JP2006520979A - Manufacture of nanoparticle thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a thin film by an ink jet printing method.
A step of preparing a suspension of magnetizable nanoparticles in a carrier fluid and depositing the fluid suspension on a substrate surface as droplets having a volume of less than about 1 nl, the deposited fluid suspension. Forming a film of magnetizable nanoparticles as a liquid residue, and forming a magnetic recording device having a film of magnetizable nanoparticles. The present invention is also broadly related to methods of forming magnetizable films, inorganic films, and protein films.

Description

Detailed Description of the Invention

(preface)
The present invention relates to the production of thin films by ink jet printing. The resulting thin film can be used for components in many applications, such as magnetic and semiconductor media.
(Background of the Invention)

  A wide range of methods such as chemical vapor deposition, molecular beam epitaxy, evaporation, sputtering, and spin coating can be used to produce a thin film ("Thin Film Material Handbook: Volume 1, Thin film deposition and processing ", 2002 edition, Nalwa, HS, Academic Press;" Thin film on glass "1997 edition, Bach Kraus, Springer-Verlag). Sputtering and electroevaporation have traditionally been the preferred methods selected for the manufacture of disk drive magnetic media in the computer industry.

  The creation of self-assembled protein arrays has attracted considerable interest because such arrays provide a variety of applications for modern nanotechnology, such as semiconductor devices and biosensors (Yun, SC et al., 2001). MRS Symposium Bulletin, j2.3 / 1-j2 / 3/6; McMillan, A et al., 2002, “Nature Materials”, 1, (4), 247-252). The process of creating a protein thin film has focused on the formation of the film by a two-step process. Initially, a two-dimensional protein array is formed on a liquid thin film. These films are then transferred to a solid substrate such as a silicon wafer. The Langmuir-Blodgett method (Britt, DW et al., “Phys. Chem. Chem. Phys.”, 2000, 2, 4594-4599) is a known film production technique involving formation of a protein array at the lipid-air interface. It is. Several other methods on this basic theme, such as the formation of self-assembled protein arrays at the air-water interface (Kobayashi, K et al., 2001, “Biosci. Biotechnol. Biochem.”, 65, (1 ), 176-179), mercury-air and liquid-gas interfaces (Nagayama, K et al., 1995, “Jpn J Appl. Phys.”, Pages 34, 3947-3954), and gallium-aqueous interfaces (Adachi, E. et al., 1998, “Chem. Phys. Lett.” 284, 440-445). Protein thin films have also been made by spray coating and vapor deposition (Goodall, S et al., 2002, “J. Aerosol Med.” 15, (3), pages 351-357).

  In the diagnostics industry, the deposition of individual units of specific proteins on solid substrates by ink jet printing has been described (Roda, A et al., 2000, “Biotechniques”, 28, (3), pages 492-496; WO 96/22533). The goal here is to obtain an array of immobilized individual proteins that can be used to sort a single target. Inkjet printing is a conventional technique for printing computer-derived information on paper (Calvert, P, 2001, “Chem. Mater.” 13, 3299-3305). Single dots can be applied for some applications, but other applications such as magnetic recording require a very smooth and continuous film.

The inventor surprisingly found that inkjet printing methods are used for the formation of thin films of proteins and magnetic particles, and the formation of thin films of magnetic and semiconductor nanoparticles at least partially encapsulated by polymeric materials. At present, it is found that an effective technique is presented.
(Summary of the Invention)

  In a first aspect of the invention, there is provided a method of forming a magnetic recording device having a film of magnetizable nanoparticles, the method comprising preparing a suspension of magnetizable nanoparticles in a carrier fluid; Depositing the fluid suspension on the substrate surface as droplets having a volume of less than about 1 nl and forming the film of magnetizable nanoparticles described above as a dry residue of the deposited fluid suspension.

  In a second aspect of the invention, a method of forming a magnetizable film is provided, the method comprising a suspension of magnetizable nanoparticles each formed at least partially within a protein shell in a carrier fluid. Preparing and depositing the fluid suspension on the substrate surface as droplets having a volume of less than about 1 nl, obtaining the magnetizable film described above on the substrate as a dry residue of the deposited fluid suspension. Process.

  In a third aspect of the invention, there is provided a method of forming a film of inorganic nanoparticles on a substrate, the method comprising the steps of forming inorganic nanoparticles each at least partially within a protein shell within a carrier fluid. Preparing a suspension and depositing the fluid suspension on the substrate surface as droplets having a volume of less than about 1 nl, and depositing the above film on the substrate as a dry residue of the deposited fluid suspension. Acquiring.

  In a fourth aspect of the present invention, there is provided a method of forming a thin film of protein on the surface of a substrate having a thickness of less than about 10 times the constituent protein particle size over substantially the entire thin film. Prepares a suspension of protein particles that have undergone a membrane filtration step in a carrier fluid, deposits the fluid suspension on a substrate surface as droplets having a volume of less than about 1 nl, Obtaining the above-mentioned film on a substrate as a dry residue of the suspension.

In a fifth aspect of the invention, a magnetic recording device having a film of magnetizable nanoparticles is provided, the particles being prepared as a suspension in a carrier fluid and as a dry residue of a deposited fluid suspension. Deposited on the substrate surface as droplets having a volume of less than about 1 nl to form the above-described film of magnetizable nanoparticles.
In order to further illustrate, but not limit, the invention, embodiments will now be described with reference to the accompanying drawings.
(Detailed description of the invention)

  The inkjet printing process involves the deposition of a small amount of liquid material, typically nanoliters or less, onto a substrate using multiple micro nozzles. Typically, this deposition process will involve either a piezoelectric or thermal assist operation of the printing nozzle. The amount of liquid deposited per droplet will generally be greater than about 0.1 picoliter, for example, greater than about 1 picoliter. This amount can be less than about 1 nanoliter, such as less than about 100 picoliters or less than about 10 picoliters. In a preferred embodiment of the invention, the amount of liquid deposited per droplet is about 3 picoliters.

  Nozzle deposition of picoliters of material allows fine tuning of the volume of material deposited on a given area of the substrate. Just prior to contacting the substrate, the droplet can have the same mass as it exits the inkjet nozzle. Alternatively, individual droplets can be subdivided into finer “sprays” below the droplets before contacting the substrate. When a droplet forms such a spray, its characteristics will be determined primarily by the size of the starting droplet and the distance of the nozzle head from the substrate. The extent to which the droplets are subdivided will then determine the area of the substrate to be covered. The fine openings provided by the ink jet printing method allow a high degree of control over the nanoparticle droplets produced by the ink jet.

  In addition, inkjet printing technology can be conveniently incorporated into industrial manufacturing processes and is likely to require significantly less raw material with respect to the mass of coating material per unit area of the substrate than in a tank-based coating system.

  If the particles are magnetic nanoparticles, they can be at least partially encapsulated within the polymeric shell. Alternatively, the magnetic nanoparticles may not be encapsulated. These particles can be formed by any means known to those skilled in the art, and preferred methods are those that provide appropriate size and dispersion control. In embodiments of the invention, the magnetic particles can be formed in a polymeric shell, such as a protein. This shell can be removed later, for example, by laser pyrolysis, leaving unencapsulated magnetic nanoparticles. Magnetic nanoparticles can be formed in surfactant micelles, which are again removed later, for example by diluting the surfactant solution to a concentration below cmc, followed by filtration. be able to.

