CN110907489A - Nanoscale thermal conductivity-electric domain in-situ characterization device based on atomic force microscope - Google Patents
Nanoscale thermal conductivity-electric domain in-situ characterization device based on atomic force microscope Download PDFInfo
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N25/00—Investigating or analyzing materials by the use of thermal means
- G01N25/20—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity
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- G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
- G01Q30/00—Auxiliary means serving to assist or improve the scanning probe techniques or apparatus, e.g. display or data processing devices
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- G—PHYSICS
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- G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
- G01Q60/00—Particular types of SPM [Scanning Probe Microscopy] or microscopes; Essential components thereof
- G01Q60/24—AFM [Atomic Force Microscopy] or apparatus therefor, e.g. AFM probes
Abstract
The invention provides a nanoscale thermal conductivity-electric domain in-situ characterization device based on an atomic force microscope, which comprises: the nanometer thermal-electromechanical signal atomic force microscope in-situ excitation platform is used for in-situ exciting a micro-area thermal-electromechanical signal to a measured nanometer functional material sample; the nanometer thermal-electromechanical signal in-situ detection platform is used for carrying out in-situ real-time detection and data processing on the micro-area thermal-electromechanical signal to obtain the micro-area thermal conductivity and the electric domain structure of the detected nanometer functional material sample, and displaying the imaging representation results of the micro-area thermal conductivity and the electric domain structure of the detected nanometer functional material sample in real time. The invention can realize in-situ, real-time and integrated characterization of nanometer functional material thermal conductivity and electric domain.
Description
Technical Field
The invention belongs to the field of instrument development, and particularly relates to a device capable of realizing nanoscale thermal conductivity of functional materials and in-situ integrated characterization of electric domain structures based on an atomic force microscope.
Background
The iron material as a novel functional material contains rich research subjects of material science and physics and a wide application prospect which can be expected, and becomes a research hotspot in the world at present. The ferrous material has abundant physical properties and has great development potential in various aspects such as information storage, the microwave field, current measurement of high-voltage transmission lines, multifunctional electronic equipment and the like.
Devices based on ferrous materials are rapidly becoming more and more integrated and miniaturized. The miniaturization of the size easily causes severe power consumption of the device and remarkable heat effect and electric leakage property. In the past, particularly, recent research is mostly focused on physical effect research such as preparation of ferrous materials, microstructure imaging, magnetoelectric coupling, electromechanical coupling, photoelectric effect and the like, and although remarkable important progress is achieved, research on application of the ferrous material functional device in closely related thermal characteristics and interaction between the ferrous material functional device and a nanostructure and magnetoelectric function is still lacked, and deep understanding of dynamic evolution of the nanoscale structure and function of the functional device under service conditions is greatly restricted.
For functional materials represented by ferrous materials, the current characterization method has the following limitations: the characterization of the thermal conductivity and the electric domain structure is completed by adopting a plurality of different sets of discrete devices, so that the real-time and synchronous detection cannot be achieved, and the in-situ characterization cannot be realized because different probes need to be replaced. Therefore, the traditional characterization method is difficult to realize in-situ, real-time and integrated characterization of the nanometer functional material thermal conductivity and the electric domain. In view of the above limitations, the inventors hope to establish a nano-photoelectric characterization system capable of realizing in-situ, lossless, real-time, dynamic and quantitative characterization of chemical components and electrical properties of nano-scale functional materials, so as to meet the urgent need of functional material characterization which is rapidly developed at present, and promote innovative research and development of novel iron functional materials and devices and application thereof in the functional field.
An Atomic Force Microscope (AFM) is one of the important tools for developing nano scientific research at present, has the unique advantages of high-precision control, nano-scale resolution and the like, becomes a mature nano detection platform, and provides an important platform basis for developing new technology and expanding new functions on the basis of the platform.
Disclosure of Invention
In view of the above, the present invention provides a nanoscale thermal conductance-electric domain in-situ characterization apparatus based on an atomic force microscope, which can implement in-situ, real-time, and integrated characterization of nano-functional material thermal conductance and electric domain.
Therefore, the nanoscale thermal conductivity-electric domain in-situ characterization device based on the atomic force microscope comprises: the nanometer thermal-electromechanical signal atomic force microscope in-situ excitation platform is used for in-situ exciting a micro-area thermal-electromechanical signal to a measured nanometer functional material sample; the nanometer thermal-electromechanical signal in-situ detection platform is used for carrying out in-situ real-time detection and data processing on the micro-area thermal-electromechanical signal to obtain the micro-area thermal conductivity and the electric domain structure of the detected nanometer functional material sample, and displaying the imaging representation results of the micro-area thermal conductivity and the electric domain structure of the detected nanometer functional material sample in real time.
