Nanowire growth

Abstract

A method for galvanically growing a plurality of nanowires (1) on a surface (2), the method comprising the steps of: a) placing a foil (3) on the surface (2), the foil (3) having a plurality of through holes (4) in which the nanowires (1) can be grown from an electrolyte; b) placing an elastic element (5) permeable to an electrolyte on the foil (3), the electrolyte contacting the foil (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

Technical Field

[0001] The present invention relates to the galvanic growth of nanowires. In particular, the present invention relates to a method and an apparatus for providing a plurality of nanowires on a surface.

Background Art

[0002] Methods and apparatuses capable of generating nanowires are known. For example, nanowires can be obtained by a galvanic process or by a method known from thin film technology. Many of the known methods generally require complex machinery and are only (not) usable in laboratories and clean rooms. In particular, most of the known methods are not suitable for industrial use.

[0003] In addition, many of the known apparatuses and methods have the drawback that each obtained nanowire varies greatly in terms of characteristics, especially with respect to quality. Generally, nanowires obtained from different growth processes are partially very different even if the same or identical machinery, starting materials, and manufacturing methods are used. Often, the quality of the nanowires depends on the skills of the user of the corresponding apparatus or the user of the corresponding method, environmental influences, or mere chance. All of these are further exacerbated because nanowires are structures that may not be visible even under an optical microscope. Therefore, in order to be able to detect the aforementioned characteristics (and especially their variations) in the first place, time-consuming tests may be required.

[0004] In particular, due to the aforementioned quality differences, it is often impossible to grow nanowires on a larger surface area with known methods and apparatuses. Therefore, when grown on a larger surface area, the characteristics of the nanowires are likely to be different in different regions within that surface area. In many applications, this can be disadvantageous.

Summary of the Invention

Means for Solving the Problems

[0005] Based on the above, the object of the present invention is to provide a method and apparatus for manufacturing multiple nanowires, particularly with consistent quality.

[0006] The aforementioned objectives are achieved by the methods and apparatus described in the independent claims. Each of the dependent claims represents a more advantageous configuration. The features detailed in the claims and specification can be combined with each other in any technically significant manner.

[0007] The present invention provides a method for galvanically growing multiple nanowires on a surface. This method is a) A step of placing a foil on a surface, wherein the foil has multiple through-holes, and nanowires can be grown from an electrolyte within these through-holes, b) A step of placing an elastic element permeable to an electrolyte onto a foil, wherein the electrolyte comes into contact with the foil via the elastic element, c) A step of galvanically growing multiple nanowires during the first growth period, d) A step of removing the elastic element, e) A step of continuing galvanic growth of multiple nanowires during the second growth period, Includes.

[0008] Steps a) and b) can be performed sequentially in any desired order, or they can be performed completely or partially in overlap. Steps c) to e) are performed after steps a) and b) in the order described.

[0009] This method allows for the production of nanowires. In this specification, a nanowire should be understood to mean any wire-shaped material having a size ranging from several nanometers to several micrometers. The nanowire may have, for example, a circular, elliptical, or polygonal base. In particular, the nanowire may have a hexagonal base.

[0010] The nanowires preferably have a length in the range of 100 nm (nanometers) to 100 μm (micrometers), and more preferably in the range of 500 nm to 60 μm. Furthermore, the nanowires preferably have a diameter in the range of 10 nm to 10 μm, and more preferably in the range of 30 nm to 2 μm. In this specification, the term "diameter" refers to a circular base, and in the case of a base that deviates from this, the same definition of diameter shall be used. It is particularly preferable that all nanowires used have the same length and the same diameter.

[0011] This method can be used with various types of nanowire materials. Conductive materials are preferred for the nanowires, and metals such as copper, silver, gold, nickel, tin, and platinum are particularly preferred. However, non-conductive materials such as metal oxides are also preferred. It is preferable that all nanowires are formed from the same material.

[0012] The surface on which nanowires are grown is preferably configured to be conductive. If the surface is not conductive and is part of a non-conductive body (such as a substrate), conductivity may be achieved by a metal coating or the like. For example, a non-conductive substrate can be coated with a thin film of metal. The metal coating makes it possible to create an electrode layer in particular. Depending on the material of the surface, the electrode layer, or both, an adhesive layer may preferably be provided between the surface and the electrode layer, and this adhesive layer promotes adhesion between the surface and the electrode layer.

