excitation of u.s. Pat. No. 4,434,131 is concerned with an ion 
atomic oxygen. AS a result, any atomic oxygen beam recovery system having an electric field diversion com- 
system which allows samples to be exposed to intense ponent. A flow of particles traverses a chamber, the 
plasma will have high levels of 130 nm vacuum ultravi- 35 particles being either charged or neutral. Neutral 
olet radiation exposure. Therefore, one could not sepa- charges are unaffected by the electric deflection unit 
rately assess the effects Of atomic oxygen exposure from while charged particles are recovered along an ion 
vacuum ultraviolet radiation exposure. recovery surface. The neutral particles pass through an 
Vacuum ultraviolet radiation exposure iS known to opening in the wall to escape. 
damage exposed Surfaces of many U.S. Pat. No. 4,886,964 describes a means of separat- 
their optical properties to change in a manner such that ing neutral and charged atomic beams using a diffrac- 
the surfaces appear darker as a result of absorbing more tion grating. A neutral beam diffracts at a different 
radiation. Such Surfaces Show Significant increases in angle than the charged beam under conditions of low 
solar absorptance. Therefore, it has not been possible to incident angles. 
distinguish effects of atomic oxygen exposure from the 45 U.S. Pat. No. 4,914,305 is directed to an apparatus 
vacuum ultraviolet radiation exposure. used for ion implantation of silicon substrate in which a 
Many materials, such as radiator coatings, have de- resolving magnet is used to steer an ion source to a set 
manding solar absorptance requirements. Poor atomic of acceleration units. The resolving magnet redirects 
oxygen durability could be inaccurately diagnosed be- charged particles 180" in route to the target material. 
cause of simultaneous vacuum ultraviolet radiation ex- 50 U.S. Pat. No. 4,921,327 describes a fiber optic wave 
posure during atomic oxygen testing. The intensity of carrier which is used to convey an ionizing radiation 
the 130 nm radiation exceeds that of anticipated in- from a source to a target. The fiber is in the shape of a 
space levels of radiation by orders of magnitude. Thus, tube which is capped at one end, thereby preventing the 
the poor performance of materials exposed to atomic passage of air while allowing the transmission of ions. A 
oxygen beams may not at all be indicative of what might 55 collection of small obstructions located at the distal 
be expected under more realistic exposure conditions. portion of the chamber reflects the ions to produce a 
It is, therefore, an object of the present invention to wider beam. 
enable a high-flux broad atomic oxygen beam to be U.S. Pat. No. 5,126,575 relates to a broad beam ion 
impinged upon the surfaces of materials while prevent- implantation device having a redirection unit for steer- 
ing undesired vacuum ultraviolet radiation from im- 60 ing an ion beam and broadening it to a set of accelera- 
pinging on these surfaces. tors prior to striking the target. 
Another object of the invention is to enable thermally U.S. Pat. No. 5,146,098 describes an ion beam con- 
accommodated atomic oxygen to be impinged upon tamination sensor having a means to establish a baseline 
surfaces while preventing undesirable 130 nm vacuum spectrum, a means to measure the detected spectrum, a 
ultraviolet radiation from damaging these surfaces. 65 comparison of the detected and baseline spectra, and a 
A further object of the invention is to use glass sur- means of producing the resultant of these to spectra. If 
faces to scatter atomic oxygen through a tortuous path the result is outside the range of acceptable parameters, 
to arrive at materials being tested. the implantation process is discontinued. 
methods Of producing atomic apparatus which is suitable for broad atomic oxygen 
BACKGROUND ART 
Prior art devices designed to allow exposure Of The separator is a curved chamber which is used to 
magnetically steer charged ions, A second deflector pies to atomic Oxygen exposure to 
causing 40 
5,280,174 
3 
DISCLOSURE O F  THE INVENTION 
The aforementioned objects of the invention are 
achieved by the apparatus of the present invention 
which is used in the containment of plasma. More spe- 
cifically, the apparatus facilitates a delivery of atomic 
oxygen beams to a test piece while preventing the ar- 
rival of vacuum ultraviolet radiation associated with the 
production of atomic oxygen plasmas from exposing the 
test piece. 
An “S” shaped plasma containment vessel directs the 
plasma flow to a test piece. The walls of the chamber 
allow UV light to pass while steering the atomic oxygen 
to the target. Auxiliary UV lamps are used to match the 
conditions found in earth orbits so that the coating 
materials are tested under conditions similar to those 
found in orbit. In this manner, controlled experiments 
are performed which identify corrosion of materials due 
to atomic oxygen plasmas independently of ultraviolet 
degradation. 
