WO2003056057A2

WO2003056057A2 - Method for coating a substrate and coated substrates obtained according to said method

Info

Publication number: WO2003056057A2
Application number: PCT/DE2002/004564
Authority: WO
Inventors: Arno Wehner; Yanka Jeliazova; Rene Franchy
Original assignee: Forschungszentrum Jülich GmbH
Priority date: 2001-12-21
Filing date: 2002-12-13
Publication date: 2003-07-10
Also published as: WO2003056057A3; DE10163551A1

Abstract

The invention relates to a method for coating a substrate A with a layer of a substance BC. The substrate A to be coated is provided, the two components B and C are provided in a gaseous or vaporous form and in coexistence with each other in the phase present above the substrate A, B being an oxidizing substance and C being an oxidant and the two together forming the oxidized layer. Component C with regard to the concentration of component B is present in at least a stoichiometric ratio with regard to the product. Component B has a more negative oxidation potential than substrate A with regard to component C. The invention provides a method for coating for example nickel with an Al2O3 layer which is characterized in that no unwanted intermediate layer is formed between nickel and Al2O3 later on.

Description

Process for coating a substrate A with a layer of components BC and substrates coated by the process

The invention relates to a method for coating a substrate A with a layer of components BC and substrates coated by the method.

Motivated by the use as a tunnel barrier in the context of tunnel magnetoresistance, the preparation of thin oxide layers has recently been intensively investigated. Thin oxide layers - usually aluminum oxide - are usually prepared using a method as described in H. Boeve, J.D. Boeck, and G. Borghs, J. Appl. Phys. 89 (2001) 482. Aluminum is deposited on a ferromagnetic substrate by evaporation or sputtering. The deposited aluminum layer is then oxidized. Various methods are used for the oxidation:

According to K. Matsuda, A. Kamijo, T. Mitsuzuka, and H. Tsuge, J. Appl. Phys. 85 (1999) 5261 the oxidation takes place at room temperature in air, which corresponds to a natural oxidation.

Oxidation with oxygen at an elevated temperature and a specified partial pressure (thermal oxidation) is another way of oxidizing the layer. It is also possible to activate the oxygen by irradiation with UV light (UV oxidation) using the preceding methods, as described in E. Girgis, H. Boeve, JD Boeck, J. Schelten, P. Rottländer, H. Kohlstedt, and P. Grünberg, J. Mag. Mag. Mat. 222 (2000) 133 is known. Another method is plasma oxidation according to JJ Sun, RC Sousa, TTP Galväo, V. Soares, TS Plaskett, and PP Freitas, J. Appl. Phys. 83 (1998) 6694.

The following problems with various degrees of severity have been identified in all of these methods:

• The aluminum layer is not completely oxidized,

Ferromagnetic substrate is inadvertently oxidized,

• the oxidation is not uniform, • or the oxide layer is not thermally stable, as described in J. Schmalhorst, H. Brückl, G. Reiss, M. Vieth, G. Gieres, and J. Wecker, J. Appl. Phys. 87 (2000) 5191.

It is therefore the object of the invention to provide a method with which the disadvantages mentioned above are eliminated. A method is to be provided with which a completely oxidized metal or semiconductor layer can be produced on a metallic or semiconducting substrate. The thickness of the layer should be freely selectable. Starting from the preamble of claim 1, the object is achieved with the features specified in the characterizing part of claim 1.

With the method according to the invention it is now possible to apply completely oxidized coatings to a substrate which are uniform and are thermally stable. The substrate is not inadvertently oxidized.

Advantageous refinements result from the subclaims.

The method according to the invention is to be described in its general configuration below.

A substrate A is placed in a chamber and two components B and C are applied to it simultaneously.

Metals or, for example, semiconductors can be considered as substrates as substrate A. For example, nickel, copper, iron, cobalt, platinum, silver, gold, chromium, manganese, gadolinium, gallium, ferromagnetic metals or alloys, such as iron-nickel alloys as metal, or Si0 ₂ , silicon, gal- lium arsenide can be used as a semiconductor.