[0013] Since the surface is conductive, it can be used as an electrode for galvanic growth of nanowires. This substrate can be a silicon substrate in particular. The surface may also be the surface of a body having a conductive structure. This body can be a silicon chip or a so-called printed circuit board (PCB).

[0014] The method described above allows for galvanic growth of nanowires within the pores of a foil on a surface. An electrolyte is used for this purpose. During nanowire growth, if the foil is in close contact with the surface and the electrolyte is uniformly spread across the entire foil, the nanowires can be produced with particularly consistent quality. In the method described above, this is achieved by dividing the growth into two stages. In the first growth stage, an elastic element is placed in contact with the foil, thereby holding the foil on the surface. Since the elastic element is permeable to the electrolyte, the electrolyte can be delivered onto the foil through the elastic element. In the first growth stage, the nanowires are grown to the extent that the foil is held on the surface by the nanowires. In the second growth stage, the elastic element is no longer needed. Therefore, the elastic element is removed, which allows the electrolyte to be spread even more uniformly across the entire surface.

[0015] In step a), the foil is placed on the surface to be grown. The foil is preferably made of a plastic material, and more particularly of a polymer material. In particular, it is preferable that the foil is attached to the surface in a way that prevents slipping. This is because slipping can degrade the quality of the grown nanowires.

[0016] The foil has multiple through-holes through which nanowires can be grown. Preferably, the holes extend through the foil so that channels are formed by the holes from the top to the bottom of the foil. In particular, the holes are preferably cylindrical in shape. However, the holes may be formed as channels with curved contours. The holes may have, for example, circular, elliptical, or polygonal bases. In particular, the holes may have hexagonal bases. Preferably, the holes are uniformly configured (i.e., preferably, the holes do not differ from adjacent holes in at least one of the size, shape, arrangement, and spacing). If nanowires are grown in steps c) and d), it is preferable that the holes are filled (especially completely) with galvanically deposited material. In this way, the nanowires will have the size, shape, and arrangement of the holes. By selecting the foil or the holes within it in this way, the properties of the grown nanowires can be determined or influenced. Therefore, the foil may also be called a “template,” “template foil,” or “pattern.”

[0017] In step b), an elastic element permeable to the electrolyte is placed on the foil. Preferably, this elastic element is configured to deliver the electrolyte at at least one delivery point. Preferably, this delivery point is flat, and particularly preferably, it is possible to deliver the electrolyte uniformly across the entire delivery area. Furthermore, it is preferable that the elastic element completely covers the foil. For example, the elastic element may be a sponge or cloth. Preferably, the elastic element is also configured to fix the foil in place. This is achieved in particular by configuring the means for supplying the electrolyte to be flat and to press the foil against its surface.

[0018] In steps c) and e), nanowires are grown. This is done first in step c) in the first growth process. For this purpose, a voltage is applied between the growth surface and the electrode. Both the surface and the electrode are in contact with the electrolyte. Thus, each nanowire is grown from the electrolyte into the pores of the foil on the surface. During the first growth period, an elastic element is placed on the foil. This prevents the foil from shifting position. In the first growth period, nanowires are formed to the extent that they hold the foil. After that, the elastic element is no longer needed. Therefore, in step d), the elastic element is removed. During the period of step d), the applied voltage may be switched off, thereby interrupting growth at this point. However, it is also possible to continue growth without interruption so that growth occurs in step d). In this case, the first and second growth periods are separated from each other only by the removal of the elastic element between these two stages. In step e), the growth of the nanowires continues over the second growth period. This is similar in principle to step c), but without the elastic element. Therefore, in step e), the elastic element is not in contact with the foil. In this case, the electrolyte can be brought into direct contact with the surface. This makes it easier to supply the electrolyte to the surface. Therefore, it is easier to ensure that sufficient electrolyte is present at all points on the surface at all times. If this is not the case, nanowires will not grow at each point even when a voltage is applied. This can impair the quality of the resulting nanowires.

[0019] The length of the first growth period is preferably at least 10% of the length of the second growth period, and more preferably at least 50% of the length of the second growth period.

