WO2014041429A2

WO2014041429A2 - A nanowire printing device and a method of printing nanowires

Info

Publication number: WO2014041429A2
Application number: PCT/IB2013/002686
Authority: WO
Inventors: Bo Pedersen
Original assignee: Qunano Ab
Priority date: 2012-09-12
Filing date: 2013-09-11
Publication date: 2014-03-20
Also published as: WO2014041429A3

Abstract

An apparatus for fabricating nanowire devices including a reservoir to hold a fluid comprising nanowires, at least one capillary configured to hold a single nanowire fluidly connected to the reservoir and a mechanism configured to transfer nanowires from the reservoir to the at least one capillary.

Description

A NANOWIRE PRINTING DEVICE AND A METHOD OF PRINTING

NANOWIRES

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims benefit of U.S. Provisional Application Serial Number 61/700,051 filed on September 12, 2012, which is incorporated herein by reference in its entirety.

FIELD

[0002] The present invention relates to manufacturing of nanowire devices, in particular methods and devices to fabricate nanowire devices comprising nanowires aligned and protruding in a pre-determined direction from a substrate.

BACKGROUND

[0003] Over recent years the interest in semiconductor nanowires has increased. In comparison with conventional planar technology, nanowire based semiconductor devices offer unique properties due to the one-dimensional nature of the nanowires, improved flexibility in materials combinations due to less lattice matching restrictions and opportunities for novel device architectures. Suitable methods for growing semiconductor nanowires are known in the art and one basic process is nanowire formation on semiconductor substrates by particle-assisted growth or the so-called VLS (vapor-liquid- solid) mechanism, which is disclosed in e.g. US 7,335,908. Particle-assisted growth can be achieved by for instance use of chemical beam epitaxy (CBE), metalorganic chemical vapor deposition (MOCVD), metalorganic vapor phase epitaxy (MOVPE), molecular beam epitaxy (MBE), laser ablation and thermal evaporation methods. However, nanowire growth is not limited to VLS processes. For example the WO 2007/102781 shows that semiconductor nanowires may be grown on semiconductor substrates without the use of a particle as a catalyst. Nanowires have been utilised to realise devices such as solar cells, field effect transistors, light emitting diodes, thermoelectric elements, etc. which in many cases outperform conventional devices based on planar technology.

[0004] Although having advantageous properties and performance, the processing of nanowire devices was initially costly. One important breakthrough in this respect was that methods for growing compound material, such as group III-V semiconductor nanowires, on Si-substrates has been demonstrated. This provides a compatibility with existing Si processing and expensive III-V substrates can be replaced by cheaper Si substrates. [0005] When producing semiconductor nanowire devices comprising nanowires grown on a semiconductor substrate utilizing the above mentioned techniques, a number of limitations are experienced:

- an MOCVD system is a complex vacuum system, which significantly contributes to the production cost for the device;

- growth is performed in batches, with inherent variations between individual batches;

- growth of a large number of nanowires over a large surface yields variations between nanowires in the same batch;

- the nanowires are grown on substrates which need to withstand temperatures of 400-700 °C; and

- to align nanowires in the vertical direction, or any other direction, requires the use of substrates with crystal orientation and controlled epitaxial growth.

SUMMARY

[0006] An embodiment relates to an apparatus for fabricating nanowire devices including a reservoir to hold a fluid comprising nanowires, at least one capillary configured to hold a single nanowire fluidly connected to the reservoir and a mechanism configured to transfer nanowires from the reservoir to the at least one capillary.

[0007] Another embodiment relates to a method of fabricating nanowire devices including loading a charged nanowire from a reservoir into a capillary configured to hold a single nanowire and depositing the nanowire from the capillary on a surface of a substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figs, la- Id are schematic diagrams illustrating a method of fabricating a nanowire device according to an embodiment.

[0009] Figs, le-lh are schematic diagrams illustrating a method of fabricating a nanowire device according to another embodiment.

[0010] Figs. 2a- 2b are schematic diagrams illustrating the operation of a nanoscale capillary nanowire printing device according to an embodiment.

[0011] Figs. 3a-3d are schematic diagrams illustrating device functions according to an embodiment.

[0012] Figs. 4a-4c illustrate a method of manufacturing of a nanoscale capillary according to one embodiment of the present invention.

