EP4301906A1

EP4301906A1 - Growth of nanowires

Info

Publication number: EP4301906A1
Application number: EP22710529.3A
Authority: EP
Inventors: Olav Birlem; Florian DASSINGER; Sebastian Quednau; Farough ROUSTAIE
Original assignee: Nanowired GmbH
Current assignee: Nanowired GmbH
Priority date: 2021-03-03
Filing date: 2022-02-22
Publication date: 2024-01-10
Also published as: US20240141542A1; TW202248113A; KR20230149837A; WO2022184503A1; JP2024509850A; CN116964249A; DE102021105125A1

Abstract

The invention relates to a method for the galvanic growth of a plurality of nanowires (1) on a surface (2), comprising: a) placing a film (3) on the surface (2), the film (3) having a plurality of through-pores (4), in which nanowires (1) can be grown from an electrolyte, b) placing an elastic element (5), which is permeable to the electrolyte, on the film (3), the electrolyte being brought into contact with the film (3) via the elastic element (5), c) galvanically growing the plurality of nanowires (1) for a first growth period, d) removing the elastic element (5), and e) continuing the galvanic growth of the plurality of nanowires (1) for a second growth period.

Description

Growth of nanowires

The invention relates to the galvanic growth of nanowires. In particular, the invention relates to a method and an arrangement for providing a large number of nanowires on a surface.

Methods and arrangements are known with which nanowires can be produced. For example, nanowires can be obtained via galvanic processes or using methods that are known from thin-film technology. What many known methods have in common is that they require complex machines and therefore usually only (can) be used in laboratories and clean rooms. In particular, most of the known methods are not suitable for industry.

Many known arrangements and methods also have the disadvantage that the nanowires obtained vary greatly in terms of their properties and, in particular, their quality. The nanowires from different growth processes regularly differ, sometimes significantly, even if the same or the same machines, starting materials and/or recipes are used. The quality of nanowires often depends in particular on the ability of the user of a corresponding arrangement or the user of a corresponding method, on environmental influences and/or simply on chance. All of this is made more difficult by the fact that nanowires are structures that sometimes cannot be visualized even with a light microscope. Extensive investigations may therefore be necessary in order to be able to determine the properties described (and in particular the fluctuations in them) at all.

With known methods and arrangements, it is often not possible, in particular because of the quality differences described, to grow larger areas with nanowires. It is likely that the properties of the nanowires differ between different areas of a larger vegetated area. This can be disadvantageous for many applications.

Proceeding from this, it is the object of the invention to present a method and an arrangement with which a large number of nanowires can be produced with a particularly consistent quality. This object is achieved with the arrangement and the method according to the independent claims. Further advantageous configurations are specified in the dependent claims. The features presented in the claims and in the description can be combined with one another in any technologically sensible way.

According to the invention, a method for galvanically growing a multiplicity of nanowires onto a surface is presented. The method comprises: a) placing a foil on the surface, the foil having a multiplicity of continuous pores in which the nanowires can be grown from an electrolyte, b) placing an elastic element permeable for the electrolyte on the foil, wherein the electrolyte is contacted with the foil via the elastic member, c) for a first growth period, galvanically growing the plurality of nanowires, d) removing the elastic member, and e) for a second growth period, continuing the galvanic growth the multitude of nanowires.

Steps a) and b) can be carried out in any order one after the other or with a complete or partial overlap. Steps c) to e) are carried out in the specified order after steps a) and b).

Nanowires can be produced with the method described. A nanowire is understood here to mean any material body that has a wire-like shape and a size in the range from a few nanometers to a few micrometers. A nanowire can, for example, have a circular, oval or polygonal base. In particular, a nanowire have a hexagonal base.

The nanowires preferably have a length in the range from 100 nm [nanometers] to 100 mΐti [micrometers], in particular in the range from 500 nm to 60 mΐti. Furthermore, the nanowires preferably have a diameter in the range from 10 nm to 10 mΐti, in particular in the range from 30 nm to 2 mΐti. The term diameter refers to a circular base area, with a base area deviating from this, a comparable definition of a diameter is to be used. It it is particularly preferred that all nanowires used have the same length and the same diameter.

