JP2000345332A - Manufacture of layer-shaped cluster - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cluster assembly useful as a ferromagnetic material, antiferromagnetic material, superconductive material, high sensitivity sensor magnetic recording substance, nanomagnet, or the like. SOLUTION: When vapor generated in a sputter chamber 10 and kept in a monodispersed state is supplied to a cluster heaping chamber 40 via a cluster developing chamber 20 and a differential evacuating chamber 30, and heaped on a substrate 42, a reactive gas, metallic vapor, one or two or more kinds of compound vapors introduced to the cluster heaping chamber 40, are reacted with a cluster in the monodispersed state. O2, N2, O3, H2 gaseous hydrogen oxide, or the like, is used as the reactive gas, carbon, Cu, Ag, Au, Al, Si, Ge, or the like, is used as the metal vapor, and an oxidized metal evaporated by sputtering, a transition metal carbonyl or an alcohol is used as the compound vapor. The surface of the cluster in the monodispersed state is modified or covered with an oxide, a nitride, a semiconductor, or different metal, or the like, and the essential function as a cluster is enhanced or another function is given to the cluster.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a layered cluster having an enhanced function or a different function provided by surface modification or surface coating with an oxide, nitride, dissimilar metal, compound or the like.

[0002]

2. Description of the Related Art Clusters, ultrafine particles, and the like are produced by vapor-phase synthesis in which raw materials are condensed after vaporization and evaporation, colloidal methods in which a precipitate from an electrolyte solution is stabilized by a surfactant, and spraying / heating a solution containing metal ions. It is manufactured by an aerosol method for decomposition, a gas atomization method for injecting a liquid metal and an inert gas from a nozzle, and a mechanical milling method for mechanically pulverizing a bulk material. The produced clusters and ultrafine particles exhibit properties not found in bulk materials. Above all, below the critical size, nano size, fluctuations in physical properties and structures become remarkable, exhibiting unique physicochemical properties different from bulk materials, and electronics, magnetic engineering,
It is expected to be applied in fields such as catalytic chemistry and biological / medical science. The critical size depends on the target property,
In the present specification, based on a particle size of about 10 nm, a size smaller than that is referred to as a cluster, and a size larger than that is referred to as an ultrafine particle.

The aerosol method, mechanical milling method, gas atomizing method and the like are suitable for mass production of clusters and ultrafine particles, but cannot control the cluster size to 10 nm or less where a new function unique to nano size can be expected.
The colloidal method has an advantage that a cluster of 10 nm or less can be synthesized in a large amount, but since the surface of the cluster is covered with an organic surfactant, there is a tendency that the functionality unique to the cluster is not sufficiently exhibited. In the gas phase method using a vacuum device, clusters are formed in a clean atmosphere. As a typical gas phase method, a gas evaporation method in which raw materials are vaporized in an atmosphere of an inert gas such as Ar or He and nucleation and growth of clusters and ultrafine particles are known. Ultrafine particles having a particle size in the range of 10 nm to 1 μm can be produced in a large amount by the gas evaporation method, but it is difficult to control the particle size distribution.

[0004] In order to stabilize chemically active ultrafine particles, a method of gradually oxidizing with the residual oxygen in a vacuum chamber or oxygen leaking into the vacuum chamber after forming the ultrafine particles to form an oxide coating on the surface of the fine particles, A method is adopted in which a mixed cluster generated by simultaneous evaporation of the cluster constituent material and the non-mixed material is subjected to heat treatment to precipitate and disperse the mixed cluster. However, these methods cannot control the cluster size and the thickness of the surface layer when producing a cluster having a size of 10 nm or less.
For example, in the case of ultrafine Co particles coated with oxide by the slow oxidation method, it is difficult to control the degree of surface oxidation and the thickness of the oxide because CoO and Co ₃ O ₄ coexist, and the electric conductivity of the surface coating layer is low. It is difficult to optimize additional functions such as optical characteristics.

[0005]

When a cluster is used directly or as a cluster as a functional material or a functional element, the fusion and coarsening of the cluster are suppressed in order to maintain the functionality specific to the size. It is necessary to form irregular or regular arrangement on the substrate in a predetermined pattern. However, clusters of the size targeted by the present invention have a higher surface activity than ultrafine particles, and furthermore have a significant lattice softening and melting effect on the surface. Ordering was difficult. When a cluster or a cluster aggregate is used as a functional material or a functional element, a process for further enhancing the characteristics of the cluster or imparting a different function is required.
However, this type of processing tends to impair the original characteristics of the cluster.

