CN107919258B - Device and method for generating controllable vortex electron beam - Google Patents

Device and method for generating controllable vortex electron beam Download PDF

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CN107919258B
CN107919258B CN201710896503.5A CN201710896503A CN107919258B CN 107919258 B CN107919258 B CN 107919258B CN 201710896503 A CN201710896503 A CN 201710896503A CN 107919258 B CN107919258 B CN 107919258B
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magnetic
magnetic field
electron beam
needle
chip
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CN107919258A (en
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田鹤
陈鑫铠
孙土来
杜凯
任天星
陈星�
陈琼阳
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Zhejiang University ZJU
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    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/02Details
    • H01J37/04Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement or ion-optical arrangement
    • H01J37/10Lenses
    • H01J37/14Lenses magnetic
    • H01J37/141Electromagnetic lenses
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/26Electron or ion microscopes; Electron or ion diffraction tubes
    • H01J37/261Details
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/10Lenses
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Abstract

The invention discloses a device for generating controllable vortex electron beams based on a TEM (transverse electric and magnetic field), which is characterized by comprising an electron gun, a vortex electron gun and a vortex electron gun, wherein the electron gun is used for generating plane electron beams; a magnetic field controller; the magnetic needle wound with the conductive coil is arranged on the plane electron beam channel through a chip controlled by electrical equipment, and the magnetic field controller generates a magnetic field with controllable strength, wherein the magnetic field is used for modulating the phase of the plane electron beam. The invention also discloses a method for generating the controllable vortex electron beam by using the device. The device forms magnetic field distribution of a magnetic monopole-like in an electron microscope to obtain a vortex electron beam with single orbital angular momentum and controllable quantum number.