  If the particles are non-magnetic particles, such as semiconductor nanoparticles, they can be at least partially encapsulated by a protein shell. Alternatively, they can be formed in an encapsulated protein shell, which is later removed, for example, by laser pyrolysis, leaving non-encapsulated non-magnetic nanoparticles.

  A magnetic recording medium is any medium having magnetic properties that allow data storage. Preferably, although not limited to the following, the recording medium will be present in the state of a hard disk drive as used, for example, in computers, audio devices, vehicles, video recorders and the like. In addition, the medium can be a magnetic tape or a magnetic card device.

In some embodiments of the present invention, the magnetic recording medium is greater than 1 Gb / 6.4516 cm ² (square inch), preferably greater than 5 Gb / 6.4516 cm ² (square inch), more preferably 10 Gb / 6.4516 cm ² (square square). Inch), and most preferably has a data recording capacity of greater than 20 gigabits / 6.4516 cm ² (square inch).

  The ink jet printer apparatus used in the present invention comprises as main components: i) a reservoir that holds a suspension of coating particles; (ii) an ink jet head; (iii) a conduit that connects the reservoir to the ink jet head; v) a coated (Vi) means for moving the inkjet head and the substrate relative to each other; (vii) suitable control means for controlling the relative movement of the inkjet head and the substrate, such as computer software Included. Optionally, a valve can be included in the conduit line connecting the reservoir to the inkjet.

  The inkjet head then typically has (i) an inlet port; (ii) a reservoir portion for the coating particle suspension; (iii) preferably a pre-sized hole, each nozzle including a smaller reservoir portion. A plurality of nozzles; (iv) suitably including a mechanism for ejecting droplets of the coating suspension from the nozzles.

  Various systems for ejecting ink droplets are known, in particular piezoelectric, heated, electrostatic and acoustic methods (Le, HP, 1998, “J. Imaging Sci. Tech.”, 42, 49-62). For example, in a bubble jet print head, each nozzle unit includes a heating element. When the temperature of the element rises momentarily to several hundred degrees, a vapor bubble is formed that causes the droplet to pass through the nozzle and move the liquid ink. In piezoelectric deposition, an electric field applied across a piezoelectric crystal, usually a ceramic, provided within the nozzle, deforms the crystal, thereby reducing the volume of the nozzle available for liquid and reducing the droplets from the orifice. To release. Any of the systems described above can be used with the present invention.

  In operation of an ink jet application apparatus suitable for the present invention, a suspension of particles is applied to a substrate through an ink jet head. In a preferred embodiment, the nozzles of the inkjet head will be arranged substantially perpendicular to the surface of the substrate. During the deposition process, the substrate and the inkjet head are moved relative to each other so that the inkjet head can add a particle suspension to the area of the substrate that requires coating. This relative movement can be performed by movement of the inkjet head, the substrate, or both. The spacing between the surface of the substrate and the ink jet nozzle can also be adjusted as needed. Such adjustment will be within the ability of one skilled in the art.

  The substrate is preferably circular, but can be any shape suitable for a given application.

In the embodiment of the present invention, the substrate surface is preferably as smooth as possible. The substrate surface may not be planar over its entire area, but it must be substantially free of local discontinuities. Regarding the surface roughness, the average surface roughness _Ra is preferably less than about 1 nm, for example about 0.1 nm. R _a is measured by detecting the average centerline moving parallel to the surface. Any trough below the centerline is inverted and calculated as a peak. The average of the peaks above the center line (including the inverted trough) is R _a which is the roughness average. The average roughness of the substrate surface can be measured using any technique known to those skilled in the art, for example, side measurement, polarization ellipticity measurement, or “atomic force microscopy”, or a combination thereof. it can. For example, an “atomic force microscope” can be used.

In an alternative aspect of the invention, the substrate has a greater degree of roughness. For example, larger than the average surface roughness R _a of the substrate is about 1 nm, greater than preferably about 5 nm. In this embodiment, the surface roughness _Ra is preferably less than about 30 nm, for example, less than about 20 nm or 10 nm. In some embodiments of the invention, it has been found that better adhesion between the substrate and the coating particles can be achieved by controlling the average size of the irregularities.

The substrate also preferably has a high surface hardness, for example a Vickers hardness greater than about 600 kg / mm, preferably greater than about 700 kg / mm. It is also desirable for the substrate to have a high stiffness, for example in a state of elastic modulus greater than about 70 GPa, preferably greater than about 80 GPa, more preferably greater than about 90 GPa. The substrate can also have a specific modulus greater than about 25 GPa, such as greater than about 30 GPa or greater than 35 GPa. It is advantageous for the substrate to have a low coefficient of thermal expansion. This is because it improves the readability of a recording device made of a coated substrate. The coefficient of thermal expansion is preferably less than 30 ppm K ⁻¹ , for example 20 ppm K ⁻¹ . In a particularly preferred embodiment, the coefficient of thermal expansion of the substrate is 10 ppm K ⁻¹ . In a preferred embodiment of the invention, the substrate has a low thermal conductivity. This increases the temperature at which the coated substrate operates efficiently as a magnetic recording device. Accordingly, a preferred embodiment of the present invention have less than 20Wm ^-1 K ^-1, for example, a 10Wm less than ^-1 K ^-1 or about 5Wm ^-1 K thermal conductivity of less than ^-1. Examples of suitable materials are glass, for example OHARA INC. Of Japan (229-1186, Kanagawa, Sagamihara, Koyama, 1-15-30, Tel: (81) 42-772-2101, Fax: (81 ) 42-774-1071, "TS-10SX" commercially available from http://www.ohara-inc.co.jp), and aluminum. When the material is aluminum, this material can be coated with Ni-phosphorus.

  In one embodiment of the present invention, as shown in FIG. 1, the substrate is arranged vertically, and the inkjet head is arranged at a right angle to the substrate (1). At least one inkjet head (2) is arranged at right angles to one side of the substrate. In another embodiment, the apparatus can include at least one ink jet head disposed on both sides of the substrate. The substrate rotates around the spindle (3) about the “X” axis, while the inkjet head device is stationary. Alternatively, the substrate may be held in a stationary position and the inkjet head may rotate about the “X” axis or move in a single “Y” plane that is substantially parallel to the surface of the substrate. it can. In a preferred embodiment of the invention, both the substrate and the ink jet are moved simultaneously. For example, the substrate can be rotated while the inkjet head device can either rotate about the “X” axis or move in the “Y” plane. In embodiments where the substrate rotates relative to the inkjet, the control means rotates as a function of the radial position of the inkjet head to ensure that the area of the substrate covered by the inkjet head is maintained substantially constant. Can be adjusted. In general, the substrate will be disk-shaped.

  Prior to coating, for example, as shown in FIGS. 1 and 2, the substrate disk will be positioned on the spindle of the inkjet adder. FIG. 2 shows a suitable positioning device comprising an arched structure (2), with individual gripping members (3) protruding radially from the structure. In the first position (FIG. 2b), each member engages the outer rim of the disc (1). Together, these members hold the disk within the arcuate structure and accurately move it to a position for positioning the disk on the spindle. After the disk is positioned on the spindle, the gripping member can be separated from the disk rim, as shown in FIG. 2a. The gripping member can be, for example, a spring forming structure or a solid pin that can expand and contract along the longitudinal axis.