[0006]

SUMMARY OF THE INVENTION The present invention has been devised to solve such a problem, and is intended to clean a cluster with an oxide, a dissimilar metal or the like which is unlikely to impair the original characteristics of the cluster. Ferromagnetic materials, antiferromagnetic materials, superconducting materials, highly sensitive sensors, magnetic recording media, An object of the present invention is to produce layered clusters and cluster aggregates that are used in a wide range of fields as magnets and exhibit a stable composite function.

In order to achieve the object, the present invention condenses gas atoms generated by sputtering in a rare gas with a sputtering source maintained in a clean atmosphere as a target to form a monodispersed cluster. , The gas is sent to the cluster deposition chamber via the cluster growth chamber and the differential exhaust chamber, and is deposited on the substrate installed in the cluster deposition chamber.
The coating is characterized by reacting one or more of metal vapor and compound vapor with a cluster in a monodispersed state. Reactive gases include O ₂ , N ₂ , O ₃ , H ₂ , and hydrocarbon gases, and metal vapors include carbon, Cu, Ag, and the like.
Au, Al, Si, Ge, semiconductors, and the like include metal oxides, transition metal carbonyls, and alcohols that are sputter evaporated as compound vapor.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, oxidation is performed only on the surface of a monodisperse cluster generated by a condensed cluster source in a plasma gas.
After surface modification such as nitriding, or by passing through a vapor of a dissimilar metal, semiconductor, compound or the like to form a surface layer, it is deposited and aggregated on a substrate. Therefore, a function for surface modification and surface coating is provided in the cluster deposition chamber. Specifically, a gas such as O ₂ or N ₂ is introduced into the cluster deposition chamber through a flow control valve to form an oxide film or a nitride film on the surface of the cluster in a monodispersed state. Further, according to the high frequency induction type sputtering method, rare gas ions can be effectively generated even in a low-pressure rare gas atmosphere of about 10 ⁻⁴ Torr, and the target material is sputtered in a clean atmosphere. In this way, the vaporized metal or semiconductor vapor collides with the cluster beam to form a metal layer or a semiconductor layer on the cluster surface.

In the present invention, for example, an apparatus having a sputtering chamber 10, a cluster growth chamber 20, a differential exhaust chamber 30, and a cluster deposition chamber 40 is used as shown in FIG. In the sputtering chamber 10, for example, a sputtering source for vaporizing a magnetic metal is installed as opposed targets 11a and 11b. Targets 11a and 11b have a diameter of 8
A disk having a thickness of about 0 mm and a thickness of about 5 mm is used. The material of the targets 11a and 11b is not particularly limited as long as it is an element constituting the cluster to be produced, and the degree of freedom in selecting the material is greatly improved. The constituent metal simple substance is the most typical material, and Au, Ag, Cu, Al, Fe, N
There are pure metals such as i, Co, Pd, Pt, W, Nb, and Ti. Semiconductors such as Si, Ge, and graphite, and insulators such as oxides can also be used.

The sputtering chamber 10 is provided with a turbo-molecular pump 12 to suppress the entry of impurity gas remaining in the chamber.
It is evacuated to a vacuum of 0 ^-7 Torr. Next, while introducing a large amount of Ar gas or He / Ar mixed gas into the sputtering chamber 10 from the carrier gas introduction nozzle 13 provided on the side wall, the mechanical booster pump 3
In step 1, the sputtering chamber 10 is evacuated at high speed. The flow rate of the Ar gas or the He / Ar mixed gas flowing into the sputtering chamber 10 is adjusted so that the partial pressure of the Ar gas or the He / Ar mixed gas in the sputtering chamber 10 becomes 1 to 10 Torr. Under this condition, for example, power of 400 W or less
When applied to the cathodes 1a and 11b (cathodes), the surfaces of the targets 11a and 11b are sputtered with ionized Ar, and the sputtering source is vaporized.

