GB2422638A

GB2422638A - A rotational actuator

Info

Publication number: GB2422638A
Application number: GB0501681A
Authority: GB
Inventors: Colin Lambert
Original assignee: Lancaster University
Current assignee: Lancaster University
Priority date: 2005-01-27
Filing date: 2005-01-27
Publication date: 2006-08-02
Also published as: GB0501681D0; WO2006079786A1

Abstract

A rotational actuator, comprising; a rotatable member 3, a support member 1, 2 which supports the rotatable member 3, the rotatable member 3 having a different chirality to that of the support member 1, 2, a particle source arranged to provide at least one particle to one of the rotatable member 3 and the support member 1, 2, such that the at least one particle impinges upon the rotatable member 3 and/or the support member 1, 2, the at least one particle experiencing a change in angular momentum due to the different chiralities of the support member 1, 2 and rotatable member 3, thereby causing rotation of the rotatable member 3 due to the principle of conservation of momentum. Also disclosed are a large number of applications of this principle.

Description

A Rotational Actuator The present invention relates to a rotational

actuator. For instance, embodiments of the present invention relative to carbon nanotube rotational actuators, and associated devices.

Actuators are devices that communicate motion to an object or causes the operation of a machine or other device. For example, an actuator could be, amongst other things, a conveyor (belt), a switch or a pump. Rotational actuators are devices that generally involve the generation and/or application of rotational motion of some kind. For example, a rotational actuator can generate rotational motion that can in turn be used to drive something linearly (e.g. a conveyor belt). Rotational actuators are used in a wide range of fields. For example rotational actuators such as motors are found in fields ranging from domestic appliances to heavy industry. Recent developments in fields such as those concerning actuators and sensors has led to an increased demand in the miniaturisation of components such as motors and the like, leading to the now well-established field of MEMS (Microelectromechanical systems). While until relatively recently such miniaturisation concerned objects of the order of millimetres and even micrometres, some applications now demand the incorporation of nanometre scale devices.

Many nanometre scale or nanoscale structures are mechanically passive in nature, such as powders and tubes. For example, carbon nanotubes, which demonstrate immense potential in terms of mechanical strength and beneficial electrical properties, are passive. Indeed, the potential of carbon nanotubes is now being realised in a wide variety of applications ranging from display panels and electron microscopes to reinforced materials. While mechanical nanoscale devices have been envisaged and proposed from the birth of the field of nanotechnology, the practical realisation of such devices has been rare.

One good example of the state of the art is the work carried out by Zetti et a!. in the paper titled Rotational Actuators Based on Carbon Nanotubes, Nature, Vol 424, 24 July 2003'. The device disclosed in this paper is illustrated in Figure 1.

The device comprises a rotational member R, which is a solid metal plate acting as a rotor plate, that is attached to a suspended support shaft C. The support shaft C is an electrically conducting carbon nanotube. The ends of the carbon nanotube C are embedded in electrically conducting anchors Al, A2 that rest on the oxidised surface of a silicon chip (not shown). The rotor plate R is surrounded by three fixed stator electrodes Sl, S2 and S3: two in-plane' stators Si, S2, which are horizontally opposed and rest on the oxidised surface of the silicon chip and a gate stator S3 which is located underneath the rotor plate R and is buried beneath the surface.

In use four independent voltage control signals can be applied to control the position, speed and direction of rotation of the rotor plate R via the use of electrostatic forces.

One voltage signal is applied to the rotor plate R and three to the stators Si, S2, S3.

Such control signals are well known in the art.

All of the dimensions of the device of Figure 1 are of the order of nanometres or microns. Although not drawn to a highly accurate scale, the Figure does represent the approximate relative sizes of the device's components. As an indication of scale, the carbon nanotube C is approximately 900nm in length. Thus, the device of Figure 1 offers a nanoscale actuator that may be desirable in various fields of research, development and manufacture.

Although demonstrating the potential for a nanoscale actuator, the device of Figure 1 has, as yet, offered little or no practical use. Although the carbon nanotube C is of the order of nanometres, the footprint' of the device is considerably larger. The need for stators SI,S2,S3 greatly increases the size of the device. The need for stators Si,S2,S3 also makes it difficult to actually use the rotational actuator for any practical purpose, it being difficult to get unhindered access to the rotor plate R. It is also difficult to successfully and accurately attach the rotor R to the nanotube C. Any small errors can easily result in damage to the nanotube and consequently the device as a whole. As a consequence of the use of stators Si,S2,S3, external driving equipment is required to provide the aforementioned signals to each stator Si,S2,S3 to generate rotation of the rotor plate R. It is an object of the present invention to obviate or mitigate at least one of the above- mentioned disadvantages.

According to the present invention, there is provided a rotational actuator, comprising a rotatable member extending along a rotational axis, a support member which is substantially coaxial with and supports the rotatable member, the rotatable member having a different chirality to that of the support member, a particle source arranged to provide at least one particle to one of the rotatable member and the support member, such that the at least one particle impinges upon the other of the rotatable member and the support member, said at least one particle experiencing a change in angular momentum due to the different chiralities of the support member and rotatable member, thereby causing rotation of the rotatable member due to the principle of conservation of momentum.

The chirality of a structure is defined by how non-symmetric (e.g. twisted) the structure is. The more chiral a structure is, the more nonsymmetric (e.g. twisted) structure is.

The inventor has realised that motion can be generated in a rotatable member by taking advantage of a difference in chirality of adjacent members, and the principle of the conservation of momentum. As particles impinge upon at least one of the members, or pass through adjacent members, the angular momentum of the particles may be altered by a change in the chirality of these members. Due to conservation of momentum, as the particles gain momentum in one direction, the members through which the particles pass or which the particles impinge upon gain momentum in the other (generally opposite) direction. Thus, rotation of a member is achieved.

By adopting such a simple principle, no stator plates or blocks are required, and no complex driving signals are required. As the operation is so simple and requires no cumbersome external apparatus, the principle can be readily applied to the field of nanotechnology.

Preferably, the rotation of the rotatable member is arranged to provide the motive power of a device.