Aiming at the urgent need of the representation of the current nano-functional material, the invention establishes a nano-thermal-electromechanical in-situ characterization device based on the characteristics of detection maturity, functional completeness, structural perfection and the like of an AFM nano platform, realizes in-situ, real-time and dynamic imaging of nano-scale thermal conductivity and electric domain structure, and provides an important in-situ nano characterization method for deeply researching the thermal/electric effect of the nano-functional material and deeply developing the nano-functional material and devices thereof.
Preferably, the nanometer thermal-electromechanical signal atomic force microscope in-situ excitation platform comprises: the system comprises an atomic force microscope platform, a magnetic base, a hot-pressing detection probe, a hot-pressing reference probe, two adjustable resistors, a signal generator and a hot-pressing imaging signal output port; the magnetic base is arranged on the atomic force microscope platform, and the measured nanometer functional material sample is arranged on the magnetic base; the hot-pressing detection probe, the hot-pressing reference probe, the two adjustable resistors and the signal generator form a Wheatstone bridge; excitation signals generated by the signal generator are applied to the hot-pressing detection probes through a micro-area thermal excitation signal transmission end, a micro-area electrical excitation signal transmission end and the Wheatstone bridge respectively; the hot-pressing detection probe is arranged on the tested nano-functional material sample and is contacted with the tested nano-functional material sample so as to detect a thermal-electromechanical signal of an excitation point of the tested nano-functional material sample; the thermo-compression imaging signal output port receives the thermo-electro-mechanical signal. Therefore, the in-situ, real-time and integrated representation of the nanometer functional material thermal conductivity and the electric domain can be effectively realized.
Preferably, the working mode of the nanometer thermal-electromechanical signal atomic force microscope in-situ excitation platform is a contact mode.
Preferably, the hot pressing detection probe is formed into a structure having the functions of micro-area thermal conduction, electromechanical signal excitation source and detection source.
Preferably, the working mode of the hot-pressing detection probe is an AFM contact mode, and the deformation quantity of the micro-cantilever serving as a feedback parameter is 0.1-5 nm.
Preferably, the diameter of the interaction contact area of the hot-pressing detection probe and the detected nanometer functional material sample is 30-100 nm. Thus, the thermal-electromechanical in-situ characterization can be made to have nanometer-scale spatial resolution.
Preferably, the working frequency range of the hot-pressing detection probe is 100Hz-10kHz, and the working current range is 1mA-100 mA.
Preferably, the hot pressing detection probe and the hot pressing reference probe in the wheatstone bridge are connected in a differential input mode to form a double-probe structure.
Preferably, the nanometer thermal-electromechanical signal in-situ detection platform comprises a front-end loop processing module, a lock-in amplifier and a data processing and displaying module which are sequentially connected, so as to perform in-situ real-time detection, processing and displaying of the micro-area thermal conductivity and the imaging representation result of the electric domain structure of the weak thermal signal and the electric signal.
Drawings
FIG. 1 is a schematic block diagram showing the structure of the nanoscale thermal conductance-electric domain in-situ characterization device based on atomic force microscope;
FIG. 2 is a block diagram schematically illustrating the structure of an AFM in-situ excitation platform in the atomic force microscope-based nanoscale thermal-electrical domain in-situ characterization device shown in FIG. 1;
FIG. 3 is a block diagram schematically illustrating the structure of the AFM in-situ detection platform in the atomic force microscope-based nanoscale thermal-electrical domain in-situ characterization device shown in FIG. 1;
fig. 4 (a) - (c) respectively show an AFM image of the surface morphology of the nano-functional material, a thermal conductivity image of the micro-region, and an electric domain structure image of the micro-region for in-situ characterization by using the nano-scale thermal conductivity-electric domain in-situ characterization device based on the atomic force microscope;
FIG. 5 shows the sample micro-area thermal conductance triple frequency signal (U) for in-situ characterization by using the nanoscale thermal conductance-electric domain in-situ characterization device based on atomic force microscope3ω) and the logarithm of the excitation frequency (ln ω);
reference numerals:
1. an AFM in-situ excitation platform;
2. an AFM in-situ detection platform;
11. an atomic force microscope stage;
12. hot-pressing the detection probe;
13. hot-pressing the reference probe;
14. a signal generator;
15, 16, an adjustable resistor;
17. a micro-area electrical excitation signal transmission end;
18. a tested nanometer functional material sample;
19. a magnetic base;
20. a micro-area thermal excitation signal transmission end;
111. a hot-pressing imaging signal output port;
111a, 111b, micro-area thermal conductivity signal output port;
111c, a micro-domain signal output port;
21. a front-end loop processing module;
22. a phase-locked amplifier;
23. and the data processing and displaying module.
