Patent Description:
Devices for generating a plasma jet are known from the prior art, for example from <CIT> or <CIT>. Such a device comprises a nozzle through which plasma is ejected in the form of a jet. The nozzle comprises a first channel, and the device is configured for flowing an ignitable gas, suitable to generate a plasma therefrom, through the first channel towards an exit opening of the nozzle. A high voltage electrode is arranged in the first channel for generating a plasma from the ignitable gas flowing in the first channel. The device is further provided for mixing a monomer precursor with the ignitable gas or the plasma generated therefrom in the first channel, such that the monomer precursor can be polymerised in the generated plasma. The monomer precursor can be provided from a second channel into the first channel, but can also be provided directly into the first channel together with the ignitable gas.

Related technologies are shown in <CIT> and <CIT>.

Such devices for generating a plasma jet known from the prior art have the disadvantage that the monomer precursor is often not well mixed with the ignitable gas or the plasma generated therefrom, such that not all monomer precursor is effectively polymerised in the plasma jet.

It is an aim of the present invention to provide a device and a method for generating a plasma jet having a better mixing of a monomer precursor in the plasma jet.

This aim is achieved according to the present invention with a device and a method for generating a plasma jet showing the technical characteristics of respectively the first independent claim and the second independent claim.

Therefore, the present invention provides a device for generating a plasma jet. Preferably, the plasma jet comprises a monomer precursor. Preferably; the plasma jet is for plasma polymerisation or plasma activation, but not necessarily limited thereto. The device comprises a nozzle. The nozzle of the device comprises an inner channel. The device is configured for flowing a first ignitable gas through the inner channel towards an exit opening of the inner channel. A high voltage electrode is arranged in the inner channel for generating a plasma from the first ignitable gas flowing in the inner channel. Preferably, the high voltage electrode is arranged along the length of the inner channel. Preferably, the high voltage electrode extends up to the exit opening of the inner channel. Preferably, a pointed tip of the high voltage electrode is located at the exit opening of the inner channel. The nozzle of the device comprises a middle channel. The middle channel surrounds the inner channel. The middle channel is electrically insulated from the inner channel. The device is configured for flowing a monomer precursor through the middle channel towards an exit opening of the middle channel. The nozzle of the device comprises an outer channel. The outer channel surrounds the middle channel. The outer channel is electrically insulated from the middle channel. The device is configured for flowing a second ignitable gas through the outer channel towards an exit opening of the outer channel. Preferably, the inner channel, the middle channel and the outer channel are circular channels. Preferably, the inner channel, the middle channel and the outer channel are coaxial channels. Preferably, the exit openings of the inner channel, the middle channel and the outer channel are coplanar. The nozzle of the device comprises a nozzle cap. The nozzle cap encloses a mixing volume located after the exit openings of the inner channel, the middle channel and the outer channel. Preferably, the nozzle cap is surrounding an end portion of the outer channel, the middle channel and the inner channel. Preferably, the nozzle cap is rotationally symmetric. Preferably, the nozzle cap is coaxial with the coaxial inner channel, middle channel and outer channel. Preferably, the nozzle cap is in an electrically conducting material. Preferably, the nozzle cap is grounded. The nozzle cap is provided with an exit opening after the mixing volume. The exit opening of the nozzle cap is smaller than the exit opening of the outer channel. Preferably, the exit opening of the nozzle cap is circular. Preferably, the exit opening of the nozzle cap is arranged in front of at least the exit opening of the inner channel. Preferably, the exit opening of the nozzle cap is coaxial with the coaxial inner channel, middle channel and outer channel. Preferably, the exit opening of the nozzle cap is arranged in a plane parallel to the plane of the exit openings of the inner channel, the middle channel and the outer channel.

The nozzle cap enclosing a mixing volume after the exit openings of the inner channel, the middle channel and the outer channel, and the nozzle cap having an exit opening after the mixing volume with a size smaller than the exit opening of the outer channel, offers the advantage that the combined flow of the plasma and possible leftover first ignitable gas, the monomer precursor, and the second ignitable gas out of the exit openings of respectively the inner channel, the middle channel and the outer channel cannot pass completely through the smaller exit opening of the nozzle cap and is circulated inside the mixing volume. With this combined flow being circulated inside the mixing volume a better mixing of the monomer precursor with the plasma and/or the ignitable gases, i.e. the first ignitable gas and the second ignitable gas, is achieved. Thereby, further plasma can be generated from the ignitable gases circulated in the mixing volume by means of the high voltage electrode in the inner channel, which preferably extends up to the exit opening of the inner channel and thus up to the mixing volume.

The outer channel providing a flow of the second ignitable gas in the mixing volume, and the exit opening of the nozzle cap being smaller than the exit opening of the outer channel, offers the advantage that the flow of the second ignitable gas is directed towards the flow of the plasma and possible leftover first ignitable gas from the inner channel and the flow of the monomer precursor from the middle channel, thereby preventing these flows from directly exiting the mixing volume through the exit opening of the nozzle cap, and thereby aiding in circulating the different flows inside the mixing volume of the nozzle cap to improve the mixing of the monomer precursor with the plasma and/or the ignitable gases.