An atmosphere with components B and C is created over the solid substrate A. Component B is a substance to be oxidized and C is an oxidizing agent. It is crucial for the product BC that it has a more negative enthalpy of formation than the undesired product AC. The formation steel pie for Al ₂ 0 ₃ is for example wise -1690.74 k / mol and that for NiO -240.80 kJ / mol. Component B can be, for example, aluminum, iron, nickel, cobalt, molybdenum, silicon, magnesium, manganese, zirconium, titanium, gallium, gadolinium or chromium or at least one component from this group. The compositions are then B, B ^λ , B ^{, λ.} Particularly mentioned sub-combinations B, B ^X are aluminum / gadolinium, aluminum / magnesium and aluminum / silicon.

Component C is an oxidizing agent that oxidizes component B. For C, for example, oxygen, water, or a mixture C, C ^λ of the two can be used, oxides of component B being formed. If mixtures of different components B are used, the corresponding mixed oxides are formed.

Components A and B can be freely selected and are not limited to the examples given. It is only important that component C oxidizes component B and product BC has a lower enthalpy of formation than product AC.

According to the invention, components B and C are brought into a gas phase or vapor phase over the substrate A. For this purpose, component B can be evaporated or sputtered, for example, that is, brought into the gas phase by ion etching. Plasma-supporting oxidation can also be used to convert component B into the gas phase. Component C is also added to the gas phase. There are preferably no further components in the gas phase. For this purpose, the chamber can be evacuated and finally be loaded with components B and C as described.

Components B and C are initially introduced in the gas phase in a ratio in which component C is present in at least the stoichiometric amount with respect to the product Bι_ _n C _ι - _ra . Here n and m are integers. However, component C can also be present in excess.

The mixture of components B and C then forms layer BC on the surface of substrate A, for example an oxide layer.

The layer BC is preferably deposited

Room temperature instead, but can also take place in a higher temperature range at which component A is not oxidized. The deposited layer is amorphous.

In a further embodiment of the invention, the deposition of the layer BC is supported by irradiation with UV light. A preferred wavelength range is found at <240 nm. Xenon lamps or sodium vapor lamps can preferably be used. The energy should be sufficient to knock out at least one electron from component B, which facilitates the oxidation of component B. The energies required are of the order of> 5 eV and should be suitable for ionizing component B.

After coating BC has been deposited on substrate A, the product can be coated with layers A and BC be annealed. This can be done by heating up to 1200 K or 1400 K. The BC coating changes into the crystalline form.

The amorphous and crystalline layers obtained in this way can be used as corrosion protection, in the semiconductor industry as a tunnel barrier, as a full catalyst or as a substrate for a supported catalyst. A layer thickness BC of approximately 0.5 nm - 3 nm, preferably 1 nm - 2 nm, is suitable for use as a tunnel barrier.

The invention is to be described below using the example of coating nickel (100) with Al ₂ 0 ₃ .

The (100) surface of a nickel crystal was chosen as the substrate. An aluminum oxide layer is produced on this substrate. The aluminum oxide layer is produced by evaporating aluminum in an oxygen atmosphere with a certain oxygen partial pressure in an ultra-high vacuum chamber (UHV chamber) at room temperature. The deposition rate of the aluminum is 0.12 - 0.4 monolayers per minute, the partial pressure of the oxygen can be between 5xl0 ^"s mbar (corresponding to an impact number of the oxygen molecules of ή, = 1.33x10 ¹³ cm ^{" 2} sec ^"1 ) and lxl0 ^{~ 6} mbar (Λ _s = 2.67x10 ¹⁴ cm ^-2 sec ^-1 ) The deposition rate of the AI and the oxygen partial pressure are coordinated so that stochiometric Al ₂ 0 ₃ can arise, which means that at least as much oxygen must be present that the reaction equation

4Al + 3O ₂ → 2Al ₂ O ₃

Formula 1) is satisfied.