Detailed Description
The present invention is further described below in conjunction with the following embodiments and the accompanying drawings, it being understood that the drawings and the following embodiments are illustrative of the invention only and are not limiting thereof.
Based on the urgent need of research of functional materials and devices at present, the invention provides a nanoscale thermal conductivity-electric domain in-situ characterization device based on an atomic force microscope, namely a scanning probe hot-pressing microscopic in-situ integrated characterization device for realizing the thermal conductivity of a nano functional material and the in-situ characterization of an electric domain structure is provided on a commercial Atomic Force Microscope (AFM) platform. The technology combines the atomic force microscope nano detection function with the imaging mechanism of thermal and electromechanical signals, establishes a nano in-situ evaluation technology with the excitation and detection characteristics of the nanoscale thermal-electromechanical imaging signals based on a commercial AFM nano detection platform, and effectively solves the key technical difficulty of the nano-scale thermal conductivity of functional materials and the in-situ characterization of electric domain structures. The novel nanotechnology not only has the unique functions of in-situ excitation and in-situ synchronous representation of a nanometer thermal-electromechanical signal, but also has the advantages of high resolution, high sensitivity, high signal-to-noise ratio and the like. The device has simple structure and strong compatibility, is suitable for being combined with different commercial AFM systems, and is a new technology which is easy to popularize and apply.
The nanoscale thermal conductivity-electric domain in-situ characterization device based on the atomic force microscope is used for detecting the characteristics of micro-area thermal conductivity, electric domain structure and the like of a measured nanometer functional material sample. The micro-region generally refers to a local area for analyzing and testing the microstructure or performance of a sample in the field of an analytical testing instrument, and can be micron-sized or nanometer-sized, which is distinguished from a macro-test. The resolution of the invention is smaller than 100nm, namely the nanometer scale.
The invention discloses a nanoscale thermal conductance-electric domain in-situ characterization device based on an atomic force microscope, which comprises: the nanometer thermal-electromechanical signal atomic force microscope in-situ excitation platform is used for providing a basic hardware platform required by the excitation of the nanometer thermal-electromechanical signal and realizing the in-situ excitation of a micro-area thermal-electromechanical signal of a detected nanometer functional material sample; the nanometer thermal-electromechanical signal in-situ detection platform is used for realizing the micro-area thermal conductivity of a detected nanometer functional material sample, the in-situ real-time detection and data processing of an electric domain structure, and displaying the micro-area thermal conductivity of the detected nanometer functional material sample and the imaging representation result of the electric domain structure in real time.
Specifically, as described in detail later, the present invention can utilize a hot-pressing probe to achieve in-situ excitation of a micro-zone thermal-electromechanical signal of a measured nano-functional material sample. After the in-situ detection platform acquires the excited micro-area thermal-electromechanical signals from the in-situ excitation platform, the in-situ detection platform can mainly utilize the phase-locked amplifier to carry out high-sensitivity detection on weak thermal conductivity signals and electric domain signals, and utilize the data processing and display module to process and image output signals of the phase-locked amplifier. The data processing and display module may be, for example, a signal processing module and a result display module of a computer platform.
The nanometer thermal-electromechanical signal atomic force microscope in-situ excitation platform further comprises: the system comprises an atomic force microscope platform, a magnetic base, a hot-pressing detection probe, a hot-pressing reference probe, a network consisting of two adjustable resistors, a signal generator, a micro-area electrical excitation signal transmission end, a micro-area thermal excitation signal output end and a hot-pressing imaging signal output end. Specifically, the magnetic base is arranged on an atomic force microscope platform, and the measured nanometer functional material sample is arranged on the magnetic base.
The measured nano-functional material sample refers to a nano-scale functional material, and can be a ferroelectric material, a multiferroic material and the like. The nanometer thermal-electromechanical signal atomic force microscope in-situ excitation platform can be, for example, an existing commercial ordinary Atomic Force Microscope (AFM), and provides a basic platform for the nanometer thermal conductivity-electromechanical in-situ characterization technology in the invention. The magnetic mount may be a component in an AFM, with a scanner underneath. Specifically, the magnetic base is connected with the scanner at the lower part and connected with the metal sheet at the bottom of the measured nanometer functional material sample at the upper part, so that the functions of fixing the sample and conducting electricity are achieved.
