Electric lamp and discharge devices – With gas or vapor – Three or more electrode discharge device
Reexamination Certificate
2000-03-21
2003-01-14
O'Shea, Sandra (Department: 2875)
Electric lamp and discharge devices
With gas or vapor
Three or more electrode discharge device
C313S639000
Reexamination Certificate
active
06507149
ABSTRACT:
DESCRIPTION
1. Technical Field
The present invention relates to a plasma cell.
2. Prior Art
Different plasma cells are available on the market at the present time. These are:
hot filament cells which are cells of simple design which can be solely used to produce monoatomic hydrogen; diatomic hydrogen dissociating itself through the energy supplied by a filament brought to a high temperature;
radio frequency and cycloelectronic resonance plasma cells, which are cells requiring complicated, very costly manufacturing, and producing ionized species which may damage surfaces;
continuous discharge plasma cells.
One cell of this latter type, available on the market and described for example in the document referenced (1) at the end of this disclosure, is illustrated in FIG.
1
. It is made up of a discharge tube
10
which curves backwards and is mounted on an ultravacuum flange
11
of CF 35 type enabling its fixation in a vacuum chamber
19
, in which pressure is in the region of 10
−5
to 10
−6
mbar. This Figure illustrates a quartz tube
12
, platinum electrodes
13
and their electrical connections
14
, a thermal glass tube
15
and a tube in stainless steel
16
. The upper part of the cell is fitted with a protective cover
17
and has a cone-shaped opening
18
through which the plasma can exit. A first flange
20
of CF 16 type provides for the addition of oxygen and a second flange
21
of the same type provides for connection to a pumping system.
A plasma is set up between the two electrodes
13
by applying a direct voltage of a few thousand volts, the current thus generated possibly varying from 20 mA to 40 mA. Ionization of the gas produces monoatomic species which exit through opening
18
and which come to react with sample
22
situated opposite the latter.
The major drawback of said cells lies in the presence of glass-metal soldering and their fragility, which means that they cannot be dismounted. These cells cannot be cleaned (deposits form on the cell walls) and therefore have a fairly short lifetime. Also, since the electrodes are not interchangeable, these cells are therefore “monogas” cells and must be replaced for each new application, the creation of an atomic species requiring the association of a gas and a specific electrode: Pt for O
2
—Stainless steel for H
2
—Mo for N
2
. . .
The purpose of the invention is to remedy the disadvantages of these cells of the prior art by providing a low-cost plasma cell, that is easy to maintain, having easily interchangeable electrodes and which can therefore be used with different types of gas.
DISCLOSURE OF THE INVENTION
The present invention relates to a plasma cell, able to be fixed into a vacuum chamber by means of a first flange, comprising an outer envelope in electric insulating material in which a gas under pressure is placed and provided in its upper part with a discharge opening, and electrodes, at least one anode and one cathode, arranged in said envelope and mounted on a second flange, at whose terminals a voltage can be applied such as to produce ionization of the gas producing the monoatomic species to be discharged through the opening, characterized in that it comprises electrodes that can be dismounted and are assembled on a second removable flange, electrically insulated separation means arranged between the cathode and anode or anodes, and a gas inlet opening.
In one advantageous embodiment, the envelope is in the shape of a glass bell. The separation means are formed of a quartz tube arranged around the cathode. The electrodes, which comprise several anodes, are arranged such as to allow electric selection of an anode. The gas inlet opening is located in the lower part of the envelope situated between the two flanges.
Advantageously, said cell can be used to create monoatomic species of different gases. Its lifetime is unlimited since it can be cleaned and the electrodes can be changed. Also, its manufacturing is much simplified.
It can be used to produce atomic species of gas from molecular sources such as hydrogen, oxygen, nitrogen, in a vacuum chamber. The monoatomic species formed in this way can, being highly reactive, be used either to dope or to change surface condition (cleaning, deoxidation, oxidation).
REFERENCES:
patent: 5427747 (1995-06-01), Kong et al.
patent: 2355375 (1978-01-01), None
patent: 01 060926 (1989-03-01), None
Magnea Noël
Picard Emmanuel
Commissariat a l 'Energie Atomique
Krebs Robert E.
O'Shea Sandra
Thelen Reid & Priest LLP
Truong Bao Q.
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