The method described can be used for a wide variety of nanowire materials. Electrically conductive materials, in particular metals such as copper, silver, gold, nickel, tin and platinum, are preferred as the material for the nanowires. However, non-conductive materials such as metal oxides are also preferred. Preferably, all nanowires are formed from the same material.

The surface on which the nanowires are to be grown is preferably designed to be electrically conductive. If the surface is part of an otherwise non-electrically conductive body (e.g. a substrate), the electrical conductivity can e.g. B. can be achieved by metallization. So e.g. B. a non-electrically conductive substrate can be coated with a thin layer of metal. In particular, an electrode layer can be produced by the metallization. Depending on the material of the surface and/or the electrode layer, it can be useful to provide an adhesive layer between the surface and the electrode layer, which provides adhesion between the surface and the electrode layer.

Due to the electrical conductivity of the surface, it can be used as an electrode for the galvanic growth of the nanowires. In particular, the substrate can be a silicon substrate. In particular, the surface can be the surface of a body that is provided with electrically conductive structures. In particular, this can be a silicon chip or a so-called printed circuit board (PCB).

With the method described, the nanowires can be grown galvanically in pores of a film on the surface. An electrolyte is used for this. The nanowires can be provided with a particularly uniform quality if the foil lies tightly against the surface during growth and the electrolyte is evenly distributed over the foil. In the method described, this is achieved by dividing the growth into two steps. In a first growth step, an elastic element rests against the foil, by which the foil is held on the surface. The elastic element is permeable to the electrolyte, so that the electrolyte can be released to the film via the elastic element. In the first growth step, the nanowires are grown as far. that the foil is held on the surface by the nanowires. In the second growth step, the elastic element is no longer required. The elastic element is thus removed, whereby the electrolyte can be evenly distributed over the surface.

In step a) the film is placed on the surface to be covered with vegetation. The foil is preferably formed with a plastic material, in particular with a polymer material. In particular, it is preferred that the film is connected to the surface in such a way that the film does not slip. This could reduce the quality of the grown nanowires.

The film has a large number of continuous pores in which the nanowires can be grown. The fact that the pores of the film are continuous is preferably realized in such a way that the pores form continuous channels from an upper side of the film to an underside of the film. In particular, it is preferred that the pores are cylindrical. However, it is also possible for the pores to be in the form of channels with a curved course. For example, a pore can have a circular, oval or polygonal base. In particular, a pore can have a hexagonal base area. Preferably, the pores are uniform (i.e., the pores preferably do not differ in size, shape, location, and/or spacing from adjacent pores). If the nanowires are grown in steps c) and d), the pores are preferably (in particular completely) filled with the electrodeposited material. This gives the nanowires the size, shape and arrangement of the pores. The properties of the nanowires to be grown can thus be determined or influenced by the choice of the foil or the pores in it. The film can therefore also be referred to as a "template", "template film" or "stencil".

In step b), an elastic element that is permeable to the electrolyte is placed on the film. The elastic element is preferably set up to release an electrolyte at least at one dispensing point. The dispensing point is preferably of flat design, it being particularly preferred that the electrolyte can be dispensed uniformly over a dispensing area. Furthermore, it is preferred that the elastic element completely covers the film. For example, the elastic element can be a sponge or a cloth. The elastic element is preferably designed in such a way that it also has a fixation the foil can cause. This can be realized in particular in that the means for providing the electrolyte is of flat design and is set up for pressing the film onto the surface.

In steps c) and e) the nanowires are grown. This takes place first according to step c) in a first growth process. For this purpose, an electrical voltage is applied between the surface to be covered and an electrode. Both the surface and the electrode are in contact with the electrolyte. The nanowires are thus grown from the electrolyte onto the surface into the pores of the film. During the first growth period, the elastic element rests on the foil. This can prevent the film from slipping. In the first growth period, the nanowires are formed to such an extent that the nanowires hold the foil. The elastic element is then unnecessary. It is therefore removed in step d). The electrical voltage applied can be switched off for the duration of step d), so that the growth is interrupted to this extent. However, it is also conceivable that the growth continues uninterruptedly, so that growth also takes place in step d). In this case, the first growth period and the second growth period are only delimited from one another in that the elastic element is removed between these two steps. In step e) the growth of the nanowires is continued for a second growth period. This is basically the same as in step c), but without the elastic element. In step e), therefore, no elastic element is in contact with the film. In this case, the electrolyte can come into direct contact with the surface. This facilitates the supply of the electrolyte to the surface. This makes it easier to ensure that there is sufficient electrolyte at all points on the surface at all times. If this were not the case, the nanowires would not grow at the respective location despite the applied electrical voltage. This could affect the quality of the nanowires obtained.

