APPARATUS AND METHOD RELATED TO CORE-SHELL MAGNETIC NANOPARTICLES AND STRUCTURED NANOPARTICLES

Abstract

One aspect of the invention requires an apparatus for forming core-shell magnetic nanoparticles comprising: a magnetic nanoparticle source operable to generate a beam of nanoparticles; at least one shell material source comprising a bore through which the beam of nanoparticles may pass; and at least one controllable magnetic field generator, operable to generate a magnetic field which at least partially surrounds the at least one shell material source, wherein nanoparticles may be received at one end of the shell material source and the movement of the nanoparticles within the bore may be controlled by the controllable magnetic field to be coated by the shell material to specified dimensions, and nanoparticles may leave the other end of the shell material source. Another aspect of the in invention is a method of manufacturing core-shell magnetic nanoparticles, wherein: a beam of magnetic nanoparticles is generated by the nanoparticles source (34); and at least one vapour of at least one shell material is generated by at least one shell material source (36, 38, 50), wherein the at least one vapour of at least one shell material is located within the field generated by a controllable magnetic field generator (80); wherein the beam of nanoparticles enter the vapour of at least one shell material source (36, 38, 50) and the movement of the magnetic nanoparticles is controlled to coat the nanoparticles with the at least one shell material to specified dimensions and subsequently the coated nanoparticles are directed from the at least one shell material source to exit the at least one shell material source.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to the production of coated nanoparticles for deposition on a substrate. In particular, the invention is related to controlling the coating process and more precisely controlling the dimensions of the coat layer or layers. The material may be used in a variety of applications.

BACKGROUND TO THE INVENTION

[0002] Magnetic materials find widespread use in modern technology. Particularly, they are to be found in nearly all electro-mechanical apparatus. The performance of magnetic materials in respect of their secondary parameters, such as coercivity and energy product, has improved greatly over the last century.

[0003] As shown in FIG. 1 a magnetic structure 10 may be formed by co-deposition on a substrate 12 of Fe nanoparticles 14 from a cluster source 16 and of Co matrix material 18 from a Molecular Beam Epitaxy (MBE) source 20. Co-deposition of Fe nanoparticles and Co matrix material results in a structure in which Fe nanoparticles are distributed through and embedded in the Co matrix. According to an alternative approach a magnetic structure, in which Co nanoparticles are distributed through and embedded in an Fe matrix, is formed by co-deposition of Co nanoparticles from the cluster source and of Fe matrix material from the MBE source.

[0004] GB2530562B describes an apparatus for coating nanoparticles. The apparatus aims to form a uniform coating on vaporised metal nanoparticles.

[0005] Nanoparticles are produced by vaporising a source of core material, in a gas-phase environment. The nanoparticles are coated by passage through a plurality of shell evaporators. The shell evaporators comprise a heated tube providing an elongate open channel. Shell material is located within the heated tube. The shell material is evaporated by the heating the tube and is deposited on the nanoparticles passing through the tube. Thus, a nanoparticle is produced comprising a core material coated in a shell material. The core-shell nanoparticle can be deposited on a substrate.

[0006] The thickness of the shell layer may be controlled by varying the operating conditions of the shell material source. The shell material source may be disposed between the source of nanoparticle cores and the substrate. In addition, the shell material source may be configured to define a space through which a beam of nanoparticle cores pass, the source being operative to form a vapour of shell material in the space, such that the vapour impinges upon a surface of each particle core. The shell material source is configured to surround the beam of particle cores. The shell material source may, for example, define a bore or tube through which the beam of particle cores passes.

[0007] Thus, it is possible to produce magnetic core-shell nanoparticles where the core material is completely or substantially completely coated, for improved electromagnetic properties.

[0008] According to the methods and apparatus described in the patents noted above, the core nanoparticles are driven from the nanoparticle source to the substrate by the atmosphere within the gas-phase environment. Typically the main driving force is a directional pressure difference caused by the pump used to evacuate the equipment. Therefore, the dimensions of the shell layer on the core nanoparticles are determined by variables such as the pump speed and the evaporation rate of the shell material in the heated tube. It will be apparent that while some of the parameters of the film deposition process may be controlled and varied, control over the shell layer dimensions is relatively coarse and limited.