[0020] The length of the first growth period and the length of the second growth period may be constant. In another preferred embodiment of the method, in step c), the transferred charge is determined from the current used for the galvanic growth of the nanowire, and step c) is terminated when the transferred charge reaches a predetermined limit value.

[0021] In this embodiment, the length of the first growth period varies. Step c) is terminated immediately when the nanowire has grown to the point where it can hold the foil without elastic elements. In this case, the progress of nanowire growth is not directly measured. Instead, the charge transferred during galvanic growth is determined. This is a measurement of the number of atoms transformed according to galvanic growth. The transferred charge can be determined by integrating over time from the current used for the galvanic growth of the nanowire. If the current intensity is constant, the charge can be obtained by multiplying the current intensity by time. The current used for the galvanic growth of the nanowire is the electron current flowing between the surface and the electrode.

[0022] In this embodiment, step c) ends when the transferred charge reaches a predetermined limit. A suitable limit can be determined by testing. This limit is preferably selected so that the foil is retained on the surface by the nanowire to a desired extent after step c) is completed.

[0023] In a more preferred embodiment of this method, the elastic element is pressed against the foil in step c).

[0024] When the elastic element is pressed against the foil, the electrolyte can be supplied more easily. For example, by pressing a sponge, the electrolyte can be squeezed out of the sponge. For this pressing, it is preferable to provide a spring. The force by which the spring presses the elastic element against the foil is adjustable. An elastic device or a plastic device, a unit or a lever mechanism of a motor-driven, hydraulic, pneumatic or a combination of these methods can also be used to generate this pressing force By adjusting this force, the liquid feeding amount of the electrolyte can be controlled. Further, the elastic element is used to press the foil against the surface, whereby the foil is held by shape fitting and fixed in a predetermined position, preventing air from being mixed in (between the foil and the surface and in the holes in the foil).

[0025] That the elastic element is pressed against the foil in step c) means that the elastic element is pressed against the foil in at least a part of step c). Preferably, the elastic element is pressed against the foil throughout the entire duration of step c).

[0026] In this embodiment, the elastic element is pressed against the foil by a force exceeding the weight of the elastic element. Therefore, the weight of the elastic element itself is not sufficient to press the elastic element as defined in this embodiment. As one of the options of this embodiment, throughout the duration of step c), the elastic element may be placed on the foil instead of being pressed against the foil.

[0027] In a more preferred embodiment of this method, the elastic element is lifted from the foil by a gripper in step d).

[0028] By this gripper, the elastic element can be automatically removed from the foil. Thereby, the whole method can be automatically performed, so that errors can be avoided. The gripper may be configured, for example, as a needle gripper.

[0029] In a further aspect of the present invention, an apparatus for galvanically growing multiple nanowires is provided. This apparatus is - A surface on which nanowires are grown, -A foil placed on a surface, the foil having multiple through holes, in which nanowires can be grown from an electrolyte in the through holes, - An elastic element that is placed on a foil and permeable to an electrolyte, and through the elastic element, the electrolyte can be brought into contact with the foil. - Gripper for removing elastic elements from the wheel It is equipped with.

[0030] The advantages and features of this method are applicable to and adaptable to this apparatus, and vice versa. It is preferable that this method be carried out by this apparatus. It is preferable that this apparatus is intended and configured to operate in accordance with this method.

[0031] In one preferred embodiment, the apparatus further comprises a control unit configured to perform at least steps c) to e) of the method. The control unit is configured to perform the method to the extent that the method is automated. Thus, the control unit may control galvanic growth, for example, by a voltage required to control the galvanic growth by the control unit. Pressing the elastic element against the wheel may be controlled by the control unit in step c) to the extent that the elastic element is pressed against the wheel by, for example, a hydraulic ram. Such a ram can be controlled by the control unit. If at least one of steps a) and b) is performed automatically, these steps may also be controlled by the control unit.

[0032] The apparatus preferably has a housing in which all elements of the apparatus are arranged. The housing preferably has a drawer compartment. An object having a surface to be grown may be inserted into the drawer and pushed into the compartment together with the drawer, with a foil placed on top and an elastic element on top of it. In this regard, the object having a surface to be grown may be placed inside the housing with a foil placed on top and an elastic element on top of it. By placing it inside the housing, a particularly user-friendly machine capable of growing nanowires is obtained.

