CN219085925U - Electron source, optical fiber pulse electron gun and electron microscope - Google Patents

Abstract

The utility model discloses an electron source, an optical fiber pulse electron gun and an electron microscope; the electron source comprises at least one needle tip, and the needle tip comprises an optical fiber inner core and an outer cladding; one end of the optical fiber inner core is made into a cone tip structure with the optical fiber radius gradually reduced; the outer cladding includes a reflective metal layer plated at the very tip of the needle tip and a reflective metal layer plated at a location on the needle tip other than the very tip. The optical fiber pulse electron gun is applied to an electron microscope and comprises an electron source, wherein one end of a needle point of the electron source is fixed in an electron microscope cavity, and the other end of the needle point is coupled with a femtosecond laser system positioned outside the electron microscope cavity; and the electrode plate unit is arranged below the needle point in the electron microscope cavity and is used for gathering and transmitting electron beams generated by the electron gun after power connection, so that higher spatial coherence is obtained compared with the traditional electron gun, and the imaging quality is improved.

Description

Electron source, optical fiber pulse electron gun and electron microscope

Technical Field

The utility model relates to the field of electron microscopy, in particular to an electron source, an optical fiber pulse electron gun and an electron microscope.

Background

The time-resolved electron microscope uses an electron pulse as a light source, and uses the principle of pumping experiments to observe a continuous dynamic process of a material from the interaction of a high-acceleration electron pulse and atoms in a sample. The quality of the electronic pulse is also the most important index of the time resolution electron microscope, and determines the time resolution. There are currently two main methods for the generation of such pulsed electrons: chopper and laser excitation.

The chopper uses electric field/magnetic field to control the deflection direction of the light beam, and then the deflection wave is cut by the aperture, so that the pulse light beam can be generated; however, the electron emissivity is affected by electric field control, a system with a repetition frequency higher than several MHz cannot be achieved by using a magnetic coil, and the frequency of the resonant cavity is fixed, so that the requirement of an ultrafast time resolution experiment cannot be completely met.

The laser excitation is to use femtosecond laser pulse to strike the needle point of the electron gun, and generate electrons when the pulse is irradiated, and no electrons are generated in the intermittent laser pulse, so as to generate corresponding femtosecond electron pulse. Thanks to the stability of pulsed lasers, which can already reach the time scale of femtoseconds, the laser excited pulse electrons have a higher time resolution than choppers. However, in the traditional laser excitation pulse electron gun, the needle point of the electron gun and the laser excitation system are separated and independent, laser needs to be introduced through a special reserved window by an external complex optical path system, the internal space of the electron microscope cavity is small, the radius of the needle point of the electron gun is small, the laser is difficult to accurately guide to the needle point, the laser can only irradiate to the needle point laterally, the front end of the needle point cannot uniformly absorb laser energy, and the spatial non-uniformity of excited electrons can be caused, so that the spatial resolution is reduced.

Disclosure of Invention

In order to overcome the defects in the prior art, one of the purposes of the utility model is to provide an electron source.

The second object of the present utility model is to provide an optical fiber pulse electron gun.

Another object of the present utility model is to provide an electron microscope including the above-mentioned optical fiber pulse electron gun.

One of the purposes of the utility model is realized by adopting the following technical scheme:

an electron source comprising at least one needle tip, the needle tip comprising an optical fiber core and an outer cladding;

one end of the optical fiber inner core is made into a cone tip structure with the optical fiber radius gradually reduced;

the outer cladding includes a reflective metal layer plated at the very tip of the needle tip and a reflective metal layer plated at a location on the needle tip other than the very tip.

Further, the optical fiber core is a bare glass optical fiber of 200 microns; one end of the bare glass optical fiber is made into a cone tip structure with the radius smaller than 100 nanometers.

Further, the emission metal layer is a W metal layer; the reflection metal layer comprises a Cr metal layer and an Au metal layer, and the Cr metal layer is arranged between the bare glass optical fiber and the Au metal layer as transition; the thickness of the Cr metal layer is 5nm, and the thickness of the Au metal layer is 30nm.