The (100) surface of Ni has approximately on the surface

8.1 l0 ¹⁴ atoms / cm ² , so after the deposition of a monolayer of aluminum, assuming that an Al atom is assigned to each Ni atom, there would be as many aluminum atoms per cm ² on the surface. At a typical deposition rate of 0.2 ML / min (ML monolayer), a monolayer is deposited in 5 minutes (300 sec). During this time, i.e. at the same time as the Al deposition, at least 1.5 times as many oxygen atoms must hit a cm ² , remain attached and react with the Al atoms. This process must not take place in succession, but must take place simultaneously, that is, the AI deposition must be in

an oxygen atmosphere. The number of impacts n _s , i.e. the number of gas molecules striking (cm ⁾ per ^second , can be calculated according to the gas kinetic theory using the following formula:

2.62 x 10 ^{22 P [mhaτ]} cm sec VJΪKJ formula (2).

where T is the absolute temperature in Kelvin, M _r , the relative molecular mass and p the gas pressure in mbar. In order to calculate the number of oxygen atoms striking ² during the deposition of a monolayer, the number of impacts ή _s must be 300 sec and a factor of 2, because of the

Dissociation of the oxygen molecules (O ₂ - 20) in two

Oxygen atoms, are multiplied. With p = lxl0 ^"7 mbar, T = 300 K and M _r = 32 results for the integral number of impacts:

Integral number of impacts = 300sec-2-ή _s = 1.60xl0 ¹⁶ - cm

Formula (3)

The condition according to formula (1) is fulfilled on the assumption that the coefficient of adhesion, that is the number of oxygen atoms remaining adhering to the number of oxygen molecules hitting, is equal to 1 from O atoms to Al atoms.

The figures show the results of the coating with the method according to the invention and for comparison according to methods according to the prior art.

It shows:

Fig.la: The layer formation according to the inventive method with deposition, additional fumigation and

Annealing. Fig.lb: A layer formation according to the prior art for comparison. Fig.2a: Auger spectrum of nickel (110) Fig.2b: Auger spectrum after deposition of Al in an oxygen atmosphere on nickel (110). Fig.2c: Auger spectrum according to Fig.2b after further gassing with oxygen. Fig.2d: Auger spectrum according to Fig.2a

Annealing. Fig.3a: Auger spectrum of nickel (110) Fig. 3b: Auger spectrum after the deposition of aluminum.

Fig. 3c: Auger spectrum of an aluminum-coated nickel (100) surface after oxidation with oxygen.

Fig.3d: Auger spectrum according to Fig.3c after annealing.

4a: Ratios of the AES intensities for Al / Ni and Al / O for the method according to the invention as a function of temperature.

4b: Ratios of the AES intensities for Al / Ni and Al / O for the product according to the prior art as a function of the temperature.

Fig.5a: EEL spectrum of the aluminum oxide layer, which was produced according to the inventive method

Fig.5b: EEL spectrum of the aluminum oxide layer, which according to the state of the

Technology was made.

Fig.6a: Electron diffraction pattern of the pure nickel (110) surface

6b: electron diffraction pattern of aluminum oxide layer which was applied by the method according to the invention.

Fig.6c: Schematic representation of Fig.6b.

Brief Description:

La schematic representation of the production of Al oxide layers on a Ni (100) substrate, AI was evaporated at an oxygen partial pressure of IxlO ^"7 mbar.

Fig. Lb Schematic representation of the production of Al oxide layers on a Ni (100) substrate, an Al layer was first evaporated on Ni (p = IxlO ^"10 mbar) and then oxidized at room temperature (oxygen partial pressure = IxlO ^{" 6} mbar for 2500 seconds).

Fig. 2 AES spectra in the kinetic energy range of 10-120 eV. The x-axis shows the kinetic energy of the AES electrons in eV. The y-axis shows the derivative of the electron distribution N (E) according to its energy dE in arbitrary

Units. The AES spectra shown here were measured on Al oxide layers that were produced by deposition of Al in an oxygen partial pressure of IxlO ^-7 mbar. a: AES spectrum of pure nickel, b: AES spectrum after deposition of AI in oxygen at a partial pressure of IxlO ^"7 mbar, c: AES spectrum after further gassing with oxygen, d: AES spectrum after annealing the layer

1400 K.

Fig. 3 AES spectra of the AI layer

Deposition at 4xl0 ^"10 mbar and subsequent oxidation in oxygen with a partial pressure of IxlO ^{" 5} mbar, a: AES of pure Ni, b: AES spectrum after the AI deposition, c: AES spectrum after oxidation of the Al layer in oxygen with a partial pressure of IxlO ^"6 mbar for 2500 seconds, d: AES spectrum after tempering the layer to 1200 K.