[0033] In a more preferred embodiment, the device further comprises a drive unit for automatically operating the gripper.

[0034] Step d) can be performed automatically by a drive unit. This drive unit may be configured to bring the gripper into contact with the elastic element in step d), for example, to grip the elastic element, or to lift the elastic element from the surface, or both. Thus, this drive unit can change the position of the gripper or actuate the gripper. Actuating the gripper should be understood as meaning that the elastic element can be gripped by the gripper and then released again. The gripper may be, for example, a needle gripper.

[0035] In a more preferred embodiment, the apparatus further comprises a movable platform for elastic elements.

[0036] In step d), the elastic element can be grasped by the gripper and lifted from the surface. The mobile platform can then be pushed between the surface and the elastic element. The elastic element can be placed on the mobile platform by the gripper and released. The elastic element can then be carried out by the mobile platform. The elastic element can then be removed from the mobile platform. This may be done automatically, for example, by moving the mobile platform so that the elastic element cannot follow the movement of the mobile platform from a separation point. This separation point may be created, for example, by guiding the mobile platform into a mobile platform housing where there is no space for the elastic element. In this case, the elastic element is hanging from the edge of the mobile platform housing. The elastic element may be placed in a compartment from which it can be manually removed.

[0037] The mobile platform may be moved automatically by a motor or the like. Preferably, the mobile platform is made of a flexible material, such as plastic. Therefore, when the mobile platform is not needed, it can be stored in a space-saving manner. For example, the mobile platform may be guided by deflection rollers, which allows the mobile platform to be stored at a position rotated 90° relative to the surface of the substrate when it is not needed.

[0038] In a more preferred embodiment, the apparatus further comprises a cleaning device for cleaning the mobile table.

[0039] The cleaning device is preferably configured to spray cleaning fluid onto a mobile platform. Cleaning can be performed, for example, after the elastic element has been unloaded by the mobile platform or removed from the mobile platform. It is preferable that the cleaning device is positioned so that the mobile platform is guided through the cleaning device once the elastic element has been removed from the mobile platform.

[0040] In a more preferred embodiment, the apparatus further comprises a voltage source connected to the electrodes and the surface for applying a voltage for growing nanowires.

[0041] The voltage source is responsible for supplying the current necessary for galvanic growth. The voltage source is preferably configured to generate pulsed voltages, particularly pulses with a pulse frequency in the range of 0.1 to 10 ms. Tests have demonstrated that pulsed voltages can improve the quality of nanowires.

[0042] In a more preferred embodiment, the apparatus further comprises a reference electrode, which is connected to the surface.

[0043] The growth of nanowires can be monitored using a reference electrode. For this purpose, the voltage between the electrode and the reference electrode can be measured by the reference electrode. The device may include one or more reference electrodes.

[0044] The electrodes are preferably connected to a voltage source via a first cable. The surface to be grown is preferably connected to a 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 voltmeter by a fourth cable, particularly independently of the second cable. The second and fourth cables are preferably directly connected to the surface. For this purpose, the surface may have corresponding contact pads, through which the second and fourth cables are connected to the surface, for example, by corresponding conductive tape. Thus, the reference electrode is not only connected to the surface by branching of the second cable, but comparisons have shown that more accurate results can be obtained by directly connecting the reference electrode to the surface.

[0045] It is preferable that the object having the surface to be grown and the reference electrode are placed inside a drawer.

[0046] The first, second, third, and fourth cables may each be divided into several parts, and these parts are connected to each other via plug-in connectors or the like. At least one of the second, third, and fourth cables may each be divided into multiple parts, so that the boundary between two adjacent parts of a corresponding cable is located at the edge of the drawer. The drawer may have corresponding connectors for each of these three cables. Thus, when the drawer is pushed into the housing, three plug-in connectors are formed, allowing electrical contact between the surface and the reference electrode. The voltmeter and voltage source are preferably located inside the housing and outside the housing for the drawer.

[0047] In one of the more preferred embodiments, the apparatus further comprises a (particularly electric) mangle for squeezing the electrolyte from the elastic element when the elastic element has been removed from the foil by the gripper.

