CN104359941B - The local locating method of one-dimensional material - Google Patents

Abstract

The invention discloses a local positioning method of a one-dimensional material. In this method, a wrapping layer formed of wrapping material is firstly formed on the surface of the one-dimensional material to make it visible under observation conditions; and then the local wrapping layer to be positioned on the one-dimensional material is removed to form a wrapping segment and a corresponding segment on the one-dimensional material. For the local exposed section, the one-dimensional material of the wrapped section is visible under the observation conditions, and the one-dimensional material of the exposed section is exposed to the surrounding environment and is invisible under the observed conditions. The visible wrapped section is used as a positioning mark for the invisible The bare section is positioned to facilitate subsequent operations such as measuring the thermal conductivity of one-dimensional materials. Compared with the existing technology, the present invention provides a method for reversibly realizing one-dimensional materials to be visible under an optical microscope, and uses the method to operate on one-dimensional materials, so that the practical application of one-dimensional materials is more extensive. The method is simple and practical, the effect is reversible, and the physical properties of the material itself will not be affected after the original appearance is restored.

Description

Local localization methods for one-dimensional materials

technical field

The invention relates to the technical field of nanomaterials, in particular to a local positioning method for one-dimensional materials.

Background technique

One-dimensional materials, especially one-dimensional nanomaterials, are materials that are extremely small in two geometric dimensions and approach or reach the macroscopic level in the other geometric dimension. This material has special excellent mesoscopic properties that some macroscopic materials do not have, such as excellent electrical properties that are highly sensitive to structure, and thermal and optical properties that are superior to macroscopic materials. Therefore, this material has broad application prospects.

However, due to its extremely small size, its morphology can only be characterized by expensive equipment such as scanning electron microscopes or even transmission electron microscopes, and the steps are cumbersome, which requires high requirements on the sample preparation process and sample properties. Efficient manipulation at the time of application or representation is equally difficult. Therefore, there is an urgent need for a method to visualize one-dimensional materials under an optical microscope. Although some one-dimensional material visualization methods have been reported, the existing methods are complex and irreversible, which easily lead to the loss of unique excellent properties of one-dimensional materials.

Accurate determination of the physical properties of 1D materials themselves is essential for the applications of such materials. However, it has always been difficult to measure the thermal, optical and other physical properties of this material. For example, in the measurement of thermal conductivity in thermal science, it is necessary to obtain the accurate temperature of the measured substance at a specific position, or the value of the thermal power passing through a certain section. In addition, for one-dimensional materials with extremely small cross-sections, the positioning accuracy must be at least micron level. It is difficult to achieve such a small detection accuracy and spatial accuracy with traditional infrared thermometers. On the other hand, the extremely small size of a one-dimensional material results in an extremely small heat capacity. When using the traditional contact temperature measurement method, when the macro-scale temperature probe contacts the material, the temperature of the material itself will change dramatically, seriously affecting the thermal state of the one-dimensional material and hindering the measurement of thermal properties. In addition, when macroscopic objects touch one-dimensional materials, it is easy to cause damage to the one-dimensional materials, destroying the physical properties of the measured one-dimensional materials, and the operation of the measurement process is also very difficult. Therefore, a non-contact method with accurate spatial precision is urgently needed for the measurement of thermal properties of one-dimensional materials.

In addition, the small size of one-dimensional materials also leads to weak thermal signals measured, which has high requirements for measuring instruments, as well as very strict requirements for the design and manufacturing process of measuring devices, so if there is a material Thermal signatures can manifest themselves, and simply probing this self-evident thermally sensitive response with another method would be of great experimental benefit.

In terms of optical performance measurement, due to the extremely small size of one-dimensional materials, the interaction area with light is very small, so the absorption cross-section and scattering cross-section are very small. According to the existing experimental equipment, the process of accurately detecting the optical signal of one-dimensional materials is complicated and difficult. The equipment required is expensive. The photothermal phenomenon of the one-dimensional material itself is a response signal spontaneously generated after the material interacts with light, and this thermal response changes with the change of light intensity and polarization, which can reduce the focus on the measurement process. The requirements of experimental factors such as light intensity fluctuations can also reflect the different response characteristics of the material itself to light.

Contents of the invention

The purpose of the present invention is to provide a method for local positioning of one-dimensional materials. This method makes invisible one-dimensional materials visible by wrapping volatile substances, and then locates invisible parts. The method is simple and practical, and the effect is reversible .

In order to achieve the above object, according to one aspect of the present invention, a method for local positioning of one-dimensional materials is provided, which is used for local positioning of one-dimensional materials under one observation condition, so as to perform desired localization of one-dimensional materials. A subsequent operation of , wherein the one-dimensional material itself is not directly visible under observation conditions; the method comprising the steps of:

forming a coating on the surface of the one-dimensional material along the one-dimensional material such that the one-dimensional material and the coating thereon as a whole are visible under observation conditions; wherein the coating is formed of a coating material that is removable from the one-dimensional material ; The wrapping layer at the local part to be positioned of the one-dimensional material is removed, thereby forming a wrapping segment and a corresponding local bare segment on the one-dimensional material, wherein, at the wrapping segment, the one-dimensional material remains wrapped by the wrapping layer, thereby Make the wrapped section visible under observation conditions; at the bare section, the one-dimensional material is directly exposed to the surrounding environment and is invisible under observation conditions; thus, it is possible to use the visible wrapped section as a positioning mark to locate the invisible exposed section .

Further, the local localization method of the one-dimensional material also includes: placing the one-dimensional material in the deposition environment of the precursor containing the wrapping material; and adjusting the parameters of the deposition environment, so that the precursor is physically or chemically deposited in the one-dimensional surface of the material to form a wrapping layer.

Further, the precursor of the encapsulation material is a gaseous form of the encapsulation material, and adjusting the parameters of the deposition environment includes reducing the temperature of the deposition environment, so that the precursor condenses on the surface of the one-dimensional material in liquid or solid form.

Furthermore, the wrapping material is a material that is easily volatilized by heat; the method for local positioning of the one-dimensional material further includes: heating the part of the one-dimensional material to be positioned, so as to remove the wrapping layer on the local surface.

