阅读说明：本技术 一种自旋极化探针的制备方法 (Preparation method of spin polarization probe ) 是由 徐庆宇 王光宇 于 2020-06-24 设计创作，主要内容包括：本发明公开了一种制备自旋极化探针的方法。具体步骤为：在扫描探针显微镜或者扫描隧道显微镜探针的基础上,在针尖表面沉积一层10-300nm厚的NiO薄膜,随后沉积一层厚度1-30nm的Al<Sub>2</Sub>O<Sub>3</Sub>薄膜。然后将针尖接触金属薄膜表面,在针尖与薄膜之间加上电压,其中针尖电压高于薄膜的电压,并设定保护电流(10<Sup>-5</Sup>A-10<Sup>-</Sup><Sup>1</Sup>A),电压加到一定数值(2V-10V)时,电阻会突然从高阻态跳变到低阻态,这时NiO和Al<Sub>2</Sub>O<Sub>3</Sub>层内部形成了金属Ni的导电细丝,即制成自旋极化的探针。这种纳米尺度自旋极化的铁磁导电细丝探针制备工艺简单。细丝的直径严格可控,精度可以达到纳米尺度；可以通过改变Al<Sub>2</Sub>O<Sub>3</Sub>薄膜的厚度,控制导电细丝顶端与探测表面的间隔,对直接导电和隧穿导电机制进行调控。<Image he="347" wi="700" file="DDA0002554243470000021.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>(The invention discloses a method for preparing a spin-polarized probe. The method comprises the following specific steps: depositing a NiO film with the thickness of 10-300nm on the surface of a needle tip on the basis of a scanning probe microscope or a scanning tunneling microscope probe, and then depositing an Al film with the thickness of 1-30nm 2 O 3 A film. Then, the tip is brought into contact with the surface of the metal film, a voltage is applied between the tip and the film, wherein the tip voltage is higher than the film voltage, and a protective current is set (10) ‑5 A‑10 ‑ 1 A) When the voltage is added to a certain value (2V-10V), the resistance suddenly jumps from the high resistance state to the low resistance state, and NiO and Al are generated 2 O 3 Inside the layer, a conductive filament of metallic Ni is formed, i.e. a spin-polarized probe is made. The nanoscale spin-polarized ferromagnetic conductive filament probe is simple in preparation process. The diameter of the filament is strictly controllable, and the precision can reach the nanometer scale; can be prepared by changing Al 2 O 3 Of filmsThickness, control the distance between the top end of the conductive filament and the detection surface, and regulate the direct conduction and tunneling conduction mechanism.)

1. A method of making a spin-polarized probe, the method comprising the steps of:

1) firstly depositing a NiO film with the thickness of 10nm-300nm on the surface of a common conductive probe;

2) then, a layer of Al with the thickness of 1nm-30nm is deposited₂O₃A film;

3) depositing NiO film and Al₂O₃The tip of the film conductive probe contacts the surface of the metal film, and the current is applied by using a current source meter to set the protective current value to 10^-5A-10^-1A；

4) Applying voltage between the needle point and the metal film, wherein the needle point voltage is higher than the film voltage, when the voltage is applied to 2V-10V, the resistance between the needle point and the film is suddenly reduced, the loop current is suddenly increased to a set protection current value, and the NiO and Al are respectively in the range of NiO and Al₂O₃Forming metal Ni conductive filaments in the layer;

5) and removing the voltage to prepare the spin-polarized needle tip.

2. The method for preparing a spin-polarized probe according to claim 1, wherein NiO and Al are sequentially deposited on the surface of the conductive probe₂O₃The film is deposited by magnetron sputtering or pulsed laser deposition.

3. The method of claim 1, wherein the common conductive probe comprises a tungsten tip or a platinum tip.

4. The method of claim 1, wherein the metal thin film comprises platinum, gold, nickel-iron or copper.

5. The method according to claim 1, wherein the value of the protective current is controlled by a current source meter and is maintained constant when the current reaches a predetermined value.

6. The method according to claim 1, wherein the thickness of the conductive filament is controlled by a predetermined magnitude of the protection current, and the conductive filament is thinner when the protection current is small, so that the probe can obtain a higher spatial resolution.

Technical Field

The invention relates to a preparation method of a spin polarization probe, and belongs to the field of material testing instruments.