DETAILED DESCRIPTION

[0013] Embodiments described herein provide devices and methods to print nanowires and nanowire arrays onto a surface from a liquid solution or suspension of nanowires. The devices and methods provide a high throughput, high yield deposition of aligned nanowires. The devices and method provide improved positioning of such nanowires with regards to precision, pattern design and yield.

[0014] Embodiments herein include controlled printing of nanowires, such as charged nanowires, from a liquid solution or suspension. Nanowires are usually interpreted as nanostructures that are of nanometer dimension in its diameter or width. As the term nanowire implies, it is the lateral size that is on the nanoscale whereas the longitudinal size is unconstrained. Such nanostructures are commonly also referred to as nanowhiskers, one dimensional nanoelements, nanorods, etc. Although these terms imply an elongated shape, the nanowires may be pyramidal or stub-like and since nanowires may have various cross- sectional shapes the diameter is in this application intended to refer to the effective diameter. Generally, nanowires are considered to have at least two dimensions each of which are not greater than 300 nm, but nanowires can have a diameter or width of up to about 1 μπι and a length of 2 or more microns, while preserving at least some of the unique properties. The one dimensional nature of the nanowires provides unique physical, optical and electronic properties. These properties can for example be used to form devices utilizing quantum mechanical effects or to form heterostructures of compositionally different materials that usually cannot be combined due to large lattice mismatch. One example is integration of semiconductor materials with reduced lattice matching constraints, which for example allow the growth of III-V semiconductor nanowires on Si substrates.

[0015] Some prior methods of manufacturing patterns and arrays of nanowires use bottom up fabrication. In these methods, the nanowires are often epitaxially grown at their dedicated position as parts of a monolithic structure. In another technique, described in U.S. Patent Application Serial No. 13/518,259, filed June 21, 2012, hereby incorporated by reference in its entirety, nanowires in liquid or gaseous solution/suspension are

perpendicularly aligned by electric field and deposited onto a film or substrate. While this technique provides advantages when manipulating the nanowires in solution/suspension, preciseness of nanowire position is not its central aim.

[0016] Figures la- Id illustrate an apparatus 100 and a method according to a first embodiment. The apparatus 100 includes a reservoir 102. The reservoir 102 includes charged (for example, an induced charge, such as a dipole, discussed in more detail below) nanowires 108, preferably in liquid solution of suspension 110 (nanowire ink). The apparatus 100 may include an array of capillaries 104 in fluid connection with the reservoir 102. The inner diameter of the capillaries 104 is such that only one nanowire can enter. The capillaries 104 may have a width or inner diameter less than 500 nm, e.g. 10-200 nm. The diameter of the capillaries 104 is greater than the diameter of the nanowire 108. The apparatus also includes a mechanism configured to transfer (load) nanowires 108 from the reservoir 102 into the capillaries 104. In an embodiment, the mechanism is electronic and includes a reference electrode 116 (Figs, lg, lh) in or adjacent to the reservoir 102, a first electrode 112 located adjacent to a first end of the capillary 104 proximal to the reservoir 102 and a second electrode 114 located adjacent a second, opposite end of the capillary 104 distal to the reservoir 102. The mechanism may be configured to hold the nanowires 108 in the capillaries 104 and to release a group of the nanowires 108 onto a substrate 106 at the same time or in sequence.

[0017] In this embodiment, movement of nanowires 108 can be controlled and directed by electric fields. The nanowires 108 can be moved from the reservoir 102 to the capillaries 104 (Fig. lb); they can be held within the capillaries 104 (Fig. lc) and they can be deposited onto a dedicated substrate 106 (Fig. Id). The nanowires may be deposited standing on one end within 70-110 degrees with respect to the surface of the substrate 106. For the purposes of this application, the term "electrically controlled charged nanowire" is to be broadly interpreted as charged nanowire whose position and motion may be regulated by electrical fields applied by voltage differences between various electrodes (such as electrodes 112, 114, 116) in contact with the nanowire ink 110. Accordingly, one aspect of the present invention provides an apparatus 100 including at least one nanoscale capillary 104, a reservoir 102 a mechanism for applying electric voltage between electrodes 116 in the reservoir 102 and one or more electrodes 112, 114 in and/or around the capillary 104. When the electric voltage is applied, the movement of charged nano wires 108 within the created electric field can be electrically controlled.