Further, the wrapping material is ice or dry ice and other substances.

Further, the deposition environment may be a solution formed from the precursor of the encapsulation material.

Further, the precursor is an organic substance distributed in the solution or an ion dissociated in the solution; optionally, the ion is a salt ion; further optionally, the solution is an aqueous solution.

Further, the wrapping material is a volatile material.

Further, the wrapping material is a material that is easily volatilized by heat; the method for local positioning of the one-dimensional material further includes: heating the part of the one-dimensional material to be positioned, so as to remove the wrapping layer at the part.

Further, the one-dimensional material is a one-dimensional nanometer material, and the observation condition is to observe the one-dimensional material with an optical microscope.

Further, the method for local positioning of the one-dimensional material further includes: removing the wrapping layer of the wrapping section after performing subsequent operations on the part of the one-dimensional material.

Further, the subsequent operation includes measuring the thermal conductivity of the one-dimensional material.

Further, the measurement of thermal conductivity includes: heating the one-dimensional material until it reaches a thermally stable equilibrium state; obtaining the positions of the first and second reference points on the one-dimensional material and the temperature in the thermally stable equilibrium state; wherein , the first reference point is the adjoining point of the abutment of the wrapped section and the bare section; the second reference point is selected from another reference point different from the adjoining point of the bare section; according to the position and temperature at the first and second reference points and The thermal conductivity is calculated based on a pre-established calculated relationship of the thermal conductivity to the positions and temperatures at the first and second reference points.

Further, the step of heating the one-dimensional material until it reaches a thermally stable equilibrium state is the same step as the step of removing the local wrapping layer of the one-dimensional material.

Further, the calculation relationship is established by associating the corresponding one-dimensional steady-state heat diffusion equations of the exposed segment and the wrapped segment.

Furthermore, the one-dimensional steady-state heat diffusion equations of the bare segment and the wrapped segment are related according to the differentiability of the temperature of the one-dimensional material at the adjacent point.

Furthermore, the position and temperature of the first and second reference points are used as two boundary conditions of the one-dimensional steady-state heat diffusion equation of the bare section; the position and temperature of the first reference point are used as the one-dimensional steady-state heat diffusion equation of the wrapped section One of the two boundary conditions of .

Further, the other of the two boundary conditions of the one-dimensional steady-state heat diffusion equation of the wrapped section is set based on the fact that the temperature of the one-dimensional material at infinity is the temperature of the surrounding environment.

Further, the calculation relationship is:

in, ΔT _H ＝T _H -T ₀ , ΔT _M ＝T _M -T ₀ ,

T ₀ is the temperature of the surrounding environment; T _M is the temperature at the first reference point; X _M is the position of the first reference point when the second reference point is selected as the coordinate origin; T _H is the second reference The temperature at the point; g is the heat exchange coefficient between the bare section of the one-dimensional material and the surrounding environment; g' is the heat exchange coefficient between the one-dimensional material and the wrapping material; P is the circumferential direction of the one-dimensional material The perimeter; A is the cross-sectional area of the one-dimensional material; κ is the axial thermal conductivity of the one-dimensional material to be measured.

Further, the step of forming the wrapped segment and the exposed segment on the one-dimensional material and the step of heating the one-dimensional material until it reaches a thermally stable equilibrium state include:

Wrapping a wrapping material on the one-dimensional material, wherein the wrapping material is a material that is easily volatile when heated;

Irradiate the wrapped one-dimensional material with the first laser to heat it, so that the wrapped material at the spot of the first laser and within a certain distance around it will volatilize from the one-dimensional material due to heat, until thermal stability equilibrium is reached State; thus, the part of the one-dimensional material that is exposed to the surrounding environment due to volatilization of the wrapping material forms a bare segment, and the part of the one-dimensional material that is adjacent to one side of the bare segment and retains the wrapping material forms a wrapping segment.

Further, the step of wrapping the wrapping material on the one-dimensional material includes: placing the one-dimensional material in a surrounding environment containing a precursor of a material easily volatilized by heat, and lowering the temperature of the surrounding environment so that the precursor condenses on the one-dimensional material The surface until wrapping one-dimensional material.

Further, the precursor is a gaseous form of the thermally volatile material; optionally, the thermally volatile material wrapping the one-dimensional material is in a solid state; further optionally, the precursor is water vapor, and the thermally volatile material wrapping the one-dimensional material The material is a layer of ice condensed by water vapor.

Further, the wrapping thickness of the one-dimensional material by the wrapping material is set to at least make the one-dimensional material with the wrapping material visible under an optical microscope; preferably, the positions of the first and second reference points are obtained under an optical microscope.

Further, the second reference point is the edge of the spot of the first laser on the side of the one-dimensional material facing the wrapping section.

Further, the step of obtaining the temperature at the second reference point on the one-dimensional material includes: measuring the peak position of the first Raman spectrum at the second reference point in a thermally stable equilibrium state and under the condition of the first laser irradiation ; Obtain the peak position of the second Raman spectrum of the one-dimensional material at the temperature of the surrounding environment; according to the peak position of the first and second Raman spectrum, obtain the temperature value of the second reference point in a thermally stable equilibrium state or relative The temperature increase value of the surrounding environment; Optionally, the peak position of the first and Raman spectra is a G mode.

Further, the step of obtaining the peak position of the second Raman spectrum includes: cooling the one-dimensional material from a thermally stable equilibrium state to the temperature of the surrounding environment; irradiating the bare section of the one-dimensional material with a second laser to obtain the second Raman spectrum Spectral peak-to-peak position; wherein, the power of the second laser is smaller than the power of the first laser, and the power of the second laser is selected so as not to produce a heating effect on the one-dimensional material as much as possible.

Further, the temperature at the first reference point is the volatilization transition temperature of the wrapping material.

Further, the one-dimensional material is a nano-scale or micro-scale material; optionally, the nano-scale one-dimensional material includes nanowires, nanotubes, nanobelts, nanofibers or nanorods, preferably a single carbon nanotube.