The vaporized atoms generated in the sputtering chamber 10 are A
cluster growth chamber 20 with a carrier gas such as r, He, etc.
Is forcibly transported. Vaporized atoms are transferred to Ar
Loses kinetic energy by colliding with He or He (in other words,
Cools) and condenses during repeated collisions. As a result, clusters nucleate and grow. The monodispersity of the generated clusters is maintained at about two orders of magnitude higher than that of a normal sputter deposition method, and the differential exhaust chamber 30 is passed through the skimmer 21 so that the growth of the generated clusters ends instantaneously. It is secured by high-speed exhaust that pulls out clusters. In order to rapidly cool the cluster in the cluster growth chamber 20 and generate a large number of nuclei, it is effective to surround the cluster growth chamber 20 with a cooling jacket 22 that circulates liquid nitrogen, cold water, and the like as necessary. The nucleation and growth of the clusters are possible even in the atmosphere cooling in which the cooling jacket 22 is omitted.

The differential exhaust chamber 30 is divided into a plurality of compartments by a partition provided with skimmers 32 and 33. Skimmer 3
The compartment between the second skimmer 33 and the outlet skimmer 33 is evacuated by a turbo molecular pump 34 to a degree of vacuum of about 10 ^-2 Torr. By this evacuation, the combined growth of the clusters passing between the skimmer 32 and the exit skimmer 33 is suppressed.
Clusters form an atmosphere with a higher degree of vacuum (specifically, 1 atmosphere).
(0 ^-5 to 10 ^-7 Torr.) Is ejected from the exit skimmer 33 into the cluster deposition chamber 40. At this time,
The clusters are in a monodispersed state in which nucleus growth and coalescence growth are suppressed, and form a beam due to the pressure difference between the differential evacuation chamber 30 and the cluster deposition chamber 40, and form a cluster.
Flows into zero. Therefore, processing such as surface modification and surface coating can be performed on the clusters in a monodispersed state in the cluster deposition chamber 40.

When the surface of the cluster is coated with a compound such as an oxide, a nitride, or a carbide, a small amount of O ₂ gas, N ₂ gas, or carbon dioxide is supplied from a gas introduction nozzle 41 provided on the side wall of the cluster deposition chamber 40. Introduce hydrogen gas and the like. These gases have a partial pressure in the cluster deposition chamber 40 of 10 ⁻⁴ to 10 ⁻⁴ .
The flow rate is adjusted to about 1 SCCM or less so as to be about 10 ^-6 Torr. When the cluster surface is modified with carbon, dissimilar metal, semiconductor, compound, etc., the vapor of carbon, dissimilar metal, semiconductor, compound, etc. is removed by using a high frequency induction type sputtering device 50 or the like arranged below the cluster deposition chamber 40. Generate or introduce a metal carbonyl to react with the cluster. At this time, it is preferable to maintain the partial pressure in the room at a level of 10 ⁻³ to 10 ⁻⁴ Torr. The cluster whose surface has been modified or coated is applied to a substrate 42 disposed in the cluster deposition chamber 40.
Deposit on top. The deposition rate and the deposited film thickness of the clusters deposited on the substrate 42 are measured by a quartz oscillator type film thickness meter 43 installed in the cluster deposition chamber 40.

The clusters whose surface is modified or coated in this way include, for example, a ferromagnetic Co cluster coated with CoO and an antiferromagnetic Cr coated with Cr ₂ O _3.
Clusters, such as superconducting Nb clusters surface-modified with Ag or Cu. Even if these clusters are aggregated by deposition on the substrate 42, there is no secondary growth due to mutual fusion, and the initial size is maintained. Therefore, magnetic characteristics and electric conduction characteristics sensitive to the cluster size can be controlled. In addition, by controlling the electrical conductivity and magnetism of the surface modification layer, the electrical and magnetic coupling between the clusters and the tunnel barrier are controlled. Therefore, a high-sensitivity sensor using the cluster surface, a ferromagnetic cluster with a large magnetization A magnetic recording medium whose surface is modified with an antiferromagnetic material, a nanomagnet for drug delivery with a high magnetic flux density at room temperature, and the like can also be manufactured.

[0015]

EXAMPLE A target having a purity of 99.9% Co was used as a target 11a.
11b and targets 11a and 11b are 1
They were placed in the metal vapor generation chamber 10 at intervals of 0 cm or more. Ar gas at a flow rate of 500 SCCM was sent from the carrier gas introduction nozzle 13 into the sputtering chamber 10, and the atmospheric pressure of the sputtering chamber 10 was maintained at a level of 1 Torr. The inlet side of the differential exhaust chamber 30 is 10 to 100 mTorr.
-10 mTorr., The cluster deposition chamber 40 is 10 ^-3 -10
^-4 Torr. A power of 300 W was applied to the targets 11a and 11b by a DC magnetron method, and Co vapor was generated from the targets 11a and 11b. The Co cluster was grown in the cluster growth chamber 20 and deposited on the substrate 42 of the cluster deposition chamber 40 via the differential evacuation chamber 30. O ₂ at a flow rate of 0.4 SCCM into the cluster deposition chamber 40
By introducing gas and reacting the O ₂ gas with the Co cluster before deposition, an oxide layer was formed on the surface of the Co cluster.