[0018] In an alternative embodiment, some steps, described above as electrically controlled, can be replaced by fluidic transfer. That is, the movement of the nanowires 108 may be driven by hydrostatic pressure and/or gravity.

[0019] In an embodiment, the capillary array 104 is located below the nano wire ink reservoir 102 with the top of the capillaries 104 open into the reservoir 102. The bottom of the capillary 104 may also be open to serve as the printing exit for the nano wire 108. [0020] In an embodiment of the method, a first step includes capturing a nano wire 108 in one or more capillary 104 in the array. This may be done by applying a voltage difference between the reference electrode 116 in the ink 110 and the electrode(s) 114 at the bottom of the capillaries 104 into which the nanowires 108 are to be provided. Nanowires 108 can be selectively loaded into some or all of the capillaries 104 by selectively applying voltage to electrodes 112 of selected capillaries 104. The electrode 112 at the top of the capillary 104 may serve multiple functions such as:

1. initially attracting nanowires 108 to approach the capillary 104 by applying a voltage difference between the reference electrode 116 and the bottom electrode 114;

2. detecting/sensing a nanowire 108 entering the capillary 104 through measurement of a charge passing by the electrode 112 (such as, a voltage fluctuation measurement on the electrode 112);

3. preventing other nanowires 108 from entering the capillary 104 once a first

nanowire 108 has entered by setting the voltage of the (top) electrode 112 as well as the bottom electrode 114 to that of or near the voltage of the reference electrode 116 after the electrode 112 detects the presence of a nano wire 108 in the capillary 104; and

4. "printing" of the nanowire 108 captured in the capillary 104 by setting the

appropriate voltage difference between the top and bottom capillary electrodes 112, 114 such that the nanowire 108 moves out the bottom opening of the capillary 104 onto the substrate surface 106.

[0021] The transfer mechanism may also be used to hold the nanowires 108 in place until all capillaries 104 loaded as discussed in more detail below. When all of the desired capillaries 104 are loaded, the nanowires 108 may be "printed" on surface 106 placed underneath the capillary array 104. Printing may be accomplished as described in 4 above.

In an embodiment, the method includes a step of making one end of the nanowires 108 stick or fix onto the surface 106. This may be done by direct surface to nanowire fixation by heating, by using an adhesive on the surface 106 and curing the adhesive after nanowire deposition, or by using a "soft" sticky coating on the surface holding the nanowire 108 in place for further processing.

[0022] In an alternative embodiment shown in Figures 2-3, the capillary array 104 could also be made such that the capillaries 104 have just one opening which serves as both the entrance for capturing the nanowires 104 and as the printing exit. In this embodiment, the capillary array 104 is first placed in contact with the reservoir 102 for loading the nanowires 108 into each capillary 104 through the opening in the capillary 104, followed by removal of the reservoir 102 and the transfer of the filled capillary array 104 to a substrate surface 106 for printing, with the surface 106 positioned opposite of the opening. [0023] In the embodiment illustrated in Figs, la to Id, the apparatus 100 includes two electrodes 112, 114 adjacent the capillaries 104; electrodes 112, 114 can surround the capillary 104 and/or be located adjacent one side of the capillary 104. In an alternative embodiment illustrated in Figs, le and If, the apparatus 100 includes an additional electrode 118 adjacent to a central portion of the capillaries 104. The voltage of the additional electrode 118 may be independently set and thereby provide greater control over the transfer and deposition of the nanowires 104. Figs, lg and lh illustrate the use of the reference electrode 116 positioned in the reservoir 102 to align and orient the nanowires 108 in the reservoir 102. The voltages of the electrodes 112, 114, 116 may be independently controlled by an electrical controller (not shown), such as a computer or dedicated circuit.

[0024] Alignment and orientation of nanowires 108 while in the solution or suspension 110 to share an unique direction is facilitated by gravity: The gold particle having a much higher density than the semiconductor rod and the suspension, will act as a sink, pointing the nanowires towards the centre of gravity. This behaviour is further strengthened if the density of the suspension is higher than the density of the semiconductor crystal.