The second purpose of the utility model is realized by adopting the following technical scheme:

an optical fiber pulse electron gun, which is applied to an electron microscope, comprises:

the electron source is characterized in that one end of a needle point of the electron source is fixed in the electron microscope cavity, and the other end of the needle point is coupled with a femtosecond laser system outside the electron microscope cavity;

and the electrode plate unit is arranged below the needle point in the electron microscope cavity and is used for gathering and emitting electron beams generated by the electron gun after being electrified.

Further, the electrode plate unit comprises a Welch cap electrode plate and an anode, the Welch cap electrode plate and the anode are sequentially arranged below a needle point in the electron microscope cavity, the Welch cap electrode plate is connected with a positive voltage to gather electrons, and the anode is connected with an accelerating voltage to generate positive attractive force so that electron beams can be accelerated to pass through an optical axis.

Further, the needle point is fixed in the electron microscope cavity through a base, and the most tip of the needle point extends out of the base and is opposite to the optical axis; the other end of the needle point is bent at the rear end of the base and led out of the electron microscope cavity from an opening at one end of the Webster cap pole piece.

Further, the electron microscope cavity is set to be a vacuum cavity, an optical fiber feed-through is arranged at a position, opposite to the opening of the Welch cap pole piece, of the electron microscope cavity, a first connector is arranged in the electron microscope cavity, and the first connector is connected with a tail fiber inside the feed-through and fused with the needle point, so that laser enters the optical fiber from the outside and is transmitted to the needle point all the way.

Further, a second connector is arranged outside the electron microscope cavity, the femtosecond laser system is connected into the optical fiber feed-through the second connector, so that laser generated by the femtosecond laser system enters the vacuum electron microscope cavity through the second connector and the optical fiber feed-through.

Further, the femtosecond laser system comprises a femtosecond laser, a beam expander group and an optical fiber coupling module which are positioned on the same optical axis, wherein laser emitted by the femtosecond laser is subjected to beam expansion through the beam expander group, and then light beams are converged and coupled to an optical fiber jumper through the optical fiber coupling module, and are transmitted to the second connector through the optical fiber jumper so as to enter the inside of the electron microscope cavity.

The third purpose of the utility model is realized by adopting the following technical scheme:

an electron microscope comprising a fibre pulse electron gun as described above.

Compared with the prior art, the utility model has the beneficial effects that:

(1) A bare glass optical fiber with a 200-micron inner core is utilized, one end of the bare glass optical fiber is manufactured into an optical fiber needle point with the radius smaller than 100 nanometers by a drawing or etching method, and a layer of metal film which is easy to reflect laser is plated at the cone point to serve as a reflecting layer so as to improve the laser conductivity; the reflecting layer is used for increasing the conductivity of laser when the radius of the optical fiber is gradually reduced, so that more laser can penetrate to the tip, and the laser reaching the tip irradiates the metal tungsten coating back, so that the optical fiber needle tip well achieves the purposes of introducing the optical fiber from the outside and exciting the optical fiber at the tip;

(2) The laser system and the needle point of the electron gun can be coupled outside the cavity by transmitting laser through the optical fiber. The laser is directly transmitted to the needle point to excite the pulse electrons, so that a pulse electron beam with high time resolution of femtosecond level is obtained, and the technical difficulty of alignment and the technical defect caused by lateral excitation are avoided;

(3) Compared with the traditional laser excitation electron gun on the market which mostly utilizes thermal emission, the optical fiber needle tip radius designed by the utility model can reach the magnitude smaller than 100nm, and the optical fiber needle tip radius is matched with a Welch cap to realize optical field emission so as to achieve higher spatial coherence. In addition, the electron gun substrate, the electron gun design and the matched cavity matched with the scheme are designed at the same time, so that a complete electron pulse generation scheme aiming at an electron microscope is provided.

Drawings

FIG. 1 is a schematic view of the layer structure of the needle tip of the present utility model;

FIG. 2 is a schematic view of the structure of the needle tip of the present utility model fixed on the base;

FIG. 3 is a schematic view of the structure of the electron gun chamber of the present utility model;

FIG. 4 is a schematic diagram of the laser coupling and optical path of the present utility model.