The outer channel providing a flow of the second ignitable gas in the mixing volume, and the exit opening of the nozzle cap being smaller than the exit opening of the outer channel, also offers the advantage that the flow of the second ignitable gas is guided along an inner wall of the nozzle cap enclosing the mixing volume towards the exit opening of the nozzle cap. This flow of the second ignitable gas shields the inner wall of the nozzle cap enclosing the mixing volume from polymerised monomer precursor in the mixing volume being deposited on said inner wall, which is undesirable since it would clog the nozzle.

In an embodiment of the device according to the present invention the mixing volume is adapted for mixing the plasma of the first ignitable gas from the inner channel, the monomer precursor from the middle channel and the second ignitable gas from the outer channel.

In the device according to the present invention the mixing volume is located within the nozzle cap.

In an embodiment of the device according to the present invention the mixing volume is located directly after the exit openings of the inner channel, the middle channel and the outer channel.

In an embodiment of the device according to the present invention the exit opening of the nozzle cap is located directly after the mixing volume.

In an embodiment of the device according to the present invention the mixing volume extends from the exit openings of the inner channel, the middle channel and the outer channel to the exit opening of the nozzle cap.

In an embodiment of the device according to the present invention the exit opening of the nozzle cap is smaller than or equal to the exit opening of the middle channel.

This embodiment is beneficial for fully directing the flow of the second ignitable gas out of the exit opening of the outer channel towards the flow of the plasma and possible leftover first ignitable gas from the inner channel and the flow of the monomer precursor from the middle channel, thereby further preventing these flows from directly exiting the mixing volume through the exit opening of the nozzle cap, and thereby aiding in circulating the different flows inside the mixing volume of the nozzle cap to further improve the mixing of the monomer precursor with the plasma and/or the ignitable gases.

In an embodiment of the device according to the present invention an inner wall of the nozzle cap is shaped for gradually guiding the flow of the second ignitable gas in the mixing volume from the exit opening of the outer channel towards the exit opening of the nozzle cap.

The inner wall of the nozzle cap enclosing the mixing volume being shaped as such is beneficial for maintaining a stable flow of the second ignitable gas along the inner wall of the nozzle cap towards the exit opening of the nozzle cap, which improves the shielding by the second ignitable gas of the inner wall against polymerised monomer precursor in the mixing volume being deposited on said inner wall.

In an embodiment of the device according to the present invention the inner wall of the nozzle cap is funnel shaped for gradually guiding the flow of the second ignitable gas in the mixing volume from the exit opening of the outer channel towards the exit opening of the nozzle cap.

The inventors have found that the funnel shape of the inner wall of the nozzle cap is a very suitable shape for gradually guiding the flow of the second ignitable gas in the mixing volume from the exit opening of the outer channel towards the exit opening of the nozzle cap.

In an embodiment of the device according to the present invention the nozzle cap is arranged for being removably connected to the nozzle of the device.

This embodiment offers the advantage that the nozzle cap can be removed from the nozzle for cleaning, or for replacement with a different type of nozzle cap, for example a nozzle cap having an exit opening of a different size.

In an embodiment of the device according to the present invention the device is configured for flowing the first ignitable gas at a predetermined first flow rate through the inner channel towards the exit opening of the inner channel. In an embodiment of the device according to the present invention the first flow rate is at least <NUM> slm, preferably at least <NUM> slm, more preferably at least <NUM> slm, and even more preferably at least <NUM> slm. In an embodiment of the device according to the present invention the first flow rate is at most <NUM> slm, preferably at most <NUM> slm, more preferably at most <NUM> slm, and even more preferably at most <NUM> slm, In an embodiment of the device according to the present invention the first flow rate is most preferably <NUM> slm.

The inventors have found that with the first flow rate of the first ignitable gas in the inner channel, and thus also of the plasma generated from the first ignitable and possible leftover first ignitable gas entering the mixing volume, being in the given range, a uniform mixing of the monomer precursor with the plasma and the ignitable gases inside the mixing volume is achieved.

In an embodiment of the device according to the present invention the device is configured for flowing the monomer precursor at a predetermined second flow rate through the middle channel towards the exit opening of the middle channel. In an embodiment of the device according to the present invention the second flow rate is at least <NUM> sccm, preferably at least <NUM> sccm, more preferably at least <NUM> sccm, and even more preferably at least <NUM> sccm. In an embodiment of the device according to the present invention the second flow rate is at most <NUM> sccm, preferably at most <NUM> sccm, more preferably at most <NUM> sccm, and even more preferably at most <NUM> sccm. In an embodiment of the device according to the present invention the second flow rate is most preferably <NUM> sccm.

The inventors have found that with the second flow rate of the monomer precursor in the middle channel, and thus also of the monomer precursor entering the mixing volume, being in the given range, a uniform mixing of the monomer precursor with the plasma and the ignitable gases inside the mixing volume is achieved.