Applying the technical scheme of the present invention, by first forming a wrapping layer along the surface of the one-dimensional material, making it visible under observation conditions, and then removing the wrapping layer on the local surface to be positioned, thereby forming a wrapping segment and a wrapping layer on the one-dimensional material. Corresponding to the partially exposed section, the invisible exposed section can be positioned using the visible wrapping section as a positioning mark.

The invention wraps the volatile substance on the one-dimensional material to form a heterogeneous structure and thicken until the size can be resolved by an optical microscope, thereby realizing the observation of the morphology of the one-dimensional material under the optical microscope. At the same time, the morphology of the one-dimensional material can be observed under an optical microscope, and then the visualization method (including but not limited to visualization) is used to measure the thermal conductivity of the one-dimensional material. In the present invention, the sample is firstly prepared and the geometric dimensions are obtained, and then wrapped into a heterostructure, and then the heterostructure is irradiated with a laser (high-power laser irradiation is used to cause the one-dimensional material to be heated, thereby causing the volatile substances on its surface to disappear), Acquisition of characteristic peaks of Raman spectrum and temperature calculation (used to measure the temperature rise at the edge of the laser spot), measurement of melting length (measurement of the length of the disappearance area of volatile substances, used as a reference standard for the far-point temperature of the heat source), model analysis, and final calculation Thermal conductivity of a one-dimensional material. The invention uses the vanishing edge of volatile substances as the temperature indicating coordinates, and conveniently measures and calculates the axial thermal conductivity of the one-dimensional material by adopting the heat steady state equation.

Compared with the existing technology, the present invention provides a method for reversibly realizing the visibility of one-dimensional materials under an optical microscope. The method is simple and practical, the effect is reversible, and the physical properties of the material itself will not be affected after the original appearance is restored. At the same time, this method is used to measure the thermal conductivity of one-dimensional materials, and the non-contact spectroscopic measurement is combined with the melting of volatile substances as the temperature reference standard, which makes the method self-adjusting (that is, it is much heated by the laser, It also melts much more), which reduces the difficulty of the determination experiment. At the same time, this method can also be used to characterize the differences in optical properties, especially the interaction between one-dimensional materials and light of different polarizations, wavelengths, and intensities. The thermal response can be used to reflect the interaction information between materials and light, avoiding the difficulty of optical detection. .

Those skilled in the art will be more aware of the above and other objects, advantages and features of the present invention according to the following detailed description of specific embodiments of the present invention in conjunction with the accompanying drawings.

Description of drawings

Hereinafter, some specific embodiments of the present invention will be described in detail by way of illustration and not limitation with reference to the accompanying drawings. The same reference numerals in the drawings designate the same or similar parts or parts. Those skilled in the art will appreciate that the drawings are not necessarily drawn to scale. In the attached picture:

Fig. 1 is a schematic structural diagram of a device under test for measuring the visualization of one-dimensional materials under an optical microscope in an embodiment of the present invention;

Fig. 2 is the optical microscope photograph of the heterogeneous structure observed under the optical microscope of the one-dimensional material in the embodiment of the present invention;

Fig. 3 is a schematic diagram of the composition of functional modules of the one-dimensional material thermal conductivity measurement system based on the visualization method in the embodiment of the present invention;

Fig. 4 is a schematic diagram of the one-dimensional material being heated by laser irradiation in an embodiment of the present invention, resulting in the disappearance of volatile substances;

Fig. 5 is an optical microscope photo of the disappearance of volatile substances after the one-dimensional material is irradiated by laser in the embodiment of the present invention; and

Fig. 6 is a fitting spectrum of Raman characteristic peaks measured when the one-dimensional material in the embodiment of the present invention is irradiated by a high-power laser and basically has no heating effect.

detailed description

The "one-dimensional material" referred to in the present invention is a nano-scale one-dimensional material or a micron-scale one-dimensional material, wherein the nano-scale one-dimensional material includes nanowires, nanotubes, nanobelts, nanofibers or nanorods.

In order to solve the problems of extremely small one-dimensional materials, such as expensive equipment such as scanning electron microscope or even transmission electron microscope, complicated steps, high requirements on the production process and sample properties, etc., as well as the extremely small The one-dimensional material of the size cannot be positioned, so that subsequent operations cannot be performed. The present invention provides a local positioning method for one-dimensional materials, which is used for local positioning of one-dimensional materials under one observation condition, so as to The required subsequent manipulations are performed locally on the one-dimensional material, which itself is not directly visible under the observation conditions.

The local positioning method includes the steps of: forming a wrapping layer on the surface of the one-dimensional material along the one-dimensional material, so that the one-dimensional material and the wrapping layer on it are visible under observation conditions as a whole; wherein, the wrapping layer can be obtained from a Formation of wrapping material for removal of one-dimensional material; removing wrapping layer at a part of one-dimensional material to be positioned, so as to form wrapping segment and corresponding exposed segment on one-dimensional material. Wherein, at the wrapping section, the one-dimensional material remains wrapped by the wrapping layer, so that the wrapping section is visible under observation conditions. At the bare section, the one-dimensional material is directly exposed to the surrounding environment and is invisible under observation conditions, so that the invisible bare section can be located by using the visible wrapping section as a positioning mark.

In an embodiment of the present invention, the local positioning method further includes: placing the one-dimensional material in a deposition environment containing a precursor of the encapsulating material, and adjusting the parameters of the deposition environment so that the precursor is physically or chemically deposited On the surface of a one-dimensional material to form a wrapping layer. The deposition environment may or may not be the surrounding environment. For example, the coating is deposited in an aqueous solution, and part of the coating is removed after taking it out. At this time, the deposition environment is the aqueous solution, which is different from the surrounding environment.

In a typical embodiment of the present invention, the deposition environment is a solution formed from the precursor of the encapsulation material. Wherein, the precursors are organic substances distributed in the solution or ions dissociated in the solution. The ions free in the solution are preferably salt ions, and the solution is preferably an aqueous solution.