In the figure: 1. an optical fiber core; 2. a Cr metal layer; 3. an Au metal layer; 4. a W metal layer; 5. a base; 6. a clamp; 7. opening holes; 8. a Welch cap pole piece; 9. an anode; 10. a metal cavity; 11. a metal seal ring; 12. an optical fiber feedthrough; 13. a diaphragm.

Detailed Description

The present utility model will be further described with reference to the accompanying drawings and detailed description, wherein it is to be understood that, on the premise of no conflict, the following embodiments or technical features may be arbitrarily combined to form new embodiments.

Example 1

The present embodiment provides an electron source that can be used in an electron microscope to increase the femto-second analysis capability of the electron microscope.

The electron source comprises at least one needle tip, as shown in fig. 1, comprising an optical fiber core 1 and an outer cladding.

One end of the optical fiber core 1 is manufactured into a cone tip structure with gradually reduced optical fiber radius by a drawing or etching method; in this embodiment, the optical fiber core 1 is a bare glass optical fiber with 200 μm, and one end of the bare glass optical fiber needs to be made into an optical fiber tip with a radius smaller than 100 nm.

The outer cladding is plated outside the optical fiber inner core 1, the outer cladding comprises a reflecting metal layer and a transmitting metal layer, the transmitting metal layer is plated at the most tip of the needle point, and the reflecting metal layer is plated at a position outside the most tip of the needle point.

After a layer of reflective metal layer is completely plated outside the optical fiber inner core 1 in the preparation process of the needle point, the reflective metal layer at the most tip of the needle point is removed and plated with an emitting metal layer, so that the emitting metal layer only exists at the most tip of the needle point, and the rest positions of the needle point are still plated with the reflective metal layer.

In this embodiment, the emission metal layer is a W metal layer 4 as an electron emission source material; the reflective metal layer comprises a Cr metal layer 2 and an Au metal layer 3, wherein the Au metal layer 3 is used for reflecting laser, and the Cr metal layer 2 is arranged between the bare glass optical fiber and the Au metal layer 3 as transition; the thickness of the Cr metal layer 2 is 5nm, and the thickness of the Au metal layer 3 is 30nm.

The laser is transmitted to the needle point at the position of 100 nanometers along the optical fiber, and as the radius of the optical fiber is smaller, the reflection angle of the laser is gradually increased when the optical fiber propagates, and finally the critical total reflection angle of the optical fiber is inevitably larger, so that a layer of metal film which is easy to reflect the laser is plated at the conical tip as a reflection layer to improve the laser conductivity, and more laser can penetrate to the tip; while the reflective coating at the fiber tip will be removed and coated with electron-emitting metal W, the laser reaching the tip will irradiate the metal tungsten coating back, exciting electrons.

The optical fiber nanoneedle point (the curvature radius of the needle point is less than 100 nm) related to the embodiment can be prepared by a CO2 laser optical fiber fusion drawing machine or a corrosion method, the front end of the optical fiber needle point is plated with metal (Cr, au and W) by utilizing an electron beam thermal evaporation system and a pulse laser deposition system, and femtosecond pulses are led into the optical fiber, so that the pulse laser excites electrons in a material to a high energy level by a tungsten metal layer which is back to the excited optical fiber needle point, the excitation mode is back irradiation excitation of the femtosecond laser, and then the high energy level electron tunneling field is matched with a proper electric field to emit femtosecond level electron pulses.

Example two

The embodiment provides an optical fiber pulse electron gun which can be applied to an electron microscope, and the electron gun comprises an electron source and an electrode plate unit as described in the first embodiment.

The needle point in the electron source is fixed in the electron microscope cavity, and the other end of the needle point is coupled with a femtosecond laser system positioned outside the electron microscope cavity; wherein, the optical fiber needle point is fixed on the electron gun base 5 so that the needle point is vertical to the plane of the base 5, and one end of the optical fiber needle point is ensured to be fixed in the direction of the light path; at the same time, the optical fiber clamp 6 can be used for fixing the optical fiber, so that the front end of the needle point is stabilized, and the cone tip extends out to be aligned with the optical axis.