The first growth period preferably has a length that is at least 10% of a length of the second growth period, preferably at least 50% of a length of the second growth period.

The length of the first growth period and the length of the second growth period can be fixed. Alternatively, the embodiment of the method is preferred in which from a step c) for the galvanic growth of Nanowires used electric current a transferred charge is determined, step c) is terminated when the transferred charge has reached a predetermined limit.

In this embodiment, the length of the first growth period is variable. Step c) is terminated as soon as the growth of the nanowires has progressed to such an extent that the nanowires can hold the film without the elastic element. The progress of the growth of the nanowires is not directly measured. Instead, the charge transferred during galvanic growth is determined. This is a measure of how many atoms have been converted according to galvanic growth. The charge transferred can be determined by time integration from the electrical current used to galvanically grow the nanowires. If the current is constant, the charge is obtained by multiplying the current by time. The electrical current used to galvanically grow the nanowires is the flow of electrons flowing between the surface and the electrode.

Step c) is terminated in the present embodiment when the charge transferred has reached a predetermined limit value. A suitable limit value can be determined by experiments. The limit value is preferably selected in such a way that the foil is held on the surface to a desired extent by the nanowires after the conclusion of step c).

In a further preferred embodiment of the method, the elastic cal element is pressed onto the film in step c).

The provision of the electrolyte can be facilitated by pressing the elastic element against the foil. For example, the electrolyte can be stimulated to escape from a sponge by pressing this sponge. A spring is preferably provided for pressing, the force with which the spring presses the elastic element against the film being adjustable. Elastic or plastic devices, motorized, hydraulic and/or pneumatic adjustment units or lever mechanisms can also be used to generate the contact pressure. By adjusting the force, the amount of electrolyte dispensed can be controlled. Furthermore, the film is pressed onto the surface via the elastic element, so that the film is form-fitting, stationary and free of air pockets (between see the foil and the surface as well as in the pores within the foil).

That the elastic element is pressed onto the film in step c) means that the elastic element is pressed onto the film at least during part of step c). The elastic element is preferably pressed against the film for the entire duration of step c).

In the present embodiment, the elastic element is pressed onto the film to the extent that the elastic element is pressed onto the film with a force that exceeds the weight of the elastic element. The inherent weight of the elastic element is therefore not sufficient for pressing in the sense of the present embodiment. As an alternative to the present embodiment, the elastic element can rest on the film for the entire duration of step c) without being pressed against the film.

In a further preferred embodiment of the method, the elastic element is lifted off the film in step d) by means of a gripper.

With the gripper, the elastic element can be automatically removed from the film. As a result, the entire method can be carried out automatically, which means that errors can be avoided. The gripper can be designed as a needle gripper, for example.

As a further aspect of the invention, an arrangement for the galvanic waxing of a multiplicity of nanowires is presented. The arrangement includes:

- a surface on which to grow the nanowires,

- a film placed on the surface, the film having a multiplicity of continuous pores in which the nanowires can be grown from an electrolyte,

- an elastic element placed on the foil and permeable to the electrolyte, whereby the electrolyte can be brought into contact with the foil via the elastic element,

- a gripper for removing the elastic element from the film.

The advantages and features of the method are applicable and transferable to the arrangement and vice versa. The method is preferred with the arrangement carried out. The arrangement is preferably intended and set up for operation in accordance with the method described.

In a preferred embodiment, the arrangement also includes a control unit which is set up to carry out at least steps c) to e) of the method. The control unit is set up to carry out the method to the extent that the method is automated. For example, the control unit can control the galvanic growth by controlling an electrical voltage required for the galvanic growth with the control unit. The pressing of the elastic element against the film can be controlled in step c) by the control unit to the extent that the elastic element is pressed against the film, for example by means of a hydraulic ram. Such a stamp can be controlled by the control unit. If steps a) and/or b) are also carried out automatically, these can also be controlled by the control unit.