[0048] The mangle may have two rollers, through which an elastic element passes. In this case, pressure can be applied to the elastic element by these rollers so that the elastic element releases the electrolyte present within it. This allows a significant portion of the electrolyte to be removed from the elastic element, making it reusable.

[0049] The present invention will be described in more detail below with reference to the drawings. The drawings show particularly preferred exemplary embodiments. However, the present invention is not limited thereto. In particular, the drawings, and especially the illustrated size ratios, are schematic only. [Brief explanation of the drawing]

[0050] [Figure 1] The present invention illustrates an apparatus for galvanically growing multiple nanowires. [Figure 2]Figure 1 shows the connection of the reference electrode for this device. [Figure 3] Figures 3a and 3b show further elements of the configuration in two different states relative to Figure 1. [Modes for carrying out the invention]

[0051] Figure 1 shows an apparatus 7 for galvanically growing multiple nanowires 1. The apparatus 7 comprises a substrate 16 having a surface 2 on which the nanowires 1 are grown. The apparatus 7 further comprises a foil 3, which has multiple through-holes 4, within which the nanowires 1 can be grown from the electrolyte. The foil 3 is placed on the surface 2. The surface 2 has a structured layer 17 with gaps 18. The nanowires 1 can be grown only within the gaps 18. Therefore, the growth of the nanowires 1 can be performed locally and selectively. Furthermore, the apparatus 7 comprises an elastic element 5 that is permeable to the electrolyte, and this elastic element 5 is placed on the foil 3. The electrolyte can be brought into contact with the foil 3 via the elastic element 5. The apparatus 7 further comprises a voltage source 12, which is connected to an electrode 13 and the surface 2 to apply a voltage for growing the nanowires 2. The voltage source 12 is also connected to a control unit 8. The ram 19 allows the electrode 13 to be pressed against the elastic element 5.

[0052] Figure 1 does not show the entire apparatus 7. Further elements are shown in Figures 2, 3a, and 3b.

[0053] Figure 2 shows further elements of the apparatus 7 in relation to Figure 1. For clarity, Figure 2 does not show all the elements described in Figure 1. Thus, in addition to the voltage source 12, electrode 13, and substrate 16 having surface 2, the apparatus 7 further has a reference electrode 14. The reference electrode 14 is connected to surface 2 via a voltmeter 20. The voltage source 12 and the reference electrode 14 are connected to surface 2 independently of each other.

[0054] Figures 3a and 3b show further elements of the apparatus 7 in relation to Figures 1 and 2. For clarity, not all elements of Figures 1 and 2 are shown in Figures 3a and 3b. In particular, it can be seen from Figures 3a and 3b that the apparatus 7 has a gripper 6 for removing the elastic element 5 from the wheel 3. Figure 3a shows the elastic element 5 on the wheel 3 resting on the surface 2 of the substrate 16. The elastic element 5 can be gripped by the gripper 6 and lifted off the surface 2. This is shown in Figure 3b. In Figure 3b, the elastic element 5 is not resting on the wheel 3, so in this sense, the apparatus 7 of the present invention is not shown in Figure 3b. The apparatus 7 includes a drive unit 9 for automatically operating the gripper 6. Furthermore, the apparatus 7 includes a movable table 10 for the elastic element 5. In Figure 3a, the movable table 10 is housed in a position rotated 90° relative to the surface 2. The reason is that the mobile platform 10 is unnecessary in the state shown in the figure. In Figure 3b, the mobile platform 10 is pressed between the surface 2 and the elastic element 5. In this way, the elastic element 5 can be placed on the mobile platform 10. Then, by returning the mobile platform 10 to the state shown in Figure 3a, the elastic element 5 can be removed by the mobile platform 10. Therefore, for example, the elastic element 5 can be separated from the mobile platform 10 by not allowing it to follow the downward movement of the mobile platform 10. As soon as the elastic element 5 is separated from the mobile platform 10, the mobile platform 10 can be cleaned by the cleaning device 11. For this purpose, the cleaning device 11 can spray cleaning fluid onto the mobile platform 10. The apparatus 7 further has an electric mangle 15, which is used to squeeze the electrolyte from the elastic element 5 when the elastic element 5 has been removed from the wheel 3 by the gripper 6. The mangle 15 has two rollers, between which the elastic element 5 can be forced to pass.

