WO1998032902A1

WO1998032902A1 - Method of manufacturing crystalline particles on a support or a substrate

Info

Publication number: WO1998032902A1
Application number: PCT/EP1998/000392
Authority: WO
Inventors: Guy R. Ester; Bernd Peter Ludwig Grimm; Erik Middelman
Original assignee: Ester Guy R; Bernd Peter Ludwig Grimm; Erik Middelman
Priority date: 1997-01-22
Filing date: 1998-01-21
Publication date: 1998-07-30

Abstract

The invention pertains to a method of crystallization of particles wherein crystal seeds are nucleated within a cage, characterized in that crystalline particles with a size larger than the cavity of the cage are formed, after a) transferring the crystal seeds into the cage, providing the cage on a support, followed by opening of the cage, or b) providing the cage on a support, opening the cage, followed by transferring the crystal seeds in the opened cage, or c) providing the cage on a support, transferring the crystal seeds to the cage, followed by opening of the cage. The crystalline particles may be transferred to a substrate. The support or substrate with the crystalline particles on it may be applied in data storage devices.

Description

METHOD OF MANUFACTURING CRYSTALLINE PARTICLES ON A SUPPORT OR A SUBSTRATE

The invention pertains to a method of manufacturing crystalline particles on a support or a substrate and to a data storage device containing the same.

The invention is in the field of data storage systems, such as magnetic tapes, computer disks, CDs, magnetic cards, and the like. It is an object of this invention to provide data storage systems with ultra-high-density data storage. Magnetic tape and other flexible magnetic data storage devices are usually made of polymeric film onto which magnetic particles are coated. In a typical method a drawn PET, PEN, or PPTA film is coated with a mixture of magnetic particles, a polymeric binder, and a solvent. The magnetic particles are obtained by milling and sieving a suitable mineral. In another method the magnetic mineral is vaporized onto the support. This method can be used for flexible magnetic devices and for magnetic hard disks, for instance, by electron beam vaporization of cobalt-nickel layers onto a PET film or onto an aluminum disc. In this process the cobalt-nickel forms a continuous layer of some hundreds of nanometers. Because the magnetic particles are relatively large, there is a large size distribution, and the magnetic particles are not domain-separated, leading to supports with limited data storage capacity, typically up to 0.1 Mb/mm². In order to obtain ultra-high-density data storage systems to attain a high density of magnetic particles, however, it is necessary to have the magnetic particles very close to each other. A prerequisite of such systems is the use of relatively small magnetic particles which are positioned as regularly and as close together

CONFIRMATION COPT as possible, and which are preferably domain-separated. The present invention offers a method of achieving these goals.

The invention therefore relates to a method of manufacturing crystalline particles wherein crystal seeds are nucleated within a cage, characterized in that the crystalline particles with a size larger than the cavity of the cage are formed, after a) transferring the crystal seeds to the cage, providing the cage on a support, followed by opening of the cage, or b) providing the cage on a support, opening the cage, followed by transferring the crystal seeds to the opened cage, or c) providing the cage on a support, transferring the crystal seeds in the cage, followed by opening of the cage.

This method allows the regular introduction of a cage onto a support, after which the magnetic crystalline particles are grown to a desired size at the sites of the cage. In this manner relatively small particles can be brought with well-defined domain separation into close proximity with each other.

The cage is a compound which has a cage-like structure in which crystal seeds can nucleate and grow to crystalline particles of a desired size.

Suitable cages are, for instance, cryptates, calixarenes, hemispherands, buckyballs, buckytubes, and proteins with a spherical tertiary structure.

Proteins are particularly suitable because their cavity can be large enough to be used as growing site for the crystalline particles. An extremely suitable protein is ferritin, apoferritin, or derivatives thereof. Ferritin occurs in the spleen and liver of higher animals, for instance in horse spleen, and is commercially available.