Preferably, wherein the support member and rotatable member are nanotubes, and most preferably are formed substantially from carbon. Alternatively, the support member and rotatable member maybe formed substantially from silicon.

Preferably, only one of the support member and rotatable member is chiral, and the other of the support member and rotatable member is non-chiral.

Preferably, at least one of the support member and rotatable member has a twisted structure, and is thereby chiral. Alternatively or additionally, at least one of the support member and rotatable member further comprises at least one adsorbed molecule, and is thereby chiral.

Preferably, the particle source is arranged to provide a stream of particles, which maybe one of an electron, an atom and a molecule. The atoms may, for example, be helium or hydrogen atoms. The stream of particles may be an electrical current, a flow of liquid or a gas.

The rotatable member may be hollow, with the support member extending within and continuously through the hollow rotatable member. Alternatively, the rotatable member may extend within and continuously through the hollow support member.

Most preferably the actuator comprises a further hollow support member, wherein a first end of the rotatable member extends within the hollow support member, and a second distant end of the rotatable member extends within the further hollow rotatable member.

According to another aspect of the present invention, there is provided a conveyor for conveying material placed thereon, comprising a plurality of rotational actuators as described above, wherein the actuators are arranged such that the rotational axis of each is in substantially the same plane, each of the plurality being arranged to convey said material. Preferably, the conveyor is arranged to convey individual molecules.

According to yet another aspect of the present invention, there is provided an electrical switch comprising a rotational actuator as described above, wherein the switch further comprises a first electrical conductor coupled to the rotatable member and a second electrical conductor, said electrical switch being switchable between a first state, in which the first electrical conductor is in electrical contact with the second electrical conductor, and a second state, in which the first electrical conductor is not in contact with the second electrical conductor, and wherein rotation of the rotatable member changes the state of the switch from at least one of said states to the other. The second electrical conductor may be a carbon nanotube.

A memory device may comprise such a switch.

According to still another aspect of the present invention, there is provided a radiation manipulation device comprising a rotational actuator as described above, wherein the rotatable member comprises a region that at least one of absorbs, transmits and reflects radiation, such that rotation of the rotatable member alters at least one of the absorption, transmission and reflection of incident radiation. Most preferably the radiation is electromagnetic.

Preferably, the region is provided by a molecule adsorbed onto a surface of the

rotatable member.

According to a still further aspect of the present invention, there is provided a method of operating an apparatus, the apparatus comprising a rotatable member extending along a rotational axis, a support member which is substantially coaxial with and supports the rotatable member, the rotatable member having a different chirality to that of the support member, the method comprising providing at least one particle to one of the rotatable member and the support member, the at least one particle impinging upon the other of the rotatable member and the support member, such that the at least one particle experiences a change in angular momentum due to the different chiralities of the support member and rotatable member, thereby causing rotation of the rotatable member by the principle of conservation of momentum.

Most preferably, the method further comprises using rotation of the rotatable member to provide the motive power of a device.

According to yet another aspect of the present invention, there is provided a pump for pumping at least one particle, comprising a rotatable member extending along a rotational axis, a first support member which is substantially coaxial with and supports a first end of the rotatable member, the rotatable member being an intrinsically chiral nanotube, and wherein the rotatable member is hollow such that rotation thereof causes an exchange of momentum between the rotatable member and said particle moving said particle along an inner surface of the rotatable member due to the intrinsic chirality of the rotatable member, and wherein the at least one particle comprises at least one atom.

Preferably, the pump further comprises a source container, from which the at least one particle enters the pump, and a delivery container, into which the at least one particle is pumped.

Preferably, a mixer may comprise a plurality of the pumps as described above, wherein each of the pumps is arranged to pump at least one particle into a mixing chamber to be mixed.

Preferably, the mixer comprises a further pump as described above, arranged to pump the at least one from particle from the mixing chamber.

According to yet still another aspect of the present invention, there is provided a memory device, comprising a pump as described above, a second support member which is substantially coaxial with and supports a second end of the rotatable member; and at least one particle located in the rotatable member, such that rotation of the rotatable member of the pump causes the at least one particle to move between the support members, a first memory state being defined when the at least one particle is located on the first support member side of the device, and a second memory state being defined when the at least one particle is located on the second support member side of the device.

According to a further aspect of the present invention, there is provided a method of detecting properties of a nanotube, comprising providing a device having a rotatable member extending along a rotational axis, the rotatable member being a nanotube; a first support member which is substantially coaxial with and supports a first end of the rotatable member, and a second support member which is substantially coaxial with and supports a second end of the rotatable member; the method comprising: i) rotating the rotatable member ii) measuring the voltage signal between the first support member and the second support member over a predetermined time interval iii) analysing the voltage signal to determine a property of the nanotube device.

Most preferably, step iii) of the method comprises taking the Fourier transform of the voltage signal.

Preferably, the frequency of rotation of the rotatable member is determined from the Fourier transform.

The rotatable member may further comprise a receptor adsorbed onto a surface thereof, the method further comprising exposing the device to an area of interest; and determining if a molecule has attached itself onto the receptor by determining the frequency of rotation of the rotatable member.

The property to be determined may be the chirality of the rotatable member wherein step iii) of the method further comprises comparing at least one property of the voltage signal with data indicative of known nanotubes, in order to determine the chirality of the rotatable member.

Most preferably, the at least one property of the voltage to be compared with the data is the Fourier transform of the voltage signal, and the data is indicative of the Fourier transform of known nanotubes.

Most preferably, a set of data indicative of known nanotubes is constructed by first measuring the chirality of the rotatable members of a plurality of devices using Raman scattering techniques, and then matching the chirality of each rotatable member to the at least one property of the voltage signal of the same rotatable member, such that a library of the at least one property of the voltage signal versus chirality is established.