[0009] It is difficult to control the shell layer or coating with much precision. With more control over the shell layer it will be possible to further exploit the properties of magnetic nanoparticles in existing and new applications.

[0010] Therefore, if it were possible to control the dimensions or the shell material more finely, it would be possible to provide magnetic nanoparticles with electromagnetic properties which are also more refined and have a better tolerance. It is the aim of the present invention to produce such nanoparticles using an apparatus and method as disclosed herein.

SUMMARY OF INVENTION

[0011] Aspects of the invention are set out in the accompanying claims.

[0012] One aspect of the invention requires an apparatus for forming core-shell magnetic nanoparticles comprising: a magnetic nanoparticle source operable to generate a beam of nanoparticles; at least one shell material source comprising a bore through which the beam of nanoparticles may pass; and at least one controllable magnetic field generator, operable to generate a magnetic field which at least partially surrounds the at least one shell material source, wherein nanoparticles may be received at one end of the shell material source and the movement of the nanoparticles within the bore may be controlled by the controllable magnetic field to be coated by the shell material to specified dimensions, and nanoparticles may leave the other end of the shell material source.

[0013] Another aspect of the invention is a method of manufacturing core-shell magnetic nanoparticles, wherein: a beam of magnetic nanoparticles is generated by the nanoparticles source (34); and at least one vapour of at least one shell material is generated by at least one shell material source (36, 38, 50), wherein the at least one vapour of at least one shell material is located within the field generated by a controllable magnetic field generator (80); wherein the beam of nanoparticles enter the vapour of at least one shell material source (36, 38, 50) and the movement of the magnetic nanoparticles is controlled to coat the nanoparticles with the at least one shell material to specified dimensions and subsequently the coated nanoparticles are directed from the at least one shell material source to exit the at least one shell material source.

[0014] Another aspect of the invention requires an apparatus for forming structure magnetic nanoparticles comprising: a nanoparticle source operable to generate a beam of magnetic nanoparticles; and at least one controllable magnetic field generator, operable to generate a magnetic field through which the beam of nanoparticles may pass, wherein nanoparticles may be controlled when within the controllable magnetic field to be arranged into a specified structure of nanoparticles.

[0015] Another aspect of the invention is a method of manufacturing structured nanoparticles wherein: a beam of magnetic nanoparticles is generated by the nanoparticles source (34) which passes through a field generated by a controllable magnetic field generator (80); wherein magnetic nanoparticles are controlled within the controllable magnetic field to build structured nanoparticles.

[0016] Another aspect of the invention requires a core-shell magnetic nanoparticle or a core-shell magnetic nanoparticle structure comprising: a magnetic core; and at least one shell layer having a layer thickness of more than 4 nm.

[0017] Another aspect of the invention is the use of magnetic core-shell nanoparticles and or structured nanoparticles in hard disk drive applications, medical applications and medical instruments, cosmetics, and or motor, generator or turbine applications.

[0018] Other aspects of the invention will become apparent from the following disclosure.

BRIEF DESCRIPTION OF DRAWINGS

[0019] In order that the present invention may be more readily understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which:

[0020] FIG. 1 illustrates the formation of a magnetic structure;

[0021] FIG. 2 shows in block diagram form apparatus for forming a magnetic structure;

[0022] FIG. 3 shows apparatus for coating a core of a nanoparticle; and

[0023] FIG. 4 shows a nanoparticle having an Fe core, a first layer of Cr and a second outer layer of a rare earth metal;

DETAILED DESCRIPTION OF THE INVENTION

[0024] It will be appreciated and understood that reference herein to magnetic nanoparticle(s) or nanoparticle(s) refers to elemental nanoparticles, alloy nanoparticles or to magnetic core-shell nanoparticles. Nanoparticles may be defined as particles of material which are between 0.5 nm and 50 nm in diameter.

[0025] Nanoparticles which are sometimes known as `simple nanoparticles` refer to uncoated nanoparticles. `Core-shell nanoparticles` refers to nanoparticles which have a core comprising a `simple nanoparticle` which is coated in a shell of other material. `Multishell nanoparticles` refer to core-shell nanoparticles where two or more layers of shell material have been used to coat the core. Each of the multilayers may be different materials, or shell materials may be repeated. Structured nanoparticles refer to structures constructed from a plurality of nanoparticles. The plurality of nanoparticles which make up a structured nanoparticles may comprise simple nanoparticles, core-shell nanoparticles, multishell nanoparticles or any combination thereof.