In an embodiment of the device according to the present invention the device is configured for flowing a carbon based monomer precursor through the middle channel towards the exit opening of the middle channel. The carbon based monomer precursor is for example styrene or methyl methacrylate, MMA.

In an embodiment of the device according to the present invention the device is configured for flowing the second ignitable gas at a predetermined third flow rate through the outer channel towards the exit opening of the outer channel. In an embodiment of the device according to the present invention the third flow rate is at least <NUM> slm, preferably at least <NUM> slm, more preferably at least <NUM> slm, and even more preferably at least <NUM> slm. In an embodiment of the device according to the present invention the third flow rate is at most <NUM> slm, preferably at most <NUM> slm, more preferably at most <NUM> slm, and even more preferably at most <NUM> slm. In an embodiment of the device according to the present invention the third flow rate is most preferably <NUM> slm.

The inventors have found that with the third flow rate of the second ignitable gas in the outer channel, and thus also of the second ignitable gas entering the mixing volume, being in the given range, a uniform mixing of the monomer precursor with the plasma and the ignitable gases inside the mixing volume is achieved.

In an embodiment of the device according to the present invention the exit opening of the nozzle cap has a diameter of at least <NUM>, preferably at least <NUM>, more preferably at least <NUM>, and even more preferably at least <NUM>. In an embodiment of the device according to the present invention the exit opening of the nozzle cap has a diameter of at most <NUM>, preferably at most <NUM>, more preferably at most <NUM>, and even more preferably at most <NUM>.

In an embodiment of the device according to the present invention the exit opening of the nozzle cap is adjustable in size. The exit opening may for example by adjustable in size by means of an iris diaphragm, such as used in a photo camera.

This embodiment offers the advantage that the size of the exit opening of the nozzle cap can easily be adapted for the use of the device according to the present invention in different applications, without having to replace the nozzle cap or making use of different devices according to the present invention having nozzle caps with exit openings of different sizes.

The present invention further provides a method for generating a plasma jet. Preferably, the plasma jet comprises a monomer precursor. Preferably; the plasma jet is for plasma polymerisation or plasma activation, but not necessarily limited thereto. The method comprises the step of flowing a first ignitable gas through an inner channel towards an exit opening of the inner channel. The method comprises the step of generating a plasma from the first ignitable gas flowing in the inner channel by means of a high voltage electrode arranged in the inner channel. The method comprises the step of flowing a monomer precursor through a middle channel towards an exit opening of the middle channel. The middle channel surrounds the inner channel. The middle channel is electrically insulated from the inner channel. The method comprises the step of flowing a second ignitable gas through an outer channel towards an exit opening of the outer channel. The outer channel surrounds the middle channel. The outer channel is electrically insulated from the middle channel. The method comprises the step of mixing the plasma of the first ignitable gas, the monomer precursor and the second ignitable gas in a mixing volume of a nozzle cap located after the exit openings of the inner channel, the middle channel and the outer channel. The method comprises the step of ejecting the mixture of the plasma of the first ignitable gas, the monomer precursor and the second ignitable gas in the mixing volume out of an exit opening of the nozzle cap located after the mixing volume. The exit opening of the nozzle cap is smaller than the exit opening of the outer channel.

In an embodiment of the method according to the present invention the first ignitable gas is flowed at a predetermined first flow rate through the inner channel towards the exit opening of the inner channel. In an embodiment of the method according to the present invention the first flow rate is at least <NUM> slm, preferably at least <NUM> slm, more preferably at least <NUM> slm, and even more preferably at least <NUM> slm. In an embodiment of the method according to the present invention the first flow rate is at most <NUM> slm, preferably at most <NUM> slm, more preferably at most <NUM> slm, and even more preferably at most <NUM> slm. In an embodiment of the method according to the present invention the first flow rate is most preferably <NUM> slm.

In an embodiment of the method according to the present invention the monomer precursor is flowed at a predetermined second flow rate through the middle channel towards the exit opening of the middle channel. In an embodiment of the method according to the present invention the second flow rate is at least <NUM> sccm, preferably at least <NUM> sccm, more preferably at least <NUM> sccm, and even more preferably at least <NUM> sccm. In an embodiment of the method according to the present invention the second flow rate is at most <NUM> sccm, preferably at most <NUM> sccm, more preferably at most <NUM> sccm, and even more preferably at most <NUM> sccm. In an embodiment of the method according to the present invention the second flow rate is most preferably <NUM> sccm.

In an embodiment of the method according to the present invention the second ignitable gas is flowed at a predetermined third flow rate through the outer channel towards the exit opening of the outer channel. In an embodiment of the method according to the present invention the third flow rate is at least <NUM> slm, preferably at least <NUM> slm, more preferably at least <NUM> slm, and even more preferably at least <NUM> slm. In an embodiment of the method according to the present invention the third flow rate is at most <NUM> slm, preferably at most <NUM> slm, more preferably at most <NUM> slm, and even more preferably at most <NUM> slm. In an embodiment of the method according to the present invention the third flow rate is most preferably <NUM> slm.