According to yet another aspect of the present invention, there is provided apparatus for detecting properties of a nanotube, comprising a device having a rotatable member extending along a rotational axis, the rotatable member being a nanotube; a first support member which is substantially coaxial with and supports a first end of the rotatable member, and a second support member which is substantially coaxial with and supports a second end of the rotatable member; a voltmeter connected to the first support member and second support member; and a signal analyser for analysing the voltage between the first support member and second support member.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying Figures, in which: Figure 1 is a perspective schematic view of the prior art rotational actuator described above; Figure 2 is a perspective view of a rotational actuator in accordance with a first embodiment of the present invention; Figure 3 is a perspective view of an alternative embodiment of a rotational actuator; Figure 4a is a plan view of a nanoscale conveyor in accordance with an embodiment of the present invention; Figure 4b is a side view of the nanoscale conveyor illustrated in Figure 4a; Figure 4c is an end on view of the nanoscale conveyor illustrated in Figure 4a; Figure 5 is a perspective view of a nanoscale electrical switch in accordance with an embodiment of the present invention.

Figure 6 is a perspective view of a nanoscale pump in accordance with an embodiment of the present invention.

Figure 7 is a perspective view of a nanoscale mixer in accordance with an embodiment of the present invention.

Figure 8 is a perspective view of a nanoscale memory device in accordance with an embodiment of the present invention.

Figure 9 is a perspective view of apparatus for determining the chirality of a nanotube in accordance with an embodiment of the present invention.

Figure 10 is a perspective view of apparatus for detecting the presence of a molecule in accordance with an embodiment of the present invention.

Figure 2 illustrates a rotational actuator comprising a support member 1, a further support member 2 and a rotatable member 3. Each of these members is a carbon nanotube. The support members 1,2 are non-chiral carbon nanotubes, such as those of the armchair type (a type of non- chiral carbon nanotube well known in the art). The rotatable member 3 is au intrinsically chiral nanotube i.e. the nanotube has an intrinsic nonsymmetric or twisted structure. Thus, the rotatable member 3 and support members 1,2 have different chiralities.

A first end of the rotatable member 3 is concentrically located within the support member 1, and is arranged such that the support member 1 overlaps the first end of the rotatable member 3. The overlap defines a first overlap portion or region 4a. A second end of the rotatable member 3 is concentrically located within the further support member 2, and is arranged such that the further support member 2 overlaps the second end of the rotatable member 3. The overlap defines a second overlap portion or region 4b.

Due to the physical interactions between the carbon nanotube support members 1,2 and the carbon nanotube rotatable member 3 (i.e. interaction of electrostatic potentials), the support members 1,2 act as substantially frictionless bearings for the

rotatable member 3.

The lengths and diameters of the nanotubes are not limited to specific values. For example, the nanotubes of the present embodiment may have diameters of the order of 1 nm and lengths ranging from Snm to thousands of nm.

The inventor has realised that causing a particle or stream of particles (application of a signal') to impinge upon (i.e. come into contact with or have an effect on) the rotatable member can, in combination with exploitation of conservation of momentum (in this case angular momentum) laws, effect rotation of the rotatable member 3 if the support member and the rotatable member have different chiralities. Different chiralities include one member being chiral, and the other non-chiral.

In use, a particle source PS is provided to introduce particles to the rotational actuator.

In this embodiment, the particles are electrons. A potential difference is applied across the rotatable member 3 via the support members 1,2, which serve as electrodes. The application of a potential difference causes a current to flow in the rotational actuator.

The current is made to flow from left to right in Figure 1, i.e. from the support member 1 to the further support member 2, and passes from the support members 1,2 to the rotatable member 3 (and vice versa) via the overlapping of electron orbitals in the overlap regions 4a, 4b.

Due to the difference in chirality between the support member 1 and the rotatable member 3, electrons constituting the current flow experience a change in angular momentum as the electrons pass from the non-chiral support member I to impinge upon and pass to the chiral rotatable member 3. This also occurs as the electrons leave the rotatable member 3 and pass into the further support member 2. Due to conservation of momentum (in this case angular momentum) laws, for the electrons to suddenly gain angular momentum, another object in the interaction causing this gain must also lose' momentum, or gain in a substantially equal and opposite direction.

Thus as the electrons enter and leave the rotatable member 3, the change in angular momentum of the electrons causes the rotatable member 3 to rotate. A rotatable actuator is realised, from which work can then be extracted.

As there are no stators surrounding the rotatable member, as there are in the prior art device, such a rotational actuator is smaller, more accessible and thus versatile.

Furthermore, as there are no stators present, no complicated driving routines are required to effect rotation of the rotatable member.

The direction of rotation of the rotatable member can be controlled by making the current flow in a certain direction, for example reversing the bias of the applied potential difference. By applying an a.c. signal to the rotational actuator, the rotatable member 3 can be made to oscillate and even resonate. Varying the current flow through the device can vary the speed of rotation of the rotatable member 3.

In the present embodiment a potential difference is applied across the rotatable member 3 induces a torque. Torque in the rotatable member 3 is the product of F and r, where r is the radius of the rotatable member 3 and F is a tangential force of the order of 1x10' N (i.e. lxl0 N per Volt applied). The inventor has found that, for the present embodiment, the frictional forces involved in opposing the torque are lx10'4 N per atom. The atoms causing this frictional force are those in the overlap regions 4a, 4b, which consist of atoms in the parts of the support members 1,2 overlapping the rotatable member 3, and the atoms in part of the rotatable 3 member being overlapped. These frictional forces are due to the interaction in the atomic potentials of the overlapping atoms.

From simple mathematics, the torque provided per volt can be divided by the frictional force per atom to reveal the upper limit of the number of atoms permissible in the overlap regions 4a, 4b for rotation to take place per volt applied. It can be seen that: l0 N per Volt applied = i04 atoms in overlap region per volt applied iO'4 N per atom in overlap region Thus, it can be seen that for rotation to take place in the rotatable member 3 of the rotational actuator of Figure 1, there can be no more than the order of 1 atoms in the total region of overlap for each Volt applied.

It will be appreciated that the aforementioned values of torque, frictional force per atom and total numbers of atoms in the overlap region 4a,4b are given by way of example only, and are dependent on, amongst other things, the arrangement, dimensions, materials of and the potential applied to the device. The above calculation illustrates that for any given rotational actuator constructed generally as detailed above (i.e. a rotational actuator that comprises nanotubes), there will typically be a maximum number of atoms permissible in the overlap regions 4a, 4b for rotation to take place.