The local positioning method of the present invention further includes: heating the part of the one-dimensional material to be positioned, so as to remove the wrapping layer at the part. The cladding layer is formed by depositing a cladding material on a one-dimensional material. In another typical embodiment of the present invention, the precursor of the encapsulation material is a gaseous form of the encapsulation material. At this time, in order to deposit the encapsulation material on the one-dimensional material, the parameters of the deposition environment need to be adjusted. Wherein, adjusting the parameters of the deposition environment includes lowering the temperature of the deposition environment, so that the precursor is condensed on the surface of the one-dimensional material in liquid or solid form. The wrapping material may be a volatile material, and the volatile material may be volatile when heated, or volatile due to changes in other environmental parameters. Preferably, the heated volatile material may be ice or dry ice.

In a typical embodiment of the present invention, the method for local positioning of the one-dimensional material further includes: removing the wrapping layer of the wrapping section after performing subsequent operations on the part of the one-dimensional material. By removing the wrapping layer of the wrapping section, the wrapping layer on the surface of the one-dimensional material is completely removed, and the entire one-dimensional material is completely exposed to the surrounding environment, and becomes invisible under the observation condition. Adopting the method of the present invention to wrap and remove the one-dimensional material has no influence on the properties of the material itself, so the visualization method is reversible.

The subsequent operation referred to in the present invention includes measuring the thermal conductivity of the one-dimensional material, but is not limited thereto. At present, very small-sized one-dimensional materials require precise positioning accuracy when measuring thermal conductivity. It is difficult to achieve small-sized detection accuracy and spatial accuracy with traditional infrared thermometers, and the macro-scale temperature in traditional contact temperature measurement methods The problem that the temperature of the material itself will change greatly when the probe touches the one-dimensional material is easy. Based on the above problem, the present invention also provides a method for measuring the thermal conductivity of the one-dimensional material. The measuring method includes: forming a wrapped section and a bare section adjacent to the wrapped section on the one-dimensional material. Wherein, at the wrapping section, the one-dimensional material is wrapped by a wrapping material different from the one-dimensional material; at the bare section, the one-dimensional material is exposed to the surrounding environment. The one-dimensional material is heated until it reaches a thermally stable equilibrium state, and the positions of the first and second reference points on the one-dimensional material and the temperature at the thermally stable equilibrium state are obtained. Wherein, the first reference point is the adjoining point at the adjoining point between the wrapped section and the exposed section, and the second reference point is selected from another reference point different from the adjacent point of the exposed section. The thermal conductivity is calculated from the positions and temperatures at the first and second reference points and based on a pre-established calculated relationship of thermal conductivity to the positions and temperatures at the first and second reference points. The location and temperature selection and calculation relationship of the first and second reference points will be described in detail later.

Wherein, the step of heating the one-dimensional material until it reaches a thermally stable equilibrium state is the same step as the step of removing the local wrapping layer of the one-dimensional material. The following firstly introduces how to form a wrapped segment and a bare segment adjacent to the wrapped segment on the one-dimensional material.

In a preferred embodiment of the present invention, the step of forming the wrapped segment and the exposed segment on the one-dimensional material and the step of heating the one-dimensional material until it reaches a thermally stable equilibrium state include: coating the wrapped material on the one-dimensional material; The first laser irradiates the wrapped one-dimensional material to heat it, so that the wrapped material at the spot of the first laser and within a certain distance around it evaporates from the one-dimensional material due to heat until it reaches a thermally stable equilibrium state. Thus, the part of the one-dimensional material that is exposed to the surrounding environment due to volatilization of the wrapping material forms a bare segment, and the part of the one-dimensional material that is adjacent to one side of the bare segment and retains the wrapping material forms a wrapping segment.

The present invention provides a method for reversibly making one-dimensional materials visible under an optical microscope, including:

1) A one-dimensional material with a certain configuration is placed in an environment containing precursors of volatile substances, where the configuration of the one-dimensional material is suspended and straddles the slit. Specifically, the configuration may be a suspended single single-walled carbon nanotube configuration in which a single carbon nanotube grows in situ and spans hundreds of micron-scale through slits. In other non-illustrated embodiments, the one-dimensional material configuration can also be attached to the substrate.

2) Change the environmental variables such as the temperature of the surrounding environment, so that volatile substances condense on the one-dimensional material, forming a heterogeneous structure and becoming thicker until its size reaches the resolution limit of the optical microscope. As shown in Figures 2-5, the temperature of the surrounding environment 106 is reduced, and the precursors of volatile substances in the surrounding environment are deposited on the one-dimensional material 105, forming a cable-like heterostructure of volatile substances-one-dimensional materials, until one-dimensional The size of the material 105 reaches within the resolution limit of the optical microscope. Since the volatile substances and the surrounding environment have different properties of reflecting or scattering light, the observation of the morphology of the tiny one-dimensional material under the optical microscope 101 is realized (see figure 2).

When the surrounding supercooled environment is broken, the volatile substances condensed on the surface of the one-dimensional material are separated, and the one-dimensional material itself restores its previous shape again, without affecting the characteristics of the one-dimensional material itself. Such condensation and volatilization can be carried out reversibly many times, which is also called the method of reversible visualization of one-dimensional materials under the optical microscope. Not visible under a microscope.

The precursors of the above-mentioned encapsulation materials are gaseous forms of materials that are volatile when heated. Heated volatile materials enveloping one-dimensional materials can assume a solid state. Further optionally, the precursor may be water vapor, the heated and volatile material wrapping the one-dimensional material is an ice layer condensed by water vapor, and the surrounding environment refers to an air environment containing water vapor. The precursors of heated and volatile materials can also be gaseous forms such as carbon dioxide, liquid forms (such as organic matter in water, etc.), and ion forms that are free in solution (such as inorganic salt ions in water, etc.) and after chemical reactions. The chemical reactants that produce the substance. Among them, the former water vapor, carbon dioxide, and organic matter in water will physically deposit on the one-dimensional material due to the decrease in temperature, forming ice, dry ice, and solidified organic matter, etc., while the latter two will chemically deposit in the environment due to changes in environmental factors. The medium is deposited on the one-dimensional material, or relies on the reaction on the one-dimensional material to generate heated and volatile substances (including precipitated salts, etc.).