In an embodiment of the method according to the present invention the method is performed by means of the device according to the present invention.

The invention will be further elucidated by means of the following description and the appended figures.

The terms so used are interchangeable under appropriate circumstances and the embodiments of the invention described herein can operate in other orientations than described or illustrated herein.

The term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It needs to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof.

Within the context of the present invention, the term "standard litre per minute", slm, is a unit of volumetric flow rate of a fluid in "litre per minute", I/min, at standard conditions for temperature and pressure, STP, which is defined as a temperature of <NUM> and an absolute pressure of <NUM> kPa.

Within the context of the present invention, the term "standard cubic centimetre per minute", sccm, is a unit of volumetric flow rate of a fluid in "cubic centimetre per minute", cm<NUM>/min, at standard conditions for temperature and pressure, STP, which is defined as a temperature of <NUM> and an absolute pressure of <NUM> kPa.

Within the context of the present invention, the term "ignitable gas" should be understood as a gas that is suitable for generating a plasma therefrom.

<FIG> and <FIG> show a nozzle <NUM> of a device according to the present invention for generating a plasma jet. The nozzle <NUM> extends along a longitudinal direction L.

The nozzle <NUM> comprises an inner channel <NUM>. The inner channel <NUM> is formed in a first quartz capillary <NUM> that is arranged along the longitudinal direction L in the nozzle <NUM>. The device is configured for flowing a first ignitable gas through the inner channel <NUM> towards an exit opening <NUM> of the inner channel <NUM>. The first ignitable gas is a gas that is suitable for generating a plasma therefrom, such as for example He, Ar, N<NUM> and O<NUM>, but any other suitable gas can be used. The inner channel <NUM> has a circular cross section and a circular exit opening <NUM>, but any other suitable shape may be used. Within the first quartz capillary <NUM>, and thus in the inner channel <NUM>, there is arranged a high voltage electrode <NUM> for generating a plasma from the first ignitable gas flowing in the inner channel <NUM>. The high voltage electrode <NUM> is a rod with a circular cross section, but any other suitable shape may be used. Preferably, the high voltage electrode <NUM> is used for Radio Frequency, RF, plasma generation of the first ignitable gas. The high voltage electrode <NUM> is needle shaped and extends along the longitudinal direction L in the inner channel <NUM> up to the exit opening <NUM> of the inner channel <NUM>, where the high voltage electrode <NUM> has a pointed tip <NUM> for an increased electrical field strength.

The nozzle <NUM> also comprises a middle channel <NUM>. The middle channel <NUM> is formed between a second quartz capillary <NUM> and the first quartz capillary <NUM>, wherein the second quartz capillary <NUM> is arranged along the longitudinal direction L in the nozzle <NUM> and surrounds the first quartz capillary <NUM>. The device is configured for flowing a monomer precursor through the middle channel <NUM> towards and exit opening <NUM> of the middle channel <NUM>. The monomer precursor may be comprised in a flow of an ignitable gas. The monomer precursor may be for example styrene or methyl methacrylate, MMA, but any other suitable monomer precursor may be used depending on the application for the plasma jet, for example for plasma polymerisation or plasma activation. The middle channel <NUM> has a circular cross section and a circular exit opening <NUM>, but any other suitable shape may be used, preferably corresponding to the shape of the inner channel <NUM> and its exit opening <NUM>. The middle channel <NUM> is electrically insulated from the inner channel <NUM> by means of the first quartz capillary <NUM>, to prevent plasma generation of an ignitable gas in the middle channel <NUM> and deposition of polymerised monomer precursor in the middle channel <NUM>.

The nozzle <NUM> also comprises an outer channel <NUM>. The outer channel <NUM> is formed between an outer wall <NUM>, <NUM> of the nozzle <NUM> and the second quartz capillary <NUM>, wherein the outer wall <NUM>, <NUM> of the nozzle <NUM> extends along the longitudinal direction L and surrounds the second quartz capillary <NUM>. The device is configured for flowing a second ignitable gas through the outer channel <NUM> towards an exit opening <NUM> of the outer channel <NUM>. The second ignitable gas may be the same gas as the first ignitable gas, but the second ignitable gas can also be a gas different from the first ignitable gas. The outer channel <NUM> has a circular cross section and a circular exit opening <NUM>, but any other suitable shape may be used, preferably corresponding to the shape of the inner channel <NUM> and the middle channel <NUM> and their respective exit openings <NUM>, <NUM>. The outer channel <NUM> is electrically insulated from the middle channel <NUM> by means of the second quartz capillary <NUM>, to prevent plasma generation of the second ignitable gas in the outer channel <NUM>.