The device may be constructed using techniques known in the art. For example, in one embodiment, the device is formed from two carbon nanotubes; an outer nanotube that will form the support members 1,2, the outer nanotube surrounding an inner nanotube that will form the rotational actuator 3. A current is passed through the nanotubes, which due to interactions between the nanotubes, passes preferentially through the outer nanotube. The nanotubes then act as an electrical fuse. Above a certain current value, determined by the properties of the tubes, the current will be sufficient in magnitude to break the outer nanotube at a point between the ends of the tube. When the tube breaks, the current is removed. The outer nanotube now forms two smaller nanotubes, which form the support members 1,2. At the place where the outer tube had broken, the inner tube is exposed, and forms the rotatable member 3 of the device.

The inventor of the present application has taken advantage of the fact that the chirality of inner nanotube(s) of a nested set (i.e. an inner nanotube surrounded by an outer nanotube) is generally random. The inventor has realised that as a consequence of this, the chirality of an outer and inner nanotube will thus often be different.

Consequently, devices may be constructed by using the above method and then testing the chirality of the tubes e.g. by spectroscopy or seeing if the device works.

Such a fabrication technique yields a similar structure to the rotational part of the prior art Zetti device i.e. an exposed inner nanotube supported by two overlapping outer nanotubes. However, the present invention does not have or require a rotor plate R, nor does it require the use of stators Si, S2, S3.

Figure 3 illustrates an alternative embodiment to the rotational actuator described with reference to Figure 2. As with Figure 2, the rotational actuator of Figure 3 comprises a support member 10, a further support member 20 and a rotatable member 30. Each of these members is a carbon nanotube. The support members 10,20 are non-chiral carbon nanotubes, such as those of the armchair type. The rotatable member is an intrinsically chiral nanotube.

A first end of the rotatable member 30 is concentrically located within the support member 10, and is arranged such that the support member 10 overlaps the first end of the rotatable member 30. The overlap defines a first overlap portion or region 40a. A second end of the rotatable member 30 is concentrically located within the further support member 20, and is arranged such that the further support member 20 overlaps the second end of the rotatable member 30. The overlap defines a second overlap portion or region 40b.

The rotational actuator of this embodiment works in the same way as that described with reference to Figure 2. Specifically, particles experience a change in angular momentum as the particles pass from the non-chiral support member I to impinge upon and pass to the chiral rotatable member 3. This also occurs as the particles leave the rotatable member 3 and pass into the further support member 2. Due to conservation of momentum (in this case angular momentum) laws, for the particles to suddenly gain angular momentum, another object in the interaction causing this gain must also lose' momentum, or gain in a substantially equal and opposite direction.

Thus as the electrons enter and leave the rotatable member 3, the change in angular momentum of the electrons causes the rotatable member 3 to rotate. A rotatable actuator is realised, from which work can then be extracted. Figure 3 and the description of it merely serve to illustrate that a rotational actuator as described herein may have various different configurations.

It will be appreciated by one skilled in the art that the rotational actuators described herein have a wide range of applications, and may provide the motive power for a wide range of devices. Such devices include material conveyors, electrical switches and electromagnetic manipulation devices. Such devices are described below by way

of example only.

Illustrated in Figures 4a-c is a conveyor in accordance with an embodiment of the present invention. The conveyor comprises a plurality of rotational actuators, identical to those described with reference to Figure 2. Thus, identical reference numerals have been used.

As can be seen from Figures 4a, 4b and 4c in combination, the plurality of rotational actuators are arranged such that the actuators all lie in the same plane, and such that the rotatable member 3 of each rotational actuator is adjacent a rotatable member 3 of another rotational actuator in the plurality. Preferably, the rotational axis RA of each of the actuators is parallel, as illustrated the Figures 4a to 4c.

In use, an electrical signal is applied to the conveyor such that the rotatable member 3 of each rotational actuator rotates in the same direction. Thus, if material is deposited on the conveyor, the materialwill be conveyed from a first location to a second location via rotation of the rotatable members 3. Thus, the device is analogous to a conveyor belt, but does not require a belt. For a device comprising carbon nanotubes, as is the case in this embodiment, the material to be conveyed could be individual molecules and the like.

It will be appreciated that the conveyor can be operated in a number of ways. For example, each rotatable member 3 of the conveyor can be operated simultaneously and continuously. Alternatively, each rotatable member 3 can be rotated when required. It will be appreciated that by reversing the direction of rotation of the rotatable members 3, the direction of material conveyance can be similarly reversed.

It will be appreciated that the conveyor can also be realised by the embodiment of the rotational actuator illustrated in, and described with reference to, Figure 3.

Using the rotational actuators of Figure 3 to construct the conveyor of Figure 4, no belt is required. A further benefit is also derivable. Referring to Figure 3, it can be seen that the rotatable member 3 is now the outermost nanotube. Thus, as well as being able to convey material, the conveyor is now able to convey itself. For example, if a signal were applied to the conveyor when the conveyor was located on a surface, rotation of the rotatable members 3 would effect linear movement of the conveyor itself. Thus, the conveyor can also be used as a means of propelling either itself or an object to which the conveyor is attached. It will be appreciated that in the embodiment of a conveyor that conveys itself, the particle source may be located on the conveyor itself, for exaniple supported by the non-rotating support members 1,2. Alternatively, the particle source may be located anywhere that allows particles to be communicated to the rotational actuators of the conveyor e.g. remotely, wherein particles may be conveyed to the rotational actuators by tubes. These tubes may be carbon nanotubes.

Referring now to Figures 5a and 5b, an electronic switch is illustrated. The switch comprises a rotational actuator as illustrated in, and described with reference to Figure 2 (and thus like features are given the same reference numerals), but has a first electrical conductor 5 coupled to the rotatable member 3. In this embodiment, the electrical conductor 5 is a molecule that has been adsorbed onto the surface of the rotatable member 3. The switch also comprises a second conductor 6, which is an electrical wire. It will be appreciated that the second conductor 6 could be a rotational actuator in accordance with an embodiment of the present invention.