The arrangement preferably has a housing within which all elements of the arrangement are arranged. The housing preferably has an opening for a drawer. An object with the surface to be overgrown can be placed in the drawer with the film placed on it and the elastic element placed on it, and pushed into the receptacle with it. To this extent, the object with the surface to be overgrown and the film placed thereon and the elastic element placed thereon can be arranged within the housing. By arranging it in a box, a particularly user-friendly machine is obtained with which the nanowires can be grown.

In a further preferred embodiment, the arrangement also includes a drive for the automated actuation of the gripper.

Step d) can be carried out automatically with the drive. The drive can be set up, for example, to bring the gripper in step d) into contact with the elastic element, to grip the elastic element and/or to lift it off the surface. With the drive, the position of the gripper can be changed and/or the gripper can be actuated. Operating the gripper means that the elastic element can be gripped with the gripper and released again. The gripper can be a needle gripper, for example. In a further preferred embodiment, the arrangement further comprises a movable shelf for the elastic element.

In step d) the elastic element can be gripped with the gripper and lifted off the surface. Then the movable shelf can be pushed between the surface and the elastic element. The elastic cal element can be placed on the movable shelf and released by the gripper. The elastic element can then be transported away with the movable shelf. The elastic element can then be removed from the movable shelf. This can be done automatically, for example by moving the movable shelf in such a way that the elastic element can no longer follow the movement of the movable element from a point of separation. The separation point can result, for example, from the fact that the movable shelf is guided into a shelf receptacle that does not offer any space for the elastic element. In this case, the elastic element gets caught on the edge of the shelf. The elastic element can be placed in a compartment from which the elastic element can be manually removed.

The movable shelf can be moved automatically, for example by a motor. The movable tray is preferably formed of a flexible material such as plastic. The mobile shelf can be stowed away to save space when not in use. For example, the moveable shelf can be guided over a deflection roller, so that the moveable shelf can be stowed rotated 90° relative to the surface when it is not needed.

In a further preferred embodiment, the arrangement further comprises a cleaning device for cleaning the movable tray.

The cleaning device is preferably set up to spray a cleaning fluid onto the movable tray. This can be done, for example, after the elastic element has been carried away with and removed from the movable tray. The cleaning device is preferably arranged in such a way that the movable tray is guided past the cleaning device in step d) after the elastic element has been removed from the movable tray. In a further preferred embodiment, the arrangement also comprises a voltage source which is connected to an electrode and the surface in order to apply an electrical voltage for the growth of the nanowires.

The voltage source serves to provide the electrical current required for the galvanic growth. The voltage source is preferably set up to generate a pulsed voltage, in particular with a pulse frequency in the range from 0.1 to 10 ms. Experiments have shown that the quality of the nanowires can be improved with a pulsed voltage.

In a further preferred embodiment, the arrangement also comprises a reference electrode which is connected to the surface.

The growth of the nanowires can be monitored with the reference electrode. For this purpose, the reference electrode can be used to measure the voltage that is present between the electrode and the reference electrode. The arrangement can include one or more reference electrodes.

The electrode is preferably connected to the voltage source via a first cable. The surface to be grown is preferably connected to the voltage source via a second cable. The reference electrode is preferably connected to a voltmeter via a third cable. The surface is preferably connected to the strain gauge by a fourth cable, particularly independent of the second cable. The second cable and the fourth cable are preferably each connected directly to the surface. For this purpose, the surface can have a respective contact pad, via which the second cable and the fourth cable are connected to the surface, for example by means of a respective conductive tape. The reference electrode is therefore not only connected to the surface in that the reference electrode is connected to a branch of the second cable. In contrast, it has been found that direct connection of the reference electrode to the surface provides more accurate results.

The object with the surface to be grown over and the reference electrode are preferably arranged in the drawer.