[0026] Apparatus

[0027] FIG. 2 shows a block diagram of an apparatus 30 for forming an enhanced magnetic structure. The apparatus 30 comprises a matrix material source 32, a nanoparticle source 34, a first shell material source 36, and a second shell material source 38. The matrix material source 32 may be, for example, a thermal evaporator device (such as an MBE device), a sputtering device, a laser ablation device, or an arc device. The nanoparticle source 34 may be, for example, a thermal evaporator device, a sputtering device, a laser ablation device, or an arc device. The first and second shell material sources may be, for example, a thermal evaporator device, a sputtering device, a laser ablation device, or an arc device.

[0028] The apparatus 30 further comprises a temperature control apparatus 42 which is operable to control the temperature of a substrate 44 and its environs. The temperature control apparatus may make use of liquid nitrogen, or any other suitable technique. The nanoparticle source 34 and the first and second shell material sources 36, 38 are preferably located in and operate in the same vacuum.

[0029] The matrix material source 32 is operable to generate a beam of matrix material. The beam of matrix material may be an atomic beam, a molecular beam, or a mixed beam, dependent upon the matrix material.

[0030] The nanoparticle source 34 is operable at the same time as the matrix material source to generate a beam of nanoparticles. The two beams are deposited simultaneously on the substrate 44 to form a magnetic structure in the form of a thin film matrix formed from deposited matrix material with nanoparticles distributed through and embedded in the matrix.

[0031] The first and second shell material sources 36, 38 of FIG. 2 may be of the same type, or may be of different types, dependent upon the material being deposited to form the respective shell layer.

[0032] FIG. 3 provides a schematic view of an exemplary shell material source 50 of the type disclosed in GB2530562B.

[0033] The shell material source 50 of FIG. 3 is of generally tubular form such that it defines a bore through which a beam of nanoparticles may pass. The shell material source 50 preferably comprises a tube of pure material 52 which is to be deposited as a layer on each of the nanoparticles passing through a thermal evaporator. The shell material source 50 further comprises a tubular heater 54 which surrounds and is adjacent the tube of pure material 52. A water cooled heat shield 56 surrounds the outwardly directed surface of the tubular heater 54 and the end faces of the tubular heater 54 and the tube of pure material 52. In use, the shell material source 50 operates to vaporise the pure material 52 with the material vapour being present in the bore of the thermal evaporator. A beam of uncoated nanoparticles 58 is received at one end of the bore of the shell material source 50 and on passing through the material vapour in the bore the nanoparticles are coated with a layer of the material. The coated nanoparticles 60 then leave the other end of the bore of the shell material source 50.

[0034] In one example of the apparatus 30, nanoparticles are coated with only one layer of material, and the second shell material source 38 of the apparatus of FIG. 2 is either absent or inoperative.

[0035] In another example of the apparatus 30, nanoparticles are coated with first and second layers of the same or different material, and the first shell material source 36, 50 comprises a tube of a first material 52 and the second shell material source 38, 50 comprises a tube of the first material or a second different material 52.

[0036] In further examples of the apparatus 30, nanoparticles are coated with third and further layers of the same or different material. Accordingly, such examples comprise shell material sources which correspond in number to the number of layers to be deposited on the nanoparticles with the plural shell material source disposed in line such that the beam of nanoparticles can pass in turn through the bore of each of the shell material sources. The exact form of each of the shell material sources depends upon the material being deposited.

[0037] The apparatus 30 further comprises a magnetic field generator 80. The magnetic field generator is preferably located outside of the evacuated environment, and in the example shown surrounds the shell material source(s) 36, 50. The magnetic field generator 80 may be coupled to and controlled by a programmable computer. The computer thereby controls when the field is generated by the magnetic field generator 80, the duration for which the field is generated, and the direction and strength of the field. A computer program is used to activate generation of the magnetic field and vary the direction and strength of the magnetic over a period of time. For example, the magnetic field may be pulsed.

[0038] Typically, an electromagnetic coil or series of coils will be used to generate a magnetic field.

[0039] In order to control the direction of the magnetic field, three sub-generators may be used. The sub-generators are arranged orthogonally, or substantially orthogonally, to each other in order to control the strength and direction of the magnetic field in three dimensional space.