In the obtained cluster, as shown in the electron micrograph of FIG. 2, an oxide layer having a thickness of about 1.5 nm was formed on the surface of a Co cluster core having an average diameter of 10 nm. In addition, fc is shown in the electron diffraction pattern of the cluster assembly.
Since diffraction rings of the c-Co phase and the NaCl type-CoO phase were observed, it is considered that the surface coating layer was CoO. When the carbon, Cu or Ag was evaporated by the high frequency induction type sputtering apparatus 50 to cover the cluster in the cluster deposition chamber 40, a cluster having a similar layer structure was generated.

The flow rate of the O ₂ gas introduced into the cluster deposition chamber 40 is changed in the range of 0 to 1 SCCM, and
Effect of O on electrical conductivity and magnetic properties of cluster assembly
₂ The effect of gas flow was investigated. As seen in FIGS. 3 (a) showing the relationship between the electric resistance ρ and the temperature T, O ₂ absolute value of the electric resistance ρ increases with increasing gas flow rate, if less O ₂ gas flow metals From a typical temperature change (positive temperature coefficient of resistance) to a semiconductor-like temperature change (negative temperature coefficient of resistance) in the case of a large amount, and minimization of electrical resistance which is presumed to be due to the localization of electrons in the middle A phenomenon was observed. The aspect of the change in the electric conduction characteristics depending on the O ₂ gas flow rate corresponds to the fact that the CoO layer changes from a discontinuous film to a continuous film, and the thickness of the CoO layer further increases. When the flow rate of the O ₂ gas was 0.4 SCCM or more, almost no increase in the absolute value of the electric resistance was detected. This indicates that the thickness of the oxide film of the multilayer cluster has an upper limit, and that a stable oxide film is formed.

As can be seen from FIG. 3B showing the relationship between the electric conductivity σ and the reciprocal of the temperature T, the log σ−1 / T
Are clearly separated in the high and low temperature ranges, suggesting that the dominant electrical conduction mechanism can be controlled in each temperature range. Next, 500 spc
Ar gas of M, O of 1 SCCM in the cluster deposition chamber 40
The relationship between the magnetoresistance and the temperature was investigated for the CoO-coated Co cluster aggregate produced by introducing _two gases. As can be seen from the investigation results in FIG. 4, the magnetoresistance effect sharply increased at low temperatures. The rapid increase in the magnetoresistance effect is considered to be due to the Coulomb blockade effect due to the charging of the nano-sized clusters.

Such a characteristic of the temperature change of the electric conduction characteristics and the magnetoresistance and the clear separation of the temperature region are not observed in the conventional granular film, but are peculiar phenomena observed in the cluster aggregate manufactured according to the present invention. From
This is considered to depend on the monodispersity of the cluster size and the uniformity of the thickness of the oxide film. Further, the flow rate 2
Ar gas at a flow rate of 50 SCCM and helium gas at a flow rate of 550 SCCM were introduced, and a flow rate of 1 SC was introduced into the cluster deposition chamber 40.
O ₂ gas of CM was introduced to form a layered cluster having a total average particle size of 6 nm. Also, the flow rate 5
Ar gas of 00 SCCM was introduced and the cluster deposition chamber 4
At 0, O ₂ gas at a flow rate of 1 SCCM was introduced to form a layered cluster having a total average particle size of 13 nm.