The first cable, the second cable, the third cable and the fourth cable can each be divided into several sections which are connected to one another, for example via plug connections. The second cable, the third cable and/or the four Each cable can be divided into sections in such a way that a respective transition between two adjacent sections of the corresponding cable is arranged on one edge of the drawer. The drawer can have a corresponding plug for each of these three cables. In this way, the surface and the reference electrode can be contacted when the drawer is pushed into the receptacle by forming the three plug-in connections. The voltage measuring device and the voltage source are preferably arranged inside the housing and outside the receptacle for the drawer.

In a further preferred embodiment, the arrangement also comprises a (in particular electrically driven) mangle for squeezing the electrolyte out of the elastic element when the elastic element has been removed from the film with the gripper.

The mangle can have two rollers between which the elastic element is moved. In this case, pressure can be exerted on the elastic element with the rollers, so that the elastic element releases electrolyte which is located in the elastic element. This allows a significant part of the electrolyte to be removed from the elastic element and reused.

The invention is explained in more detail below with reference to the figures. The figures show a particularly preferred embodiment to which the invention is not limited. The figures and the proportions shown therein are only schematic. Show it:

1: an arrangement according to the invention for the galvanic growth of a large number of nanowires,

Fig. 2: an interconnection of a reference electrode for the arrangement

figure 1,

3a and 3b: further elements of the arrangement from FIG. 1 in two different states.

1 shows an arrangement 7 for the galvanic growth of a multiplicity of nanowires 1. The arrangement 7 comprises a substrate 16 with a surface 2 on which the nanowires 1 are to be grown. The arrangement 7 further comprises a film 3 placed on the surface 2, which has a multiplicity of continuous pores 4, in which the nanowires 1 are grown from an electrolyte be able. The surface 2 has a structuring layer 17 with omissions 18 . The nanowires 1 can be grown in the gaps 18 only. The growth of the nanowires 1 can thus take place locally selectively. Furthermore, the arrangement 7 comprises an elastic element 5 placed on the foil 3 and permeable to the electrolyte. The electrolyte can be brought into contact with the foil 3 via the elastic element 5 . In addition, the arrangement 7 includes a voltage source 12 which is connected to an electrode 13 and the surface 2 for applying an electrical voltage for the growth of the nanowires 1 . The voltage source 12 is also connected to the control unit 8 . The electrode 13 can be pressed against the elastic element 5 with a stamp 19 .

The arrangement 7 is not fully shown in FIG. Additional elements are shown in Figures 2, 3a and 3b.

FIG. 2 shows further elements of the arrangement 7 from FIG. 1. For the sake of clarity, not all elements from FIG. 1 are shown in FIG. Thus, in addition to the voltage source 12, the electrode 13 and the substrate 16 with the upper surface 2, the arrangement 7 also has a reference electrode 14. The reference electrode 14 is connected to the surface 2 via a voltmeter 20 . The voltage source 12 and the reference electrode 14 are bonded to the surface 2 independently of one another.

3a and 3b show further elements of the arrangement 7 from FIGS. 1 and 2. For the sake of clarity, not all elements from FIGS. 1 and 2 are shown in FIG. 3a and 3b. It can be seen in FIGS. 3a and 3b in particular that the arrangement 7 has a gripper 6 for removing the elastic element 5 from the film 3. FIG. In Fig. 3a the state is shown in which the elastic element 5 on the film 3 on the upper surface 2 of the substrate 16 rests. The elastic element 5 can be gripped with the gripper 6 and lifted off the surface 2 . This is shown in Figure 3b. Since the elastic element 5 in FIG. 3b no longer rests on the film 3, an arrangement 7 according to the invention is no longer shown in FIG. 3b. The arrangement 7 comprises a drive 9 for the automated actuation of the gripper 6. In addition, the arrangement 7 comprises a movable shelf 10 for the elastic element 5. In FIG the moveable tray 10 is not needed in the condition shown. In Fig. 3b the movable shelf 10 is sandwiched between the surface 2 and the elastic element 5. pushed. In this way, the elastic element 5 can be placed on the movable tray 10 . Subsequently, the elastic element 5 can be transported away with the movable shelf 10 by the movable shelf 10 being moved back into its state shown in FIG. 3a. The elastic element 5 can be detached from the movable shelf 10, for example, in that the elastic element 5 does not follow the downward movement of the movable shelf 10. As soon as the elastic element 5 has detached from the movable tray 10, the movable tray 10 can be cleaned with a cleaning device 11. For this purpose, the movable Ab position 10 can be sprayed with a cleaning fluid by the cleaning device 11 who the. The arrangement 7 also has an electrically driven mangle 15 for squeezing the electrolyte out of the elastic element 5 when the elastic element 5 has been removed from the foil 3 with the gripper 6 . The mangle 15 has two rollers between which the elastic element 5 can be moved under the action of force.