BRIEF DESCRIPTION O F  THE DRAWINGS 
The objects, advantages, and novel features of the 
invention will be more fully apparent from the follow- 
ing detailed description when read in connection with 
the accompanying drawings wherein: 
FIG. 1 is a schematic view showing the preferred 
embodiment of the invention; and 
FIG. 2 is a schematic view of an alternate embodi- 
ment of the invention. 
BEST MODE FOR CARRYING OUT THE 
INVENTION 
Atomic oxygen produced by a microwave or electri- 
cal discharge of an oxygen plasma produces a mixture 
of thermal neutral atoms, oxygen ions, and metastable 
species. As a result of the de-excitation process, vacuum 
ultraviolet radiation is produced in the region of the 
flowing plasma. This radiation, which is most intense at 
130 nm, is prevented from impinging upon samples by 
means of routing the atomic oxygen atoms through a 
sufficiently tortuous path, such that the vacuum ultravi- 
olet radiation is obstructed from arriving on the sam- 
ples, yet the atomic oxygen continues to arrive at the 
sample surfaces. 
Referring now to the drawings, there is shown in 
FIGS. 1 and 2 schematic views of apparatus con- 
structed in accordance with the present invention. A 
material sample 10 is mounted on a support 12 in a 
chamber 14. A line 16 connected to a suitable vacuum 
source such as a pump, not shown, is utilized to evacu- 
ate the chamber 14, thereby establishing a vacuum envi- 
ronment for the material 10. 
An ECR microwave power system 18 is operably 
connected to a tuner 20 through a dummy load and 
circulator 22 for producing atomic oxygen which is 
supplied to the chamber 14 through waveguides 24 and 
26. The atomic oxygen passes through a pair of magnets 
28 and 30 to a glass liner 32, as shown in both FIGS. 1 
and 2. 
According to the preferred embodiment of the pres. 
5 
10 
15 
20 
25 
30 
35 
40 
45 
50 
55 
60 
I 
ent invention a curied glass or fused silica pipe -34 is 
connected to the glass liner 32 and conveys the atomic 
oxygen to the material sample 10. An important feature 
of the invention is that the glass pipe 34 has an “S” 65 
shaped configuration. A pair of UV lamps 36 and 38 are 
positioned adjacent to the material sample 10 at the 
discharge end of the pipe 34. 
4 
As can be seen in FIG. 1, atomic oxygen is ducted to 
the “S” bend in the glass pipe or duct 34. The glass has 
minimal reflection for vacuum ultraviolet radiation and 
high absorptance, resulting in negligible vacuum ultra- 
violet radiation arriving at the surface of the material 
sample 10. Because the atomic oxygen is a low energy 
thermal beam, impingement of ions and metastables on 
the glass walls will tend to convert these species to 
thermal energy a t o p  as well. Thus, the beam of atomic 
oxygen impinging on the material sample 10 will be 
largely devoid of ion, metastable, and vacuum ultravio- 
let radiation content. 
DESCRIPTION O F  ALTERNATE 
EMBODIMENT O F  THE INVENTION 
Referring now to FIG. 2 there is shown an alternate 
embodiment of the invention wherein the atomic oxy- 
gen beam from the glass liner 32 is deflected off a triang- 
ular glass prism 40 which obstructs the UV illumination 
of the material 10 in the holder 12. The triangular glass 
prism 40 may be fused silica or glass. The triangular 
glass prism 40 has a sheet of a non ultraviolet radiation 
transmitting material, such as aluminum foil, placed in 
the middle of it to prevent longer wavelength ultravio- 
let radiation that is greater than 200 nm from impinging 
on the material 10 as well. 
Surrounding the triangular glass prism 40 are glass 
rectangles 42 which scatter the atomic oxygen back 
onto the material 10. The glass used in the rectangles 42 
for deflection or rerouting of atomic oxygen is prefera- 
bly Si02. It is contemplated that fluorosilicate, soda 
lime, or other metal oxide glasses can be used for the 
glass rectangles 42. 
It is apparent from both devices shown in FIGS. 1 
and 2 that the intent of the invention is to prevent unde- 
sired vacuum ultraviolet radiation from impinging on 
the material 10. However, it may be desirable to have 
controlled vacuum ultraviolet or ultraviolet radiation 
exposure of the material 10. This is facilitated by pro- 
viding the auxiliary UV lamps 36 and 38 shown in both 
FIGS. 1 and 2. These lamps are used to provide con- 
trolled vacuum ultraviolet exposure of the material 10 
while preventing undesirable 130 nm exposure. 
