CN107919258B - A device and method for generating a controllable vortex electron beam - Google Patents

Abstract

The invention discloses a device for generating a controllable vortex electron beam based on TEM, which is characterized by comprising an electron gun to generate a plane electron beam; a magnetic field controller; On the plane electron beam channel, the magnetic field controller generates a magnetic field with controllable strength, and the magnetic field is used to modulate the phase of the plane electron beam. The invention also discloses a method for generating a controllable vortex electron beam by using the above device. The device forms a magnetic monopole-like magnetic field distribution in an electron microscope to obtain a vortex electron beam with a single orbital angular momentum and a controllable quantum number.

Description

A device and method for generating a controllable vortex electron beam

technical field

The invention belongs to the field of vortex electron beam generation, and in particular relates to a device and method for generating a controllable vortex electron beam.

Background technique

Predictions and experiments in recent years have shown that changing the basic structure of the electron wavefront can make the electron wave have many specific properties, which can realize new functions in commonly used transmission electron microscopes. If the reconstructed electron beam has a continuous vortex wavefront, the electron beam is called a vortex electron beam. In a vortex electron beam, the electron probabilistic current follows a vortex path, in the direction of along-axis propagation, with an azimuthal momentum component.

A single vortex beam can be described by Ψ∝f(r) exp(ilφ) exp(ik _z z), where (r, φ, z) are cylindrical coordinates; k _z is the forward momentum of the beam; l is the vortex order, also known as the topological charge, a single vortex bundle changes phase by 2πl in a loop around the vortex center. In a single vortex beam, the vortex order l is proportional to the number of windings (a key parameter describing the vortex), in addition, the vortex order l is also related to the beam's orbital angular momentum (OAM), which is a vortex bunch of very interesting properties. Vortex electron beams carrying orbital angular momentum have great potential for nanoparticle manipulation (rotation, movement, confinement, etc.) as well as magnetic detection (with the promise of atomic resolution).

Various methods have been investigated to generate vortex electron beams in order to control the phase of manipulating electron waves to generate specific orbital angular momentum quantum numbers. Up to now, the methods of generating vortex electron beams include: phase plate method, holographic reconstruction method, and magnetic-like monopole field method.

The phase plate method refers to the use of a vortex phase plate to convert a plane wave incident on the vortex phase plate into a vortex wave. The researchers verified the generation of vortex electron beams by means of plane electron beam interference. A 2π phase difference will produce a vortex electron beam with a topological charge of 1. Although the phase plate method can generate vortex electron beams, it has the following disadvantages: (1) the number of topological charges generated is low, which cannot meet the requirements in many cases; (2) the service life of the phase plate is limited, mainly because: The plate material is unstable under the action of high-energy electron beams, and is easily damaged and polluted; (3) the processing of the phase plate is difficult, and the ideal vortex structure cannot be achieved. Vortex electron beam.

Holographic reconstruction is by far the most common method used to generate electron eddy current beams. The researchers observed the vortex electron beam using the holographic aperture, but the generated vortex electron beam is a multi-beam carrying different orbital angular momentum, and expanding its application requires a single electron beam, which needs to be selected from multiple beams. There is great difficulty. In addition, the holographic aperture blocks most of the electron beam, resulting in a large loss of intensity, low efficiency, and a weak signal in electron microscopic characterization.

The magnetic-like monopole field method refers to the use of the magnetic-like monopole characteristics at the end of a small magnetic needle to act on the incident electron beam, and a vortex electron beam is generated according to the Aharonov-Bohm effect. Although this method solves the disadvantage that the holographic reconstruction method blocks most of the electron beams, the magnetic field generated by the small magnetic needle is uncontrollable and cannot generate vortex electron beams with different orbital angular momentums.

SUMMARY OF THE INVENTION

In view of the above, the present invention provides an apparatus and method for generating a vortex electron beam. The device is capable of generating a vortex electron beam with controllable orbital angular momentum.

The first embodiment of the present invention provides a device for generating a controllable vortex electron beam based on a TEM (transmission electron microscope), including:

An electron gun, which produces a flat electron beam;

Magnetic field controller;

A magnetic needle wound with a conductive coil is disposed on the plane electron beam channel through a chip loaded by an electrical device, and is acted by the magnetic field controller to generate a magnetic field with a controllable intensity, and the magnetic field is used to modulate the phase of the plane electron beam.