Background

The scanning tunnel microscope researches information of various materials such as the surface relief morphology, the energy band structure of the film and the like through the measurement of tunneling current between the needle point and the surface. The tunneling current is also influenced by the relative magnetization direction between the thin film and the needle point, so that the magnetic related information such as the magnetic domain, the spin polarizability and the like of the thin film can be measured.

The conventional spin-polarized probe is prepared by depositing a magnetic thin film on the surface of the probe of a scanning tunneling microscope, so that the spatial resolution is affected by the size of the tip. The stray field generated by the simultaneous preparation of continuous magnetic thin films is very large, typically with a tip-to-thin detection surface spacing of approximately 1 nm. Therefore, a process for preparing a ferromagnetic needle tip capable of reaching a nano scale is urgently needed.

In order to overcome the defects of the existing probe preparation process, the invention provides a preparation process for obtaining a nanoscale ferromagnetic conductive needle tip.

Disclosure of Invention

The technical problem is as follows: the invention aims to provide a preparation method of a spin-polarized ferromagnetic conductive needle tip with the size of nanometer.

The technical scheme is as follows: the preparation method of the spin-polarized ferromagnetic conductive needle tip comprises the following steps:

1) firstly depositing a NiO film with the thickness of 10nm-300nm on the surface of a common conductive probe;

2) then, a layer of Al with the thickness of 1nm-30nm is deposited₂O₃A film;

3) depositing NiO film and Al₂O₃The tip of the thin film conductive probe is contacted with the metal thin film, the current is applied by using a current source meter, and the protective current value is set to be 10^-5A-10^-1A；

4) Applying voltage between the needle point and the metal film, wherein the needle point voltage is higher than the film voltage, when the voltage is applied to 2V-10V, the resistance between the needle point and the film is suddenly reduced, the loop current is suddenly increased to a set protection current value, and the NiO and Al are respectively in the range of NiO and Al₂O₃Forming metal Ni conductive filaments in the layer;

5) and removing the voltage to prepare the spin-polarized needle tip.

Wherein the content of the first and second substances,

NiO and Al are deposited on the surface of the conductive probe in sequence₂O₃The film is deposited by magnetron sputtering or pulsed laser deposition.

The common conductive probe comprises a tungsten wire tip, a platinum wire tip and the like.

The metal film comprises platinum, gold, nickel iron, copper and the like.

The protection current value is controlled by a current source meter and is kept unchanged after the current reaches a set value.

The thickness of the conductive filament is controlled by the set protection current, and the conductive filament is thinner when the protection current is small, so that the probe can obtain higher spatial resolution.

The nanoscale spin-polarized ferromagnetic conductive needle tip is prepared by using a resistance change effect, and Ni ions in the NiO layer are gathered together and reduced to form a conductive filament in the process of applying voltage. Because the needle point is protruded, the field intensity nearby is the largest, so that only one conductive filament is formed at the needle point, and the diameter is in a nanometer scale. Meanwhile, the conductive filament is driven by voltage to penetrate into Al₂O₃Film, substantially throughout the entire Al₂O₃A film.

The spacing between the spin-polarized ferromagnetic conductive filament and the contact detection surface can be detected by depositing Al₂O₃The thickness of the layer is controlled such that when the thickness is less than 8nm, the conductive filaments extend directly to the surface and can be in direct contact with the detection surface, Al₂O₃When the thickness of the layer is more than 8nm, the end part of the conductive filament has a very small distance with the surface, when the needle point contacts with the detection surface, the conductive filament does not directly contact with the surface, and the conductive mechanism becomes a tunneling effect.

Has the advantages that:

(1) the nanoscale spin-polarized ferromagnetic conductive filament probe is simple in preparation process.

(2) The diameter of the filament is strictly controllable, and the precision can reach the nanometer scale;

(3) can be prepared by changing Al₂O₃The thickness of the film, the spacing between the top end of the conductive filament and the detection surface, and the direct conduction and tunneling conduction mechanism are regulated and controlled.

(4) The probe can be repeatedly used, and the surface of the probe is provided withDeposited NiO/Al₂O₃After the layer is removed, the layer is prepared again according to the process and can be reused.

Drawings

FIG. 1 is a schematic view of the structure of a probe.