The electrode plate unit is arranged below the needle point in the electron microscope cavity and is used for gathering and emitting electron beams generated by the electron gun after being electrified. As shown in fig. 2, the electrode plate unit comprises a wegener cap electrode plate 8 and an anode 9, and the wegener cap electrode plate 8 and the anode 9 are sequentially arranged below the needle point in the electron microscope cavity. Wherein, the power line is communicated with the upper part of the electron microscope cavity to generate different electric potentials at the electron gun, the Welch cap pole piece 8 and the anode 9, in particular: the weskit cap pole piece 8 will switch on a positive voltage with respect to the electron gun to achieve the effect of critical field emission, said weskit cap pole piece 8 switching on a positive voltage to collect electrons excited by said needle tip. While the anode 9 is switched on to accelerate the voltage to generate positive attractive force to accelerate the concentrated electron beam through the optical axis and into the electron microscope lower end system. The distance from the needle tip to the electronic base 5 and the needle tip to the Welch cap pole piece 8 is adjusted to be optimal according to simulation and experimental data.

As shown in fig. 3, the needle tip is fixed in the electron microscope cavity through the base 5, and the other end of the needle tip is bent at the rear end of the base 5 and led out of the electron microscope cavity from the opening 7 at one end of the wegener's cap pole piece 8. In this embodiment, the electron microscope cavity is a vacuum cavity, and in order to ensure vacuum, the cavity is composed of a plurality of metal sealing rings 11 and a metal cavity 10. In addition, in order to ensure that the vacuum is ensured to be simultaneously accessed into the optical fiber, an optical fiber feed-through 12 is arranged at the position, opposite to the opening 7 of the Welch cap pole piece 8, of the electron microscope cavity, and laser is guided into the vacuum cavity through the feed-through.

A first connector is arranged in the electron microscope cavity, and is connected with a tail fiber in the feed-through and fused with the needle point; and a second connector is arranged outside the electron microscope cavity, and the femtosecond laser system is connected into the optical fiber feed-through 12 through the second connector. Wherein, the first connector and the second connector can adopt FC/APC connector to realize optical fiber connection.

When the actual cavity works, the electrostatic potential is used for reducing the work function, laser output by the femtosecond laser system is transmitted to the needle point from outside through the optical fiber feed-through 12 to back excite the electronic pulse, and then the electronic pulse beam is accelerated to form a pulse electronic beam for detecting the sample, and enters the lens group and the sample chamber through the diaphragm 13.

In this embodiment, as shown in fig. 4, the femtosecond laser system includes a femtosecond laser, a beam expander set and an optical fiber coupling module, which are located on the same optical axis, wherein the femtosecond laser emitted by the femtosecond laser is expanded by the beam expander set, and the beam expander set is composed of a convex lens and a concave lens; the laser beam used in this example was extended from original 2 to 3mm to 12 to 18mm.

The laser after beam expansion is coupled to an optical fiber jumper through the optical fiber coupling module, and is transmitted to the second connector through the optical fiber jumper so as to enter the inside of the electron microscope cavity. The optical fiber coupling module comprises an optical fiber collimator which is used for converging light beams to 2.5 mu m so as to be conveniently coupled into an optical fiber jumper. After entering the jumper, the laser propagates along the jumper to the fiber feedthrough 12 and passes through the fiber feedthrough 12 through the FC/APC connector to enter the vacuum cavity; and is connected with the tail fiber in the optical fiber feed-through 12 through the FC/APC jumper in the cavity, and the jumper is cut off at a proper position and fused with the fiber needle point with the drawn coating, so as to finally achieve the purpose that laser enters the optical fiber from the outside and is transmitted to the fiber needle point all the way.

In order to achieve the ultra-fast electron microscopy effect, generating a pulsed beam is critical for stroboscopic imaging. Strobe imaging samples with millions of pump excitations and generates an image with electronic pulses. This method can generate an image with high spatial resolution. Meanwhile, the pulse width is a main influencing factor for determining the time resolution of the ultra-fast electron microscope experiment, and the embodiment can obtain higher time resolution than a chopper by using a femtosecond laser as excitation; and the needle point electron gun with the needle point radius smaller than 100nm can obtain higher spatial coherence than the traditional electron gun, and improve imaging quality.