An effective monopole field is generated at the tip of a nanoscale magnetized ferroneedle. The Aharanov-Bohm effect can be used to understand the effect of this monopole field on the electron beam. When a plane electron wave interacts with a hypothetical magnetic monopole, a vortex electron beam is created. A closed charge path containing magnetic flux can obtain the Aharonov-Bohm (A-B) phase:

是常数，c是光速。A is the magnetic vector potential, which is a mathematical tool used in quantum physics and has real meaning, and A*ds refers to the magnetic flux in the surrounding area. e is the charge,

is a constant and c is the speed of light.

Even if the electron does not pass through the area with the magnetic field lines, the A-B phase can still be generated due to quantum mechanical effects. Whereas in classical mechanics there would be no effect because there is no force acting on the charge. In the region of infinite cylindrical magnetic field lines, the A-B effect is often discussed. Because this avoids special effects at special points where the magnetic field is B=rotA. The form is as follows:

r is the radius of the cylinder, r is the radial vector.

Calculating the Aharonov-Bohm phase of the electrons traversing the magnetic flux lines of the semi-infinite cylinder perpendicularly yields an equation that depends on the linear azimuth of the cylinder ends:

This means that passing electrons will indeed transition into a vortex state:

Ψ _out = Ψ _in exp(imφ)

是量子化的，这个导致一个整数m(g＝mc/(2*e)),一个完美的相涡旋拓扑电荷m。where m depends on the charge of the magnetic monopole and φ is the azimuth angle in the plane perpendicular to the electron wave propagation. For a true unipolar field, the charge here

is quantized, this leads to an integer m (g=mc/(2*e)), a perfect phase vortex topological charge m.

Therefore, the present invention utilizes a magnetic field controller to control the current flowing through the coil, so as to control the size of the magnetic field at the tip of the magnetic needle, thereby obtaining controllable vortex electron beams with different orbital angular momentums.

The chip is a carrier containing electrode sheets, which supports and connects the conductive coils. The carrier sheet can be a glass sheet, a silicon wafer, or an alumina ceramic sheet, or the like.

Preferably, the chip can be a sample chip.

Preferably, the electrical device is an electrical sample rod or an aperture rod.

Preferably, the magnetic needle is horizontally arranged on the surface of the chip, and the tip of the magnetic needle is placed in the center of the chip.

Preferably, the conductive coil on the magnetic needle is connected to one end of the electrode sheet of the chip, and a magnetic field control loop is formed with the magnetic field controller via an electrical device that loads the chip. After the chip is placed in the electrical equipment, the other end of the electrode sheet in the chip is connected to one end of the electrode sheet in the electrical equipment, and the internal circuit is connected with the external magnetic field controller to form a complete system.

Preferably, an aperture hole is provided at the center of the chip. Further, the aperture hole has a diameter of 30-80um, and a suitable aperture diameter is beneficial to obtain single, controllable orbital angular momentum vortex electrons with stable shape bundle.

Preferably, the diameter of the magnetic needle is 1-20um, and the length is 80-200um.

Preferably, the preparation method of the magnetic needle wound with the conductive coil is as follows: first, select a magnetic wire with a diameter of 1-20 μm, and deposit an insulating layer on the surface of the magnetic wire; then, on the surface of the insulating layer A conductive layer is electroplated, and the conductive layer is cut into coils to form magnetic needles wound with conductive coils.

The magnetic wire is a linear material with magnetic properties, which can be Ni, FeNi alloy, or CoNi alloy. Preferably, the magnetic wire is Ni.

Preferably, the specific process of depositing an insulating layer on the surface of the magnetic wire is as follows: first, the organic solvent and ammonia water are mixed, ultrasonicated and left to stand, and then mixed with TEOS and ultrasonicated to form an insulating liquid; then , stirring and heating the magnetic wire in the insulating liquid to form an insulating layer. The organic solvent is isopropanol, cyclohexane and the like.

Preferably, the insulating material is SiO ₂ and Al ₂ O ₃ .