  In order to load the disc into the inkjet add-on device, the disc holding spindle (3) can be retracted to the first position by the control device (4). Next, the substrate disk is moved to a position in the additional device shown in FIG. The disc is positioned in the additional device such that the center of the disc hole coincides with the longitudinal axis of the telescopic spindle. The telescoping spindle can then be inserted through the center hole of the disc. The disc is then fixedly attached to the spindle. A person skilled in the art can apply disk fixing means, such as washers, robotically to ensure that the disk is sufficiently fixed in a plane perpendicular to the longitudinal axis of the spindle, so that the spindle is at the desired speed. It will be appreciated that the disk rotates to maintain its position in a single plane when rotating at. For example, the spindle can have an expandable cross-sectional area so that it extends to fill the center hole of the disk and locks the disk in a right angle position. One skilled in the art will also readily recognize that various devices can be used to rotate the spindle.

  In another embodiment shown in FIG. 4, the substrate is held on the spindle in a substantially horizontal plane. The inkjet head (1) is positioned on the substrate (2) and can move parallel to the plane “X”. In operation, the substrate rotates about the axis “X” of the spindle (3) while the inkjet head device is stationary. Alternatively, the substrate is held in a stationary position and the inkjet head moves in a plane “X” that is substantially parallel to the surface of the substrate. In a preferred embodiment of the invention, both the substrate and the inkjet head are moved simultaneously. For example, the substrate rotates while the inkjet head device moves in the plane “X”.

  In operation, those skilled in the art will understand that when the substrate is in the position where the coating is to be performed, the substrate will be securely engaged to the holding means, for example a spindle. “Certain” means that the substrate will not substantially deviate from the position of the substrate in a single plane, thereby requiring any damage without damaging either the inkjet head or the substrate. Ink jet printing can be executed with a degree of effectiveness.

  In the apparatus used in the present invention, those skilled in the art will appreciate that the dimensions of the inkjet head can be selected according to the particular application. For example, an inkjet head, such as that described above for some embodiments of the apparatus shown in FIGS. 1 and 2, for example, held in a stationary position, has a longitudinal dimension of the disk to which it is applied. It can be designed to be substantially equal to the radius. Furthermore, the number of nozzles used in a particular head will be determined by the area of the surface intended to be coated by that inkjet head. One skilled in the art will appreciate that the number of nozzles and the dimensions of the nozzles can be designed according to the particular application and that the inkjet adder can be configured to accommodate different heads interchangeably.

  In a preferred embodiment of each aspect of the invention described, the substrate is treated to facilitate dispersion of a suspension of particles applied thereon. Such treatment can include chemical, mechanical, or radiation treatment, or a combination thereof. For example, chemical treatments include the use of a wetting agent such as alcohol, eg “propan-1-ol” or “NP40” (Accurate Chemical and Scientific, Westbury, NY, 11590 USA, Use of dispersants / surfactants such as Tel: (516) 333-2221 (800) 645-6264, Fax: (516) 997-4948). The dispersant can be applied to the substrate prior to the addition of the particle suspension. Alternatively, the dispersant and / or wetting agent can be added to the suspension containing the particles formed as a film on the substrate. The amount of wetting or dispersing agent required for optimal coating of the substrate will depend on the particular suspension, but the amount added will be in the nozzle when there is no additional jet power from within the inkjet head. It is preferably an amount that does not reduce the surface tension at the nozzle orifice to a value that is insufficient to maintain suspension.

  In some embodiments of the invention, the substrate surface is pretreated prior to coating. This can be performed, for example, by mechanical processing or radiation processing. Mechanical treatment can include, for example, cleaning by chemical-mechanical polishing. The radiation treatment preferably includes exposure of the substrate to UV light.

  The source of the pretreatment agent can generally be arranged in the same plane as the inkjet head (4). Typically, the disc rotates in the indicated direction (arrow), and a pretreatment agent, for example a radiation beam or chemical wetting agent, will contact the substrate before the substrate is applied to the inkjet head. The duration of the pretreatment and the time interval between the pretreatment and the coating will depend on the application. For example, the pretreatment agent source and the inkjet head can operate substantially simultaneously, and the pretreatment includes a single pass of the substrate in the range targeted by the pretreatment agent source. To be done. In other embodiments, certain areas of the substrate are processed in several passes through the disc of interest by the pretreatment agent source. Next, a certain time interval will elapse before the particles are deposited on the substrate by inkjet printing.

  It is preferred to use an apparatus as shown in FIG. 1, wherein the apparatus has an inkjet head disposed substantially perpendicular to the substrate, and a UV light source head (4), which is also substantially relative to the substrate. It includes an inkjet head and a UV light source arranged in planes substantially parallel to each other so as to emit a beam in a perpendicular plane.

  The film can also be treated after deposition of the particles on the substrate, for example by UV curing or infrared radiation, or by heating. The film can, for example, heat the substrate to a temperature of at least about 300 ° C. in a conventional annealing furnace, or anneal subsequent to particle deposition by exposure to a laser beam. It is particularly preferred that the film be annealed when annealing is intended for use as a component in a magnetic recording device because annealing greatly improves the magnetic properties of the film.

  In many aspects of the present invention, such as magnetic nanoparticle films used in magnetic recording media, the surface of the film is preferably as smooth and flat as possible. The film surface may not be completely flat across its entire surface, but it must be free of substantial local discontinuities due to the proximity of the read head during operation. For example, the discontinuity in the film surface should preferably be less than about 13 nm in height above the magnetic surface. This is because, in the case of magnetic nanoparticles encapsulated in an apoferritin shell, an acceptable level of discontinuous size on the film surface is about 1 particle size (encapsulation for effectiveness as a magnetic recording medium). Mean that it includes the encapsulated shell).

  In particular, when the substrate is relatively smooth on the length scale of the coating particles, it is also preferred that the film thickness be no more than 2 particle sizes (including any encapsulated shell) across the entire film.

  Thus, in a preferred embodiment of the invention, the film is in the form of a substantially continuous monolayer. In order to reduce the occurrence of film thickness discontinuities due to the boundary between the coated and uncoated substrate areas, the film must be substantially continuous.

For example, the inventors have been able to perform magnetic recording on a magnetizable device comprising magnetic nanoparticles encapsulated with ferritin on a substrate having an average surface thickness R _a of less than about 1 nm. Variation in film thickness on the substrate is on the order of 25 nm (a single ferritin particle has a diameter on the order of half of this value).

  In other aspects of the invention where the film is not used as a data storage medium, the smoothness of the film surface may be less important. The required smoothness of the film depends on the particular application, but in some embodiments, for example, the average surface roughness of the film is about 5 particle sizes (including any encapsulated shell) or about 3 or 2 It can be about 10 particle sizes or less, such as a particle size or less.

  Since the substrate exhibits different degrees of roughness according to different aspects of the invention, the film thickness at a given point on the film surface will depend to some extent on the degree of surface roughness of the lower substrate. Thus, in some aspects of the invention, it is preferred that the film thickness does not change depth over about 10 times the diameter of the constituent particles (including any encapsulated shell) substantially throughout the film, More preferably, it is not more than about 5 times the particle size, more preferably not more than about 3 or 2 times the particle size. Although the absolute thickness of the film will depend on the particle size, films made according to the present invention will typically have a thickness of less than about 500 nm, more preferably less than about 100 nm, and most preferably less than about 50 nm. . In particularly preferred embodiments of the invention, the film thickness is less than about 30 nm substantially throughout the film.

  When the present invention is concerned with a method of forming a magnetic recording device by depositing magnetic or magnetizable nanoparticles on a substrate as a droplet having a volume of less than about 1 nl, for example by ink jet printing, the magnetic particle May be encapsulated or unencapsulated.