The arrangement 7 also includes a control unit 8, which is set up to carry out steps c) to e) of the following method: a) placing a film 3 on the surface 2, the film 3 having a large number of continuous pores 4, in where the nanowires 1 can be grown from an electrolyte th, b) placing an elastic element 5 permeable to the electrolyte on the film 3, the electrolyte being brought into contact with the film 3 via the elastic element 5, c) for one first growth period, galvanic growth of the multiplicity of nanowires 1, the elastic element 5 being pressed onto the film 3, d) removing the elastic element 5 by lifting the elastic element 5 off the film 3 using a gripper 6, and e) for a second growth period, continuing to galvanically grow the plurality of nanowires 1.

In step c), a transferred charge is determined from the electric current used for the galvanic growth of the nanowires 1, step c) being terminated when the transferred charge has reached a predetermined limit value. Reference List

1 nanowire

2 surface 3 foil

4 pore

5 elastic element

6 grippers

7 arrangement 8 control unit

9 drive

10 moveable tray

11 cleaning device

12 voltage source 13 electrode

14 reference electrode

15 deficiency

16 substrate

17 patterning layer 18 omission

19 stamps

20 tension meter

Claims

patent claims

1. A method for galvanically growing a multiplicity of nanowires (1) on a surface (2), comprising a) placing a foil (3) on the surface (2), the foil (3) having a multiplicity of continuous pores (4) in which the nanowires (1) can be grown from an electrolyte, b) placing an elastic element (5) permeable to the electrolyte on the foil (3), the electrolyte being connected to the foil via the elastic element (5). (3) being contacted, c) for a first growth period, galvanically growing the plurality of nanowires (1), d) removing the elastic element (5), and e) for a second growth period, continuing to galvanically grow the plurality of nanowires (1).

2. The method as claimed in claim 1, wherein a transferred charge is determined from an electric current used in step c) for the galvanic growth of the nanowires (1), and step c) is terminated when the transferred charge has reached a predetermined limit value.

3. The method according to any one of the preceding claims, wherein the elastic element (5) in step c) is pressed onto the film (3).

4. The method according to any one of the preceding claims, wherein the elastic element (5) is lifted in step d) by means of a gripper (6) from the film (3).

5. Arrangement (7) for the galvanic growth of a multiplicity of nanowires (1), comprising: a surface (2) onto which the nanowires (1) are to be grown, a film (3) placed on the surface (2), wherein the film (3) has a large number of continuous pores (4) in which the nanowires (1) can be grown from an electrolyte, an elastic element (5) placed on the film (3) and permeable to the electrolyte, wherein the electrolyte can be brought into contact with the foil (3) via the elastic element (5). a gripper (6) for removing the elastic element (5) from the film (3).

6. Arrangement (7) according to claim 5, further comprising a control unit (8) which is set up to carry out steps c) to e) of a method according to one of claims 1 to 4.

7. Arrangement (7) according to claim 5 or 6, further comprising a drive (9) for the automated actuation of the gripper (6).

8. Arrangement (7) according to any one of claims 5 to 7, further comprising a movable tray (10) for the elastic element (5).

9. An arrangement (7) according to claim 8, further comprising cleaning means (11) for cleaning the movable tray (10).

10. Arrangement (7) according to any one of claims 5 to 9, further comprising a voltage source (12) which is connected to an electrode (13) and the surface (2) for applying an electrical voltage for the growth of the nanowires (1). is.

11. Arrangement (7) according to claim 10, further comprising a reference electrode de (14) which is connected to the surface (2).

12. Arrangement (7) according to any one of claims 5 to 11, further comprising a mangle (15) for squeezing the electrolyte out of the elastic element (5) when the elastic element (5) with the gripper (6) from the film ( 3) has been removed.