[0040] There may be provided magnetic field generators 80, separately controllable, for each of the shell material sources 36, 38, 50. In one arrangement, a single magnetic field may extend entirely or partially over one of the shell material sources 36, 38, 50. In another arrangement, a first magnetic field generated by a first magnetic field generator may cover a first end of a shell material source, and a second magnetic field generated by a second magnetic field generator may cover a second end of the shell material source. Of course, it will be understood that additional magnetic field generators 80 (e.g. third magnetic field generator, fourth magnetic field generator etc.) may be used in combination or separately with one or more shell material sources 36, 38, 50 in order to exert a force on the nanoparticles moving through the shell material source, and dependent on the control and number of layered shells required.

[0041] Each of the magnetic field generators or sub-generators may work in collaboration, through a computer, to control magnetic nanoparticles moving through the shell material source to coat the magnetic core nanoparticles, or previously coated core-shell nanoparticles, with a layer of the shell material to specified dimensions, e.g. thickness.

[0042] Process

[0043] An apparatus, such as the apparatus described above, may be used to manufacture an enhanced magnetic structure.

[0044] Matrix material and magnetic nanoparticles may be deposited on the substrate by operation of a matrix material source and a nanoparticle source respectively. The matrix material and the nanoparticles may be deposited simultaneously, for example by simultaneous operation of the two sources. The source of matrix material may be provided by any suitable process or apparatus, including, for example, a thermal evaporator, such as a Molecular Beam Epitaxy (MBE) apparatus, a sputtering apparatus, a laser ablation apparatus or an arc apparatus. The nanoparticle source may be provided by any suitable process or apparatus, including, for example a thermal gas aggregation apparatus, a sputtering apparatus, a laser ablation apparatus, or an arc apparatus.

[0045] Deposition of the magnetic nanoparticles by way of vacuum assisted deposition of magnetic nanoparticles in the gas phase and more specifically by way of deposition of a beam of gas-phase magnetic nanoparticles, comprises causing a beam of magnetic nanoparticles to impinge upon the matrix as the matrix forms. The beam may be generated by any suitable source, such as a gas phase source, a cluster beam source, such as a gas aggregation source, a sputtering source, or a laser ablation source or an arc source. The gas phase source may be operative to produce a beam of particle cores absent their shell layer.

[0046] Deposition of the shell layer may be by vacuum assisted deposition of shell material vapour. Shell material vapour may therefore be provided in the same vacuum as a source of nanoparticle cores. The shell material vapour may be generated by a thermal source, for example a thermal evaporator (such as an MBE source) or by sputtering, by laser ablation, or by an arc process. The temperature of a thermal source of nanoparticles may be determined by the shell material to be deposited, e.g. 800.degree. C. for silver and 1000.degree. C. for iron. Any gases used in the composition may be introduced at low pressure.

[0047] Using known apparatus and processes, the time the core nanoparticles spend in the shell deposition chamber or source is limited and is primarily controlled by the pressure difference caused by the vacuum pump, thus there is limited control of the shell layer.

[0048] However, as noted above, the known apparatus is modified to comprise one or more magnetic field generators. In the manufacture of magnetic core-shell nanoparticles, deposition of each shell layer may be by vacuum assisted deposition from a thermal evaporator as described above.

[0049] The magnetic field generator is activated to generate a magnetic field prior to the beam of nanoparticles entering the shell material source, or just as the beam of nanoparticles enters the shell material source. As the nanoparticles comprise a magnetic material, the magnetic field exerts a force on the nanoparticles. The strength and direction of the magnetic field is controlled in order to direct the nanoparticles.

[0050] For example, the magnetic force experienced by the nanoparticles resulting from the magnetic field may act to reduce the speed of the nanoparticles, thereby causing them to spend a longer period of time in the shell material source. The force may act to increase the speed of the nanoparticles, thereby causing them to spend a shorter period of time in the shell material source. The force may act to deflect the nanoparticles in a direction having a component which is perpendicular to a path passing through the bore of the shell material source, thereby causing them to pass through the shell material source closer to the shell material itself. The force may act to rotate the nanoparticles as they pass through the shell material source. The force may act to hold the nanoparticles stationary or substantially stationary within the shell material source for a certain length of time.