Further preferably, the specific process of depositing an insulating layer on the surface of the magnetic wire is as follows: first, the organic solvent and ammonia water are mixed, ultrasonicated for 3-10 min, and left to stand, and then mixed with the insulating material, ultrasonicated for 1 ～5min to form an insulating liquid; then, the magnetic wire is placed in the insulating liquid, and the reaction is stirred at 25～65° C. for 3h～6h to form an insulating layer with a thickness of 1～5um.

Preferably, the material of the conductive layer is Cu, Au, and Pt, and more preferably, the material of the conductive layer is Cu. Preferably, the thickness of the conductive layer is 0.1-2um.

Preferably, the magnetic field controller is an electrical appliance or element capable of controlling the output of different currents, and may be a sliding resistor, a current generator, or the like.

A second embodiment of the present invention provides a method for generating a controllable vortex electron beam using the above-described apparatus.

A third embodiment of the present invention provides an apparatus for generating a controllable vortex electron beam, comprising:

Electron guns for generating planar electron beams;

Magnetic field control unit;

The electronic phase modulation unit is acted by the magnetic field control unit to generate a magnetic field with controllable intensity, and the magnetic field is used to modulate the phase of the plane electron beam.

Preferably, the electronic phase modulation unit may be a magnetic needle wound with a conductive coil. The magnetic field control unit is a current controller.

Compared with the prior art, the embodiments provided by the present invention have the following advantages:

(1) It overcomes the shortcomings of unstable phase plate method, limited service life, difficult processing, low electron beam intensity of holographic aperture method and uncontrollable orbital angular momentum of magnetic-like monopole method. A magnetic monopole-like magnetic field distribution is formed in the microscope to obtain a vortex electron beam with a single orbital angular momentum and a controllable quantum number.

(2) The magnetic field controller can control the magnetic field strength at the tip of the magnetic needle by adjusting the coil current, so that vortex electron beams with different orbital angular momentum can be obtained.

Description of drawings

1 is a schematic structural diagram of a device for generating a controllable vortex electron beam in a TEM provided by Embodiment 1;

FIG. 2 is a simulation diagram of the magnetic field after the magnetic needle wound with the conductive coil prepared in Example 2 is energized.

Detailed ways

In order to describe the present invention more specifically, the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

Example 1

Referring to FIG. 1 , this embodiment provides a device for generating a controllable vortex electron beam in a TEM. The device includes: an electrical sample rod 1 , a sample chip 2 , a magnetic needle 3 wound with a conductive coil, and a magnetic field controller 4 . The end of the electrical sample rod 1 is provided with a mounting groove, and the electrode at the tail is connected to the magnetic field controller 4; the center of the sample chip 2 is provided with a diaphragm hole 5, which is placed in the mounting groove, and one end of the electrode in the sample chip 2 is connected to the sample The electrodes in the rod 2 are connected; the magnetic needle 3 wound with the conductive coil is placed horizontally on the surface of the sample chip 2, and the tip of the magnetic needle 3 wound with the conductive coil is aligned with the center of the aperture hole 5, and the conductive coil and the electrode sheet of the sample chip 2 are separated. connected at one end.

In this embodiment, the magnetic field control unit is a current controller. The diameter of the aperture 5 is 50um.

The magnetic needle 3 is connected to the sample chip 2 by a focused ion beam instrument. The specific process is as follows:

First, stick one end of the magnetic needle 3 with a tungsten needle (only in physical contact at this time), and spray Pt on the contact part, so that the tungsten needle and the magnetic needle 3 are in firm contact;

Then, use the nanomanipulator to slowly lift the tungsten needle (the speed should not be too fast to prevent the magnetic needle from falling), move it to the top of the sample chip 2, align the tip of the magnetic needle 3 with the center of the through hole 5 and place it on the sample chip 2, Pt is plated on the contact place between the tail of the magnetic needle 3 and the chip to make it fixed;

Finally, the tungsten needle and the magnetic needle 3 are cut off to complete the electrical connection between the magnetic needle 3 and the sample chip 2 .

Example 2

The present embodiment provides a method for preparing the magnetic needle 3, specifically:

First, a magnetic wire with a diameter of 10um and a length of 100um is selected, and the magnetic wire is Ni.