[0055] The apparatus 7 further comprises a control unit 8. The control unit 8 is configured to perform steps c) to e) of the method described below, which is: a) A step of placing a foil 3 on a surface 2, wherein the foil 3 has multiple through holes 4, and nanowires 1 can be grown from the electrolyte within these through holes 4. b) A step of placing an elastic element 5 that allows the electrolyte to permeate onto the foil 3, wherein the electrolyte comes into contact with the foil 3 via the elastic element 5, c) During the first growth period, the elastic element 5 is pressed against the foil 3 while galvanically growing multiple nanowires 1, d) The step of removing the elastic element 5 by lifting it from the wheel 3 with the gripper 6, e) A step of continuing galvanic growth of multiple nanowires 1 during the second growth period, Includes.

[0056] In step c), the transferred charge is determined from the current used to galvanically grow the nanowire 1, and if the transferred charge reaches a predetermined limit, step c) is terminated. [Explanation of Symbols]

[0057] 1 nanowire 2 surface 3 foils 4 holes 5 Elastic elements 6 Gripper 7 Equipment 8 Control Unit 9 Drive unit 10 Mobile platform 11 Cleaning devices 12 Voltage source 13 electrodes 14 Reference electrode 15 Mangle 16 circuit boards 17 Structured layer 18 gaps 19 Lamb 20 Voltmeter

Claims

1. A method for galvanically growing multiple nanowires (1) on a surface (2), a) A step of placing the foil (3) on the surface (2), The wheel (3) has a plurality of through holes (4), The steps include: growing the nanowire (1) from the electrolyte in the through-hole (4); b) The step of placing the elastic element (5) that permeates the electrolyte onto the foil (3), The electrolyte comes into contact with the foil (3) via the elastic element (5), and c) The step of galvanically growing the plurality of nanowires (1) during the first growth period, d) The step of removing the elastic element (5), e) The step of continuing the galvanic growth of the plurality of nanowires (1) during the second growth period, Includes, In step c), the transferred charge is determined from the current used for the galvanic growth of the nanowire (1), and, Step c) ends when the transferred charge reaches a predetermined limit value. method.

2. The method according to Claim 1, The elastic element (5) is pressed against the wheel (3) in step c). method.

3. The method according to claim 1 or 2, In step d), the elastic element (5) is lifted from the wheel (3) by the gripper (6). method.

4. A device (7) for galvanically growing multiple nanowires (1), - A surface (2) on which the nanowire (1) is grown, - The foil (3) placed on the surface (2), The wheel (3) has a plurality of through holes (4), A foil (3) in which the nanowire (1) can be grown from the electrolyte within the through-hole (4), - An elastic element (5) that is placed on the foil (3) and permeates the electrolyte, The elastic element (5) allows the electrolyte to be brought into contact with the foil (3), - A gripper (6) for removing the elastic element (5) from the wheel (3), - A control unit (8) configured to perform steps c) to e) of the method according to any one of claims 1 to 3 and Equipped with Device (7).

5. The apparatus (7) according to claim 4, The device (7) further comprises a drive unit (9) for automatically operating the gripper (6). Device (7).

6. The apparatus (7) according to claim 4 or 5, The apparatus (7) further comprises a movable platform (10) for the elastic element (5). Device (7).

7. The apparatus (7) according to claim 6, The apparatus (7) further comprises a cleaning device (11) for cleaning the mobile table (10). Device (7).

8. The apparatus (7) according to any one of claims 4 to 7, The device (7) further comprises a voltage source (12), The voltage source (12) is connected to the electrode (13) and the surface (2) to apply a voltage for growing the nanowire (1). Device (7).

9. The apparatus (7) according to claim 8, The apparatus (7) further comprises a reference electrode (14), The reference electrode (14) is connected to the surface (2). Device (7).

10. The apparatus (7) according to any one of claims 4 to 9, The device (7) further comprises a mangle (15), The mangle (15) is for squeezing the electrolyte from the elastic element (5) when the elastic element (5) has been removed from the foil (3) by the gripper (6). Device (7).

Images