The first quartz capillary <NUM>, the second quartz capillary <NUM> and the outer wall <NUM>, <NUM> of the nozzle <NUM> are coaxial, such that the inner channel <NUM>, the middle channel <NUM> and the outer channel <NUM> are coaxial, and such that the exit openings <NUM>, <NUM>, <NUM> of the inner channel <NUM>, the middle channel <NUM> and the outer channel <NUM>, which are located in the same plane, are concentric.

The nozzle <NUM> also comprises a nozzle cap <NUM>. The nozzle cap <NUM> extends along the longitudinal direction L. An upper portion <NUM> of the nozzle cap <NUM> forms a part of the outer wall <NUM> of the nozzle <NUM> that surrounds the outer channel <NUM> of the nozzle <NUM>. A lower portion <NUM> of the nozzle cap <NUM> extends beyond the exit openings <NUM>, <NUM>, <NUM> of the inner channel <NUM>, the middle channel <NUM> and the outer channel <NUM>, and encloses there a mixing volume <NUM>. The mixing volume <NUM> is located within the nozzle cap <NUM>. At the end of the mixing volume <NUM> the nozzle cap <NUM> is provided with an exit opening <NUM>, which is also the exit opening <NUM> of the nozzle <NUM>. The mixing volume <NUM> is located directly after the exit openings <NUM>, <NUM>, <NUM> of the inner channel <NUM>, the middle channel <NUM> and the outer channel <NUM>, and the mixing volume <NUM> extends from the exit openings <NUM>, <NUM>, <NUM> of the inner channel <NUM>, the middle channel <NUM> and the outer channel <NUM> to the exit opening <NUM> of the nozzle cap <NUM>. The exit opening <NUM> is a circular opening, but any other suitable shape may be used, preferably a shape corresponding to the shape of the exit openings <NUM>, <NUM>, <NUM> of the inner channel <NUM>, the middle channel <NUM> and the outer channel <NUM>. The nozzle cap <NUM> is coaxial with the outer channel <NUM>, the middle channel <NUM> and the inner channel <NUM>, such that the exit opening <NUM> of the nozzle cap <NUM> is coaxial with the exit openings <NUM>, <NUM> ,<NUM> of the inner channel <NUM>, the middle channel <NUM> and the outer channel <NUM>.

In the embodiment shown, the exit opening <NUM> of the nozzle cap <NUM> has a size which is smaller than the size of the exit opening <NUM> of the middle channel <NUM>, i.e. the exit opening <NUM> has a circumference or outer perimeter which is smaller than, i.e. falls within, the circumference or outer perimeter of the exit opening <NUM> of the middle channel <NUM>. In alternative embodiments, the size of the exit opening <NUM> of the nozzle cap <NUM> can however be smaller or larger, but is at least smaller than the size of the exit opening <NUM> of the outer channel <NUM>. Preferably, the exit opening <NUM> of the nozzle cap <NUM> has a diameter of at least <NUM>, preferably at least <NUM>, more preferably at least <NUM>, even more preferably at least <NUM>, and at most <NUM>, preferably at most <NUM>, more preferably at most <NUM>, even more preferably at most <NUM>.

The inner wall <NUM> of the lower portion <NUM> of the nozzle cap <NUM> which encloses the mixing volume <NUM> is funnel shaped for gradually guiding, within the mixing volume <NUM>, the flow of the second ignitable gas that is coming out of the exit opening <NUM> of the outer channel <NUM> towards the exit opening <NUM> of the nozzle cap <NUM>, and thus directed towards the flow of the monomer precursor coming out of the exit opening <NUM> of the middle channel <NUM> and the flow of the plasma and possible leftover first ignitable gas coming out of the exit opening <NUM> of the inner channel <NUM>.

The exit opening <NUM> of the nozzle cap <NUM>, in this embodiment, being smaller than the exit opening <NUM> of the middle channel <NUM>, and the flow of the second ignitable gas being directed within the mixing volume <NUM> towards the exit opening <NUM> of the nozzle cap <NUM> has the effect that the flows of the plasma and possible leftover first ignitable gas out of the inner channel <NUM>, the monomer precursor out of the middle channel <NUM> and the second ignitable gas out of the outer channel <NUM> do not directly exit the mixing volume <NUM> through the exit opening <NUM> of the nozzle cap <NUM> but are circulated for a while inside the mixing volume <NUM>. With these flows being circulated inside the mixing volume <NUM> of the nozzle cap <NUM> a better mixing of the monomer precursor with the plasma and the ignitable gases inside the mixing volume <NUM> is achieved, and thus in the plasma jet that is ejected out of the exit opening <NUM> of the nozzle cap <NUM>. This results in a more complete polymerisation of the monomer precursor in the plasma jet.