Example III

This embodiment provides an electron microscope including the optical fiber pulse electron gun described in embodiment two. The components of the objective lens, the signal collecting device, etc. included in the electron microscope are disclosed in the prior art and will not be described in detail here.

The electron microscope in this embodiment and the electron gun in the foregoing embodiment are based on another aspect of the same inventive concept, and the electron gun has been described in detail in the foregoing, so that those skilled in the art can clearly understand the structure and implementation of the electron microscope in this embodiment according to the foregoing description, and the details are omitted herein for brevity.

The above embodiments are only preferred embodiments of the present utility model, and the scope of the present utility model is not limited thereto, but any insubstantial changes and substitutions made by those skilled in the art on the basis of the present utility model are intended to be within the scope of the present utility model as claimed.

Claims (10)

1. An electron source comprising at least one tip, said tip comprising an optical fiber core and an outer cladding;

one end of the optical fiber inner core is made into a cone tip structure with the optical fiber radius gradually reduced;

the outer cladding includes a reflective metal layer plated at the very tip of the needle tip and a reflective metal layer plated at a location on the needle tip other than the very tip.

2. The electron source of claim 1, wherein the fiber optic core is a 200 micron bare glass fiber; one end of the bare glass optical fiber is made into a cone tip structure with the radius smaller than 100 nanometers.

3. The electron source of claim 2, wherein the emissive metal layer is a W metal layer; the reflection metal layer comprises a Cr metal layer and an Au metal layer, and the Cr metal layer is arranged between the bare glass optical fiber and the Au metal layer as transition; the thickness of the Cr metal layer is 5nm, and the thickness of the Au metal layer is 30nm.

4. An optical fiber pulse electron gun, characterized by being applied to an electron microscope, comprising:

an electron source according to any one of claims 1 to 3, wherein one end of the needle point is fixed in the electron microscope cavity, and the other end is coupled with a femtosecond laser system outside the electron microscope cavity;

and the electrode plate unit is arranged below the needle point in the electron microscope cavity and is used for gathering and emitting electron beams generated by the electron gun after being electrified.

5. The optical fiber pulse electron gun according to claim 4, wherein the electrode plate unit comprises a wegian cap electrode plate and an anode, the wegian cap electrode plate and the anode are sequentially arranged below a needle point in the electron microscope cavity, the wegian cap electrode plate is connected with a positive voltage to collect electrons, and the anode is connected with an accelerating voltage to generate positive attractive force so as to enable electron beams to accelerate through an optical axis.

6. The optical fiber pulse electron gun according to claim 5, wherein the needle tip is fixed in the electron microscope cavity through a base, and the most tip of the needle tip extends out of the base and is opposite to the optical axis; the other end of the needle point is bent at the rear end of the base and led out of the electron microscope cavity from an opening at one end of the Webster cap pole piece.

7. The optical fiber pulse electron gun according to claim 6, wherein the electron microscope cavity is a vacuum cavity, an optical fiber feed-through is arranged at a position, opposite to the opening of the Welch cap pole piece, of the electron microscope cavity, a first connector is arranged in the electron microscope cavity, and the first connector is connected with a tail fiber inside the feed-through and fused with the needle point, so that laser enters the optical fiber from the outside and is transmitted to the needle point all the way.

8. The optical fiber pulse electron gun according to claim 7, wherein a second connector is arranged outside the electron microscope cavity, the femtosecond laser system is connected into the optical fiber feed-through the second connector, and laser generated by the femtosecond laser system enters the vacuum electron microscope cavity through the second connector and the optical fiber feed-through.

9. The optical fiber pulse electron gun according to claim 8, wherein the femtosecond laser system comprises a femtosecond laser, a beam expander group and an optical fiber coupling module which are positioned on the same optical axis, wherein laser emitted by the femtosecond laser is converged and coupled to an optical fiber jumper through the optical fiber coupling module after being expanded by the beam expander group, and is transmitted to the second connector through the optical fiber jumper to enter the interior of the electron microscope cavity.

10. An electron microscope comprising a fibre pulse electron gun according to any of claims 4 to 9.

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