The hot-pressing detection probe, the hot-pressing reference probe, the two adjustable resistors and the signal generator form a Wheatstone bridge, and further the thermoelectric bridge circuit is formed. Two adjustable resistors are arranged in the thermoelectric bridge loop, wherein one first adjustable resistor connected with the hot-pressing detection probe is used for adjusting the working current of the hot-pressing detection probe, so that the hot-pressing detection probe is in the optimal working state; another second adjustable resistor connected to the hot pressed reference probe is used to adjust the bridge balance to suppress the fundamental signal output. Furthermore, a nonlinear element can be adopted in the thermoelectric bridge loop to adjust the frequency tripling harmonic component related to the measured nanometer functional material sample micro-area thermal conduction signal, so that the harmonic signal sensitivity is improved.
The first end of the hot-pressing imaging signal output port is connected with the end, connected with the Wheatstone bridge, of the hot-pressing detection probe, and the second end of the hot-pressing imaging signal output port is connected with the end, connected with the Wheatstone bridge, of the hot-pressing reference probe. The voltage (in the present invention, an alternating voltage signal) generated by the signal generator is applied to the hot-pressing detection probe through the output of the micro-area electrical excitation signal transmission end, the micro-area thermal excitation signal transmission end and the wheatstone bridge, and the hot-pressing detection probe is placed on and contacted with the measured nano-functional material sample to detect the thermal-electrical-mechanical signal of the excitation point of the measured nano-functional material sample.
Specifically, the thermal conductivity signal is generated by the heat exchange effect between the hot-pressing detection probe and the measured nanometer functional material sample; the electromechanical signal is generated by the inverse piezoelectric effect of the tested nanometer functional material sample under the applied voltage. The thermal conductivity signal is an electrical signal of the hot-pressing detection probe; the electromechanical signal is a micro-cantilever deformation signal of the hot-pressing detection probe. The thermal conductivity signal is output by a Wheatstone bridge, the electromechanical signal can be converted into an electric signal through a photoelectric four-quadrant to be output, and then the electric signal is sent to the nanometer thermal-electromechanical signal in-situ detection platform through a hot-pressing imaging signal output port. The sample electrical/thermal excitation signal is a local signal, namely a micro-area signal, which is excited by the physical action between the probe and the sample.
The work mode of the atomic force microscope platform is a contact mode. In the mode, a relative constant force is kept by a hot-pressing detection probe to scan the surface of the measured nanometer functional material sample point by point.
The hot-pressing detection probe is a conductive probe which has the functions of micro-area thermal, electromechanical signal excitation source and detection source, is of a V-shaped structure, is made of Pt/Rh material, and has the characteristic of a thermistor, namely the resistance value of the thermistor changes along with the temperature change of the probe. The probe has three functions of a micro-area heat source, a micro-area temperature sensor, micro-area voltage application and the like, and is single in structure and convenient to use. The thermocompression detection probe can be any conventional probe having the above-described functions and structures. The working mode of the hot-pressing detection probe is an AFM contact mode, and the probe keeps a relatively constant force to scan the surface of the sample point by point; the deformation of the microcantilever as a feedback parameter is 0.1-5nm, and the diameter of the contact area of the microcantilever and the measured nanometer functional material sample is 30-100 nm.
The working frequency range of the hot-pressing detection probe can be 100Hz-10kHz, and the working current range can be 1mA-100 mA. In addition, the hot-pressing reference probe and the hot-pressing detection probe form a double-probe structure and are connected in a differential input mode, so that the influence of environmental temperature interference is effectively overcome, the detection sensitivity of the thermal conductivity coefficient of the micro area to be detected is improved, the accuracy of test data is ensured, and the test working condition is reduced.
The resistance ranges of the two adjustable resistors can be respectively 80-180 omega. The signal generator may be an existing signal generator, such as Agilent 33210, which may output an ac voltage signal.
In addition, the nanometer thermal-electromechanical signal in-situ detection platform (i.e. the nanometer thermal-electromechanical signal in-situ characterization platform) comprises a front-end loop processing module, a phase-locked amplifier and a data processing and displaying module which are connected in sequence. The front-end loop processing module can comprise a front-end circuit, an amplifying circuit, a protection circuit and the like so as to realize impedance transformation on the output signal of the thermoelectric loop, and simultaneously has the functions of improving the signal amplitude and protecting, and the phenomenon that the next-stage circuit and instrument are damaged due to overload generated when the bridge is unbalanced or the signal is distorted is prevented. The front-end circuit, the amplifier circuit, and the protection circuit may be any circuits having any structures capable of realizing the above-described functions. The phase-locked amplifier has the advantages of high measurement sensitivity, strong anti-interference performance, linear and non-linear detection functions, capability of meeting the working requirements of the system and the like, and can realize high-sensitivity detection of weak thermal conductivity signals. The data processing and display module may include a computer platform based signal processing module and a result display module. The nanometer thermal-electromechanical signal in-situ detection platform is used for realizing in-situ real-time detection, processing and displaying of micro-area thermal conductivity and electric domain structure imaging representation results of weak thermal-electromechanical signals.