  When the particles are encapsulated, the encapsulating material can include organic or inorganic materials such as siloxanes, silanes, or derivatives thereof. “Encapsulated” means particles coated with a polymeric material or particles formed within a preformed cavity of polymeric material. The encapsulating material can be a continuous single structure, for example a multimeric protein comprising several polypeptide chains. Alternatively, the encapsulating material at least partially encloses the inorganic material and either stays in a nearby but separate structure or interacts with adjacent structures to form a multi-component structure. It can exist as a separate single structure.

  The encapsulating material preferably includes a single component that acts to accommodate core magnetic nanoparticles having a diameter of about 100 nm or less (or its maximum size in the case of spherical particles), or a few components that act together. Can do. Preferably, this diameter is about 50 nm or less, more preferably about 20 nm or less. This dimension is determined at least in part by the size of the encapsulating material. Alternatively, the encapsulating material can include suitable openings that can contain and retain magnetic particles even though they are not completely enclosed, e.g., the openings within the polymer It can be formed by a ring.

  In aspects of the invention relating to the formation of magnetizable films and magnetic recording devices, the core magnetizable nanoparticles should not be so small that they cannot maintain ferromagnetism at ambient temperature. Ambient temperature is typically greater than about 0 ° C, for example greater than about 15 ° C. The ambient temperature is usually less than about 50 ° C., for example, less than about 30 ° C. This means that for operation at ambient temperature, magnetizable nanoparticles will typically be larger than about 2 nm.

  In a preferred embodiment, the encapsulating material can be an organic polymer that we mean a molecule or assembly of molecules and can have a molecular weight of up to about 1500 kD, usually less than about 500 kD. Such organic macromolecules can be surfactants, polymers, or proteins.

  When the present invention relates to a method of forming a magnetizable film or a film of inorganic nanoparticles on a substrate, the particles are at least partially formed within the encapsulated protein, but when deposited on the substrate, the encapsulated or Any of non-encapsulation may be used. When the inorganic nanoparticles are semiconductor nanoparticles, in some embodiments of the invention, the deposition of these particles in a non-encapsulated state on the substrate results in a semiconductor film having a higher packing density. It is preferable because it brings about.

  When the various aspects of the invention involve proteins, the proteins can be naturally derived or can be derived from other sources including artificial proteins, eg, recombinant proteins.

  In some preferred embodiments of the first, second, and third aspects of the invention, the protein serves as an encapsulating material that at least partially surrounds the inorganic particles. In a preferred embodiment, the inorganic particles comprise a magnetic metal or alloy, or a semiconductor material.

  In an embodiment of the fifth aspect of the invention, the protein is not bound to other materials at least during the formation of the film on the substrate.

  Proteins suitable for use in the present invention include flagellar LP rings, bacteriophages, chaperonins such as bacteria GroEL and GroES, DPS, and viral capsids. For example, DPS is a ferritin homolog and a 12-mer DNA protection protein, which includes a hollow core and a void in the triple axis. The flagellar LP ring is a ring-shaped structure having an inner diameter of about 13 nm and an outer diameter of about 20 nm. They can be guided to fill in an ordered array extending over several μm with a thickness on the order of 13 nm. At a lower concentration, a dimer having a thickness of about 26 nm may be formed.

  In a highly preferred embodiment of the invention relating to proteins, the protein is one of the ferritin family. The present invention most preferably utilizes ferritin, which is an iron storage protein used to form inorganic particles with nanoscale internal cavities. Ferritin has a molecular weight of 450 kD. Ferritin has been utilized for iron metabolism across species and its structure is highly conserved among them. Ferritin consists of 24 subunits, which self-assemble to provide a hollow shell with an outer diameter of roughly 12 nm. Ferritin has an 8 nm diameter cavity, which normally contains about 4500 iron (III) atoms in the form of paramagnetic ferrihydrite. This ferrihydrite can be removed (ferritin lacking ferrihydrite is called "apoferritin") and other substances can be incorporated. The subset within ferritin is tightly packed, but there are channels into the cavity on the triple and quadruple axes.

  A preferred protein for use in various aspects of the invention relating to proteins is apoferritin having a cavity with a diameter on the order of about 8 nm.

  Ferritin can be found naturally in vertebrates, invertebrates, plants, fungi, yeasts and bacteria. Ferritin can also be produced synthetically by genetic engineering techniques. Such synthetic species can be the same as the natural species, but it is also possible to synthesize variants that retain the basic property of being able to accommodate particles within their internal cavities. The use of all such natural and synthetic species of ferritin is considered within the scope of the present invention.

  Ferritin can be converted to apoferritin by dialysis against a buffered sodium acetate solution under a stream of nitrogen. For example, reductive chelation with thioglycolic acid is one that can be used to remove the ferrihydrite core. Thereafter, repeated dialysis against sodium chloride solution can be followed to completely remove the reduced ferrihydrite core from the solution. Apoferritin has a cavity of about 8 nm in a relaxed state. Since this protein can be stretched to accommodate particles larger than those with a diameter of 8 nm, the core nanoparticles (in other words, the core material excluding the encapsulating material) have a diameter up to about 15 nm. be able to.

  When the present invention relates to the formation of a thin film of magnetic nanoparticles in its various embodiments, the magnetic nanoparticles, which can be either encapsulated or unencapsulated, are cobalt, iron, or nickel, metal alloys, rare earths and transitions. It includes either ferrimagnetic or ferromagnetic metals such as metal alloys, M-type ferrites or spinel type ferrites. This metal or alloy is aluminum, barium, bismuth, cerium, chromium, cobalt, copper, dysprosium, erbium, europium, gadolinium, holmium, iron, lanthanum, lutetium, magnesium, molybdenum, neodymium, nickel, niobium, palladium, platinum, One or more of praseodymium, promethium, samarium, strontium, terbium, thulium, titanium, vanadium, ytterbium, and yttrium, or any mixture thereof can be included.

  Preferably, the magnetic nanoparticles are cobalt-nickel, iron-platinum, cobalt-palladium, iron-palladium, samarium-cobalt, dysprosium-iron-turbide, or neodymium-iron boride, iron-cobalt-platinum, It includes binary alloys or ternary alloys of cobalt-nickel-platinum or cobalt-nickel-chromium. More preferably, the above-mentioned nanoparticles are cobalt or platinum and alloys thereof, for example, an alloy of cobalt and platinum.

  In a preferred embodiment of the first aspect of the invention, the magnetic nanoparticles are encapsulated by a protein material.

  In a preferred embodiment of the third aspect of the invention, the particles are either magnetic nanoparticles or semiconductor nanoparticles encapsulated by a protein material. In particular embodiments of this aspect of the invention, the magnetic particles comprise either a cobalt / platinum alloy or an iron / platinum alloy, which are encapsulated by apoferritin or DPS.

  Magnetic nanoparticles are typically a single metal or multi-metal ion source for which a suspension of an encapsulating material such as an organic polymer in an aqueous medium contains or constitutes the core magnetic nanoparticles. Can be prepared by a process combined with In this step, a metal ion source is preferably added incrementally to the encapsulant source. For example, the cation and anion source can be added in an amount sufficient to provide more than one atom of cation and anion source per encapsulation shell per iteration. The cation and anion source should be added in an amount sufficient to provide less than 200 atoms of cation and anion source per encapsulation shell per repetition, preferably less than 100 atoms per encapsulation per encapsulation. Can do. Preferably, the cation and anion source can be added in an amount sufficient to provide about 50 atoms of cation and anion source per encapsulation. These low concentrations can be achieved by serial dilution of a solution containing a cation and anion source. The metal ion source can be a single metal or multi-metal salt constituting the magnetic nanoparticles, such as ammonium tetrachloroplatinate. Alternatively, although less preferred at the present time, the metal ion source can be present in a composition to which the organic polymer source is added.