Fig.4 The ratios of the AES intensity (peak to peak) of Ni (848 eV) to AI (metallic at 1396 eV, Al ³⁺ at 1378 eV) and from AI to oxygen as a function of the tempering temperature (K). The

AES intensity ratios are plotted in arbitrary units. a: after production of the Al oxide layer by simultaneous Al deposition in an oxygen atmosphere, b: after production of the Al oxide layer by Al

Deposition followed by oxidation at IxlO ^"6 mbar.

5 High-resolution electron energy loss spectra. A: EEL spectrum of Al oxide layers produced by Al deposition in oxygen with a partial pressure of IxlO ^"7 mbar, b: EEL spectrum of Al oxide layers produced by deposition of Al of oxidation in oxygen with a partial pressure of IxlO ^"6 mbar for 2500 seconds.

Fig. 6 electron diffraction patterns (LEED pattern) with a primary energy of the electrons of 122 eV. a: Electron diffraction pattern of the pure (100) surface of Ni. b: electron diffraction pattern of an Al oxide layer which was produced by deposition of Al in an oxygen atmosphere of IxlO ^"7 mbar, then the layer was annealed to 1300 K. c: Schematic representation of the electron diffraction pattern from Fig. 6b. A pseudo do-twelve-fold ring structure, through a hexagonal structure with two domains that are 90 °

According to the invention was AI with a deposition rate of

0.2 ml / min deposited in an oxygen atmosphere with an oxygen partial pressure of lx 10 ^"7 mbar at room temperature, corresponding to an Al layer thickness of 16 Å. As shown in FIG. La, it can be seen that at the end of the deposition of aluminum in This oxygen atmosphere in the resulting aluminum oxide layer on Ni (100) contains only Al ³⁺ ions and no metallic aluminum, which means that stoichiometric Al ₂ O _{3 has} formed during the deposition with oxygen the state of the layer no longer. The oxide layer produced at room temperature is amorphous.

When the layer is subsequently tempered, the atomic ratio of Al to O atoms (Al / O) remains constant even up to 1400 K, the atomic ratio of Al to Ni being constant up to approximately 1200 K. This proves that the thin aluminum oxide layer is stable at least up to 1200 K. In addition, a well-ordered, crystalline oxide layer forms at annealing up to 1300 K, which leads to a sharp pattern in the electron diffraction pattern. For comparison, another common method was chosen, as described by H. Boeve, JD Boeck, and G. Borghs in J. Appl. Phys. 89 (2001) 482 to prepare a thin layer of aluminum oxide. Here, 16 Å of aluminum was first deposited under UHV conditions (ultra-high vacuum conditions) and then oxidized to saturation with oxygen at IxlO ^"6 mbar. Saturation with oxygen is reached after about 2500 seconds. FIG. 1b shows clear indications the existence of unoxidized aluminum atoms, which means that metallic Al atoms can also be found in the oxide layer, since the atomic ratio of O to Ni is saturated, it is proven that it is impossible to find a 16 Å thick

Oxidize layer completely at an oxygen partial pressure of IxlO ^"6 mbar. The number of impacts shown in FIG

18 atoms

2500sec-2-ιi = 1.33x10 cm

Formula (4)

This is far more than about the oxidation of the deposited ones

5 monolayers of aluminum (corresponding to 2xl0 ¹⁵ atoms) would be necessary, but metallic aluminum can still be found in or under the aluminum oxide layer. During the annealing of the layer produced using this comparison method, a clear decrease in the Al / Ni ratio is observed. This can be attributed to the diffusion of the unoxidized aluminum into the volume of the nickel crystal.