The nanoscale thermal conductivity-electric domain in-situ characterization device (namely, the nanoscale thermal conductivity-electric domain in-situ characterization device) based on the atomic force microscope, which is established by adopting the structure, solves the great technical problems of thermal conductivity of a nano functional material, in-situ excitation of an electric domain structure and synchronous detection. The novel nanometer characterization device realizes in-situ excitation and in-situ detection of nanometer thermal-electromechanical signals, expands the physical property evaluation function of nanometer functional materials which are not possessed by the existing commercial atomic force microscope, and provides an important in-situ and nanometer characterization device for in-depth research of the thermal-electromechanical properties of the nanometer functional materials and the in-depth development of the nanometer functional materials and devices.
The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values exemplified below.
The following examples are the results of applying the atomic force microscope-based nanoscale thermal conductivity-electric domain in-situ characterization apparatus to the thermal conductivity of the nano-functional material micro-region and the electric domain structure, so as to further illustrate the effects of the present invention, but are not limited to the following examples.
The nano-scale thermal conductivity-electric domain in-situ characterization device based on the atomic force microscope has a working principle structure as shown in figure 1, and comprises two parts: an AFM in-situ excitation platform 1 for nano thermal-electromechanical signals and an AFM in-situ detection platform 2 for nano thermal-electromechanical signals. The AFM in-situ excitation platform 1 is used for providing an AFM platform foundation for developing a new nano thermal-electromechanical signal in-situ characterization technology and realizing in-situ excitation of thermal-electromechanical signals such as nano functional material micro-area thermal conductivity, electric domain structure and the like on the basis; and the AFM in-situ detection platform 2 is used for realizing in-situ real-time detection and processing of thermal-electromechanical signals such as the micro-area thermal conductivity and the electric domain structure of the nano functional material and displaying in-situ characterization results of the micro-area thermal conductivity and the electric domain structure.
The structure diagram of the AFM in-situ excitation platform 1 is shown in fig. 2, and mainly includes an atomic force microscope platform 11, a magnetic base 19, a hot-pressing detection probe 12, a hot-pressing reference probe 13, a signal generator 14, adjustable resistors 15 and 16, a micro-area electrical excitation signal transmission terminal 17, a micro-area thermal excitation signal transmission terminal 20, a hot-pressing imaging signal output port 111, and the like. Wherein, the hot pressing detection probe 12, the hot pressing reference probe 13, the two adjustable resistors 15 and 16 and the signal generator 14 form a Wheatstone bridge. Further, the present invention constitutes a thermoelectric bridge circuit. Preferably, the thermocompression detection probe 12 and the thermocompression reference probe 13 in the wheatstone bridge are connected by a differential input method to form a dual-probe structure.
Specifically, two adjustable resistors 15 and 16 in the thermoelectric bridge loop are provided, wherein one adjustable resistor 15 is used for adjusting the working current of the hot-pressing detection probe 12, so that the hot-pressing detection probe 12 is in an optimal working state; another adjustable resistor 16 is used to adjust the bridge balance to suppress the output of the fundamental signal. Meanwhile, a nonlinear element is adopted in the thermoelectric bridge loop to adjust the frequency tripling harmonic component related to the thermal conduction signal of the micro-area of the thermoelectric material to be detected, so that the sensitivity of the harmonic signal is improved.
In addition, the micro-area electrical excitation signal transmission terminal 17 is an output port of the signal generator 14; the micro-area electrical excitation signal transmission terminal 17 is connected with a scanner of the atomic force microscope 11, and the scanner is positioned below the magnetic base 19. Similarly, the microdomain thermal excitation signal transmission terminal 20 is an output port of the signal generator 14 and is connected to one end of a wheatstone bridge formed by adjustable resistors 15/16 and the like.