  The mixture of organic polymer and metal ions can be agitated to ensure homogeneity. If the magnetic nanoparticles are to contain an elemental metal or alloy, a reduction is performed on the composition, thereby forming nanoparticles within the organic polymer cavity. This reaction is preferably carried out under an inert atmosphere in order to prevent the metal nanoparticles from oxidation which can degrade their magnetic properties. The reduction / oxidation process can be repeated during the addition of metal ions (which can be the same or different in each cycle) and the nanoparticles accumulate.

  The reaction mixture is formed at a temperature lower than the preferred temperature at which magnetic nanoparticles can be formed, and can then be raised to that temperature. Alternatively, the encapsulant source to which the metal ion source will be added can be kept at a temperature of at least 24 ° C. and the metal ion source can be added to it.

  Proteins can usually resist temperatures up to 70 ° C. before they lose their ternary structure. Thus, in embodiments where the encapsulating material is a protein, the temperature of the reaction can vary up to about 70 ° C. For these embodiments, the reaction temperature is preferably kept above 25 ° C., eg, above about 35 ° C. This temperature is preferably kept below about 60 ° C., eg, below about 50.

  During the formation of the encapsulated magnetic nanoparticles used in the present invention, the aqueous medium is maintained at an alkaline pH during the formation of the magnetic core nanoparticles in the polymer template. The pH is preferably kept in the range of 7.5 to 8.5. This can be achieved by the use of a buffer solution. The appropriate solution will depend on the encapsulant used.

  Following preparation of the nanoparticles, the nanoparticles are placed in a carrier fluid before being deposited on the substrate surface. When the nanoparticles are prepared in suspension, the suspension can form a component of the carrier fluid or the entirety thereof. Alternatively, the nanoparticles can be removed from the suspension from which the particles were prepared and resuspended in the carrier fluid. The physical properties of the fluid can be adjusted based on the application. For example, in the case of protein-encapsulated nanoparticles, ambient conditions such as temperature, pH, and ionic strength are kept at appropriate levels to avoid unwanted damage to the protein prior to deposition.

  The characteristics of the carrier fluid can be altered to provide easy deposition of fluid droplets on the substrate. For example, the surface tension of the carrier fluid can be altered to provide improved spreadability. The carrier fluid can be aqueous or non-aqueous and can have additional additives to alter its physical properties. In a preferred embodiment, the carrier fluid is water.

  When the present invention relates to the deposition of inorganic nanoparticles encapsulated by a polymeric material by an ink jet printing method, the inorganic nanoparticles are preferably semiconductor particles.

  In a highly preferred embodiment of the third aspect of the invention, a method of forming a film of semiconductor nanoparticles is provided, the particles comprising any of CdS, CdSe, CdTe, ZnS, ZnSe, or ZnTe. They are encapsulated by apoferritin or DPS.

  In some embodiments of any of the first, second, or third aspects of the invention, the encapsulating shell is removed to leave inorganic particles without a coating after the nanoparticles are deposited on the substrate. can do.

  In other embodiments of the invention, the encapsulating material can be treated to leave a residue surrounding the core nanoparticles, for example, the polymeric shell places the substrate at a high temperature, for example, on the order of about 300 ° C. Can be carbonized. Alternatively, laser pyrolysis can be used when it is required to carbonize the nanoparticles in situ. The organic polymer shell can be dissipated, for example, by pyrolyzing the nanoparticle film at high temperatures above about 500 ° C. This is preferably performed, for example, by controlling the inertness of the atmosphere by introducing hydrogen or nitrogen into the pyrolysis vessel.

  Other methods can also be used to remove the protein encapsulating material, including, for example, enzymatic degradation or pH denaturation. In particular, the protein can be digested with a protease or the pH of the composition is outside the range where the protein is stable, for example lower than about pH 4.0 or higher than about 9.0. It can be denatured by adjusting the value. The denatured protein material can then be removed, for example, by washing the substrate or exposing the substrate to a gas stream. In a preferred embodiment, the protein is denatured by adjusting the pH of the composition to a value lower than about 4.0.

  Formation of a smooth film of nanoparticles by inkjet printing can be facilitated by pretreatment of a liquid suspension of particles that increases the monodispersity of the particles. Furthermore, this pretreatment can promote film formation by removing unwanted debris. "Monodispersity" means that the degree to which the size of individual magnetic nanoparticles changes within the composition of the present invention is small. This variation, measured relative to the largest nanosize dimension, should usually be less than about 20%, preferably less than about 10%, and most preferably less than about 5%. For compositions with a relatively large average size, such as about 50 nm, this variation is preferably at the lower end of the above range, whereas for relatively small particles, such as about 10 nm, this variation The variation can be at the upper end of the above range. The size of the particles according to the invention can be measured, for example, using transmission electron microscopy (TEM). In embodiments of the invention in which the core nanoparticles are encapsulated by a polymer or protein shell, it may be necessary to remove the shell in a representative sample of the encapsulated nanoparticles prior to measuring the size of the core nanoparticles. This can be done using any method known to those skilled in the art, for example, any of the previously detailed methods of pyrolysis is used.

  The inventor can increase the monodispersity of the encapsulated nanoparticles by subjecting the liquid composition comprising the nanoparticles to a microporous membrane filtration step before depositing it on the substrate, for example, by ink jet printing. I found out that I can do it. Furthermore, this preparatory process is useful in removing unwanted debris in many cases.

  The composition of encapsulated nanoparticles, which is preferably aqueous in the prefiltration step, but other solvents such as alcohols or alkanes can also be used in some embodiments, is processed in the microporous membrane filtration step. Is done. In this filtration step, the composition is introduced into one side of the filter and filtered through the membrane. The nanoparticles used in the present invention are preferably present in the composition at a concentration ranging from about 0.1 to about 20 mg / ml. In embodiments, the pH of the composition is preferably in the range of about 7 to about 8.5. Preferably, during the filtration step, the composition is subjected to a positive applied pressure. For example, the applied pressure may be greater than about 1 psi, such as greater than about 5 psi. Typically, the pressure will be less than about 20 psi, such as less than about 15 psi. The filtrate containing the nanoparticle composition is then recovered.

  Membrane filters are a known structure, which is distinguished from non-membrane filters by the fact that the membrane is monolithic, i.e. it has a structure that is permanently bonded so that its solid structure forms a continuous solid phase. The In contrast, non-membrane filters are formed by fibers that are held fixed by mechanical entanglement or other surface forces. Membrane filters can be made with a narrow pore size distribution and very small pores when needed. The microporous membrane used in the present invention has pores in the approximate range of about 0.02 to about 10 μm, preferably less than about 1 μm, and most preferably less than about 0.5 μm, and can be used in the present invention. Specific examples of pore sizes are about 0.2 μm pores and 0.1 μm pores. The microporous filter for sorting particles used in the present invention can be made of various materials including polymers, metals, ceramics, glass, and carbon. Typically, the membrane is made of, for example, polysulfone, polyethersulfone (PES), polyacrylate, polyvinylidene, such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), cellulose, cellulose ester, or copolymers thereof. It will be formed of polymer materials known to be used for membrane filtration in such art. When the encapsulating material is a protein, the membrane will preferably be selected to include a low protein binding material such as polyethersulfone or polyvinylidene. Such microporous filters are commercially available from Millipore Corporation (Bedford, Mass.).