In experiments carried out by HAM d. Gronckel, H. Kohlstedt, and C. Daniels, as in Appl. Phis. A 70 (2000) 435 published an aluminum layer was deposited on cobalt and then oxidized at room temperature in pure oxygen at atmospheric pressure for five minutes. The samples were stored in air at room temperature for one week. It emerged from this work that aluminum layers thicker than

10A, were not fully oxidized. On the other hand, it was found that two-step plasma oxidation (deposition of 5 Å Al followed by oxidation and then deposition of 7 Å followed by oxidation) resulted in an improvement in the tunnel properties of the oxide layer (KS Yoon, JK Park, JHChoi , JY Yang, CH Lee, C. 0. Kim, JP Hong, and TW Kang, Appl. Phys. Lettr 79 (2001) 1160).

embodiment

FIG. 1 a shows a schematic representation of the preparation of the thin aluminum oxide layer on the (100) surface of a nickel crystal by deposition of Al atoms in a corresponding oxygen atmosphere. First, an oxygen partial pressure of IxlO ^-7 mbar (corresponding to an impact number of 2.67xl0 ¹³ O ₂ molecules / cm ² sec) was set. Then aluminum was deposited, which immediately reacts with the oxygen. The deposition takes place at room temperature by evaporation from a crucible at a rate of 0.2 monolayers per minute. Assuming an adhesion coefficient of one, there is enough oxygen to produce stoichiometric Al ₂ O ₃ . The condition is still fulfilled if the adhesive coefficient is significantly less than one. The resulting Al ₂ O ₃ is then added at room temperature Oxygen is gassed for 2500 seconds at an oxygen partial pressure of IxlO ^"6 mbar and then annealed in steps from 100 K to 1200 K. Thereafter, annealing is carried out in 50 K steps up to 1400 K. At this temperature the decomposition of the Al ₂ O ₃ layer begins from the Ni surface.

FIG. 1b shows a method in which Al was first deposited on the (100) surface of the Ni and then this layer was oxidized. The aluminum was made under UHV

Conditions (4xl0 ^{~ 10} mbar) deposited. The deposition rate and time are chosen as in the previous method. The oxidation was carried out in an oxygen atmosphere with a partial pressure of IxlO ^-6 mbar to saturate the layer with oxygen. It turns out that although the atomic ratio of 0 to Ni does not change with further exposure of the layer to oxygen, both metallic and oxidized aluminum are present in the layer after the oxidation. This is indicated in the diagram where the metallic aluminum is located in the interface between the oxide layer and the Ni substrate. Annealing this layer in 100 K steps up to 1200 K leads to the diffusion of the remaining metallic aluminum into the volume of the Ni substrate. It is from the publication of SH Lu, D. Tian, ZQ Wang, YS Li, and F. Jona, in Solid State Comm. 67 (1988) 325 discloses that an Ni ₃ Al alloy is formed by tempering aluminum deposited on Ni (100). After tempering to 1300 K, the aluminum oxide layer is completely desorbed.

FIG. 2 shows Auger spectra (AES, Auger electron spectroscopy) in the range of the kinetic energies of 10-120 eV, which were recorded during the preparation with the method according to the invention. FIG. 2a shows the AES spectrum of the pure nickel (100) surface with the two corresponding AES transitions at 61 eV and 102 eV. After the deposition of aluminum in an oxygen atmosphere (Figure 2b) there are two AES transitions at 35 eV and 51 eV, which are characteristic of triple ionized aluminum (Al ³⁺ ). A transition at 68 eV would be expected for metallic aluminum, to which there are no indications in FIG. 2b. The fact that the AES spectrum, shown in FIG. 2c, has not changed after the further gassing with oxygen suggests that stoichiometric Al ₂ O ₃ is already formed during the deposition. Figure 2d shows the AES spectrum after annealing the layer to 1400 K. In addition to the AES transitions characteristic of Al ₂ O ₃ , AES signals at 61 eV and 102 eV can be seen, which are characteristic of nickel. This indicates that desorption of the Al ₂ O ₃ begins at this temperature and the Ni substrate reappears.