While several embodiments of the invention have 
been shown and described, it will be apparent that the 
geometry of the glass piping shown in FIG. 1 and the 
glass enclosure and triangular prism shown in FIG. 2 
can be widely varied, depending on the size of the mate- 
rial 10 as well as the geometry of the plasma source 
region. It is contemplated that various structural modi- 
fications may be made to the devices shown in FIGS. 1 
and 2 without departing from the spirit of the invention 
or the scope of the subjoined claims. 
What is claimed: 
1. Apparatus for exposing material to atomic oxygen 
a chamber, 
means for mounting said material in said chamber, 
means for evacuating said chamber with said material 
mounted therein for establishing a vacuum envi- 
ronment for said material, 
means for producing atomic oxygen atoms from oxy- 
gen plasma wherein vacuum ultraviolet radiation is 
produced, 
means for conveying said atomic oxygen atoms into 
said chamber, and 
means for routing said atomic oxygen atoms to said 
material through a sufficiently tortuous path so that 
comprising 
5 
5,280,174 
6 
vacuum ultraviolet radiation is obstructed from 
arriving at said material while atomic oxygen con- 
tinues to arrive at said material. 
evacuating said chamber with said material mounted 
therein thereby establishing a vacuum environment 
for said material, 
wherein vacuum ultraviolet radiation is produced, 
conveying said atomic oxygen into said cham- 
routing said atomic oxygen atoms to =id material in 
said chamber through a sufficiently tortuous path 
so that vacuum ultraviolet radiation is obstructed 
from arriving at said material while atomic oxygen 
continues to arrive at said material. 
12. A method as claimed in claim 11 wherein the 
atomic oxygen atoms are produced by microwave 
13. A method as claimed in claim 12 wherein vacuum 
ultraviolet radiation at 130 um is produced. 
14. A method as claimed in claim 13 including routing 
said atomic oxygen atoms to said material dong an 6,s,, 
15. A method as claimed in claim 14 wherein the path 
is formed by a glass pipe. 
16. A method as claimed in claim 14 wherein the path 
is formed by a fused silica pipe. 
17. A method as claimed in claim 13 wherein the 
Oxygen atoms are routed to said material with a triangu- 
lar prism and uv illumination of the material is ob- 
structed. 
18. A method as claimed in claim 17 wherein the 
30 oxygen atoms are routed by a triangular prism of a glass 
material selected from the group consisting of Si02, 
fluorosilicate, soda lime, and other metal oxide. 
19. A method as claimed in claim 18 including inhibit- 
ing longer wavelength ultraviolet radiation greater than 
2. Apparatus as claimed in claim 1 wherein the means producing atomic Oxygen from Oxygen piasma 
5 for producing atomic oxygen atoms includes a micro- 
wave power system. ber, and 
3. Apparatus as claimed in claim 2 wherein the vac- 
uum ultraviolet radiation is at 130 nm. 
4. Apparatus as claimed in claim 3 including a Pipe 10 
having a “S’ shaped configuration for routing said 
atomic oxygen atoms to said material. 
5. Apparatus as claimed in claim 4 wherein the pipe is 
glass. 
6. Apparatus as claimed in claim 4 where the pipe is l5 power* 
fused silica. 
7. Apparatus as claimed in claim 3 where the means 
for routing the oxygen atoms to said material include a 
triangular prism which obstructs WV illumination of 2o 
the material. 
8. Apparatus as claimed in claim 7 wherein the triang- 
ular prism is of a glass material selected from the group 
consisting of Si02 fluorosilicate, soda lime, and other 
metal oxide glasses. 
9. Apparatus as claimed in claim 8 wherein the triang- 
ular glass prism contains a sheet of a non ultraviolet 
radiation transmitting material for inhibiting longer 
wavelength ultraviolet radiation greater than 200 nm 
from impinging on the material. 
10. Apparatus as claimed in claim 9 wherein the sheet 
is aluminum foil. 
11. A method for exposing material to atomic oxygen 
comprising 
path in cham&r. 
25 
35 200 nm from impinging on the material. 
mounting said material in a chamber, * * * * *  
45 
50 
55 
65 


Method and apparatus for producing a thermal atomic oxygen beam

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