  The membrane filter can be a membrane disk, but other forms of membranes can also be used in the present invention.

  Importantly, the inventors have found that the filter pore size can be several orders of magnitude larger than the particle size of the nanoparticulate material in order to achieve the production of a stable nanoparticle composition. For example, when the particles used in the present invention are encapsulated by ferritin, the particles have a diameter of about 12 nm. The inventors have found that stable preparation of ferritin-encapsulated nanoparticles that are resistant to aggregation can be achieved using 0.2 μm and 0.1 μm filters.

  Typically, the nanoparticles used in the present invention will have all of their dimensions within a nanosize range that is typically at least about 1 nm and not more than about 100 nm, preferably not more than about 50 nm, more preferably not more than about 20 nm. . Preferably, the magnetic or semiconductor nanoparticles of the present invention are substantially spherical and have a diameter in the range of about 1-100 nm. However, the present invention extends to magnetic particles having a single dimension that is not within the nanosize range.

  When the present invention involves magnetic nanoparticles, the pretreatment purification step includes a magnetic fractionation step of the encapsulated magnetic nanoparticles. This step is delayed under gravity or by application of positive pressure while applying a magnetic field to the composition so that the particles in the composition are spatially separated according to their magnetic properties. Passing the medium through. Since the magnetic properties of magnetic nanoparticles will be determined by the size of the core magnetic nanoparticles, whether encapsulated or not, this method is a composition in which the inner core particles have a high degree of monodispersity. Means are also provided for obtaining.

  The retardation medium may comprise steel, eg, type “IV 20L” or another suitable soft magnetic material in powder, beads, or other form known in the art. The retarding medium does not chemically react with the composition to damage or change the structure of the magnetic nanoparticle composition, but the magnetic particles are in some form of attraction interaction while the magnetic nanoparticles pass through the fractionation device. It is preferred to include materials that can be made to have.

  Those skilled in the art will appreciate that many means can be utilized for magnetic fractionation, magnetic wire, magnetic powder chromatography, and field flow fractionation techniques. In a preferred embodiment of the invention, the composition passes through a cylinder containing magnetic powder at a flow rate in the range of about 0.2 to 10 milliliters / minute. Magnetic fractionation also provides the advantage of allowing the fluid medium in which the nanoparticles are suspended to be exchanged.

  If the particles are magnetic particles, the pretreatment step can include both steps in either or any order of the filtration step or the magnetic fractionation step.

  The invention will now be described with reference to the following non-limiting examples.

Example

  Apoferritin was produced as described in WO 98/22942.

  Example 1: Synthesis of cobalt / platinum nanoparticles in apoferritin

  Buffer apoferritin to 0.05 M 4- (2-hydroxylethyl) -1-piperazineethane-sulfonic acid (HEPES) buffer buffered to pH 7.5 to 8.5 or pH 7.5 to 8.5 Dispersed in any of the 0.25 M AMPSO prepared. Next, aliquots of 0.1 M cobalt (II) acetate solution and 0.1 M ammonium tetrachloroplatinate (II) solution were added and the mixture was stirred at a temperature between 35 ° C and 50 ° C. Subsequently, reduction using sodium borohydride was performed. Several additions of metal salt and subsequent reduction resulted in apoferritin whose core was substantially occupied by Co / Ni crystals (Mayes, E, 2002. “J. Magn. Soc. Japan.”). 26, (8), 932-935, Warne, B et al., 2000, "IEE Bulletin Related to Magnetics", 36, 3009-3011).

  Example 2: Synthesis of iron-platinum nanoparticles in apoferritin

  Apoferritin is dispersed in 50 mM 3-([1,1-dimethyl-2-hydroxyl] amino) -2-hydroxypropane sulfonic acid (AMPSO) solution and buffered to pH 8.5-8.9. The temperature of the suspension was maintained between 40 ° C and 70 ° C. Aliquots from degassed solutions of ammonium iron (II) sulfate (25 mM) and tetrachloroplatinate (II) ammonium (25 mM) were added incrementally to the apoferritin suspension. Aliquots of added iron (II) and platinum (II) corresponded to 100 atoms per apoferritin molecule. Following each addition of iron (II), a stoichiometric aliquot of trimethylamine-N-oxide (25 mM) corresponding to 2/3 of iron (II) was added. After each addition of platinum (II), a suitable reducing agent, such as sodium borohydride or hydrazine, was added in stoichiometric amounts. Except for the addition of iron (II) oxidant, which was immediately followed by the addition of iron (II) to the reaction suspension, the interval between increments of aliquot addition was about 15 minutes. The addition was done until the apoferritin core was substantially occupied by the magnetite / platinum (0) core. The suspension was then dialyzed against water and filtered through a 2 μm filter prior to concentration or use as prepared.

  Example 3: Inkjet printing of ferritin on a glass substrate

  The glass substrate was cleaned using an Oliver Design (SN252) multiple cassette disk cleaning system.

  An Epson inkjet printer (Photo 1290) was used in the following procedure. An aqueous suspension of ferritin having a protein concentration of about 2-10 mg / ml was introduced using a syringe into the head of a printer having a -5 cm static head (about 0.075 psi).

  The disk was mounted on a disk holding cassette and placed at a stationary position under the inkjet head. Ferritin suspensions were deposited on glass disks at various head speeds ranging from 10 to 100 centimeters / second.

  In some cases, the disks were subjected to another round of inkjet printing using the same ferritin material.

  The disc was removed after ferritin deposition and analyzed by "atomic force microscope". This additional step has been found to result in a filter having a thickness in the range of 100 nm to 12 nm, the latter being characteristic of a ferritin monolayer. A sample AFM micrograph is shown in FIG.

  Example 4: Inkjet printing of apoferritin-encapsulated cobalt-platinum on a glass substrate

  Glass substrates were cleaned using an Oliver Design (SN252) multiple cassette disc cleaning system.

  An Epson inkjet printer (Photo 1290) was used in the following procedure. Aqueous suspension of apoferritin-encapsulated cobalt / platinum alloy according to Example 1 having a protein concentration of about 2-10 mg / ml (which can contain up to 0.2% hydrazine) using a syringe Introduced into the head of a printer with a -5 cm static head (about 0.075 psi).

  The disc was loaded into a disc holding cassette and placed stationary under the inkjet head. Apoferritin-encapsulated metal alloy compositions were deposited on glass disks at various head speeds ranging from 10 to 100 centimeters / second.

  In some cases, the disks were subjected to another round of inkjet printing using the same apoferritin-encapsulated cobalt-platinum material.

  Example 5: Inkjet printing of ferritin on glass substrate pretreated with UV light

  Glass substrates were cleaned using an Oliver Design (SN252) multiple cassette disc cleaning system.

  The substrate was exposed to a UV light source (wavelength 172 nm) (USHIO) under a nitrogen atmosphere prior to inkjet printing. Specifically, the substrate was placed about 2 mm from quartz glass containing a UV filament and exposed to UV light for about 20 to 40 seconds.

  An Epson inkjet printer (Photo 1290) was used in the following procedure. An aqueous suspension of ferritin having a protein concentration of about 2-10 mg / ml (which can contain up to 0.2% hydrazine) is transferred to a -5 cm static head (about 0. 075 psi) was introduced into the printer head.