FIG. 3 shows AES spectra in the kinetic energy range from 10 to 120 eV, during the preparation according to the prior art method described in FIG. 1b

- Al deposition with a layer thickness of 16A followed by subsequent oxidation - was recorded. FIG. 3a again shows the AES spectrum of the pure Ni (100) surface. After the deposition of aluminum at p = 4xl0 ^{~ 10} mbar (UHV), an AES spectrum is obtained which is shown in Fig. 3b. Here you can see an AES

Transition at 68 eV the metallic AI is assigned. This is a clear difference to Figure 2b - after Al deposition in an oxygen atmosphere - where only AES transitions were found that correspond to ionic aluminum. After oxidation of the 16A thick aluminum layer at IxlO ^"6 mbar for 2500 seconds, the AES spectrum shows the transitions characteristic for Al ³⁺ at 35 eV and 51 eV as well as the transition characteristic for metallic aluminum at 68 eV (Figure 3c) This suggests a coexistence of metallic and oxidized aluminum as indicated in FIG. 2b.

FIG. 4 shows the dependence of the ratios of AES intensities for AI to Ni (Al / Ni) and of AI to 0 (Al / O) measured for higher-energy Auger transitions (nickel: 848 eV, metallic aluminum: 1396 eV, aluminum ions Al ³⁺ : 1378 eV, and oxygen: 503 eV). The AES signals, measured from peak to peak in the dN (E) / dE spectrum, are taken as the AES intensity. The reason for considering these AES transitions, in contrast to FIG. 2, lies in the greater exit depth of the Auger electrons with higher kinetic energy. Thus, while only layers close to the surface contribute to the AES signal formation in FIG. 2, Auger electrons, which are released in deeper layers, also contribute to the signal formation in FIG. 4. The mean free path of

Electrons is ₃ : 7 in Al ₂ O. 3 A at 50 eV, 18 A at 800 eV,

27.9A at 1400 eV. This enables the signal from the substrate - the signal from nickel - to be used as a reference. FIG. 4 now shows the ratios of the AES intensities of the aluminum transition (Al ³⁺ : 1378 eV) to the nickel transition (Ni: 848 eV). For the preparation method according to the invention according to FIG. 4a (deposition in speaking oxygen atmosphere) the AES ratio Al / Ni and Al / O remains constant up to a temperature of 1250 K. Only then does the Al / Ni ratio decrease significantly, which is due to the desorption of the oxide layer. In contrast, the Al / O ratio remains constant up to a temperature of 1400 K, which indicates a uniform decrease in aluminum and oxygen from the surface in the high temperature range. FIG. 4b shows the corresponding conditions for the oxide layer which was produced in the prior art by Al deposition followed by oxidation. An almost continuous decrease in the AES ratios Al / Ni and Al / O is found (AI: 1396 eV, Ni: 848 eV and 0: 503 eV), which suggests a diffusion of the metallic aluminum into the volume of the substrate. The decrease in the Al / O ratio also suggests that there is an excess of metallic aluminum after the oxidation and a diffusion of the metallic aluminum into the volume of the Ni substrate takes place during Te perns. On the other hand, a thin NiAl or Ni ₃ Al layer could also form during the tempering at the interface of the aluminum oxide and the Ni substrate.

Alumina occurs in nature in several modifications. Amorphous aluminum oxide, which forms during room temperature oxidation, is characterized in that the Al ions are only in tetrahedral coordination. The α-Al ₂ 0 ₃ modification, which is the high temperature phase of the aluminum oxide and which is called corundum, contains Al ions which are only coordinated octahedrally.

In between there are many Al ₂ 0 ₃ modifications in which the Al ³⁺ ions can occur in both coordinations. To clarify the question about which modification of the aluminum oxides, high-resolution electron energy loss spectroscopy (EELS) investigations were carried out. FIG. 5a shows an EEL spectrum of the aluminum oxide layer, which was produced by Al deposition using the process according to the invention in a corresponding oxygen atmosphere and was subsequently heated to 1300 K. In Figure 5a, the x-axis shows the energy loss. The elastic line is observed at the loss energy = 0, and the loss energy of the electrons in wave numbers cm ^"1 , corresponding to the excitation of a vibration in the oxide. The y-axis shows the intensity of the scattered electrons in normable arbitrary units (wE). In FIG 5a two losses are observed at 640 and 900 cm ^"1 , which indicate that the stable α-modification was produced in this way. This is the only thermally stable modification of aluminum oxide.