In a preferred embodiment, to achieve an optimal mixing of the monomer precursor with the plasma and the ignitable gases inside the mixing volume <NUM> of the nozzle cap <NUM>, a first flow rate of the first ignitable gas in the inner channel <NUM> is at least <NUM> slm, preferably at least <NUM> slm, more preferably at least <NUM> slm, even more preferably at least <NUM> slm, and at most <NUM> slm, preferably at most <NUM> slm, more preferably at most <NUM> slm, even more preferably at most <NUM> slm, and most preferably <NUM> slm. A second flow rate of the monomer precursor in the middle channel <NUM> is at least <NUM> sccm, preferably at least <NUM> sccm, more preferably at least <NUM> sccm, even more preferably at least <NUM> sccm, and at most <NUM> sccm, preferably at most <NUM> sccm, more preferably at most <NUM> sccm, even more preferably at most <NUM> sccm, and most preferably <NUM> sccm. A third flow rate of the second ignitable gas in the outer channel <NUM> is at least <NUM> slm, preferably at least <NUM> slm, more preferably at least <NUM> slm, even more preferably at least <NUM> slm, and/or at most <NUM> slm, preferably at most <NUM> slm, more preferably at most <NUM> slm, even more preferably at most <NUM> slm, and most preferably <NUM> slm.

The nozzle cap <NUM> is removably connected to the nozzle <NUM>, which is beneficial for cleaning the nozzle cap <NUM> or for replacing the nozzle cap <NUM> with a different type of nozzle cap <NUM>, for example a nozzle cap <NUM> having a differently sized exit opening <NUM>. For removably connecting the nozzle cap <NUM> to the nozzle <NUM>, the outer wall <NUM> at an upper portion <NUM> of the nozzle <NUM> is provided with an external screw thread <NUM> and the upper portion <NUM> of the nozzle cap <NUM> is provided with an internal screw thread <NUM>, such that the nozzle cap <NUM> can be screwed onto the outer wall <NUM> of the upper portion <NUM> of the nozzle <NUM>. It should however be clear, that the nozzle <NUM> and the nozzle cap <NUM> may also be provided with different means for removably connecting the nozzle cap <NUM> to the nozzle <NUM>.

The flow of the first ignitable gas out of the inner channel <NUM>, the monomer precursor out of the middle channel <NUM> and the second ignitable gas out of the outer channel <NUM> being circulated in the mixing volume <NUM> of the nozzle <NUM>, for a more uniform distribution of the monomer precursor in the plasma jet, is demonstrated experimentally as further detailed below.

<FIG> shows Schlieren images of a plasma jet generated by means of a device according to an embodiment of the present invention. For this experiment a device was used with a nozzle <NUM> of which the mixing volume <NUM> has a circular exit opening <NUM> with a diameter of <NUM>. In the left image, only the inner channel <NUM> was active with a flow rate of argon gas, Ar, of <NUM> slm. For the middle image, the middle channel <NUM> was also activated, in addition to the inner channel <NUM>, with a flow rate of Ar of <NUM> sccm. Here, for demonstration purposes Ar was chosen, although it is not a monomer precursor. For the right image, the outer channel <NUM> was also activated, in addition to the inner channel <NUM> and the middle channel <NUM>, with a flow rate of Ar of <NUM> slm.

<FIG> shows that when only the inner channel <NUM> is in use, as shown in the left image, the plasma jet has the longest section of laminar flow regime. When the inner channel <NUM> and the middle channel <NUM> are in use, as shown in the middle image, the length of the section of laminar flow regime decreases due to the higher total flow out of the exit opening <NUM> of the nozzle <NUM>. When the inner channel <NUM>, the middle channel <NUM> and the outer channel <NUM> are all in use, the transition to turbulent regime happens at a closer distance from the exit opening <NUM> of the nozzle <NUM> as even higher total flow is passing through said exit opening <NUM>. Moreover, in this case, the plasma jet receives additional thrust due to the mixing volume <NUM> in the nozzle cap <NUM> where the flows coming out of the inner channel <NUM>, the middle channel <NUM> and the outer channel <NUM> circulate for a while.

<FIG> shows Schlieren images of an effluent coming out of a device according to an embodiment of the present invention. For this experiment a device was used with a nozzle <NUM> of which the mixing volume <NUM> has a circular exit opening <NUM> with a diameter of <NUM>. In the left two images, the inner channel <NUM> was active with a flow rate of Ar of <NUM> slm and the middle channel <NUM> with a flow rate of Ar and styrene of <NUM> sccm. In the first of these two images, the high voltage electrode <NUM> of the device was not active, such that the effluent is merely the combination of the flows out of the inner channel <NUM> and the middle channel <NUM>. In the second of these two images, the high voltage electrode <NUM> of the device was active, such that the effluent is a plasma jet. For the right two images, the outer channel <NUM> was also activated, in addition to the inner channel <NUM> and the middle channel <NUM>, with a flow rate of Ar of <NUM> slm. In the first of these two images, the high voltage electrode <NUM> of the device was not active, such that the effluent is merely the combination of the flows out of the inner channel <NUM>, the middle channel <NUM> and the outer channel <NUM>. In the second of these two images, the high voltage electrode <NUM> of the device was active, such that the effluent is a plasma jet.