[0025] Alignment and orientation of nanowires 108 while in the solution or suspension 110 to share an unique direction is facilitated when the nanowires 108 comprise any kind of electrical dipole. Electrical dipoles may be provided by an axial pn-junction in a

semiconductor nanowire (e.g. one end p-type and the other end n-type), a heterostructure (i.e. a nanowire with one end having different composition from the other end), a

metal/semiconductor interface (e.g. a metal catalyst on one end of the nanowire) or surface functionalization (e.g. a difference in functionalization between ends of the nanowire) in combination with an electrical field within the nanowire ink aligned in parallel or close to parallel with the capillaries 104. However, general parallelization of solution nanowires 108 in an electric field is possible without such anisotropy.

[0026] Figs. 2a- 2b illustrate the operation of an apparatus 100 with one opening according to an embodiment. In an embodiment, the apparatus includes two electrodes 112, 114 adjacent the capillary 104 and a reference electrode 116 in the reservoir 102. The reference electrode 116 is used to generate a potential gradient between the reservoir 102 and the capillary 104, such as V and ground (0 volts). The nanowire 108 can be held in the capillary by setting a voltage difference between the upper and lower electrodes 112, 114 adjacent the capillary 104, such a voltage V and V-dV applied to the electrodes 114 and 112, respectively, and setting the reference electrode 116 to 0 volts.

[0027] As illustrated in Figs. 3a-3d, the operations (loading, holding, depositing) of the capillary 104 may performed by varying the relative potential of the three electrodes 112, 114, 116. For example, if the voltages V_x, V_g, Vi of the electrodes 112, 114, 116 are set as illustrated in Figure 3a (Vi > 0, V_g = 0, V_x > 0), the capillary 104 is blocked. That is, a nanowire 108 will not enter the capillary 104. If the voltages V_x, V_g, Vi of the electrodes 112, 114, 116 are set as illustrated in Figure 3c (Vi < 0, V_g = 0, V_x >= 0), the capillary 104 is unblocked. In this configuration, the nanowire 108 may enter the capillary 104. If the voltages V_x, V_g, Vi of the electrodes 112, 114, 116 are set as illustrated in Figure 3c (Vi < 0, V_g = 0, 0> V_x > Vi), the nanowire 108 is held in the capillary 104. If the voltages V_x, V_g, V_; of the electrodes 112, 114, 116 are set as illustrated in Figure 3d (Vi < 0, V_g = 0, V_x = Vi), the potential gradient will induce the nanowire 108 to exit the capillary 104. A voltage source and a controller, such as a dedicated control circuit and/or a special or general purpose computer may be used to control the voltages applied to the electrodes.

[0028] U.S. Patent Application Serial No. 61/660,310, filed on June 15, 2012, hereby incorporated by reference in its entirety, describes manipulation of charged molecules, specifically charged DNA molecules. U.S. Patent Application Serial No. 61/660,310 also describes a method of forming nanoscale capillaries that may be used in the manipulation of charged molecules. [0029] Figs. 4a-4c sequentially illustrate an exemplary, thus non-limiting, method of manufacturing of said nanoscale capillary according to one embodiment of the present invention shown in Figs. 2 and 3. For the sake of simplicity and without limitation, the illustrated method is split into three main phases. These are growth of a nanowire, provision of electrodes and creation of a nanoscale capillary itself. The capillary is formed by providing a nanowire, forming at least one layer around the nanowire, and removing the nanowire such that the capillary remains in the at least one layer.

[0030] In the first phase, illustrated in Fig. 4a, a substrate 31 is provided. By way of example, said substrate may be made of silicon, silicon-on-oxide (SOI), sapphire or a suitable III-V-compound semiconductor. Obviously, for industrial applications, the substrate may be replaced by a wafer suitable for fabrication of, for example integrated circuits. In the exemplary method of Figs. 4a-4c an auxiliary layer 32 is grown on said substrate. Said auxiliary layer acts as a buffer, i.e. it accommodates difference in the crystallographic structure of the substrate and the subsequently grown structures. This layer is typically made from a III-V compound semiconductor, such as InAs. Its thickness ranges from 100 nanometers to one micron. Subsequently, a vertical, essentially one-dimensional