With respect to the obtained cluster aggregate of each particle size, a magnetization curve at 5K was examined. As can be seen from the investigation results in FIG. 5, in the CoO-coated Co cluster aggregate having an average particle diameter of 6 nm, the coercive force when cooled without a magnetic field (ZFC) is H _C = 2.4 kOe, and when cooled in a magnetic field (FC). )
The coercive force of the has become very large and H _C = 5.0kOe. Further, the hysteresis curve of the sample FC cooled in the magnetic field is asymmetric with respect to the positive and negative external magnetic fields, and a strong exchange interaction between the ferromagnetic Co core and the antiferromagnetic CoO surface layer works. It is suggested that

As shown in FIG. 6, the coercive force H _C and the shift amount ΔH _C of the hysteresis curve increase according to the O ₂ gas flow rate, but are saturated at 0.5 SCCM. This also suggests that there is an upper limit to the thickness of the oxide film as in the measurement result of the electric resistance. Further, there is a clear correlation between the coercive force H _C and the shift amount ΔH _C , as shown in FIG. 7, and the exchange between the ferromagnetic phase (Co core) and the antiferromagnetic phase (CoO coating). It quantitatively shows that the interaction not only shifts the hysteresis curve, but also significantly increases the coercivity itself. From the survey results on magnetic properties,
The effect of assembling the layered clusters in which the surface of the monodispersed clusters is covered with an oxide film having a substantially constant thickness is confirmed. When the ferromagnetic Co cluster was coated and modified with an antiferromagnetic substance other than the oxide, a cluster aggregate having a high coercive force even at room temperature was obtained.

[0022]

As described above, in the present invention, the monodispersed clusters generated by the condensation method in plasma gas are reacted with a reactive gas, a metal vapor, a semiconductor vapor, a compound vapor, or the like to form the clusters. After surface modification or surface coating, it is deposited on the substrate. According to this method, the clean surface of the cluster having a particle size of 10 nm or less is coated with an oxide, a nitride, a dissimilar metal, or the like. The present invention provides a functional material or a functional element applied to a cluster and used in a wide range of fields as a ferromagnetic material, an antiferromagnetic material, a superconducting material, a high-sensitivity sensor, a magnetic recording medium, a nanomagnet, and the like.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an apparatus for depositing a condensed cluster in plasma gas used in the present invention.

FIG. 2 is an electron micrograph of a CoO-coated Co cluster.

FIG. 3 is a graph showing a relationship between electric resistance (a) and electric conductivity (b) of CoO-coated Co cluster aggregate and temperature.

FIG. 4 is a graph showing the relationship between the magnetoresistance and temperature of a CoO-coated Co cluster aggregate.

FIG. 5 is a graph showing a magnetization curve at 5 k of a CoO-coated Co cluster aggregate.

FIG. 6 is a graph showing the influence of the O ₂ gas flow rate on the coercive force and the shift amount of the hysteresis curve of the CoO-coated Co cluster aggregate.

FIG. 7 is a graph showing a correlation between a coercive force and a shift amount of a hysteresis curve.

[Explanation of symbols]

10: Sputter chamber 11a, 11b: Target (sputter source) 12: Turbo molecular pump 13: Carrier gas introduction nozzle 20: Cluster growth chamber 21: Skimmer 22:
Cooling jacket 30: Differential exhaust chamber 31: Mechanical booster pump 32: Skimmer 33: Exit skimmer 34: Turbo molecular pump 40: Cluster deposition chamber 41: Nozzle for gas introduction
42: Substrate 43: Thickness gauge 50: High frequency induction type sputtering device

Continuation of the front page (72) Inventor Toyohiko Konno 1-3-3 Mikamine, Taishiro-ku, Sendai-shi, Miyagi F term (reference) 4K029 BA41 BA43 BA55 BA58 CA06 DA04

Claims (4)

[Claims] 1. A monodisperse cluster is formed by condensing gas atoms generated by sputtering in a rare gas with a sputter source maintained in a clean atmosphere as a target, and forming a cluster growth chamber and a differential exhaust chamber. And then into the cluster deposition chamber, and when depositing on a substrate installed in the cluster deposition chamber, one or two of reactive gas, metal vapor, and compound vapor introduced into the cluster deposition chamber.
A method for producing a layered cluster, comprising reacting at least one species with a cluster in a monodispersed state to coat the cluster. 2. O ₂ , N ₂ , O ₃ , H
_{2. The} method for producing a layered cluster according to claim 1, wherein one or more kinds of hydrocarbon gases are used. 3. The method for producing a layered cluster according to claim 1, wherein one or more of carbon, metal, and semiconductor generated by sputtering are used as the metal vapor. 4. One or two of a metal oxide, a transition metal carbonyl and an alcohol sputter evaporated as a compound vapor.
The method for producing a layered cluster according to claim 1, wherein at least one species is used.