The term "crystal seeds" means ions, atoms, molecules, or aggregates thereof, which can nucleate and grow to a crystalline particle. The use of ferritin and apoferritin for the synthesis of inorganic nanophase materials has been disclosed in US patent 5,358,722, and by Meldrum et al. in Nature, Vol. 349, pp. 684-687 (1991 ). The synthesis of magnetic minerals by using these proteins has been disclosed by Meldrum et al. in Science, Vol. 257, pp. 522-523 (1992). According to these references, ferritin is a hollow sphere of 8-9 nm internal diameter containing native mineral ferrihydrite. The ferrihydrite can be removed from the ferritin by dialysis, after which apoferritin remains, which is the same protein hollow sphere without a mineral. By a redox-driven reaction within apoferritin of redox- active metal ions, for instance manganese oxide or uranyl oxyhydroxide, the protein is reconstituted with another mineral than the native ferrihydrite. These known methods to reconstitute ferritin result in crystalline particles which fit into the cavity of ferritin, and thus have a maximum size of 8-9 nm. Although such magnetic particles can be synthesized and can be applied as catalyst or in electro-optical devices, they are too small to be ferromagnetic and are only paramagnetic or superparamagnetic, and therefore not suitable for data storage. Further, no method has been disclosed which uses this technique to obtain domain-separated particles for for high- density data storage.

One aspect of the invention is coating the cage, preferably a protein cage, onto a support. By coating the protein cage onto the support, followed by growing the crystalline particles in the (opened) cage, domain separation of the crystalline particles can be achieved. The technique of coating proteins onto a support as such is well-known in the art, and is, for instance, a common method for making diagnostic devices. Coating of ferritin onto a polycarbonate support has been disclosed in J. Colloid and Interface Sci., Vol. 78, pp. 144 (1980). The polycarbonate support can be immersed in a solution of ferritin, after which a mono-layer of ferritin is adsorbed onto the hydrophobic surface of the support.

The present invention solves the problem of obtaining magnetic particles which are suitable for ultra-high-density data storage by replacing native ferrihydrite with another (magnetic) mineral using (apo)ferritin as the cage, coating the ferritin onto a support, and allowing such a mineral to grow to a desired size larger than the cavity of the cage.

The invention further provides a method of growing crystals in a cage, characterized in that the crystals are metals and the cage is provided on a support.

In one embodiment of the invention ferritin is coated onto a support, after which ferrihydrite is removed, or apoferritin is coated onto the support directly, and crystalline seeds are nucleated and grown in the cavity of apoferritin to maximally the size of the cavity, which is 8-9 nm for (apo)ferritin. The shell of the protein ferritin is opened to allow the crystal to grow to a size larger than the cavity of ferritin.

In another embodiment the crystal seeds are introduced into the cavity of apoferritin, after which the protein is coated onto the support. The cage is then opened, after which the crystalline particles are grown to a size larger than the cavity of the cage.

According to either of the above-mentioned methods the cage can be opened immediately after bringing the crystal seeds into the cavity and the crystal then grows to the desired size, or crystals can be first grown to maximally the size of the cavity, after which the cage is opened and the crystal can be grown further to the desired size. Optionally, the cage can be removed after opening thereof.

Opening of the cage can be performed by pyrolysis in an inert atmosphere, by treatment (immersion) with suitable solvents such as ammonia, by ozone-UV treatment, by corona discharge, or by plasma etching techniques such as RIE (reactive ion etching).

In another embodiment ferritin is coated onto the support and ferrihydrite is removed, or apoferritin is coated onto the support directly, after which the cage is opened, crystal seeds are transferred to the opened cage and allowed to nucleate, after which the crystal is grown to the desired size. The opened cage can be removed after or before the growth of the crystal to the desired size as desired.

It is also possible to coat the cage on a support, after which the array of cages is transferred to another support.

In another embodiment a substrate is applied onto the crystalline particles after having been grown to a particle size larger than the cavity of the cage, after which the support and, optionally, the opened cage are removed.