As shown in FIG. 3 , the present invention also provides a system for measuring the thermal conductivity of a one-dimensional material by reversibly visualizing the one-dimensional material under an optical microscope. The thermal conductivity measurement system includes a sample preparation module, a geometric size acquisition module, a visualization or wrapping one-dimensional material module, a laser irradiation melting evaporation module, a Raman spectrum characteristic peak position acquisition and temperature calculation module, and a melting A length measurement module and a calculation module.

The sample preparation module can be used to grow or place the measured one-dimensional material in a certain configuration on a certain substrate 104 . It is preferable to use the device shown in FIG. 1 (commercial Linkam THMS600 temperature control station) to place the one-dimensional material of a certain configuration in the environment containing the precursor of the volatile substance and conveniently change the environmental variables such as the temperature of the surrounding environment. The one-dimensional material can be placed on the substrate in a certain configuration by micromachining, or the one-dimensional material can be grown on the substrate by in-situ growth method. Specifically, the method of chemical vapor deposition can be used to grow carbon nanotubes, because the growth conditions are suitable for growth in flight mode, the carbon tubes fly up and fly over the rear receiving substrate, and when the temperature drops, the carbon nanotubes 105 land on a slit with hundreds of microns. On the receiving substrate at the rear, a structure in which carbon tubes at both ends are attached to the substrate 104 and there is a suspension segment in the middle is formed.

The geometric dimension acquisition module is used to acquire the geometric dimension of the measured object, including the cross-sectional area A and the perimeter P of the cross-sectional periphery of the measured object. The geometric size acquisition module can realize its measurement function through the substrate attached to the one-dimensional material and various microscopes (including electron microscope and atomic force microscope, etc.). It can be observed under a transmission electron microscope or a scanning electron microscope, or can be determined by means of AFM, STM, or echelon. For carbon nanotube samples, electron diffraction and high-resolution electron microscopy can be used to directly observe to determine the chirality of single-walled carbon nanotubes, and then look up the table to obtain the cross-sectional area and perimeter of the carbon nanotubes. If the cross-section of the measured object is a solid circle, measure the diameter d of the circle to obtain the cross-sectional area of the circle as A=0.25πd ² , P=πd. If the cross-section of the measured object is a ring, measure the outer diameter d and wall thickness b of the circle to obtain the cross-sectional area A=πb(db), P=πd. In a specific embodiment of the present invention, the object to be measured is a single-walled carbon nanotube, and its cross section can be understood as an extremely thin-walled circular ring. Electron diffraction is performed on the suspended carbon nanotube by TEM, and relevant data are calculated according to the diffraction pattern. , the chirality of the carbon tube can be obtained by consulting the literature, as found in this embodiment (21,4), and then the diameter d of the carbon tube can be obtained by looking up the table, and its wall thickness b is approximately a constant of 0.34nm, and the transverse The cross-sectional area is A=0.34πd, P=πd.

Visualize or wrap one-dimensional materials into heterogeneous structural modules, which are used to attach volatile substances on the surface of one-dimensional materials, to the extent that they can be seen under an optical microscope or can be characterized under an electron microscope. This module can achieve visibility, but it can also not reach the level of visibility, only need to wrap volatile substances on the surface. In a specific embodiment of the present invention, as shown in Figure 1, the sample is placed on a temperature control platform 102, the surrounding environment 106 is air that is closed and contains water vapor, and the temperature control platform 102 can provide stable air at -100°C environment. The temperature of the temperature control platform begins to decrease. When the temperature drops to -87°C, the water vapor of the precursor of volatile substances in the surrounding environment 106 reaches a saturated state due to the temperature drop, and quickly condenses into ice 103, which is attached to the carbon nanotubes 105 to form a cable structure until the ice layer thickens and finally becomes visible under an optical microscope 101 .

To reach an equilibrium state, the 1D material coated with the coating needs to be heated. The laser irradiation melting evaporation module, as shown in Figure 4-5, is used to irradiate the heterogeneous structure with high-power laser, causing the one-dimensional material 105 to be heated, and then transfer the heat to the surrounding volatile substances 103, resulting in the disappearance of the volatile substances 103 . In a preferred embodiment of the present invention, the polarization direction of the 514nm laser emitted from the optical microscope 101 is irradiated parallel to the axis of the carbon nanotubes, causing the carbon nanotubes 105 to be heated, thereby melting the ice layer 103 wrapped around them. Under the optical microscope 101 , it appears that the carbon nanotubes around the laser irradiated area are invisible again, as shown in FIG. 5 , forming a bare segment 107 of a one-dimensional material.

The thermally stable equilibrium state can be obtained during the process of forming the bare section 107, or it can be obtained by continuing to irradiate after forming the bare section, so as to obtain the thermally stable equilibrium state of the one-dimensional material. When the one-dimensional material reaches a thermally stable equilibrium state, the positions of the first and second reference points and the temperature in the thermally stable equilibrium state must be selected. When the positions of the first and second reference points are selected differently, the calculation relational expressions are also different. In one embodiment of the present invention, the relationship between the position and temperature at the first and second reference points is calculated by combining the one-dimensional steady-state heat diffusion equations corresponding to the exposed segment and the wrapped segment respectively established by association. Preferably, the correlation is based on the differentiability of the temperature of the one-dimensional material at the adjoining points of the wrapped and bare sections. For example, the position and temperature of the first and second reference points are used as two boundary conditions of the one-dimensional steady-state heat diffusion equation of the bare section, and the position and temperature of the first reference point are used as two boundary conditions of the one-dimensional steady-state heat diffusion equation of the wrapped section. one of the boundary conditions. The other of the two boundary conditions of the one-dimensional steady-state heat diffusion equation for the wrapped segment is set based on the temperature of the one-dimensional material at infinity being the temperature of the surrounding environment.

In a specific embodiment of the present invention, the temperature of the first reference point is the volatilization transition temperature of the wrapping material. The temperature value can be determined by consulting literature or experiment. The second reference point is the edge of the spot of the first laser on the side of the one-dimensional material facing the wrapping section.