  The disc was loaded into a disc holding cassette and placed stationary under the inkjet head. Ferritin compositions were deposited on glass disks at various head speeds ranging from 10 to 100 centimeters / second.

  In some cases, the disks were subjected to another round of inkjet printing using the same batch of ferritin.

  AFM micrographs of non-radiation and UV radiation samples are shown in FIG.

  Example 6: Inkjet printing of apoferritin-encapsulated iron-platinum on a glass substrate pretreated with UV light

  The glass substrate was cleaned using an Oliver Design (SN252) multiple cassette disk cleaning system.

  The substrate was exposed to a UV light source (wavelength 172 nm) (USHIO) under a nitrogen atmosphere prior to inkjet printing. Specifically, the substrate was placed about 2 mm from quartz glass containing a UV filament and exposed to UV light for about 20 to 40 seconds.

  An Epson inkjet printer (Photo 1290) was used in the following procedure. An aqueous suspension of apoferritin-encapsulated iron / platinum alloy according to Example 2 having a protein concentration of about 2-10 mg / ml (which can contain up to 0.2% hydrazine) using a syringe Introduced into the head of a printer with a -5 cm static head (about 0.075 psi).

  The disc was loaded into a disc holding cassette and placed stationary under the inkjet head. Apoferritin-encapsulated metal alloy compositions were deposited on glass disks at various head speeds ranging from 10 to 100 centimeters / second.

  In some cases, the disks were subjected to another round of ink jet printing using the same apoferritin-encapsulated cobalt-platinum material.

  Example 7: Inkjet printing of apoferritin-encapsulated cobalt-platinum on a glass substrate pretreated with UV light

  The glass substrate was cleaned using an Oliver Design (SN252) multiple cassette disk cleaning system.

  The substrate was exposed to a UV light source (wavelength 172 nm) (USHIO) under a nitrogen atmosphere prior to inkjet printing. Specifically, the substrate was placed about 2 mm from quartz glass containing a UV filament and exposed to UV light for about 20 to 40 seconds.

  An Epson inkjet printer (Photo 1290) was used in the following procedure. Aqueous suspension of apoferritin-encapsulated cobalt / platinum alloy according to Example 1 having a protein concentration of about 2-10 mg / ml (which can contain up to 0.2% hydrazine) using a syringe Introduced into the head of a printer with a -5 cm static head (about 0.075 psi).

  The disc was loaded into a disc holding cassette and placed stationary under the inkjet head. Apoferritin-encapsulated metal alloy compositions were deposited on glass disks at various head speeds ranging from 10 to 100 centimeters / second.

  In some cases, the disks were subjected to another round of inkjet printing using the same apoferritin-encapsulated cobalt-platinum material.

It is a figure of the inkjet printing apparatus with which the board | substrate was arrange | positioned in the vertical position. It is a figure of the board | substrate positioning apparatus in a 1st board | substrate non-engagement position and a 2nd board | substrate engagement position. It is a figure of the inkjet printing apparatus with a spindle in a retracted position. It is a figure of the inkjet printing apparatus with which the board | substrate has been arrange | positioned in the horizontal position. It is a figure which shows the tap mode AFM image of ferritin deposited on the glass substrate. It is a figure which shows the tap mode AFM image of ferritin deposited on (a) non-radiation glass substrate and (b) glass substrate radiated | emitted with UV light.

Explanation of symbols

1 Substrate 2 Inkjet head 3 Spindle

Claims (86)