Description

Device and method for generating controllable vortex electron beam
Technical Field
The invention belongs to the field of vortex electron beam generation, and particularly relates to a device and a method for generating a controllable vortex electron beam.
Background
Predictions and experiments in recent years demonstrate that: altering the basic structure of the electron wavefront can impart many specific properties to the electron wavefront that enable new functions in conventional 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 probability current follows a vortex path, with an azimuthal momentum component in the direction of propagation along the axis.
A single vortex bundle can be composed of Ψ ^ f (r). exp (il φ). exp (ik)zz), where (r, φ, z) is a cylindrical coordinate; k is a radical ofzIs the forward momentum of the beam; l is the swirl order, also known as the topological charge number, and a single swirl bundle changes phase by 2 pi l in a loop around the center of the swirl. In a single vortex beam, the vortex order l is proportional to the number of windings (a key parameter for describing vortex), and is also related to Orbital Angular Momentum (OAM) of the beam, which is very unique to a vortex beamInteresting properties. Vortex electron beams carrying orbital angular momentum have great potential for applications in nanoparticle manipulation (rotation, movement, confinement, etc.) and magnetic detection (expected to achieve atomic resolution).
To control the phase of the steering electron wave to produce a specific orbital angular momentum quantum number, various methods have been developed to produce a vortex electron beam. To date, one method of generating a swirling electron beam includes: phase plate method, holographic reconstruction method, and quasi-magnetic monopole field method.
The phase plate method is a method of converting a plane wave incident on a vortex phase plate into a vortex wave by using the vortex phase plate. Researchers have verified the generation of a vortex electron beam by means of planar electron beam interference. A phase difference of 2 pi will produce a vortex electron beam with a topological charge number of 1. Although the phase plate method can generate vortex electron beams, the phase plate method has the following defects: (1) the generated topological charge number is low, and the requirement cannot be met in many times; (2) the phase plate has a limited lifetime, mainly because: the phase plate material is unstable under the action of high-energy electron beams and is easy to damage and pollute; (3) the phase plate is difficult to process, an ideal vortex structure cannot be achieved, and the phase plate with the similar step structure does not generate a single vortex electron beam.
Holographic reconstruction methods are by far the most common methods for generating electron vortex beams. Researchers have observed a vortex electron beam using a holographic diaphragm, but the generated vortex electron beam is a plurality of electron beams carrying different orbital angular momentum, and expanding the application thereof requires a single electron beam, and there is a great difficulty in selecting a single beam from the plurality of beams. In addition, the holographic diaphragm can block most of electron beams, the intensity loss is large, the efficiency is low, and the signals are weak in electron microscopic characterization.
The magnetic monopole field-like method is characterized in that the characteristic of a magnetic monopole at the end of a small magnetic needle is utilized to act on an incident electron beam, and a vortex electron beam is generated according to the Aharonov-Bohm effect. Although the method solves the defect that the holographic reconstruction method shields most of electron beams, the magnetic field generated by the small magnetic needle is uncontrollable and can not generate vortex electron beams with different orbital angular momentum.
Disclosure of Invention
In view of the foregoing, the present invention provides an apparatus and method for generating a vortical electron beam. The device can generate vortex electron beams with controllable orbital angular momentum.
A first embodiment of the present invention provides an apparatus for generating a controlled vortex electron beam based on a TEM (transmission electron microscope), comprising:
an electron gun generating a planar electron beam;
a magnetic field controller;
the magnetic needle wound with the conductive coil is arranged on the plane electron beam channel through a chip loaded by the electrical equipment, and is acted by the magnetic field controller to generate a magnetic field with controllable strength, and the magnetic field is used for modulating the phase of the plane electron beam.
An effective unipolar field is generated at the tip of the nanoscale magnetized ferromagnetic needle. The Aharanov-Bohm effect can be used to understand the effect of such a unipolar field on the electron beam. When a planar electron wave interacts with an imaginary magnetic monopole, a swirling electron beam will be generated. A closed charge path containing magnetic flux can achieve the Aharonov-Bohm (A-B) phase:
Figure BDA0001422272680000031
a is the magnetic vector potential, a mathematical tool used in quantum physics, and is of real significance, and afds refers to the magnetic flux of the surrounding region. e is the electric charge of the organic compound,
Figure BDA0001422272680000032
is constant and c is the speed of light.
This a-B phase can still be produced by quantum mechanical effects even if the electrons do not cross the region with magnetic field lines. Whereas in classical mechanics there would be no effect due to the absence of forces acting on the charge. In the region of infinite cylindrical field lines, the A-B effect is often discussed. Since this avoids special effects at special points where the magnetic field is B-rotA. The form is as follows:
Figure BDA0001422272680000033
r is the cylinder radius, r is the radial vector.
Calculating the Aharonov-Bohm phase of electrons passing perpendicularly through the flux lines of a semi-infinite cylinder will result in an equation that depends on the linear azimuth of the cylinder ends:
Figure BDA0001422272680000034
this means that the passing electrons will indeed turn into a vortex state:
Ψout=Ψinexp(imφ)
where m depends on the charge of the magnetic monopole and phi is the azimuth angle in the plane perpendicular to the propagation of the electron wave. For a true unipolar field, where the charge is
Figure BDA0001422272680000041
Is quantized, which results in an integer m (g ═ mc/(2 × e)), a perfect phase vortex topological charge m.
Therefore, the invention utilizes the magnetic field controller to regulate and control the current flowing through the coil, and can regulate and control the magnetic field size of the magnetic needle tip, thereby obtaining the controllable vortex electron beams with different orbital angular momentum.
The chip is a slide containing electrode plates and has supporting and connecting effects on the conductive coil. The carrier sheet can be a glass sheet, a silicon sheet or an alumina ceramic sheet and the like.
Preferably, the chip may be a sample chip.
Preferably, the electrical device is an electrical sample rod or a diaphragm rod.
Preferably, the magnetic needle is horizontally arranged on the surface of the chip, and the needle point of the magnetic needle is arranged at the center of the chip.
Preferably, 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. After the chip is placed in the electrical equipment, the other end of the electrode plate in the chip is connected with one end of the electrode plate in the electrical equipment and is connected with an external magnetic field controller by utilizing an internal circuit to form a complete system.
Preferably, the center of the chip is provided with a diaphragm hole, further, the diameter of the diaphragm hole is 30-80 um, and the proper diaphragm diameter is favorable for obtaining single and controllable orbital angular momentum vortex electron beams with stable forms.
Preferably, the diameter of the magnetic needle is 1-20 um, and the length is 80-200 um.
Preferably, 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 1-20 um, and depositing an insulating layer on the surface of the magnetic wire; then, a conducting layer is electroplated on the surface of the insulating layer, and the conducting layer is cut into coils to form magnetic needles wound with conducting coils.
The magnetic wire is a wire material having magnetism, and may be Ni, FeNi alloy, or CoNi alloy, and 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: firstly, mixing an organic solvent and ammonia water, performing ultrasonic treatment and standing treatment, and then mixing and performing ultrasonic treatment on the organic solvent and TEOS to form an insulating liquid; then, the magnetic wire is stirred in the insulating liquid and is heated to react, and an insulating layer is formed. The organic solvent is isopropanol, cyclohexane, etc.
Preferably, the insulating material is SiO2、Al2O3
Further preferably, the specific process of depositing an insulating layer on the surface of the magnetic wire comprises: 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, the magnetic wire is placed in the insulating liquid, and the insulating layer with the thickness of 1-5 um is formed after stirring reaction for 3-6 h at the temperature of 25-65 ℃.
Preferably, the conductive layer is made of Cu, Au, or Pt, and more preferably, the conductive layer is made of Cu. Preferably, the thickness of the conductive layer is 0.1-2 um.
Preferably, the magnetic field controller is an electric appliance or an element capable of controlling and outputting different currents, and may be a sliding resistor, a current generator, or the like.
A second embodiment of the invention provides a method of generating a controlled vortical electron beam using the apparatus described above.
A third embodiment of the invention provides an apparatus for generating a controlled vortical electron beam comprising:
an electron gun for generating a planar electron beam;
a magnetic field control unit;
and the electronic phase modulation unit is acted by the magnetic field control unit to generate a magnetic field with controllable strength, and the magnetic field is used for modulating the phase of the planar 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 implementation mode provided by the invention has the following advantages:
(1) the defects that a phase plate method is unstable, the service life is limited, the processing difficulty is high, the intensity of an electron beam is low in a holographic diaphragm method and the orbital angular momentum is uncontrollable in a similar magnetic monopole method are overcome, and based on the similar magnetic monopole principle, magnetic field distribution of the similar magnetic monopole is formed in an electron microscope to obtain the vortex electron beam with single orbital angular momentum and controllable quantum number.
(2) The magnetic field controller can regulate and control the magnetic field intensity of the tip of the magnetic needle by regulating and controlling the current of the coil, so that vortex electron beams carrying different orbital angular momentum can be obtained.
Drawings
FIG. 1 is a schematic structural diagram of an apparatus for generating a controlled vortex electron beam applied in a TEM provided in example 1;
fig. 2 is a graph simulating the magnetic field after the magnetic needle wound with the conductive coil prepared in example 2 is electrified.
Detailed Description