FIG. 5b shows an EEL spectrum of an aluminum oxide layer which was produced using the method according to the prior art, ie by Al deposition followed by oxidation followed by tempering to 1200 K. The spectrum shows three losses at 420. 640 and 880 cm ^"1. These losses are typical of several modifications of aluminum oxide, all of which are not thermally stable. In the literature, under the same conditions, the formation of γ - Al ₂ O ₃ or Θ-Al ₂ 0 _3. In both spectra, the amplification factor (x10) of the loss intensity shows that the metallic Ni surface has oxidic, ionic compounds which are characterized by large dynamic dipole moments, as is to be expected for aluminum oxide. Another indication that there is on the Ni surface after Al deposition in an oxygen atmosphere, followed by tempering to 1300 K according to the invention

Methods that form α-Al0 ₃ modification show electron diffraction (LEED) investigations. FIG. 6a shows a diffraction pattern of the pure (100) surface of nickel, recorded at a primary energy of the electrons of 122 eV. FIG. 6b shows an electron diffraction pattern of the aluminum oxide layer produced according to the invention after annealing at 1300 K. A pseudo-twelve-fold ring structure can be seen, which can be explained by a hexagonal structure with two domains which are rotated 90 ° relative to one another. This hexagonal structure together with the electron energy loss spectrum in FIG. 5a indicates that the modification of aluminum oxide is present here. For a better understanding of the diffraction patterns, substrate points are identified by circles in FIG. 6c and additional points originating from the oxide are identified by stars.

Claims

Patent claims

1. A method for coating a substrate A with a layer of a substance BC, in which component B can be a sub- ^combination of different components B, B, B ^λλ , characterized in that

- that the substrate A to be coated is presented,

- The two components B and C, of which B is the substance to be oxidized and C is an oxidizing agent, which together form the oxidized layer, coexistently in the one located above the substrate A.

Phase are presented in gaseous or vaporous form,

- wherein component C is present with respect to the concentration of component B at least in a stoichiometric ratio with respect to the product and

- the product BC has a more negative enthalpy of formation than the undesirable product AC.

2. The method according to claim 1, characterized in that a metal is used as substrate A.

3. The method according to claim 2, characterized in that an alloy is used as the metal.

4. The method according to claim 2 or 3, characterized in that at least one component of the metal Group Ni, Cu, Fe, Au, Cr, Co, Mn, Gd, Ag, Pt, Ga Fe / Ni alloy or a ferromagnetic metal is used.

5. The method according to claim 1, characterized in that a semiconductor is used as substrate A.

6. The method according to claim 5, characterized in that at least one component from the group Si0 ₂ , Si, GaAs is used as the semiconductor.

7. The method according to any one of claims 1 to 6, characterized in that as substance B at least one component from the group of Al, Fe, Co, Ni, Ti, Mo, Si, Mg, Mn, Gd, Zr, Ga and Cr is used.

8. The method according to any one of claims 1 to 7, characterized in that at least one component from the group 0 ₂ , H ₂ 0 is used as component C.

9. The method according to any one of claims 1 to 8, characterized in that component B is brought into the gas or vapor phase by evaporation or by sputtering.

10. The method according to any one of claims 1 to 9, characterized in that the layer BC at room temperature on the Surface of the substrate A forms.

11. The method according to any one of claims 1 to 10, characterized in that UV light is irradiated during the process.

12. The method according to claim 11, characterized in that light of a wavelength λ <240 nm is irradiated.

13. The method according to any one of claims 1 to 12, characterized in that the product is heated after the coating.

14. The method according to claim 13, characterized in that the heating to a temperature in a range from T> room temperature to 1200 K takes place.

15. With a substance BC coated substrate A, characterized in that it was produced by the method according to any one of claims 1 to 13.

16. With a substance BC coated substrate A according to claim 14, characterized in that the layer BC has a thickness of 0.5 nm to 3 nm.

17. Substrate A coated with a substance BC, characterized in that component B is completely oxidized and there is no intermediate layer consisting of an alloy AB or component B.

18. Coated with Al ₂ 0 ₃ nickel support, characterized in that the Al ₂ 0 _{3 is present} in an α-modification.

19. Use of coated substrates according to one of claims 14 to 17 or produced according to one of claims 1 to 13 as a tunnel barrier or corrosion protection.