The tested nanometer functional material sample 18 is arranged on a magnetic base 19 of the atomic force microscope platform 11, and the hot-pressing detection probe 12 is arranged on and contacted with the tested nanometer functional material sample 18 so as to detect the thermal-electromechanical signal of the excitation point of the sample. The thermal-electrical-mechanical imaging signal output port 111 receives the thermal-electrical-mechanical imaging signal of the measured nanometer functional material sample through the first end 111a and the second end 111b which are micro-area thermal conductivity signal output ports and the third end 111c which is a micro-area electrical domain signal output port. The first end 111a of the thermocompression imaging signal output port is connected to the end of the thermocompression detection probe 12 connected to the wheatstone bridge, and the second end 111b thereof is connected to the end of the thermocompression reference probe 13 connected to the wheatstone bridge. The hot-pressing imaging signal output port 111 can realize the output of the detected nano functional material micro-area thermal conductance triple frequency multiplication signal and the electric domain imaging signal. The thermal imaging signal output port 111 outputs the thermal imaging signal to the AFM in-situ excitation platform 1, which will be described later, and particularly outputs the thermal imaging signal to the front-end loop processing module 21 of the AFM in-situ excitation platform 1.
The AFM in-situ excitation platform 1 is used for providing a basic hardware platform required by excitation of nano thermal-electromechanical signals and realizing in-situ excitation of micro-area thermal conductivity and electric domain structure imaging signals.
Specifically, the AFM in-situ excitation platform 1 for nano thermal-electromechanical signals has the functions of in-situ excitation of nano thermal conductivity and electric domain structure imaging signals mainly due to the heat exchange interaction between the hot-pressing detection probe 12 and the tested functional material sample 18 and the unique inverse piezoelectric effect of the functional material.
For micro-zone thermal conductance, the physical process of its excitation can be expressed as follows: when the signal generator 14 applies a periodic excitation voltage signal to the heater probe 12 through the micro-domain thermal excitation signal transmission terminal 20, the heater probe 12 increases in temperature (above room temperature), resulting in an increase in the resistance of the heater probe 12. When the hot-pressing detection probe 12 is in contact with the measured nano-functional material sample 18, the hot-pressing detection probe 12 will exchange heat with the measured nano-functional material sample 18 due to the temperature difference between the two. The heat exchange effect induces the surface temperature of the hot pressing detection probe 12 and the resistance value change of the resistance sensitive to the temperature, because the hot pressing detection probe 12 is one end of a bridge arm of a Wheatstone bridge, the resistance value change of the hot pressing detection probe 12 causes the bridge circuit of the Wheatstone bridge to be unbalanced, a frequency tripling higher harmonic voltage output signal is generated and output through the hot pressing imaging signal output port 111, and the frequency tripling higher harmonic voltage output signal is directly related to the micro-area thermal conductivity of the measured nano functional material sample 18.
Specifically, according to the principle of triple frequency thermal conductivity characterization, when a probe passes through a sinusoidal alternating current with an angular frequency of ω, a temperature fluctuation with a frequency of 2 ω is generated on a sample due to the double frequency relationship between the current and the heating power. At this time, since the resistance of the probe is linearly related to the temperature change, the resistance of the probe also has a change component with a frequency of 2 ω. The current of angular frequency omega and the resistance variation component of 2 omega jointly determine the voltage variation V of angular frequency 3 omega generated at two ends of the probe3ωAnd its temperature fluctuation T with the probe angular frequency 2 omega2ωIs in direct proportion. Temperature fluctuation T2ωDependent on the thermal conductivity lambda of the micro-area of the material in contact with the probe, and hence the frequency-tripled higher harmonic voltage V3ωRelating to the thermal conductance of the sample micro-area. The basic principle of utilizing an atomic force microscope to perform thermal conductivity imaging is described above, and the core is the characterization principle of the triple frequency thermal conductivity of the material. Thus, in-situ excitation of micro-zone thermal conductance is achieved.
For the micro-domain structure imaging signal, the physical process of excitation can be expressed as follows: the signal generator 14 applies a periodic excitation voltage signal to act between the hot pressing detection probe 12 and the lower surface of the measured nanometer functional material sample 18 through the electrical excitation signal transmission terminal 17, and the hot pressing detection probe 12 performs contact scanning on the surface of the measured nanometer functional material sample 18. The thermocompression detection probe 12 is a conductive probe having a thermistor characteristic. When the hot-pressing detection probe 12 is in contact with the measured nanometer functional material sample 18, due to the specific inverse piezoelectric effect of the functional material, the measured nanometer functional material sample 18 generates vibration with the same frequency as the excitation voltage, the vibration is detected by the hot-pressing detection probe 12, converted into an electric signal through the photoelectric four-quadrant detector of the atomic force microscope 11, and output through the micro-domain imaging signal output port 111c and the hot-pressing imaging signal output port 111, and the converted electric signal is directly related to the micro-domain structure information of the measured nanometer functional material sample 18.