[0051] By using the magnetic force to control the nanoparticles while they are within the shell material source, the user may exercise greater control over the shell coating applied to the nanoparticles. For example, if more time is spent in the shell material source or the nanoparticles pass closer to the shell material itself, a thicker coating of shell material will be applied to the nanoparticles. If the nanoparticles are rotated as they pass through the shell material source, a more uniform layer of shell material will be deposited on the nanoparticles. If the position of the nanoparticles is translated to move closer to the source of the shell material on one side (without rotation), an asymmetrical coating may be applied.

[0052] Control of the magnetic field generator and therefore of the coating applied to the nanoparticles may be assisted by use of a computer. A sequence of different field generations may be programmed in order to control the nanoparticles in a series of movements to result in the manufacture of nanoparticles with particular dimensions.

[0053] As will be understood from the foregoing, the nanoparticles source 34 may produce a continuous stream of nanoparticles while in operation. The nanoparticles may be slowed down on entering the shell material source, so that they travel relatively slowly through the shell material source, and the nanoparticles may optionally also be accelerated as they leave the shell material source. Alternatively, or in addition, the nanoparticles may be deflected in a transverse direction having a component that is perpendicular to the main axis of the shell material source. A combination of such movements may be caused to take place by the magnetic field generator, such as movement (possibly oscillating movement) back and forth in the transverse direction, or a movement in a spiral or helical path through the shell material source. However, in such embodiments a continuous or substantially continuous stream of nanoparticles may pass through the shell material source from the nanoparticle source 34.

[0054] In other embodiments, as the nanoparticles pass through the shell material source, the movement of the nanoparticles may be controlled by the field generated by the magnetic field generator so that the nanoparticles are held by the magnetic field in a stationary or substantially stationary position. Accordingly, nanoparticles will accumulate in the shell material source until they are released by the magnetic field (e.g. by being accelerated towards the substrate 44). The result is "batches" of processed nanoparticles which may then proceed to subsequent stages of processing or for deposition on the substrate. In such an approach, the nanoparticle source 34 may be controlled to produce pulses or batches of nanoparticles, or alternatively the nanoparticle source 34 may produce a continuous stream of nanoparticles. The magnetic field generator 80 may also operate in a "pulsed" manner (i.e. produce one or more magnetic fields which vary over time, throughout the production of one "batch", in a pattern that may then be repeated for a subsequent batch) in order to produce batches of nanoparticles.

[0055] For simplicity only one magnetic field generator has been described. As noted above, magnetic field generators may be used in connection with each shell coating stage. Furthermore, a series of generators may be used together, or generators may comprise one or more sub-generators which are located orthogonally to each other to control movement in three dimensions.

[0056] According to one example, only one layer of material is deposited on the nanoparticles. As stated above, the second shell material source 38 of FIG. 2 is therefore either absent or inoperative. The matrix material source 34 generates a beam of nanoparticles of diameters in the range of 0.5 nm to 5 nm. The diameter of the nanoparticles is determined by controlling the operating conditions of the matrix material source 34, for example the power level and the gas pressure therein. The beam of nanoparticles passes through the bore of the first shell material source 36 which comprises a tube 52 of a shell material, for example either Co or Ag and the movement of the nanoparticles is controlled by a magnetic field generated by the magnetic field generator 80. Each nanoparticle is thereby coated with a layer of the shell material to a thickness of between 1 and 10 atomic layers. The operating conditions of the first shell material source 36 are determined by the material to be deposited, and the required thickness of the shell layer concerned. For example, in the case of a thermal evaporator, the operating temperature for Ag is about 800.degree. C.

[0057] If it is desired to increase the range of thicknesses of the shell layer the operating temperature need only be increased slightly because vapour pressure is very sensitive to temperature. For example, to double the thickness of an Ag layer it is only necessary to increase the temperature by about 50.degree. C. Alternatively, the speed of the nanoparticles may be decreased. If it is desired to produce a more uniform layer, the nanoparticles are caused to rotate. In order to `fine tune` the dimension of the shell layer, the magnetic field generation is adjusted.

[0058] In this example, the matrix material source 32 operates at the same time as the nanoparticle source 34 to generate a beam of matrix material, for example Co or Ag, such that the matrix material beam is of the same material as the coating on the nanoparticles. The matrix material beam and the beam of nanoparticles are deposited simultaneously on the substrate 44 to form a magnetic structure comprising a matrix in which nanoparticles are embedded.