FIG. 2 NiO layer thickness 150nm, Al₂O₃When the layer thickness is 3.5nm, the film shows anisotropic magnetoresistance effect together with NiFe film, which indicates that Ni conductive filament penetrates Al₂O₃The surface of the layer is communicated with the NiFe film.

FIG. 3 NiO layer thickness 150nm, Al₂O₃When the thickness of the layer is 20nm, the film and the NiFe film show tunneling magnetoresistance effect, which indicates that the Ni conductive filament does not penetrate into Al₂O₃There is a small gap between the surfaces of the layers.

Detailed Description

1) Firstly, selecting a conductive probe, and growing NiO and Al on the surface of the probe in sequence by utilizing magnetron sputtering or pulse laser deposition technology₂O₃Layer, NiO layer thickness controlled between 10nm and 300nm, Al₂O₃The thickness of the layer is controlled between 1nm and 30 nm;

2) contacting the probe tip with the metal surface, connecting the probe tip and the metal surface with the positive and negative electrodes of a power supply respectively, increasing voltage in a continuous scanning manner, and setting a protection current in a range of 10^-5A to 10^-1A is between;

3) when the voltage is increased to a certain value, the loop current value is suddenly increased to the set protection current value and is not increased any more, and then the current can be cut off to lift the needle point. Thus, a ferromagnetic conductive tip with nano-scale spin polarization is prepared.

The invention is further illustrated by the following figures and examples, in which some of the preparation conditions are only illustrated as typical and not limiting. FIG. 1 is a schematic illustration of a prepared needle tip, with only the conductive filaments being conductive and the surrounding NiO and Al₂O₃Are non-conductive and the size of the conductive filament determines the spatial resolution of the needle tip. With NiO and Al₂O₃Are all thatNonmagnetic, only the conductive filaments are Ni conductive filaments, and the ferromagnetic material is strictly confined to the filament region, rather than the entire film being ferromagnetic metal, thereby effectively avoiding stray fields.

1) When the thickness of the NiO layer is 150nm, Al₂O₃When the thickness of the layer is 3.5nm, the needle point is contacted with the surface of the NiFe metal film, the magnetoresistance effect is measured when the film is converted into a low resistance state under the external voltage, as shown in figure 2, the direction of a magnetic field and the direction of current are different, the magnetoresistance effect is different, the current is positive magnetoresistance effect when the current is vertical to the magnetic field, and is negative magnetoresistance effect when the current is parallel to the magnetic field, which is a typical anisotropic magnetoresistance effect, and shows that the Ni conductive filament is directly communicated with the surface of the NiFe at the moment, and penetrates through the whole Al metal film₂O₃And (3) a layer.

2) When the thickness of the NiO layer is 150nm, Al₂O₃When the thickness of the layer is 20nm, the needle point is in contact with the surface of the NiFe metal film, the magnetoresistance effect is measured when the NiFe metal film is converted into a low resistance state under the external voltage, as shown in figure 3, the direction of a magnetic field is different from the direction of current, the magnetoresistance effect is the same, the current is a negative magnetoresistance effect when the current is vertical to the magnetic field, the current is a negative magnetoresistance effect when the current is parallel to the magnetic field, and a butterfly-shaped curve is shown, which is a typical tunneling magnetoresistance effect and indicates that the Ni conductive filament is not directly communicated with the surface of the NiFe at the moment, the conductive mechanism is a tunneling effect, and the Ni conductive filament does₂O₃And (3) a layer.

Compared with the traditional probe, the simple preparation method of the spin-polarized probe can effectively improve the spatial resolution, and meanwhile, the conductive filament is ferromagnetic and has spin polarization, so that the simple preparation method of the spin-polarized probe can be used for performing magnetic property related measurement in a scanning probe microscope, such as magnetic domain observation, spin polarization rate measurement and the like, and has a plurality of specific application ways. It should be noted that modifications may be made by those skilled in the art without departing from the principles of the present invention, such as replacing Al with other insulating oxides₂O₃A layer, in which a layer of Ni is deposited to increase Ni source before the NiO layer is deposited, a layer of metal such as Cu, Ag, Au, etc. is deposited, orSuch as the power failure immediately after the current reaches the protection value, should be considered as the protection scope of the present invention.