In a typical embodiment of the present invention, the method for obtaining the temperature at the second reference point on the one-dimensional material includes: measuring the first temperature at the second reference point under the condition of thermally stable equilibrium and the first laser irradiation The peak position of the Mann spectrum is used to obtain the peak position of the second Raman spectrum of the one-dimensional material at the ambient temperature; according to the peak position of the first and second Raman spectrum, the temperature of the second reference point in a thermally stable equilibrium state is obtained. The temperature value or the temperature rise value relative to the surrounding environment. Of course, the present invention is not limited to Raman spectroscopy, and other methods can also be used to obtain the temperature value of the second reference point in a thermally stable equilibrium state or the temperature rise value relative to the surrounding environment. Preferably, the step of obtaining the peak position of the second Raman spectrum includes: first cooling the one-dimensional material from a thermally stable equilibrium state to the temperature of the surrounding environment, and then irradiating the bare segment of the one-dimensional material with a second laser to obtain the second Raman spectrum peak position. Wherein, the power of the second laser is lower than the power of the first laser, and the power of the second laser is selected so as not to produce a heating effect on the one-dimensional material as much as possible.

Specifically, a Raman spectrum characteristic peak acquisition and temperature calculation module is used. As shown in Figure 3, it is used to obtain the Raman spectrum characteristic peak frequency difference between the high-power laser irradiation and the irradiated point without heating effect, and is used to calculate the temperature increase ΔT _H at the edge of the laser spot when it is irradiated by the laser. Preferably, the measurement of the characteristic peaks of the Raman spectrum should be performed after the high-power laser causes the volatilization and condensation of volatile substances to reach a stable dynamic equilibrium, and the laser power used in the melting process and the Raman spectrum measurement process should be the same. For different one-dimensional materials, the detected Raman characteristic peaks are different.

In a specific embodiment of the present invention, the one-dimensional material used is a single carbon nanotube, the characteristic Raman peak is the G mode of the carbon tube, and the volatile substance is ice. Because the ice on the surface of the carbon nanotubes will stretch the carbon tubes, which will affect the G-mode of the carbon nanotubes, after 10 minutes of high-power laser irradiation, the surface ice layer will no longer change. At this time, continue to use high-power laser irradiation to collect carbon The peak position ω _H of the tube G mode is 1588.6cm ^-1 in this embodiment, then turn off the laser, reduce the laser power to make it a low-power laser, and irradiate the carbon tube again to collect the cooled down carbon tube Raman spectrum G mode The peak position ω _L is 1589.0 cm ^-1 in this example. When using a low-power laser to collect the characteristic peaks of the Raman spectrum of one-dimensional materials, try to avoid the existence of heating effects. The above acquisitions are made by multiple measurements to ensure accuracy. Check the literature to know the red shift percentage of the peak position of a single carbon tube at T ₀ , α _T0 = (dω/dT)T ₀ /ω _T0 , at around -100°C is α _-100°C = 8×10 ^-6 / K, according to the formula, the temperature rise of the irradiated point due to laser irradiation is calculated as ΔT _H =Δω/α _T0 /ω _T =(1589.0-1588.6)/(8×10 ^-6 )/1588.6=32K.

After the bare segment 107 is formed on the one-dimensional material, its length needs to be measured. The bare section 107 is the area melted after heating, that is, the length of the invisible area under the optical microscope. As shown in 4-5, the melting length measurement module is used to obtain the length of the invisible region 107 under the optical microscope left by the disappearance of the surrounding volatile substances 103 after the heterogeneous structure is irradiated by the laser. The temperature designation standard for the temperature rise caused by the axial heat transfer of dimensional materials. The measurement module can be measured by an optical microscope, or the sample can be placed in a scanning electron microscope (SEM) under the premise of ensuring that the volatile substances remain unchanged, and the length of the exposed section 107 can be measured more accurately under the SEM, and can even be measured according to The shape of the volatile substance 103 is deduced by other methods to deduce the position and temperature of the first reference point, that is, the temperature distribution is simulated according to these temperature-sensitive phenomena. In this embodiment, the length of the melting region of the ice layer, that is, the exposed section 107, can be directly observed under an optical microscope. According to the scale calculation, it is 4 microns in this embodiment, and the laser spot of about 2 microns is subtracted to obtain x _M =1 μm .

The calculation module is used to calculate the thermal conductivity of the one-dimensional material according to the measured data and experimental system parameters such as the temperature rise value of the second reference point of the one-dimensional material, the geometric size of the one-dimensional material, and the melting length of the heterogeneous structure . The theory based on it is the one-dimensional steady-state heat diffusion equation and may include the temperature of each point of one-dimensional material should satisfy the differentiable property.

As shown in FIGS. 1-6 , the present invention takes a single carbon tube as an example, and describes the bare section 107 and the wrapped section 103 respectively in combination with two one-dimensional steady-state heat diffusion equations. As shown in FIG. 4 , because of the symmetry of the bare section 107 and the wrapped section 103 in the one-dimensional material sample, we only take one side as the research object.

For the bare section 107 of the carbon tube, according to the one-dimensional steady-state heat diffusion equation, the temperature at any position on the carbon nanotube satisfies:

Take the first reference point as the boundary between the bare carbon tube section and the ice-wrapped section, and the temperature at this point X _M is T _M ; take the second reference point as the temperature of the carbon tube at the edge of the laser spot is _TH , the The point is another reference point on the bare segment than the first reference point. Using these two boundary conditions, the analytical solution of this equation can be obtained as T(x)=ae ^mx +be ^−mx +T ₀ . in ΔT _H =T _H -T ₀ , ΔT _M =T _M -T ₀ .

And for a section 103 of ice wrapping, use boundary condition equally: get the first reference point and be the position X _M of the boundary of carbon tube bare section and ice wrapping section (in this formula, coordinate origin is set as this point, also namely this The temperature at x=0) is T _M . And because the temperature of the carbon tube will drop to room temperature within a relatively small distance (usually more than ten microns), so there is T(∞)=T ₀ . The wrapped section also satisfies another one-dimensional steady-state heat diffusion equation According to the above two boundary conditions, the analytical solution of the second equation can be obtained as T(x)=ΔT _M e ^-m'x +T ₀ , where

In nature, the function of the temperature of the material to the position should satisfy the differentiable condition (that is, approach from the left and right ends, the temperature value is the same at the same point, and the first derivative of the temperature is the same at the same point), that is, the temperature distribution of the same object should be differentiable. Since the function of temperature to position does not appear step-like jumps (the boundary conditions shared by the above two equations), it must also satisfy that the first-order derivative should be equal to the left and right, so we have Simplifying this equation, the position and temperature at the first and second reference points are calculated as follows:

in, ΔT _H =T _H −T ₀ , ΔT _M =T _M −T ₀ .