A method of forming a magnetic recording device having a film of magnetizable nanoparticles, comprising:
Preparing a liquid of magnetizable nanoparticles in a carrier fluid;
Depositing the fluid suspension as droplets having a volume of less than about 1 nl on a substrate surface to form a film of magnetizable nanoparticles as a dry residue of the deposited fluid suspension;
A method comprising the steps of:   The method of claim 1, wherein the fluid suspension is deposited on the substrate using an inkjet printing method.   3. A method according to claim 1 or claim 2, wherein the magnetic nanoparticles are formed at least partially within a polymeric shell.   The method of claim 3, wherein the polymer shell is a protein.   The method according to claim 4, wherein the protein is apoferritin or DPS.   6. The method of any one of claims 3-5, wherein the polymeric shell is carbonized by subsequently exposing the nanoparticle film to a high temperature in excess of 300 <0> C.   6. The method of any one of claims 3-5, wherein the polymeric shell is subsequently dissipated by pyrolyzing the nanoparticle film at a temperature greater than 500C. The average surface roughness R _a of the substrate is less than about 1 nm, the method according to any one of claims 1 to 7. The average surface roughness R _a of the substrate ranges from about 5nm to about 20 nm, the method according to any one of claims 1 to 7.   10. A method according to any one of claims 1 to 9, wherein the substrate is treated to promote dispersion of a suspension of added nanoparticles.   The method of claim 10, wherein the treatment comprises a chemical treatment, a mechanical treatment, or a radiation treatment.   The method of claim 11, wherein the radiation treatment comprises exposure of the substrate to UV light.   13. A method according to any one of claims 1 to 12, wherein the film is processed following deposition of the nanoparticles on the substrate.   The method of claim 13, wherein the film is annealed after deposition of the nanoparticles on the substrate.   15. A method according to any one of the preceding claims, wherein the thickness of the film is not substantially greater than two particle sizes (including any encapsulated shell) through the film.   16. The method of any one of claims 1 to 15, wherein the discontinuities in the film surface are less than about 13 nm in height.   The method according to any one of claims 1 to 16, wherein the magnetic nanoparticles have a diameter of 20 nm or less (or a maximum diameter in the case of non-spherical particles).   The method according to claim 1, wherein the magnetic nanoparticles comprise an alloy of cobalt and platinum.   19. A method according to any one of claims 1 to 18, wherein the magnetic nanoparticles are encapsulated.   The method of claim 19, wherein the encapsulating material is a protein.   21. The method of claim 20, wherein the protein is apoferritin or DPS.   22. A method according to any one of claims 19 to 21 wherein the composition of encapsulated nanoparticles undergoes a microporous membrane filtration step prior to deposition on the substrate.   The method according to claim 22, wherein the pore diameter of the membrane filter is in the range of 0.02 to 10 μm.   24. A method according to claim 22 or claim 23, wherein the membrane comprises polyethersulfone or polyvinylidene.   25. A method according to any one of claims 1 to 24, wherein the magnetic nanoparticles undergo a magnetic fractionation step prior to deposition on the substrate. A method of forming a magnetizable film comprising:
Preparing a suspension of magnetizable nanoparticles each formed at least partially within a protein shell within a carrier fluid;
Depositing the fluid suspension on a substrate surface as droplets having a volume of less than about 1 nl, obtaining a magnetizable film on the substrate as a dry residue of the deposited fluid suspension;
A method comprising the steps of:   27. The method of claim 26, wherein the fluid suspension is deposited on the substrate using an ink jet printing method.   28. The method of claim 26 or claim 27, wherein the protein shell is carbonized by subsequently exposing the nanoparticle film to a high temperature in excess of 300 <0> C.   28. A method according to claim 26 or claim 27, wherein the protein shell is dissipated by subsequently pyrolyzing the nanoparticle film at a temperature greater than 500 <0> C. The average surface roughness R _a of the substrate is less than about 1 nm, the method according to any one of claims 29 claim 26. The average surface roughness R _a of the substrate ranges from about 5nm to about 20 nm, the method according to any one of claims 29 claim 26.   32. A method according to any one of claims 26 to 31, wherein the substrate is treated to facilitate dispersion of the suspension of added nanoparticles.   35. The method of claim 32, wherein the treatment comprises a chemical treatment, a mechanical treatment, or a radiation treatment.   34. The method of claim 33, wherein the radiation treatment comprises exposure of the substrate to UV light.   35. A method according to any one of claims 26 to 34, wherein the film is processed following deposition of the nanoparticles on the substrate.   36. The method of claim 35, wherein the film is annealed after deposition of the nanoparticles on the substrate.   37. A method according to any one of claims 26 to 36, wherein the thickness of the film does not vary substantially more than about 3 diameters of the constituent particles (including any encapsulated shell) through the film. The average surface roughness R _a of the film is not greater than about 3 diameter (including any encapsulating shells), The method according to any one of claims 37 to claim 26.   39. A method according to any one of claims 26 to 38, wherein the composition of encapsulated nanoparticles undergoes a microporous membrane filtration step prior to deposition on the substrate.   40. A method according to any one of claims 26 to 39, wherein the magnetic nanoparticles have a diameter of 20 nm or less (or a maximum diameter in the case of non-spherical particles).   41. A method according to any one of claims 26 to 40, wherein the magnetic nanoparticles comprise an alloy of cobalt and platinum.   42. A method according to any one of claims 26 to 41, wherein the encapsulating material is a protein.   43. The method of claim 42, wherein the protein is apoferritin or DPS.   44. The method of any one of claims 26 to 43, wherein the composition of encapsulated nanoparticles undergoes a microporous membrane filtration step prior to deposition on the substrate.   45. The method of claim 44, wherein the membrane filter has a pore size in the range of 0.02 to 10 [mu] m.   46. A method according to claim 44 or claim 45, wherein the membrane comprises polyethersulfone or polyvinylidene.   47. A method according to any one of claims 26 to 46, wherein the magnetic nanoparticles undergo a magnetic fractionation step prior to deposition on the substrate. A method of forming a film of inorganic nanoparticles on a substrate,
Preparing a suspension of inorganic nanoparticles each formed at least partially within a protein shell within a carrier fluid;
Depositing the fluid suspension on a substrate surface as droplets having a volume of less than about 1 nl and obtaining a film on the substrate as a dry residue of the deposited fluid suspension;
A method comprising the steps of:   49. The method of claim 48, wherein the fluid suspension is deposited on the substrate using an ink jet printing method.   50. The method of claim 48 or claim 49, wherein the protein shell is carbonized by subsequently exposing the substrate to a high temperature in excess of 300 <0> C.   50. The method of claim 48 or claim 49, wherein the polymeric shell is dissipated by subsequently pyrolyzing the nanoparticle film at a temperature greater than about 500 <0> C. The average surface roughness R _a of the substrate is less than about 1 nm, the method according to any one of claims 51 claim 48. The average surface roughness R _a of the substrate ranges from about 5nm to about 20 nm, the method according to any one of claims 51 claim 48.   54. A method according to any one of claims 48 to 53, wherein the substrate is treated to promote dispersion of a suspension of added nanoparticles.   55. The method of claim 54, wherein the treatment comprises a chemical treatment, a mechanical treatment, or a radiation treatment.   56. The method of claim 55, wherein the radiation treatment includes exposure of the substrate to UV light.   57. A method according to any one of claims 48 to 56, wherein the film is processed following deposition of the nanoparticles on the substrate.   58. The method of claim 57, wherein the film is annealed after deposition of the nanoparticles on the substrate.   59. A method according to any one of claims 48 to 58, wherein the thickness of the film does not vary so deeply that it exceeds about 3 diameters of the constituent particles (including any encapsulated shell). The average surface roughness R _a of the film is not greater than about 3 diameter (including any encapsulating shells), The method according to any one of claims 59 claim 48.   61. A method according to any one of claims 48 to 60, wherein the inorganic nanoparticles comprise a magnetic material or a semiconductor material.   64. The method of claim 61, wherein the inorganic nanoparticles comprise a semiconductor material.   64. The method of claim 62, wherein the inorganic nanoparticles are semiconductor nanoparticles comprising CdS, CdSe, CdTe, ZnS, ZnSe, or ZnTe encapsulated by apoferritin or DPS.   64. A method according to any one of claims 48 to 63, wherein the composition of encapsulated nanoparticles undergoes a microporous membrane filtration step prior to deposition on the substrate.   65. A method according to any one of claims 48 to 64, wherein the magnetic nanoparticles have a diameter of 20 nm or less (or a maximum diameter in the case of non-spherical particles).   66. A method according to any one of claims 48 to 65, wherein the protein shell comprises apoferritin or DPS.   67. A method according to any one of claims 48 to 66, wherein the composition of encapsulated nanoparticles undergoes a microporous membrane filtration step prior to deposition on the substrate.   68. The method of claim 67, wherein the pore size of the membrane filter is in the range of 0.02 to 10 [mu] m.   69. The method of claim 67 or claim 68, wherein the membrane comprises polyethersulfone or polyvinylidene. A method of forming a protein thin film on a surface of a substrate,
Having a thickness of less than 10 times the diameter of the constituent protein particles through a substantially thin film;
Preparing a suspension of protein particles that have undergone a membrane filtration step in a carrier fluid;
Depositing a fluid suspension on the substrate surface as droplets having a volume of less than about 1 nl and obtaining the film on the substrate as a dry residue of the deposited fluid suspension;
A method comprising the steps of:   71. The method of claim 70, wherein the fluid suspension is deposited on the substrate using an ink jet printing method. Surface roughness R _a of the substrate is less than about 1 nm, the method according to any one of claims 70 or claim 71. Surface roughness R _a of the substrate ranges from about 5nm to about 20 nm, The method of claim 70 or claim 71.   74. The method of any one of claims 70 to 73, wherein the substrate is treated to promote dispersion of the suspension of added protein particles.   75. The method of claim 74, wherein the treatment comprises a chemical treatment, a mechanical treatment, or a radiation treatment.   76. The method of claim 75, wherein the radiation treatment includes exposure of the substrate to UV light.   77. A method according to any one of claims 70 to 76, wherein the film is processed following deposition of the protein particles on the substrate.   78. A method according to any one of claims 70 to 77, wherein the film is annealed after the deposition of the protein particles.   79. A method according to any one of claims 70 to 78, wherein the thickness of the film does not vary so deeply that it exceeds the three diameters of the constituent protein particles throughout the film. The surface roughness R _a of the film is not greater than about 3 particle size, method of any one of claims 79 claim 70.   81. The method of any one of claims 70 to 80, wherein the protein is apoferritin or DPS.   82. A method according to any one of claims 70 to 81, wherein the composition of protein nanoparticles undergoes a microporous membrane filtration step prior to deposition on the substrate.   83. The method of claim 82, wherein the membrane filter has a pore size in the range of 0.02 to 10 [mu] m.   84. The method of claim 82 or 83, wherein the membrane comprises polyethersulfone or polyvinylidene. A magnetic recording device having a film of magnetizable nanoparticles,
Magnetizable nanoparticles are prepared as a suspension in a carrier fluid and deposited on the substrate surface as droplets having a volume of less than about 1 nl, and the magnetizable nanoparticles as a dry residue of the deposited fluid suspension Forming a film of particles,
A device characterized by that.   86. The magnetic recording device of claim 85, wherein the nanoparticles are deposited on the substrate by an ink jet printing method.

Images