In a further embodiment a hydrophobic binder layer is applied between the cage and the support. Preferably, such a layer comprises a group which is able to covalently bond with the cage. More preferably, such a group comprises an oxiranyl groups, such as epoxysilane or oxiranyl containing polyethers and (fluoridated) bisphenol A derivatives.

For data storage purposes the crystalline particles are ferro-magnetic. To maintain the domain separation, the crystalline particles are preferably grown in a direction perpendicular to the support. Anisotropic crystal growth is possible by habit modification, for example, by use of dopants. Another method for maintaining domain separation between the crystalline particles is the introduction of, preferably non-magnetic, trace impurities prior to, or during growth. Due to segregation of the impurities to the crystal growth interface during growth, a boundary of said impurities will exist between neighbouring crystalline particles, thus ensuring domain separation. A method for obtaining magnetic domain separation is etching of the crystalline particles formed.

The crystals can be grown by using conventional techniques, such as super-saturated vapor crystallization, electroless plating, electrolytic crystallization, ALE (atomic layer epitaxy), LFE (liquid phase epitaxy), CVD (chemical vapor deposition), MOCVD (metal organic CVD), PVD (physical vapor deposition), and the like. Methods which can be used at relatively low temperatures are preferred.

Suitable supports for the purpose of this invention are plastics, polymeric films, non-ferro-magnetic metals such as aluminum, silicon, and glass. In the case of ferritin as a cage, glass is preferred because of the ease with which a regular and high-density protein coating can be obtained.

Suitable substrates are materials which are used as a support for data storage, such as polymeric films of PET, PEN, or PPTA. A mono-layer of ferritin can be obtained by Langmuir-Blodgett coating or by applying a hydrophobic support, for example polystyrene, onto a drum which is immersed in a ferritin solution. When the crystalline particles have been grown to the desired size in a manner as explained above, an oxiranyl- coated film, for instance a PET film, is pressed against the upper part of the drum, after which the ferritin mono-layer is transferred to the film, because ferritin binds more strongly to the oxiranyl-containing film than to the hydrophobic support.

The invention further pertains to a data storage device comprising a support or a substrate with on it the crystalline particles as obtained by any one of the above-mentioned methods. After deposition of the crystalline particles on the support or the substrate by one of the presently claimed methods, the data storage device is finished by methods commonly known in the art.

The invention is further illustrated by the following examples.

Example I

Melinex® type 901 W with a thickness of 36 μm (PET film) was coated by reverse roll coating with a thickness of 10 nm with an epoxy-coating according to US patent 3,879,430, having a thickness of 10 nm, of the formula:

The coated film was immersed in a solution of 4g of apoferritin in 11 of 0.15M sodium chloride solution in water at 50°C. After 5 min the film was immersed in water for 1 min and then in a solution of 100 g of cobalt acetate, 5 g of dimethyl aminoborane (DMAB), 50 g of sodium citrate, 50 g of lactic acid, and 3 g of thiodiglycol in 1 I of water for 5 min. The film was immersed in distilled water and dried, after which the ferritin derivative was opened by removing part of the protein using oxygen plasma etching. The film was immersed in an electroless cobalt plating solution of 100 g of cobalt acetate, 5 g of DMAB, 50 g of sodium citrate, 50 g of lactic acid, and 3 g of thiodiglycol in 1 I of water, after which the crystals were allowed to grow to a size of 11 nm. The film was rinsed with water and provided with a protective coating of DLC (diamond-like carbon).

Example 2

A solution was prepared of 4 g of apoferritin, 25 g of cobalt sulfate, 4 g of DMAB, 25 g of sodium succinate, and 15 g of sodium sulfate in 11 of water. In the ferritin cobalt crystals were formed with a size of 5-8 nm. The ferritin derivative was dissolved in water at a pH 5 at 60°C. Discs of temperature- resistant glass (Corning 7059) were provided with a 100 nm layer of SiC by CVD. These glass discs were immersed in a solution of the ferritin derivative, to form a mono-molecular layer of ferritin at the surface. The discs were slowly removed from the solution and then slowly immersed in distilled water and slowly removed therefrom. The discs were dried and heated to 900°C in an inert atmosphere. During this treatment, the protein was removed, the cobalt crystals remaining on the SiC surface. The discs were introduced into a vacuum chamber, and the pressure was lowered to 10^"6 Pa. A cobalt source was heated by electron-beam evaporation, and in an atmosphere of super-saturated cobalt vapor at 900°C cobalt crystals were allowed to grow on the discs to a size of 10 nm. The discs were removed, cooled, and protected with a non-magnetic film of 2-12 nm of DLC.