<FIG> shows that when only the inner channel <NUM> and middle channel <NUM> are in use, the effluent flow transits to the turbulent regime close to the exit opening <NUM> of the nozzle <NUM>. When the inner channel <NUM>, the middle channel <NUM> and the outer channel <NUM> are all in use, additional mixing occurs inside the mixing volume <NUM> of the nozzle cap <NUM>. This extra volume provides time and space to form a "united" stream that flows out of the exit opening <NUM> of the nozzle <NUM>. A higher gas temperature, caused by the flows coming out of the inner channel <NUM>, the middle channel <NUM> and the outer channel <NUM> being circulated inside the mixing volume <NUM> and being exposed to the pointed tip <NUM> of the high voltage electrode <NUM> and thus heated thereby, may also explain the better contrast in the second image of the two right images in comparison to the second image of the two left images.

The aforementioned increase in temperature of the plasma jet due to the flows coming out of the inner channel <NUM>, the middle channel <NUM> and the outer channel <NUM> being circulated inside the mixing volume <NUM> of the nozzle <NUM>, is also demonstrated by means of the experiments of <FIG> and the experiment of <FIG>.

<FIG> show the temperature, i.e. the gas temperature TGAS, the rotational temperature estimated for OH, Trot OH, and the rotational temperature estimated for N<NUM>, Trot N<NUM>, of the plasma jet coming out of the exit opening <NUM> of the nozzle <NUM>, measured by means of Rayleigh scattering of a laser beam pointed through the plasma jet. For these experiments a device was used with a nozzle <NUM> of which the mixing volume <NUM> has a circular exit opening <NUM> with a diameter of <NUM>. For the first experiment of <FIG>, only the inner channel <NUM> was active with flow rates of Ar of <NUM> slm, <NUM> slm and <NUM> slm. For the second experiment of <FIG>, the middle channel <NUM> was also activated with flow rates of Ar of <NUM> sccm, <NUM> sccm, <NUM> sccm and <NUM> sccm, and this in addition to the inner channel <NUM> having a flow rate of Ar of <NUM> slm. Here, for demonstration purposes Ar was used in the middle channel <NUM>, although it is not a monomer precursor. For the third experiment of <FIG>, the outer channel <NUM> was also activated with flow rates of Ar of <NUM> slm, <NUM> slm, <NUM> slm and <NUM> slm, and this in addition to the inner channel <NUM> having a flow rate of Ar of <NUM> slm and the middle channel <NUM> having a flow rate of Ar of <NUM> sccm.

<FIG> show that increasing the flow rate in any one of the inner channel <NUM>, the middle channel <NUM> and the outer channel <NUM> causes a decrease in temperature of the plasma jet. As can be seen in <FIG>, adding Ar gas to the middle channel <NUM>, while keeping a <NUM> slm flow rate of Ar in the inner channel <NUM>, does not change the temperature significantly due to small flow rates. As can be seen in <FIG>, the highest temperatures are obtained when the inner channel <NUM>, the middle channel <NUM> and the outer channel <NUM> are all in use. This outcome is explained by a prolonged stay of the flows coming out of the inner channel <NUM>, the middle channel <NUM> and the outer channel <NUM> inside the mixing volume <NUM> of the nozzle cap <NUM>, due to said flows being circulated for a while inside the mixing volume <NUM>.

<FIG> shows the surface temperature of a substrate exposed to a plasma jet generated by means of a device according to an embodiment of the present invention, wherein the surface temperature was measured by means of an infrared camera and at the centre of the exposed area. For this experiment a device was used with a nozzle <NUM> of which the mixing volume <NUM> has a circular exit opening <NUM> with a diameter of <NUM>. For a first series of measurements, the inner channel <NUM> was active with an Ar flow rate of <NUM> slm and the middle channel <NUM> with flow rates of Ar and styrene of <NUM> sccm (■), <NUM> sccm (•) and <NUM> sccm (▲). For a second series of measurements, the outer channel <NUM> was also activated with flow rates of Ar of <NUM> slm (▼), <NUM> slm (◆) and <NUM> slm (◄), and this in addition to the inner channel <NUM> having a flow rate of Ar of <NUM> slm and the middle channel <NUM> having a flow rate of Ar and styrene of <NUM> sccm.

<FIG> shows that increasing the flow rates results in a lower temperature of the substrate at all experimental conditions. The flow rate of Ar and styrene in the middle channel does not significantly influence the substrate temperature. Significantly higher substrate temperatures were observed when the inner channel <NUM>, the middle channel <NUM> and the outer channel <NUM> were all in use. This is due to the gas dynamic inside the mixing volume <NUM> of the nozzle cap <NUM>, which causes the flows coming out of the inner channel <NUM>, the middle channel <NUM> and the outer channel <NUM> being exposed to the pointed tip <NUM> of the high voltage electrode <NUM> for longer and thus heated thereby.

The uniform distribution of the monomer precursor in the plasma jet is demonstrated by means of the experiment of <FIG> and the experiments of <FIG>.