[0059] Each magnetic nanoparticle may comprise a plurality of shell layers over the core. The shell layers may be of the same material as each other or one another or different material to each other or one another. The process may therefore comprise a deposition step for each shell layer.

[0060] Alternatively, different shell materials may require different deposition techniques, and each may be provided. The plural shell material sources may be disposed in line whereby, for example, a first source provides for deposition of a first shell layer and a second source provides for deposition of a second shell layer over the first shell layer. Subsequent shell layers may be deposited on the previous shell layer by respective sources.

[0061] For simplicity, and for comparison with known systems, the process of manufacturing the desired nanoparticles has been described as being deposited on a substrate once the processing steps to coat the nanoparticles have been completed. It is not necessary that the processed nanoparticles are deposited on a substrate. Instead, the nanoparticles may be collated and kept, for example, in a solution. The need to deposited the processed nanoparticles on a substrate or collated and kept in another way will depend on the ultimate purpose or subsequent proceeding required.

[0062] Again, for simplicity and for comparison with known systems, the foregoing has described a co-deposition process with a matrix. The use of a matrix material is independent from the processing of the nanoparticles. Accordingly, it is not necessary to use a matrix material in deposition on a substrate nor use a matrix material with other methods of collating the processed nanoparticles.

[0063] Product

[0064] If required, the matrix material may be a single element, an alloy of more than one element, or a combination thereof. The single element, alloy or combination may include embedded gas atoms and/or molecules. The matrix material may be a metal and, more specifically, one of a transition metal and a rare earth metal, or an alloy containing a transition metal and/or a rare earth metal, and may include embedded gas atoms and/or molecules.

[0065] Core-shell nanoparticles are nanoparticles having a core of a core material and a shell layer covering the core, the shell layer being of shell material, different to the core material. A core-shell nanoparticle may be provided with more than one shell layer. The core material may be a single element, an alloy of more than one element, or a combination thereof. The single element, alloy or combination may include embedded gas atoms and/or molecules. The shell layer material may be a single element, an alloy of more than one element, or a combination thereof. The single element, alloy or combination may include embedded gas atoms and/or molecules.

[0066] Each core-shell magnetic nanoparticle may comprise a core formed from a magnetic transition metal and a shell layer of either a magnetic or nonmagnetic transition metal. The nonmagnetic transition metal may be a Group 11 metal such as gold or silver. Thus, examples of core/shell layer composition may be Fe/Co Co/Fe, Fe/Ag, Co/Ag, Fe/Au or Co/Au.

[0067] A surface of the shell layer may define an exterior surface of the magnetic nanoparticle and therefore the diameter of the nanoparticle.

[0068] In a deposited material, where used the matrix material may be of the same material as the shell layer. For example, each magnetic nanoparticle may comprise a Fe core covered at least in part with a layer of Co and the matrix material may be Co. By way of further example, each magnetic nanoparticle may comprise a Co core covered at least in part with a layer of Au and the matrix material may be Au. Use of the same material may reduce the likelihood of the particle cores coming into contact even at volume fractions much higher than the percolation threshold.

[0069] Each magnetic nanoparticle, for example, may have a diameter not exceeding around 10 nm, although the nanoparticles could be between 0.5 nm and 50 nm. The magnetic moment per atom of magnetic nanoparticles of smaller diameters has been found to be significantly higher compared with bulk structures formed from the same material. For higher magnetic moment, each magnetic nanoparticle may therefore have a diameter substantially in the range 0.5 nm to 5 nm.

[0070] In examples of core-shell nanoparticles, the shell layer may have a thickness of between around 0.2 nm and 4 nm as may be achieved from known methods, also. However, with known methods it is unlikely that the layer will be complete, i.e. there may be gaps such at the covering of the core is less than 90% complete. According to the apparatus and methods/processes disclosed herein, it is possible to achieve complete or total covering of the core, i.e. 100% complete. For example, considering a batch of 100 nanoparticles, the average of the percentage coating of individual nanoparticles will be at least 90%.