Then, an insulating layer is deposited on the surface of the magnetic wire.

In this embodiment, the specific process of depositing an insulating layer on the surface of the magnetic wire is as follows:

(1) Measure an appropriate amount of organic solvent (the organic solvent can be cyclohexane, isopropanol) and put it in a three-necked flask, and drop an appropriate amount of deionized water with a pipette, stir for about 10 minutes, and then add an appropriate amount of ammonia water , ultrasonicate for about 10 minutes at room temperature, and let stand; (2) after mixing the above-treated organic solvent with TEOS, ultrasonicate for about 5 minutes at room temperature to form an insulating liquid; (3) place the fixed magnetic wire in a beaker, put the The insulating liquid was slowly dropped into the beaker, and the reaction was stirred at 45 °C for 6 h to form an insulating layer with a thickness of 2 μm.

Next, a conductive layer is electroplated on the surface of the insulating layer. In this embodiment, the process is specifically:

(1) Select copper as the conductive material, and soak the surface of the copper sheet and the magnetic wire with methanol to prevent organic pollution; (2) Connect the copper sheet to the positive pole of the regulated AC power supply, and fix the conductive glue of the magnetic wire covering the insulating layer with the Connect the negative pole of the regulated AC power supply, turn on the power supply, and start electroplating. During the electroplating process, the copper sheet of the anode undergoes an oxidation reaction: Cu-2e ^- →Cu ²⁺ , and the cathode undergoes a reduction reaction of copper ions on the online surface: Cu ^{2 +} +2e ^- →Cu, forming a conductive layer with a thickness of 0.5um.

Finally, the conductive layer is cut into coils to form magnetic needles wound with conductive coils. In this embodiment, the process adopts the FIB cutting method.

The magnetic field simulation test of the magnetic needle wound with the conductive coil is carried out by using COMSOL software, and the test result is shown in Figure 2. It can be seen from Figure 2 that the tip of the magnetic needle has a strong magnetic field when the current is applied, and the magnetic field strength when the current is 2A (Figure 2B) is much greater than that when the current is 1A (Figure 2A).

The above-mentioned specific embodiments describe in detail the technical solutions and beneficial effects of the present invention. It should be understood that the above-mentioned embodiments are only the most preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, additions and equivalent substitutions made within the scope shall be included within the protection scope of the present invention.

Claims (1)

1. An apparatus for generating a controlled vortex electron beam based on a TEM, comprising:

an electron gun generating a planar electron beam;

a magnetic field controller;

the magnetic needle is wound with the conductive coil, is arranged on the plane electron beam channel through a chip loaded by electrical equipment, and generates a magnetic field with controllable strength under the action of the magnetic field controller, and the magnetic field is used for modulating the phase of the plane electron beam;

the conductive coil on the magnetic needle is connected with one end of an electrode plate of the chip, and forms a magnetic field control loop with the magnetic field controller through electrical equipment loading the chip;

the electrical equipment is an electrical sample rod or a diaphragm rod; the magnetic needle is horizontally arranged on the surface of the chip, and the needle point of the magnetic needle is arranged in the center of the chip; a diaphragm hole is formed in the center of the chip, and the diameter of the diaphragm hole is 30-80 microns; the diameter of the magnetic needle is 1-20 μm, and the length of the magnetic needle is 80-200 μm;

the preparation method of the magnetic needle wound with the conductive coil comprises the following steps: firstly, selecting a magnetic wire with the diameter of 2-20 mu m, and depositing an insulating layer on the surface of the magnetic wire; then, electroplating a conducting layer on the surface of the insulating layer, and cutting the conducting layer into coils to form magnetic needles wound with the conducting coils;

the specific process of depositing an insulating layer on the surface of the magnetic wire comprises the following steps: firstly, mixing an organic solvent and ammonia water, performing ultrasonic treatment for 3-10 min, standing, then mixing with an insulating material, and performing ultrasonic treatment for 1-5 min to form an insulating solution; then, putting the magnetic wire into the insulating liquid, and stirring and reacting for 3-6 h at 25-65 ℃ to form an insulating layer with the thickness of 1-5 mu m.

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