Wherein, T ₀ is the temperature of the surrounding environment (here -100° C.), and T _M is the temperature at the first reference point. ΔT _M can be determined by changing the temperature of the surrounding environment until the remaining substances around the one-dimensional material are melted and evaporated or directly sublimated to a critical point, so as to determine that because the temperature of the point irradiated by the laser rises, the heat propagates along the one-dimensional material to the substance The critical point at which melting and sublimation can occur, that is, the equivalent temperature at the edge point where matter disappears. X _M is the coordinates of the first reference point when the second reference point is selected as the coordinate origin, _TH is the temperature at the second reference point, and g is the heat between the bare section of the one-dimensional material and the surrounding environment Exchange coefficient (here, it can be known as g≈0.1MW/(m ² ·K) by consulting the literature), g' is the heat exchange coefficient between the one-dimensional material and the wrapping material that wraps it, where g' represents the carbon tube The heat exchange coefficient between it and the ice that wraps it (referring to the literature can be known as g'≈1.6MW/(m ² ·K)). P is the circumference of the one-dimensional material (that is, the carbon tube) in the circumferential direction, and the data can be obtained by consulting the literature. A is the cross-sectional area of the one-dimensional material, and κ is the axial thermal conductivity to be measured of the one-dimensional material.

In this way, the relational expression that must be satisfied between the axial thermal conductivity κ to be measured and the previous measured value of the one-dimensional material is found, and the thermal conductivity κ is implicit in m. In this embodiment, the positive solution of the above equation is calculated as 2617W/(m·K) by bringing in the data.

In a typical embodiment of the present invention, the steps of measuring the thermal conductivity of a one-dimensional material using a visualization method (including but not limited to visualization, which can be just wrapped and invisible under an optical microscope) include:

In step S101, a one-dimensional material of a certain configuration is prepared on a certain substrate. Among them, micromachining can be used to place one-dimensional materials in a certain configuration on the substrate, or grow on the substrate in situ. In a typical embodiment of the present invention, a single carbon nanotube is grown in situ on a self-made substrate by chemical vapor deposition to form a one-dimensional material sample with a 100-micron suspended configuration.

Step S102, obtaining the required geometric dimensions of the one-dimensional material.

Step S103, placing the substrate containing the analyte in an environment containing the precursor of the volatile substance, and lowering the temperature to T ₀ , so that the volatile substance condenses on the one-dimensional material, resulting in the one-dimensional material-easy Volatile substances form heterogeneous structures and become thicker. Specifically, the sample to be tested is placed on a temperature control platform surrounded by a closed air environment containing water vapor. When the temperature of the temperature control platform drops to the set -100°C, the water vapor condenses on the carbon nanotubes. above, forming cable structures until the ice layer thickens and eventually becomes visible under an optical microscope. Wrapping volatile substances on the surface of one-dimensional materials can realize visualization, but it is not necessary, as long as volatile substances are wrapped on the surface.

Step S104, locate the one-dimensional material under the optical microscope, and irradiate the center of the heterostructure (cable structure) with a high-power laser, causing the one-dimensional material to be heated, and then transfer the heat to the surrounding volatile substances, causing the volatile substances to volatilize and expose Bare one-dimensional material, and until the melting length is stable and no longer grows, reaching a thermally stable equilibrium state.

Step S105, when the high-power laser irradiation is stable, collect the peak position of the Raman spectrum of the one-dimensional material at high temperature (the peak position of the first Raman spectrum), reduce the laser power until the heating effect on the one-dimensional material can be ignored, and collect the peak position of the low temperature The peak position of the Raman spectrum of the time-one-dimensional material (the peak position of the second Raman spectrum), and the temperature increase ΔT _H of the one-dimensional material after laser irradiation is calculated. For different one-dimensional materials, the detected Raman characteristic peaks are different.

Step S106 , measuring the length of the exposed one-dimensional material, taking the edge of the laser spot as the coordinate origin, and calculating the distance X _M from the edge of the one-dimensional material spot to the edge of the heterostructure.

Step S107, calculate the thermal conductivity of the one-dimensional material according to the measured data such as the temperature rise value of the one-dimensional material at the edge of the laser spot irradiated by the laser, the geometric size of the one-dimensional material, the melting length of the heterostructure, and the experimental system parameters Rate.

Among them, because the substrate will affect the heat transfer and intrinsic properties of the one-dimensional material, and TEM may cause radiation damage, etc., in order to reduce the influence of the substrate and TEM, the present invention provides a TEM structure characterization and A method for preparing an in-situ grown carbon tube receiving substrate for optical thermal detection, comprising:

Step S201, use ultraviolet lithography to make a 100-micron slit (special for optical thermal) on the double-polished 100 silicon wafer. covered with photoresist).

In step S202 , a 5 μm silicon nitride layer is plated on the photolithographic side by PECVD method, and the photoresist is stripped, that is, grooves are formed in the slit region.

In step S203 , use the front-to-back alignment method to lithographically etch a millimeter-scale rectangular pattern on the back surface of the silicon wafer, so that the rectangular area wraps the wide and narrow slits mentioned above. (The rectangular area is covered with photoresist).

In step S204, the PECVD method is used to plate a 5 μm silicon nitride layer on the photoresist side, and the photoresist is stripped, that is, grooves are formed in the rectangular area.

In step S205 , a tetramethylammonium hydroxide (TMAH) solution is refluxed in a water bath at 90° C. to etch silicon without affecting silicon nitride for more than 10 hours to form a through slit structure.

The receiving substrate prepared by the method of the present invention can allow the electron beam in the TEM to pass through the narrow through slit, which avoids the bombardment damage of the high-energy electron beam to the long suspended carbon tube; also because the slit is narrow, reducing The shaking of carbon tubes is eliminated, and it is convenient to take electron diffraction pattern photos and high-resolution TEM images.