In use a signal is applied to the rotational actuator in order to effect rotation of the rotatable member 3 as previously described. Rotation can be such that the rotatable member 3 brings the first electrical conductor 5 into electrical contact with the second electrical conductor 6, and then rotation is ceased, such that an electrical current is allowed to flow from the first conductor 5 to the second conductor 6, and vice versa.

This situation is illustrated in Figure 5a. Alternatively, as illustrated in Figure 5b, the rotation can be such that the rotatable member 3 removes the first electrical conductor from being in contact with the second electrical conductor 6, and then rotation is ceased, such that a current cannot flow from the first electrical conductor 5 to the second electrical conductor 6, and vice versa. Thus, an electrical switch is realised.

It will be appreciated that the switch described will remain in a conducting or non- conducting state unless a signal is sent to the rotational actuator effecting further rotation. Thus, it will be further appreciated that one or more of these switches can be used as a memory device or memory store. Each switch can be set to be high' or low' (i.e. conducting or non- conducting). The state of the switch can be read by measuring the electrical resistance between the first electrical conductor 5 and the second electrical conductor 6. A relatively high resistance corresponds to the switch being low' or non-conducting, whereas a relatively low resistance corresponds to the switch being high' or conducting. It will be appreciated that other ways and means can be employed to read the status of the switch. For example electrical conductor 6 could be a single electron transistor, an extremely sensitive device used for measuring charge. In this case, the change in capacitance of the switch could be used to determine the state of the switch.

The rotational actuator described herein can also be used as a manipulator of radiation. In manipulating the radiation, the rotational actuator can affect the way incident radiation is transmitted, absorbed or reflected.

For example, the rotatable member 3 of the rotational actuator may comprise a radiation absorption, transmission and/or reflection region. The region can consist of a molecule adsorbed onto the surface of the rotatable member 3. The molecule can be chosen to have specific radiation absorption, transmission and/or reflection region properties specific to radiation of interest. For example, the molecule may absorb electromagnetic radiation of a given wavelength (or wavelength range e.g. UV, Ultraviolet) when in a specific orientation with respect to the radiation. Rotation of the rotatable member 3 can effect the orientation of the molecule, such that the rotational actuator acts as an active filter of the UV electromagnetic radiation in question.

Most preferably, the radiation to be manipulated is electromagnetic in nature. It will be appreciated however that the radiation could be of other forms, such as a or I particles.

It will be appreciated that the use of the rotational actuator as an active UV filter is given by way of example only. One of ordinary skill in the art will appreciate that using the same principles, the rotational actuator has wide applicability in the optics and display industries. For example, reflective molecules (or other reflective material) could be adsorbed onto a surface of the rotatable member 3. By control of the degree of rotation of the rotatable member 3, and thus exposure of the molecule to incident radiation, selective reflection]absorption of the radiation can be achieved. It will be appreciated that this would have a clear application in the display industry, for example as part of a reflective display device.

Any of the aforementioned applications can also be realised using, amongst others, the embodiment of the rotational actuator illustrated in and described with reference to Figure 3.

It will be appreciated by one of ordinary skill in the art that the rotational actuator as described herein, and the applications of the rotational actuator, have been given by way of example only. It will be appreciated that various modifications can be made to the rotational actuator and the application of the rotational actuator, without detracting from the invention, which is defined by the claims.

For example, the rotational actuators described thus far have been described with reference to a support member 1 and a further support member 2. However, the rotational actuator may comprise just a single support member and a rotatable member 3. In one example, the rotatable member 3 is hollow (i.e. permits a tube to be located within the rotatable member 3), and the support member extends within and continuously through the hollow rotatable member 3. In another example the support member is hollow, and the rotatable member 3 extends within and continuously through the hollow support member.

The support member(s) 1,2 and rotatable member 3 maybe of various dimensions. For example, the support member(s) 1,2 and rotatable member 3 may have a diameter in the range of 0.OSnm to 1 pm. Preferably, the support member(s) I,2 and rotatable member 3 have a diameter in the range of 0.O5nm to 1 OOnm. Most preferably, the support member 1,2(s) and rotatable member 3 have a diameter in the range of 0.O5nm to lOnm.

The support member(s) 1,2 and rotatable member 3 maybe between 0.O5nm and 50gm in length. Preferably, the support member(s) 1,2 and rotatable member 3 are between 0.O5nm and 5gm in length. Most preferably, the support member(s) 1,2 and rotatable member 3 are between 0.lnm to 1gm in length.

For example, the principles of the operation of the rotational actuator have been described with reference to the support member 1, further support member 2 and rotatable member 3 having a carbon nanotubes structure. It will be appreciated these members may be nanotubes formed from other materials such as silicon or boron nitride, or from other chiral molecules or atomic chains possessing chirality. The members do not necessarily need to be nanotubes, or indeed members on the nanometre scale.

Thus far, the chirality of the members 1,2,3 has been discussed in terms of an intrinsically twisted structure (or, indeed, lack thereof). However, it will be appreciated that the chirality of the members 1,2,3 can be affected in other ways. For example, a molecule can be adsorbed onto an otherwise non-chiral member. By making the arrangement non-symmetrical, a degree of chirality is introduced to the member-molecule combination.

Rotation of the rotatable member 3 has been described using the flow of electrons, and the change in angular momentum, as the applied signal and thus the driving force.

However, any material whose angular momentum changes when the structure through which the material is passing (or which the material is impinging upon) becomes chiral is suitable. For example, when the support member, further support member and rotatable member 1,2,3 are all nanotubes, the flow of a gas or a liquid can be used to effect rotation of the rotatable member 3. For example, the material could be a stream of particles such as a flow of helium or hydrogen atoms.