Example 3

A solution of 4 g of apoferritin in 1 I of water was brought to pH 7.5 by

0.15M sodium chloride, 0.1 M Tris, and hydrochloric acid. A glass disc (Corning 7059) with a surface ruggedness <10 Ra (nm) was coated with a standard solution of the epoxy-coating of Example 1 in methylethylketone. The coating was dried and the disc was immersed in the apoferritin solution for 10 min. The disc was immersed in a solution of ethanol and water for 1 min, after which the apoferritin was opened by immersion in an aquous solution of hydrochloric acid in water having a pH 3.5. The disc was immersed in the cobalt bath according to Example 1 for 5 min, after which cobalt crystals were formed in the opened protein cage. The cobalt and DMAB concentrations were adjusted to obtain a crystal growth of 2 nm/min. After the cobalt crystals had reached a size of 10 nm, the disc was removed, rinsed with distilled water, and dried. A 5 nm coating of DLC was applied by sputtering to protect the surface.

Example 4

A glass disc (Corning 7059) was coated with 5 nm of aluminum by MOCVD. The surface was made hydrophobic by plasma polymerization of butadiene to polybutadiene. The surface was coated with a mono-layer of ferritin by immersing the disc in a solution of cobalt crystal containing ferritin. The disc was pyrolyzed at 600°C and cooled to 200°C, after which cobalt crystals were grown by MOCVD of cobalt carbonyl [Co(CO)₈] to a size of 10 nm. A protective DLC coating of 5 nm thickness was applied, and onto it a 2 nm thick lubricant layer was coated by plasma polymerization of freon.

Claims

Claims:

1. A method of manufacturing crystalline particles wherein crystal seeds are nucleated within a cage, characterized in that crystalline particles with a size larger than the cavity of the cage are formed, after a) transferring the crystal seeds to the cage, providing the cage on a support, followed by opening of the cage, or b) providing the cage on a support, opening the cage, followed by transferring the crystal seeds to the opened cage, or c) providing the cage on a support, transferring the crystal seeds to the cage, followed by opening of the cage.

2. The method according to claim 1 wherein the crystal seeds are tranferred to the cage, followed by providing the cage on a support, after which the cage is opened and crystalline particles with a size larger than the cavity of the cage are formed.

3. The method according to claim 1 wherein the cage is provided on the support, after which the cage is opened and the crystal seeds are transferred in the opened cage, after which crystalline particles with a size larger than the cavity of the cage are formed.

4. The method according to any one of claims 1-3 wherein a substrate is applied onto the crystalline particles after they have been grown to a particle size larger than the cavity of the cage, after which the support and, optionally, the opened cage are removed.

5. The method according to any one of claims 1-4 wherein a hydrophobic binder layer is applied between the cage and the support.

6. The method according to claim 5 wherein the hydrophobic binder layer comprises a group which is able to covalently bond with the cage.

7. The method according to claim 6 wherein the hydrophobic binder layer comprises an oxiranyl group.

8. The method according to any one of claims 1-7 wherein the cage is a protein cage, preferably ferritin, apoferritin, or a derivative thereof.

9. The method according to any one of claims 1-8 wherein the crystalline particles having a size larger than the cavity of the cage are ferromagnetic.

10. A method of growing crystals in a cage, characterized in that the crystals are metals and the cage is provided on a support.

11. A data storage device comprising a support or a substrate with on it the crystalline particles as obtained by the method according to any one of claims 1-9.