The present invention also provides a method for in-situ growing the measured carbon nanotubes on the above-mentioned self-made substrate, including:

Step S301, spin-coat a hemoglobin solution with a concentration of 5 mg/ml as a catalyst precursor on a silicon wafer with an oxide layer, heat to 800° C. for 20 minutes in an air environment, and cool to room temperature to serve as a catalyst carrier.

Step S302, put the catalyst carrier prepared in step S301 close to the carbon tube receiving substrate, put it on a quartz plate at the same time, and push it into the furnace at 950°C. The hydrogen gas is introduced to fully reduce the iron oxide particles on the catalyst carrier to iron.

Step S303, according to the volume ratio of hydrogen and methane 2:1 into the furnace body into the mixed gas of hydrogen and methane, and make the carbon nanotubes grow for 20 minutes, the carbon nanotubes will fly, fly over and land on the carbon tube receiver on the substrate. The present invention adopts the configuration of upstream catalyst substrate and downstream receiving substrate, so that the prepared carbon nanotubes fly to the downstream and directly straddle the slit to form a single suspended carbon nanotube sample configuration. Finally, the temperature is lowered to room temperature, and the receiving substrate containing carbon nanotubes is taken out.

The one-dimensional carbon nanotubes are grown in situ on the self-made substrate. Since the self-made substrate is designed with a wide slit and a narrow slit, the wide slit is used for optical and thermal experiments, and has a large span without being affected by both sides of the substrate. The characteristics of bottom impact; the narrow slit is used for the electron beam to pass through, which can prevent the electron beam bombardment radiation from affecting the material quality of the optical thermal test, and avoid the shaking caused by the electron beam bombardment; the narrow slit has a positioning protrusion, which is convenient for the optical microscope Matching with the positioning of the electron microscope improves the experimental efficiency.

So far, those skilled in the art should appreciate that, although a number of exemplary embodiments of the present invention have been shown and described in detail herein, without departing from the spirit and scope of the present invention, the disclosed embodiments of the present invention can still be used. Many other variations or modifications consistent with the principles of the invention are directly identified or derived from the content. Accordingly, the scope of the present invention should be understood and deemed to cover all such other variations or modifications.

Claims (16)

1. A local positioning method for a one-dimensional material, which is used to locate a part of the one-dimensional material under an observation condition, so as to perform a required follow-up operation on the part of the one-dimensional material, wherein the The one-dimensional material itself is not directly visible under the viewing conditions; the method comprises the steps of: A wrapping layer is formed on the surface of the one-dimensional material along the one-dimensional material, so that the one-dimensional material and the wrapping layer thereon are generally visible under the observation conditions; wherein the wrapping a layer is formed by an encapsulating material removable from said one-dimensional material; Using laser heating to remove the wrapping layer at the part of the one-dimensional material that needs to be positioned, so as to form a wrapping segment and a bare segment corresponding to the part on the one-dimensional material, wherein, in At the wrapped section, the one-dimensional material remains wrapped by the wrapping layer such that the wrapped section is visible under the viewing conditions; at the exposed section, the one-dimensional material is directly exposed to the surrounding environment Invisible under the viewing conditions; thus, the invisible exposed section can be positioned using the visible wrapped section as a positioning mark. 2. The local positioning method according to claim 1, further comprising: placing the one-dimensional material in a deposition environment containing a precursor of the encapsulating material; and The parameters of the deposition environment are adjusted so that the precursor is physically or chemically deposited on the surface of the one-dimensional material to form the encapsulation layer. 3. The local positioning method according to claim 2, wherein the precursor of the wrapping material is a gaseous form of the wrapping material, and the parameters of the regulation and control deposition environment include reducing the temperature of the deposition environment to The precursor is caused to condense on the surface of the one-dimensional material in liquid or solid form. 4. The local positioning method according to claim 2, wherein the wrapping material is a heat-volatile material; the method further comprises: The portion of the one-dimensional material to be positioned is heated to remove the wrapping layer at the portion. 5. The local positioning method according to claim 4, wherein the wrapping material is ice or dry ice. 6. The local positioning method according to claim 3, wherein the deposition environment is a solution formed from the precursor of the encapsulation material. 7. The local localization method according to claim 6, wherein the precursor is an organic substance distributed in the solution or an ion dissociated in the solution. 8. The local positioning method according to claim 6, wherein the wrapping material is a volatile material. 9. The local positioning method according to claim 8, wherein the wrapping material is a heat-volatile material; the method further comprises: The portion of the one-dimensional material to be positioned is heated to remove the wrapping layer at the portion. 10. The local positioning method according to any one of claims 1-9, wherein the one-dimensional material is a one-dimensional nanomaterial, and the observation condition is to observe the one-dimensional material with an optical microscope . 11. The local positioning method according to any one of claims 1-9, further comprising: After the localization operation of the one-dimensional material, the wrapping layer on the wrapping section is removed. 12. The local positioning method according to any one of claims 1-9, wherein the subsequent operation comprises measuring the thermal conductivity of the one-dimensional material. 13. The local positioning method according to claim 12, wherein the measurement of the thermal conductivity comprises: heating the one-dimensional material until it reaches a thermally stable equilibrium state; Obtaining the positions of the first reference point and the second reference point on the one-dimensional material and the temperature in the thermally stable equilibrium state; wherein the first reference point is the wrapped segment and the bare segment an adjoining point at the adjoining point of ; the second reference point is selected from another reference point of the exposed segment that is different from the adjoining point; Calculated according to the position and temperature at the first reference point and the second reference point and based on the pre-established calculation relationship between the thermal conductivity and the position and temperature at the first reference point and the second reference point Obtain the thermal conductivity. 14. The local positioning method according to claim 13, characterized in that, the step of heating the one-dimensional material until it reaches a thermally stable equilibrium state is the same as placing the wrapping layer at the local part of the one-dimensional material The removed step is the same step. 15. The local positioning method according to claim 7, wherein the ions are salt ions. 16. The local positioning method according to claim 7 or 15, characterized in that the solution is an aqueous solution.