All of the aforementioned embodiments have been described with reference to electrons or other material passing through the entire rotational actuator i.e. from the support member 1, through the rotatable member 3 and to the further support member 2. However, flow of material through the rotational actuator is not essential. Material may impinge upon the overlap region 4a, and then be reflected backwards i.e. not flowing through the rotatable member 3 as described above. As long as the angular momentum of the material changes upon reflection, so will the angular momentum of the rotatable member 3. Thus, if the angular momentum of the reflected material alters upon reflection from the rotatable member 3, and the frictional forces as described above are not overbearing, the rotatable member 3 will rotate.

As has been described above, the rotational actuator as described herein can have a wide variety of different structures and configurations, and a consequential wide variety of applications. The inventor has realised, however, that by causing rotation of an intrinsically chiral nanotube (i. e. a twisted tube), a device akin to the Archimedes' screw is created.

An Archimedes' screw is a device that, when rotated, causes material to pass from a first position to a second position due via transportation along the screw thread of the device. Depending on the configuration of the screw, material may pass through the volume of the screw if the screw has an internal thread, or along the outer surface of the screw if the screw has an external thread.

As a consequence of this effect, the Archimedes' screw can be made to convey material. For example, the screw can be used as a pump. Material to be conveyed or pumped can be electrons, atoms or molecules.

Just as rotation of the screw at different speeds will necessarily cause material to be conveyed at different speeds, the device can also work in reverse. For example, causing material to impinge upon and pass through the screw will make the screw rotate. Depending on which way the device is operated, properties of the material or screw can be obtained. For example, the rate of fluid flow can be determined from the speed of rotation of the screw.

What the inventor has realised is that this principal can be applied on the nanoscale using a nanoscale rotational actuator. A particularly suitable rotational actuator is that described above, when the rotatable member 3 is an intrinsically chiral nanotube.

Application of this principle on the nanoscale has a wide variety of practical applications, examples of which are given below.

Illustrated in Figure 6 is a nanoscale pump according to an embodiment of the present invention. The pump is structurally identical to the rotational actuator of Figure 2, and is constructed and operated in exactly the same way. Rotatable member 3 is an intrinsically chiral (i.e. twisted) nanotube.

Rotation of the rotatable member 3 causes material 100 within the member to pass along the length of the member 3. The arrows in Figure 6 indicate an exemplary direction of rotation of the rotatable member 3 and flow of material. The material is made to move through the member due to the chirality (or screw thread like structure) of the member. The material moves along the inner chiral surface of the rotatable member. In this embodiment, the material 100 comprises Carbon-60 molecules 100, although it will be appreciated that other material can also be conveyed. For example, electrons, helium atoms and hydrogen atoms may be conveyed. When particles with an electrical charge are conveyed, a potential difference is established between the support members 1,2. Measuring this potential difference (or voltage) can yield information about the pump, details of which are given below.

As with a conventional Archimedes' screw, it will be appreciated that rotation of the rotatable member 3 also acts to draw material into the pump. Furthermore, it will be appreciated that reversing the direction of rotation of the rotatable member causes the material 100 to flow in the opposite direction.

One or more pumps can be used to form an active filter. The pumps can be arranged such that material to be filtered lies on a feed' or input side of the pump. When the pump is activated, material is passed through the pump and out to a permeate' or output side. It will be appreciated that due to the scale of nanotubes, an array of the pumps can either form, or be incorporated into, a sheet of material to form an active membrane filter.

An extension of the simple pump concept of Figure 6 is given in Figure 7, which illustrates a more complex device that can be used to mix different sources of particles. The device effectively consists of two of the pumps of Figure 6, with the important difference being that the pumps feed into the same supporting member 2a, where mixing takes place. This further supporting member 2a then feeds into a second rotatable member 3a, which acts as a pump to take material away from the place of mixing 2a. The structure of two nanotubes merging into one is one that occurs naturally. Exposure of inner nanotubes for rotational purposes 3 is achieved in exactly the same manner as described in relation to the rotational actuator of Figure 2. The inner tubes of each of the would-be pumps can be exposed individually (by applying a potential difference across a single would-be pump to break the outer nanotube) or simultaneously (by applying a potential difference across all of the would-be pumps to break the outer nanotubes).

Selective rotation of the rotatable members 3 of the two pumps is used to selectively mix the material being fed into each pump 100, 101. For example, one of the pumps may be deactivated such that only one of the materials is pumped through the mixer (not shown). Alternatively, rotation of the rotatable members 3 may be calibrated such that a predefined mix of material is pumped from the mixer. The ratio of materials in the mix can be affected accordingly.

It will be appreciated that, in using selective mixing of materials, chemical reactions can also be controlled. It will also be appreciated that the two pump system is given by way of example. The system may be much more complex, with more pumps feeding material into a mixing chamber, and more pumps removing material from that chamber.

As well as simply pumping material, the nanoscale pump of Figure 6 may be used to form more elaborate devices. For example, Figure 8 illustrates how the pump of Figure 6 may be used as a memory device.

The memory device of Figure 8 is identical in structure to the pump of Figure 6, and operates in exactly the same way. However, prior to exposure of the inner tube for rotational purposes, the nested nanotubes are immersed in a fluid such that particles pass into the inner tube. When the inner tube (rotatable member 3) is then exposed, particles to be used in the memory devices are already located within the device. It will be appreciated that particles may be also be drawn into the device via rotation of the rotatable member 3 (as with the pump, described above).

By pumping a set number of particles to one side of the device, a first memory state can be defined i.e. on'. Such a process is illustrated in Figures 8a to 8d, where five particles 100 are pumped from the support member I to the further support member 2 via rotation of the rotatable member 3. Without further rotation of the rotatable member 3, the materials will reside on the further support member 2 side of the device. Thus, a non-volatile memory state is defined. To reverse the state of the memory device i.e. to off', the rotatable member 3 is rotated in the opposite direction, drawing the particles 100 to the support member 1 side of the device.

The state of the memory device can be read in a number of ways. For example, the support member I or further support member 2 may be in contact with a single electron transistor (not shown) which is an extremely sensitive device used for measuring electric charge. The location of the particles 100 will affect the capacitance of the transistor, from which the state of the switch can be derived. Alternatively, the resistance of the support members 1,2 can be determined, an appropriate change in the resistance reflecting a change in the state of the memory device.