nanostructure 33, such as nanowire or a nanotube, is grown on the auxiliary layer. In this example, said nanostructure is a nanowire grown catalytically in a high-yield VLS-process (Vapor-Liquid-Solid), wherein a gold particle serves as a catalyst and also allows precise positioning of the future nanowire. The diameter of thus grown nanowires is substantially of the same magnitude as the diameter of the catalytic particle. Accordingly, the thickness of the grown nanowire may be precisely controlled. Same is true for its length that is determined by the duration of the growth. For the application at hand, manufacturing of said nanoscale capillary, the required width of the nanowire is typically about between 10 and 500 nanometer, whereas length of the grown nanowire lies between 0.5 and 5 microns. Here, the grown nanowire is made of same material as the auxiliary layer (InAs), but any other semiconductor or insulating material suitable for nanowire growth is equally conceivable. Once a nanowire of desired dimensions has been grown, a layer of insulating material 34 is deposited, typically using Atomic Layer Deposition (ALD), across the auxiliary layer such that the auxiliary layer and the nanowire become completely encapsulated. This material is typically a dielectric, i.e. an electric insulator that can be polarized by an applied electric field. Normally aluminum oxide (AI₂O₃) is used but even other materials having dielectric properties, such as silicon dioxide (S1O₂) and hafnium oxide (Hf0₂), may be used. The thickness of the deposited layer varies between 2 and 200 nanometer.

[0031] In the second phase, illustrated in Fig. 4b, where the electrodes are provided, another layer 35 is firstly applied on top of the deposited dielectric layer. One purpose of said layer is to provide structural stability. The nanowire thereby becomes at least partially embedded in the applied layer 35. Said applied layer is in this embodiment made of photo resist material such as SI 813 that normally is spun onto the dielectric layer 34. The previously deposited dielectric layer 34 is subsequently removed from the non-embedded portion 36 of the nanowire 33 (i.e., from the exposed upper portion of the nanowire). A further electrically conductive material layer 37 is subsequently deposited, at least in the region immediately adjacent to the nanowire. A gate electrode 37 that circumferentially surrounds the nanowire (or is located at the side of the nanowire) is hereby created by deposition of layer 37. By way of example, said gate electrode 37 is made of a metal such as tungsten, a heavily doped semiconductor, such as polysilicon or an alloy, such as a silicide. In this embodiment, the previously described heavily doped semiconductor auxiliary layer 32 makes up a first electrode (e.g., 114 in Figures 2-3), but a dedicated electrode grown analogously to the gate electrode (e.g., as shown in Figure 1) and positioned at a distance from said gate electrode 37, preferably adjacent to the base of the nanowire 33, i.e. bottom of the future capillary (e.g., 104 in Figures 1-3), is equally conceivable.

[0032] In the third phase, illustrated in Fig. 4c, where the nanoscale capillary is created, another insulating layer 38, such as Al₂03 is deposited. One of its purposes is to ensure sufficient electric isolation of the previously created gate electrode 37. Subsequently, another layer of photo resist material 39 is deposited. In the next step, the nanowire 33 is rendered radially exposed 40 by removing the uppermost section of the hitherto created structure, for example by using sputter etching or chemical mechanical polishing. In a subsequent step, the nanowire 33 is removed. For example, the material of the nanowire 33 is for instance selectively etched (wet or dry) away, thus creating a tube-like hollow nanostructure 41 (i.e., opening) that substantially delimits the nanoscale capillary (e.g., 104 in Figures 1-3). The auxiliary layer 32 acts as an electrode (e.g., 114 in Figures 2-3) alongside the created gate electrode 37 (e.g., 112 in Figures 1-3).

[0033] If desired to form the capillary having two openings, as shown in Figure 1, then the opening 41 is etched further until it is exposed through the layer 32 and substrate 31. Alternatively, the substrate 31 and/or layer 32 may be selectively removed or delaminated after opening 41 is formed in Figure 4c, to form the capillary 104 with two openings shown in Figure 1.

[0034] It is to be understood that the method is not limited to manufacturing a nanoscale capillary with a single gate electrode. On the contrary, the above described process of manufacturing of the nanoscale capillary is easily modified so as to include formation of multiple gates. Specifically, if layer 32 is removed in the final device as described above, then the second gate electrode 114 is formed around the nanowire before forming layer 34 in Figure 4a.

[0035] Additionally, other techniques may be used to make the capillaries. For example, instead growing the nanowire 33 from a metal catalyst particle, the nanowire may be grown elsewhere and deposited over substrate 31 or the nanowire 33 may be grown without using a catalyst particle through a hole in a mask layer made by nanoimprint, electron beam or x-ray lithography, as described in U.S. Patent Application Serial No. 12/308,249, filed December 11, 2008, hereby incorporated by reference in its entirety. Alternatively, the capillary 104 may be made by masking a membrane, forming openings in the mask by any suitable lithography technique, and etching the capillary holes 104 in the membrane.