Specifically, in the electric domain structure imaging mode, the alternating voltage U ═ U0cos (ω t) is applied between the probe and the lower electrode of the sample, where U0Is the direct component of the alternating voltage and ω is the angular frequency. The inverse piezoelectric effect enables a ferroelectric sample to vibrate along with the same frequency of an external voltage, and ferroelectric domain imaging can be realized by detecting the vibration of the micro-cantilever and the sample together through a phase-locked amplification system and modulating a first-order resonance signal (piezoelectric response signal). The inverse piezoelectric effect causes the thickness of the sample to change to
Wherein amplitude A ═ U0dzz，dzzThe magnitude of the amplitude directly reflects the magnitude of the piezoelectric coefficient of the sample for the piezoelectric strain coefficient in the direction perpendicular to the surface of the sample. Phase of piezoelectric response signal for material with polarization vector parallel to z-axis
Reflecting the direction of polarization of the domain structure, if the polarization vector is parallel to the applied voltage
If the polarization vector is antiparallel to the applied electric field, the corresponding
The 0 ° and 180 ° phase changes of the micro-cantilever resonance are therefore directly related to the antiparallel ferroelectric domains. This indicates that the regions of opposite polarization orientation, under the applied AC electric field, each have opposite vibration phases, and thus different contrasts appear in the piezoelectric response image. The basic principle of utilizing an atomic force microscope to perform domain structure imaging is that the inverse piezoelectric effect of a material is utilized. Therefore, in-situ excitation of the micro-area electric domain structure imaging signal is also realized.
The signal generator 14 also provides a working power supply of a thermal loop formed by the hot-pressing detection probe 12, the hot-pressing reference probe 13, the two adjustable resistors 15 and 16 and the micro-area thermal excitation signal transmission end 20, and the signal amplitude and frequency of the working power supply are adjustable. The signal amplitude is compatible with the operating current of the thermocompression detection probe 12, while the signal frequency is compatible with the periodic excitation voltage signal required for the micro-domain thermal conductivity detection and the micro-domain structure detection.
The tested nanometer functional material sample 18 and the magnetic base 19 form a sample table, and are bonded by conductive adhesives, so that the mechanical stability of the sample and the effective transmission of signals are effectively ensured.
And the hot-pressing imaging signal output port 111 is used for outputting a detected nano functional material micro-area thermal conductance triple frequency signal and an electric domain structure imaging signal. The thermo-compression imaging signal output port 111 may be, for example, an integrated BNC port, and respectively corresponds to the micro-domain thermal conduction signal output and the electrical domain signal output. Leads at two ends of the micro-area thermal conductance frequency tripler signal are from one end of a hot-pressing detection probe 12 and one end of a hot-pressing reference probe 13. And the leads at the two ends of the micro-domain structure imaging signal are from the micro-cantilever of the hot-pressing detection probe 12 and the signal generator 14.
The front-end loop processing module 21 includes a front-end circuit, an amplifying circuit, a protection circuit, etc., and can improve the output signal amplitude of the thermal-electromechanical signal, and has a protection function to prevent the next-stage circuit and instrument from being damaged by overload generated when the signal is distorted.
The lock-in amplifier 22 may be a high-sensitivity lock-in amplifier, for example, a Signal Recovery 7280 type, which has the advantages of high measurement sensitivity, strong interference immunity, linear and nonlinear detection functions, capability of meeting the system operation requirements, and the like, and can realize high-sensitivity detection of weak thermal-electromechanical signals.
The data processing and displaying module 23 includes a signal processing module and a result displaying module of the AFM-based computer platform, and may convert the electrical signal of the lock-in amplifier into an imaging result showing the micro-domain thermal conductivity and the electric domain structure, so that the imaging result showing the micro-domain thermal conductivity and the electric domain structure may be used in real time.
The following is an example of characterizing the micro-domain thermal conductivity and electric domain structure of a multiferroic functional material by applying the atomic force microscope-based nano-scale thermal conductivity-electric domain in-situ characterization device of the present invention, and the results are shown in fig. 4 and 5.
FIG. 4 shows BiFeO3The functional material micro-area thermal conductivity and the in-situ imaging result of the electric domain structure. Wherein, the image (a) is an AFM appearance image of the sample, and the image (b) is a frequency tripling thermal conductivity image of the sample. As can be seen from the figure, the thermal conductivity image shows completely different information from the topographic image of figure (a). Showing the spatially non-uniform distribution of the micro-zone thermal conductance. And (c) an image of the electric domain structure obtained in situ in the corresponding area of the sample clearly shows the distribution of the electric domain structure, and the bright and dark contrasts in the image show different spontaneous polarization orientations of the electric domain structure.