As described above, in an Archimedes' screw, the rate of fluid flow through/along the screw can be determined from the speed of rotation of the screw. Likewise, the rate of fluid flow can yield the rotational speed of the screw, and even properties of the screw thread. The inventor has realised that this principle can be applied to the nanoscale device, such that the chirality of the rotational member 3 can be determined.

At present, the chirality of nanotubes (even in a nested set) is determined via Raman scattering techniques. Raman scattering techniques are an accurate method of characterisation, but are also expensive and time consuming.

Illustrated in Figure 9 is the nanoscale pump of Figure 6, but with a voltmeter V connected across the rotatable member 3, via the support member I and further support member 2.

Rotation of the rotatable member 3 will cause an alternating voltage to be established between the support member 1 and further support members 2, due to electrons being pumped through the rotatable member 3. This voltage can be measured using a sensitive voltmeter such as that incorporating a single electron transistor. The voltage will be periodic in time, and a Fourier transform of the voltage signal will yield a peak at the frequency of varying voltage (which corresponds directly to the rotational frequency of the rotatable member 3). The Fourier transform will also have a unique series of peaks at other frequencies, dependent on the relative chiralities of the inner and outer nanotubes. Due to this dependency, the chirality of the nanotubes can be characterised.

Initially, the chirality of the constituent nanotubes of a multitude of devices can be directly measured using Raman scattering. The same devices can then be subjected to the above-mentioned process, such that the quantitatively accurate but expensive Raman scattering results can be correlated with the Fourier transform results. In this way, the abovementioned apparatus for determining chirality can be calibrated'. A library of Fourier transforms (or a set of data indicative of the Fourier transforms) can be established which, due to prior Raman scattering techniques, have quantitative chirality values associated with them. Thus, the cheap and simple apparatus of Figure 9 can, in conjunction with this library (or set of data), be used to determine the chirality of nanotubes. It will also be appreciated by the skilled person that the data set may comprise qualitative information, which in itself contains information useful for determining properties of the nanotubes. For instance, that a predetermined shape of graph (e.g. having a predetermined number of peaks, or peaks at certain frequencies) indicates a particular chirality. Again, this easily obtained qualitative data set can be compared with known quantitative measurements to reveal quantitative information via the cheap and simple apparatus of Figure 9.

The description of Figure 9 discloses one method of determining the frequency of rotation of the rotatable member 3. Changes in the frequency of rotation of the rotatable member 3 for a given applied input signal can be used to determine changes in properties of the member 3 or objects coupled thereto. An example of how this can be used practically is given in Figure 10.

Figure 10 is a detection device that, in this embodiment, is used for single molecule detection. The basic structure of the device is the same as that of Figure 9. However, a receptor molecule 200 has been adsorbed onto the surface of the rotatable element, in a manner well known in the art. As stated above, application of a constant signal to the rotatable element 3 will yield a frequency of rotation. When a molecule 201 attaches itself to the receptor 200, this frequency will change, as the load' on the rotatable element has changed. Thus, a change in frequency of rotation corresponds to detection of the molecule 201.

It will be appreciated that, depending on the type of receptor 200 and molecule 201, the molecule 201 may be detachable from the receptor 200, and the device reused.

While the rotation of the rotatable members of the devices of Figure 6 to 10 has been described in relation to the device of Figure 2 (i.e. causing particles to impinge upon the rotatable member), it will be appreciated that rotation can be affected in other ways. However, the use and associated operation of the device of Figure 1 is preferred, due to the small footprint of the device and high sensitivity (due to no cumbersome apparatus either attached to or surrounding the rotatable member 3). It will be appreciated that rotation of the rotatable members 3 of the devices of Figures 6 to 10 can be affected using the apparatus and method disclosed in the Zetti paper described previously, as long as the rotatable member 3 is an intrinsically chiral nanotube.

Claims

1. A rotational actuator, comprising: a rotatable member extending along a rotational axis; a support member which is substantially coaxial with and supports the rotatable member, the rotatable member having a different chirality to that of the support member; a particle source arranged to provide at least one particle to one of the rotatable member and the support member, such that the at least one particle impinges upon the other of the rotatable member and the support member, said at least one particle experiencing a change in angular momentum due to the different chiralities of the support member and rotatable member, thereby causing rotation of the rotatable member due to the principle of conservation of momentum.

2. The rotational actuator as claimed in claim 1, wherein the rotation of the rotatable member is arranged to provide the motive power of a device.

3. The rotational actuator as claimed in claim 1 or claim 2, wherein the support member and rotatable member are nanotubes.

4. The rotational actuator as claimed in claim 1, 2 or 3, wherein the support member and rotatable member are formed substantially from carbon.

5. The rotational actuator as claimed in claim 1, 2 or 3, wherein the support member and rotatable member are formed substantially from silicon.

6. The rotational actuator as claimed in any preceding claim, wherein only one of the support member and rotatable member is chiral, and the other of the support member and rotatable member is non-chiral.

7. The rotational actuator as claimed in any preceding claim, wherein at least one of the support member and rotatable member has a twisted structure, and is thereby chiral.

8. The rotational actuator as claimed in any preceding claim, wherein at least one of the support member and rotatable member further comprises at least one adsorbed molecule, and is thereby chiral.

9. The rotational actuator as claimed in any preceding claim, wherein the particle source is arranged to provide a stream of particles.

10. The rotational actuator as claimed in any preceding claim, wherein said particle is one of an electron, an atom and a molecule.

11. The rotational actuator as claimed in any preceding claim, wherein the rotatable member is hollow, and the support member extends within and continuously through the hollow rotatable member.

12. The rotational actuator as claimed in any of claims 1 to 10, wherein the support member is hollow, and the rotatable member extends within and continuously through the hollow support member.

13. The rotational actuator as claimed in claim 12, further comprising a further hollow support member, wherein a first end of the rotatable member extends within the hollow support member, and a second distant end of the rotatable member extends within the further hollow rotatable member.