[0071] In other examples, making use of the apparatus and process disclosed herein, the shell layer may have a specified thickness of more than 4 nm and could be significantly higher. For some applications between 2 nm and 20 nm has been found to be useful. In terms of atomic layers, the thickness of the shell layer may be between 1 and 10 atomic layers or greater than 10 atomic layers using the apparatus and process disclosed herein. The diameter of the core and the thickness of the shell layer may be determined independently from one another. The diameter of the core and the thickness of the shell layer may be specified by the application of and requirements for the nanoparticles.

[0072] An exemplary structured nanoparticle is shown schematically in FIG. 4 which shows a perspective view of a Co core coated with a layer of each of Cr and a rare earth metal (i.e. Ho or Dy). FIG. 4 also shows a section through a coated nanoparticle 70 with Co forming the core 72, Cr forming a layer immediately over the Co core and either Ho or Dy forming an exterior layer immediately over the Cr layer. FIG. 4 further shows a beam of nanoparticles 78 after deposition of the Cr layer and Ho or Dy layer. The matrix material source 32 is operative at the same time as the nanoparticle source 34 to generate a matrix material beam of either Ho or Dy such that the beam is of the same material as the outer coating on the Co nanoparticles. The matrix material beam and the beam of nanoparticles are deposited simultaneously on the substrate 44 to form a magnetic structure comprising a matrix in which nanoparticles are embedded.

[0073] A magnetic structure may thereby be formed in which magnetic core-shell nanoparticles are distributed through and embedded in the matrix material. The magnetic structure is typically formed as a thin film on the substrate. The deposited thin film can be used in various applications or further processed as needed in the ultimate application. However, as discussed above, deposition on a substrate is not essential, nor is the use of a matrix material.

[0074] Structured Nanoparticles

[0075] Structured nanoparticles refer to structures constructed from a plurality of nanoparticles. The plurality of nanoparticles which make up a structured nanoparticles may comprise simple nanoparticles, core-shell nanoparticles, multishell nanoparticles or any combination thereof.

[0076] As will be appreciated from the foregoing, magnetic (simple or core only) nanoparticles or magnetic core-shell nanoparticles may be manipulated individually using controllable magnetic fields.

[0077] A plurality of nanoparticles may be used as `building blocks` to create a structure. Structures may be constructions from simple, core-shell or multishell nanoparticles. In order to make the `blocks` `stick` to each other, they may be magnetised. In order to break apart the `blocks` they may be de-magnetised.

[0078] By controlling individual or groups/batches of nanoparticles in the magnetic field, it is possible to move them into position to form a structure. Thus, it is possible to build a variety of formations using nanoparticles as building blocks.

[0079] One or more magnetic field generators may be used to create a magnetic field to act on magnetic nanoparticles before they are deposited on a substrate. As with use in conjunction with a shell material source, the magnetic field may be generated by more than one magnetic field generator(s) which are used in collaboration to provide a controlling force on nanoparticles which enter the field. The magnetic field generator(s) may be used, together with a computer, for specific time periods and to cause specific translational and rotational movements of nanoparticles. Thus, a program can be used to cause a series of movements to create nanoparticle structures in a building phase.

[0080] For structured nanoparticles, the core may be of a magnetic material. The core material may be a single element, an alloy of more than one element, or a combination thereof. The single element, alloy or combination may include embedded gas atoms and/or molecules. More specifically the magnetic material may be a magnetic transition metal, such as one of Fe, Co and Ni.

[0081] For structured magnetic nanoparticles, the magnetic nanoparticles i.e. the core nanoparticles, may be at least in part covered with a shell layer of material. Typically the shell material is different to that of the core and reduces the likelihood of cores coming into contact with each other when deposited on the substrate.

[0082] The building phase or process can be used in serieswith coating nanoparticles. Nanoparticles may be coated individually, before entering the building phase. Alternatively, nanoparticle structures may be coated after the building phase. Further, a combination of coated and uncoated nanoparticles may be used. Still further, nanoparticles may receive one or more coating layers, then enter a building phase, and subsequently receive one or more additional coating layers. Finally the structures may be deposited on a substrate, with or without a matrix material.

[0083] In one example, the nanoparticles may be formed into a formation which comprises an external structure which at least partially surrounds an internal space, such as a cube formation, a pyramid formation, or a polyhedron formation, for use as a container. Other material may be trapped inside the internal space of the formations. If and when the contained material is required to be released, the container may be collapsed by de-magnetising the structure, thus releasing the contained material.