<FIG> shows a picture of a plasma polymerised coating on a silicon substrate applied by means of a device according to an embodiment of the present invention. For this experiment a device was used with a nozzle <NUM> of which the mixing volume <NUM> has a circular exit opening <NUM> with a diameter of <NUM>. The coating was deposited on the substrate by moving the plasma jet backwards and forwards along a straight line above the substrate. The deposition speed was <NUM>/s, the deposition duration was <NUM> and the moving distance was <NUM>. For a first experiment, of which the results are shown on the right, the inner channel <NUM> was active with a flow rate of Ar of <NUM> slm and the middle channel <NUM> with a flow rate of Ar and styrene of <NUM> sccm. For a second experiment, of which the results are shown on the left, the outer channel <NUM> was also activated with a flow rate of Ar of <NUM> slm, and this in addition to the inner channel <NUM> having a flow rate of Ar of <NUM> slm and the middle channel <NUM> having a flow rate of Ar and styrene of <NUM> sccm.

<FIG> shows that the coating deposited without employing the outer channel <NUM>, as can be seen on the right, is narrow due to the styrene monomer precursor in the plasma jet being located close to the centre of the plasma jet. The coating deposited with the inner channel <NUM>, the middle channel <NUM> and the outer channel <NUM> all active, as can be seen on the left, is more spread out and thus wider, due to the styrene monomer precursor being more uniformly distributed in the plasma jet.

<FIG> shows the atomic concentration of a silicon substrate, i.e. the surface silicon concentration of the silicon substrate, detectable through a plasma polymerised coating applied by means of a device according to an embodiment of the present invention, wherein the atomic concentration was measured by means of X-ray photoelectron spectroscopy, XPS, along the width of the coating. For this experiment a device was used with a nozzle <NUM> of which the mixing volume <NUM> has a circular exit opening <NUM> with a diameter of <NUM>. The coating was deposited on the substrate by moving the plasma jet backwards and forwards along a straight line above the substrate. The deposition speed was <NUM>/s, the deposition duration was <NUM> and the moving distance was <NUM>. For a first measurement (■), the inner channel <NUM> was active with a flow rate of Ar of <NUM> slm, the middle channel <NUM> with a flow rate of Ar and styrene of <NUM> sccm, and the outer channel <NUM> was not active (OFF). For a second measurement (•), the outer channel <NUM> was also activated (ON) with a flow rate of Ar of <NUM> slm, and this in addition to the inner channel <NUM> having a flow rate of Ar of <NUM> slm and the middle channel <NUM> having a flow rate of Ar and styrene of <NUM> sccm.

<FIG> shows that the coating deposited with the inner channel <NUM>, the middle channel <NUM> and the outer channel <NUM> all active, fully covers the silicon substrate over the entire width of the coating, due to the styrene monomer precursor being uniformly distributed in the plasma jet. The coating deposited without employing the outer channel <NUM>, on the other hand, only fully covers the silicon substrate in a smaller range, due to the styrene monomer precursor in the plasma jet being located close to the centre of the plasma jet.

<FIG> shows for the coated silicon substrate of the experiment of <FIG>, the atomic concentration of the silicon substrate, i.e. the surface silicon concentration of the silicon substrate, detectable through the plasma polymerised coating, but now after the coated silicon substrate has been submerged in water for a period of <NUM> hours.

Claim 1:
A device for generating a plasma jet, wherein a nozzle (<NUM>) of the device comprises:
an inner channel (<NUM>), wherein the device is configured for flowing a first ignitable gas through the inner channel (<NUM>) towards an exit opening (<NUM>) of the inner channel (<NUM>), wherein a high voltage electrode (<NUM>) is arranged in the inner channel (<NUM>) for generating a plasma from the first ignitable gas flowing in the inner channel (<NUM>);
a middle channel (<NUM>), wherein the middle channel (<NUM>) surrounds the inner channel (<NUM>), wherein the middle channel (<NUM>) is electrically insulated from the inner channel (<NUM>), wherein the device is configured for flowing a monomer precursor through the middle channel (<NUM>) towards an exit opening (<NUM>) of the middle channel (<NUM>); and
an outer channel (<NUM>), wherein the outer channel (<NUM>) surrounds the middle channel (<NUM>), wherein the outer channel (<NUM>) is electrically insulated from the middle channel (<NUM>), wherein the device is configured for flowing a second ignitable gas through the outer channel (<NUM>) towards an exit opening (<NUM>) of the outer channel (<NUM>);
a nozzle cap (<NUM>), wherein the nozzle cap (<NUM>) encloses a mixing volume (<NUM>) located after the exit openings (<NUM>, <NUM>, <NUM>) of the inner channel (<NUM>), the middle channel (<NUM>) and the outer channel (<NUM>), wherein the mixing volume (<NUM>) is located within the nozzle cap (<NUM>), and wherein the nozzle cap (<NUM>) is provided with an exit opening (<NUM>) after the mixing volume (<NUM>), wherein the exit opening (<NUM>) of the nozzle cap (<NUM>) is smaller than the exit opening (<NUM>) of the outer channel (<NUM>).