14. A conveyor for conveying material placed thereon, comprising a plurality of rotational actuators as claimed in any preceding claim, wherein the actuators are arranged such that the rotational axis of each is in substantially the same plane, each of the plurality being arranged to convey said material

15. The conveyor of claim 14, wherein the conveyor is arranged to convey individual molecules.

16. An electrical switch comprising: a rotational actuator as claimed in any one of claims 1 to 13, wherein the switch further comprises a first electrical conductor coupled to the rotatable member; and a second electrical conductor; said electrical switch being switchable between a first state, in which the first electrical conductor is in electrical contact with the second electrical conductor; and a second state, in which the first electrical conductor is not in contact with the second electrical; and wherein rotation of the rotatable member changes the state of the switch from at least one of said states to the other.

17. The electrical switch as claimed in claim 16, wherein the second electrical conductor is a carbon nanotube.

18. A memory device comprising an electrical switch as claimed in claim 16 or 17.

19. A radiation manipulation device comprising: a rotational actuator as claimed in any one of claims 1 to 13, wherein the rotatable member comprises a region that at least one of absorbs, transmits and reflects radiation, such that rotation of the rotatable member alters at least one of the absorption, transmission and reflection of incident radiation.

20. The radiation manipulation device as claimed in claim 19, wherein the radiation is electromagnetic radiation.

21. The radiation manipulation device as claimed in claim 19 or claim 20, wherein the region is provided by a molecule adsorbed onto a surface of the rotatable member.

22. A method of operating an apparatus, the apparatus comprising: a rotatable member extending along a rotational axis; a support member which is substantially coaxial with and supports the rotatable member, the rotatable member having a different chirality to that of the support member; the method comprising providing at least one particle to one of the rotatable member and the support member, the at least one particle impinging upon the other of the rotatable member and the support member, such that the at least one particle experiences a change in angular momentum due to the different chiralities of the support member and rotatable member, thereby causing rotation of the rotatable member by the principle of conservation of momentum.

23. The method of claim 22, further comprising using rotation of the rotatable member to provide the motive power of a device.

24. A pump for pumping at least one particle, comprising: a rotatable member extending along a rotational axis; a first support member which is substantially coaxial with and supports a first end of the rotatable member, the rotatable member being an intrinsically chiral nanotube; and wherein the rotatable member is hollow such that rotation thereof causes an exchange of momentum between the rotatable member and said particle, moving said particle along an inner surface of the rotatable member due to the intrinsic chirality of the rotatable member, and wherein the at least one particle comprises at least one atom.

25. The pump as claimed in claim 24, wherein the pump further comprises a source container, from which the at least one particle enters the pump, and a delivery container, into which the at least one particle is pumped.

26. A mixer comprising a plurality of the pumps as claimed in claim 24 or claim 25, wherein each of the pumps is arranged to pump at least one particle into a mixing chamber to be mixed.

27. A mixer as claimed in claim 26 wherein the mixer comprises a further pump as claimed in claim 24, arranged to pump the at least one from particle from the mixing chamber.

28. A memory device, comprising: a pump as claimed in claim 24; a second support member which is substantially coaxial with and supports a second end of the rotatable member; and at least one particle located in the rotatable member, such that rotation of the rotatable member of the pump causes the at least one particle to move between the support members, a first memory state being defined when the at least one particle is located on the first support member side of the device, and a second memory state being defined when the at least one particle is located on the second support member side of the device.

29. A method of detecting properties of a nanotube, comprising: providing a device having a rotatable member extending along a rotational axis, the rotatable member being a nanotube; a first support member which is substantially coaxial with and supports a first end of the rotatable member, and a second support member which is substantially coaxial with and supports a second end of the rotatable member; the method comprising: i) rotating the rotatable member ii) measuring the voltage signal between the first support member and the second support member over a predetermined time interval iii) analysing the voltage signal to determine a property of the nanotube device.

30. The method as claimed in claim 29, wherein step iii) of the method comprises taking the Fourier transform of the voltage signal.

31. The method as claimed in claim 30, wherein the frequency of rotation of the rotatable member is determined from the Fourier transform.

32. The method as claimed in claim 31, wherein the rotatable member further comprises a receptor adsorbed onto a surface thereof, the method further comprising: exposing the device to an area of interest; and determining if a molecule has attached itself onto the receptor by determining the frequency of rotation of the rotatable member.

33. The method as claimed in any of claims 29 to 32, wherein a property to be determined is the chirality of the rotatable member, and wherein step iii) of the method further comprises comparing at least one property of the voltage signal with data indicative of known nanotubes, in order to determine the chirality of the rotatable member.

34. The method as claimed in claim 33, wherein the at least one property of the voltage to be compared with the data is the Fourier transform of the voltage signal, and the data is indicative of the Fourier transform of known nanotubes.

35. The method as claimed in claim 33 or claim 34, wherein a set of data indicative of known nanotubes is constructed by first measuring the chirality of the rotatable members of a plurality of devices using Raman scattering techniques, and then matching the chirality of each rotatable member to the at least one property of the voltage signal of the same rotatable member, such that a library of the at least one property of the voltage signal versus chirality is established.

36. Apparatus for detecting properties of a nanotube, comprising: a device having a rotatable member extending along a rotational axis, the rotatable member being a nanotube; a first support member which is substantially coaxial with and supports a first end of the rotatable member, and a second support member which is substantially coaxial with and supports a second end of the rotatable member; a voltmeter connected to the first support member and second support member; and a signal analyser for analysing the voltage between the support member and second support member.

37. The apparatus as claimed in claim 36, wherein the voltmeter comprises a single electron transistor.

38. A rotational actuator substantially as hereinbefore described with reference to the accompanying figures.

39. A device substantially as hereinbefore described with reference to the accompanying figures.

40. A pump substantially as hereinbefore described with reference to the accompanying figures.

41. Apparatus for detecting properties of a nanotube substantially as hereinbefore described with reference to the accompanying figures.

42. A method substantially as hereinbefore described with reference to the accompanying drawings.