[0036] Although the foregoing refers to particular preferred embodiments, it will be understood that the invention is not so limited. It will occur to those of ordinary skill in the art that various modifications may be made to the disclosed embodiments and that such modifications are intended to be within the scope of the invention. All of the publications, patent applications and patents cited herein are incorporated herein by reference in their entirety.

Claims

WHAT IS CLAIMED IS:

1. An apparatus for fabricating nanowire devices comprising:

a reservoir to hold a fluid comprising nano wires;

at least one capillary configured to hold a single nanowire fluidly connected to the reservoir; and

a mechanism configured to transfer nanowires from the reservoir to the at least one capillary.

2. The apparatus of claim 1, wherein the mechanism is configured to hold and release the nanowires from the capillary.

3. The apparatus of claim 1, wherein the at least one capillary comprises an array of capillaries.

4. The apparatus of claim 1, wherein the mechanism is electronic.

5. The apparatus of claim 4, wherein the nanowires are charged and have a diameter or width between 10 and 200 nm.

6. The apparatus of claim 4, wherein the mechanism comprises one or more electrodes in the reservoir and one or more electrodes adjacent the at least one capillary.

7. The apparatus of claim 6, further comprising an electrical controller to control a voltage between the one or more electrodes in the reservoir and the one or more electrodes adjacent to the at least one capillary.

8. The apparatus of claim 6, further comprising a first electrode located adjacent a first end of the capillary and a second electrode located adjacent a second, opposite end of the capillary.

9. The apparatus of claim 6, wherein at least one of the first and second electrodes is configured as a sensor.

10. The apparatus of claim 1, wherein the mechanism hydraulic.

11. The apparatus of claim 1, wherein the at least one capillary comprises a tube open at both ends and the capillary has a diameter or width less than 500 nm.

12. A method of fabricating nanowire devices comprising:

loading a charged nanowire from a reservoir into a capillary configured to hold a single nanowire; and

depositing the nanowire from the capillary on a surface of a substrate.

13. The method of claim 12, wherein loading the nanowire comprises generating an electric field between the reservoir and the capillary.

14. The method of claim 12, wherein loading the nanowire comprises generating a hydrostatic pressure between the reservoir and the capillary.

15. The method of claim 12, wherein loading the nanowire comprises loading the nanowire in a first end of the capillary and depositing the nanowire comprises depositing the nanowire out of a second, opposite end of the capillary.

16. The method of claim 12, further comprising sensing the nanowire on loading or depositing the nanowire by monitoring a voltage on an electrode adjacent the capillary.

17. The method of claim 12, further comprising generating an electric field to prevent more than one nanowire entering the capillary.

18. The method of claim 12, wherein deposing the nanowire comprises setting a voltage difference between a first electrode located adjacent a first end of the capillary and a second electrode located adjacent a second, opposite end of the capillary to move the charged nanowire from the capillary to the surface of the substrate.

19. The method of claim 12, further comprising holding the nanowire in the capillary while moving the capillary to a substrate or moving a substrate to the capillary.

20. The method of claim 12, further comprising:

selectively loading nano wires into a plurality of capillaries; and

holding the nanowires in place until the capillaries are loaded.

21. The method of claim 12, further comprising fixing the nanowire to the surface of the substrate.

22. The method of claim 21, wherein fixing the nanowire comprises one or more of heating the substrate and nanowire, curing an adhesive on the surface of the substrate or using a sticky coating on the surface of the substrate.

23. The method of claim 12, further comprising generating a dipole in the nanowire by applying an electric field to form the charged nanowire and to at least one of load or deposit the nanowire.

24. The method of claim 12, wherein:

a plurality of nanowires are deposited standing on one end within 70-110 degrees with respect to the surface of the substrate; and

the nanowires are substantially aligned with each other.

25. The method of claim 12, wherein the nanowire is loaded from a solution or suspension.

26. The method of claim 12, where in the capillary is formed by providing a nanowire, forming at least one layer around the nanowire, and removing the nanowire such that the capillary remains in the at least one layer.

27. The method of claim 12, wherein:

multiple nanowires are deposited standing on one end;

the nanowires share a common direction; and

the nanowires are substantially aligned with each other.