In order to more specifically describe the present invention, the following detailed description is provided for the technical solution of the present invention with reference to the accompanying drawings and the specific embodiments.
Example 1
Referring to fig. 1, the present embodiment provides an apparatus for generating a controlled vortex electron beam applied in a TEM, the apparatus comprising: the device comprises 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 part is connected with the magnetic field controller 4; a diaphragm hole 5 is arranged at the center of the sample chip 2 and is arranged in the mounting groove, and one end of an inner electrode of the sample chip 2 is connected with an inner electrode of the sample rod 2; the magnetic needle 3 wound with the conductive coil is horizontally arranged on the surface of the sample chip 2, the tip of the magnetic needle 3 wound with the conductive coil is aligned with the center of the diaphragm hole 5, and the conductive coil is connected with the other end of the electrode plate of the sample chip 2.
In this embodiment, the magnetic field control unit is a current controller. The diaphragm aperture 5 has a diameter of 50 um.
The magnetic needle 3 is connected to the sample chip 2 by adopting a focused ion beam instrument, and the specific process is as follows:
firstly, sticking one end part of the magnetic needle 3 by a tungsten needle (only physically contacting at the moment), and spraying Pt on the contact part to ensure that the tungsten needle is stably contacted with the magnetic needle 3;
then, slowly lifting the tungsten needle by using a nanometer manipulator (the speed cannot be too high, and the magnetic needle is prevented from falling off), moving the tungsten needle to the upper surface of the sample chip 2, aligning the tip of the magnetic needle 3 with the center of the through hole 5, placing the tungsten needle on the sample chip 2, and plating Pt on the contact part of the tail part of the magnetic needle 3 and the chip to fix the tungsten needle;
and finally, cutting off the tungsten needle and the magnetic needle 3 to complete the electric connection between the magnetic needle 3 and the sample chip 2.
Example 2
The embodiment provides a method for preparing a magnetic needle 3, which specifically comprises the following steps:
firstly, 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) measuring an appropriate amount of organic solvent (cyclohexane or isopropanol) and placing in a three-necked flask, dripping an appropriate amount of deionized water with a liquid-transferring gun, stirring for about 10min, adding an appropriate amount of ammonia water, performing ultrasonic treatment at room temperature for about 10min, and standing; (2) mixing the treated organic solvent with TEOS, and performing ultrasonic treatment at room temperature for about 5min to form an insulating solution; (3) and (3) placing the fixed magnetic wire in a beaker, slowly dropping the insulating liquid into the beaker, and stirring and reacting for 6 hours at 45 ℃ to form an insulating layer with the thickness of 2 um.
Then, a conductive layer is electroplated on the surface of the insulating layer. In this embodiment, the process specifically includes:
(1) selecting copper as a conductive material, and soaking the surfaces of the copper sheet and the magnetic wire with methanol to prevent organic matters from being polluted; (2) connecting a copper sheet with the positive pole of a voltage-stabilizing alternating current power supply, connecting a conductive adhesive fixedly wrapping an insulating layer magnetic wire with the negative pole of the voltage-stabilizing alternating current power supply, starting the power supply to start electroplating, and in the electroplating process, performing oxidation reaction on the copper sheet at the anode: cu-2 e-→Cu2+The cathode is subjected to the reaction that copper ions are reduced on the surface of the wire: cu2++2e-→ Cu, a conductive layer is formed to a thickness of 0.5 um.
And finally, cutting the conducting layer into coils to form magnetic needles wound with the conducting coils. In this example, the FIB cutting method was used for this process.
The COMSOL software was used to perform a magnetic field simulation test on the magnetic needle wound with the conductive coil, and the test results are shown in FIG. 2. As can be seen from fig. 2: under the condition of current, the magnetic needle tip has a stronger magnetic field, and when the current is 2A (figure 2B), the magnetic field intensity is far larger than that of the current is 1A (figure 2A).
The above-mentioned embodiments are intended to illustrate the technical solutions and advantages of the present invention, and 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, and any modifications, additions, equivalents, etc. made within the scope of the principles of the present invention should be included in the 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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CN104285272A (en) * 2011-12-20 2015-01-14 安特卫普大学 Generation of charged particle vortex waves
CN104303256A (en) * 2011-12-20 2015-01-21 安特卫普大学 Charged particle vortex wave generation
CN106711003A (en) * 2017-02-15 2017-05-24 聚束科技(北京)有限公司 Electron source generating device and electron beam control method

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US7019308B2 (en) * 2004-09-01 2006-03-28 Leica Microsystems Lithography Ltd. Thermal compensation in magnetic field influencing of an electron beam

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104285272A (en) * 2011-12-20 2015-01-14 安特卫普大学 Generation of charged particle vortex waves
CN104303256A (en) * 2011-12-20 2015-01-21 安特卫普大学 Charged particle vortex wave generation
CN106711003A (en) * 2017-02-15 2017-05-24 聚束科技(北京)有限公司 Electron source generating device and electron beam control method

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