[0084] Uses

[0085] The form of the structured magnetic nanoparticles depends on their intended use.

[0086] As disclosed in GB2510228B, magnetic structures as produced and described may be used to form a write head for use in a device. The more accurate control of the shell layer(s) allows for improved tolerances and performance of an electromagnetic data storage device.

[0087] Structured magnetic nanoparticles may also be used in other hard disk drive (HDD) applications.

[0088] Magnetic nanoparticles may also be useful in medical applications and products for human consumption, for example, for the delivery of materials (e.g. drugs) to specific locations in the body. Structured magnetic nanoparticles may be particularly useful in these applications.

[0089] For example, nanoparticles which are coated in Ag, alumina or other noble metal are medically inert. Therefore, the nanoparticles can be safely used to deliver magnetic material to specific locations in the body. Other combinations of core-shell may also be suitable for particular medical treatments. For example, Fe-core FeO-shell nanoparticles may be incorporated in a water-dispersible powder comprising grains of matrix material embedded with one or more nanoparticles. The powder may be produced by depositing a thin film of matrix-nanoparticle material, where the nanoparticles are Fe-core FeO-shell material. The film is subsequently processed to produce grains of matrix material embedded with the nanoparticles. Alternatively, rather than depositing the nanoparticle material on a substrate, the nanoparticles are collated and kept in solution.

[0090] Other treatments may require a high concentration of magnetic material to be delivered in a specific location, and with no danger of percolation, such as in the treatment of tumours. Coated nanoparticles are particularly useful in controlling the percolation level.

[0091] As disclosed in GB2537777A, coated nanoparticles may be used in cosmetics.

[0092] Other applications include use in motors, generators or turbines. For example, using a deposited film of magnetic nanoparticles to produce laminate or coiled material. The films are arranged in a laminated structure and pressed to produce a rotor or stator for use in electric machines. In particular, this application benefits from increased magnetic moment due to the reduced percolation rate of coated nanoparticles.

[0093] Further, a combination of techniques may be used to improve some systems. For example, in MRI imaging, a laminated structure of nanoparticle films, similar to those that could be used to produce rotors or stators, could be used to improve the magnetic density of the magnetic core. Further, a magnetic nanoparticle solution may be administered to a patient, prior to being scanned by the MRI machine. The nanoparticle solution acts as a contrast enhancer to improve detection of internal structures being imaged. Each technique independently improves the contrast and therefore data collection from the scan.

[0094] As will be appreciated, by better controlling the deposition of shell material on a shell-core nanoparticle structure, it is possible to better control specific properties of nanoparticles.

[0095] When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

[0096] The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1-17. (canceled)

18. An apparatus for forming structured nanoparticles, comprising: a magnetic nanoparticle source operable to generate a beam of magnetic nanoparticles; and at least one controllable magnetic field generator operable to generate a magnetic field through which the beam of magnetic nanoparticles pass; whereby magnetic nanoparticles within the beam of magnetic nanoparticles passing through the controllable magnetic field are arranged into structured nanoparticles.

19. The apparatus of claim 18, further comprising: at least one shell material source comprising a bore through which the beam of magnetic nanoparticles pass to coat the structured nanoparticles.

20. A method of manufacturing structured nanoparticles, comprising: generating a beam of magnetic nanoparticles from a source of magnetic nanoparticles source; passing the generated magnetic nanoparticles through a magnetic field generated by a controllable magnetic field generator; wherein magnetic nanoparticles within the beam of magnetic nanoparticles passing through the magnetic field build structured nanoparticles.

21. The method of claim 20, further comprising: depositing the structured nanoparticles on a substrate.

22. The method of claim 20, further comprising: collating the structured nanoparticles in a solution.

23. A core-shell magnetic nanoparticle structure, comprising: a nanoparticle having a magnetic core; and at least one shell layer around the magnetic core having a thickness between 0.2 nm and 4 nm, wherein the at least one shell layer provides a coating of at least a 90% of the magnetic core.

24. The core-shell magnetic nanoparticle structure of claim 23, wherein the at least one shell layer completely coats the magnetic core.

25. The core-shell magnetic nanoparticle structure of claim 23, wherein an average of the coating of the magnetic core of the nanoparticles within a group of at least 100 of the nanoparticles is at least 90%.

26. (canceled)

27. (canceled)

28. (canceled)

29. (canceled)