Fig. 5 shows the relationship between the signals of the points A, B, C, D at four points in (b) of fig. 4 and the logarithm of the angular frequency ln ω of the excitation frequency. Where points a, D are inside the electric domain, points B and C are at the domain wall. According to the relevant near-field thermal imaging conditions, the thermal conductivity relationship of the four points can be expressed as λ a > λ B ═ λ C > λ D, that is, for the BFO thin film electric domain, the electric domain with the polarization orientation parallel to the film wire direction has high thermal conductivity, the electric domain deviating from the film wire direction has low thermal conductivity, and the thermal conductivity at the domain wall is between the two.
The above examples show that the scanning hot-pressing microscope device established based on the atomic force microscope of the invention solves the key technical problems of functional material and device micro-area thermal conductivity and electric domain structure high-resolution microscopic imaging. The novel microscopic imaging device realizes the in-situ excitation and in-situ detection of the internal thermal conductivity and electric domain structure of functional materials and devices, expands the function of functional material thermal-electromechanical in-situ evaluation which is not possessed by the existing commercial atomic force microscope, and provides an important new in-situ characterization method for deeply researching the thermal and electrical properties of the functional materials and devices.
In summary, the outstanding advantages of the present invention are that the atomic force microscope imaging function (i.e. atomic force microscope nano detection function), the triple frequency detection principle of macroscopic thermal conductivity and the inverse piezoelectric effect of the functional material (i.e. imaging characterization principle of electric domain structure) are combined to establish a nano in-situ evaluation device based on the atomic force microscope and having nano thermal, electrical excitation and detection characteristics, and the novel nano hot-pressing integrated characterization device not only has the unique functions of nano functional material thermal conductivity, electric domain structure imaging signal in-situ excitation, in-situ characterization, but also has the advantages of high resolution, high sensitivity, high signal-to-noise ratio, etc., and has the advantages of simple structure, strong compatibility, and is suitable for wide popularization and application. Therefore, the invention solves the great technical problems of nano thermal conduction in the nano functional material and in-situ excitation and detection of the electric domain structure, and can be applied to strategic emerging materials such as nano materials, functional materials and the like and industries thereof.
As the present invention may be embodied in several forms without departing from the spirit of essential characteristics thereof, the present embodiments are therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description herein, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the appended claims.
Claims (9)
1. A nanoscale thermal conductance-electric domain in-situ characterization device based on an atomic force microscope is characterized by comprising:
the nanometer thermal-electromechanical signal atomic force microscope in-situ excitation platform is used for in-situ exciting a micro-area thermal-electromechanical signal to a measured nanometer functional material sample;
the nanometer thermal-electromechanical signal in-situ detection platform is used for carrying out in-situ real-time detection and data processing on the micro-area thermal-electromechanical signal to obtain the micro-area thermal conductivity and the electric domain structure of the detected nanometer functional material sample, and displaying the imaging representation results of the micro-area thermal conductivity and the electric domain structure of the detected nanometer functional material sample in real time.
2. The apparatus of claim 1,
the nanometer thermal-electromechanical signal atomic force microscope in-situ excitation platform comprises:
the system comprises an atomic force microscope platform, a magnetic base, a hot-pressing detection probe, a hot-pressing reference probe, two adjustable resistors, a signal generator and a hot-pressing imaging signal output port;
the magnetic base is arranged on the atomic force microscope platform, and the measured nanometer functional material sample is arranged on the magnetic base;
the hot-pressing detection probe, the hot-pressing reference probe, the two adjustable resistors and the signal generator form a Wheatstone bridge;
excitation signals generated by the signal generator are applied to the hot-pressing detection probes through a micro-area thermal excitation signal transmission end, a micro-area electrical excitation signal transmission end and the Wheatstone bridge respectively;
the hot-pressing detection probe is arranged on the tested nano-functional material sample and is contacted with the tested nano-functional material sample so as to detect a thermal-electromechanical signal of an excitation point of the tested nano-functional material sample;
the thermo-compression imaging signal output port receives the thermo-electro-mechanical signal.
3. The apparatus of claim 2,
the working mode of the nanometer thermal-electromechanical signal atomic force microscope in-situ excitation platform is a contact mode.
4. The apparatus according to claim 2 or 3,
the hot-pressing detection probe is formed into a structure with the functions of micro-area thermal conduction, an electromechanical signal excitation source and a detection source.
5. The apparatus according to any one of claims 2 to 4,
the working mode of the hot-pressing detection probe is an AFM contact mode, and the deformation of the micro-cantilever serving as a feedback parameter is 0.1-5 nm.
6. The apparatus according to any one of claims 2 to 5,
the diameter of the interaction contact area of the hot-pressing detection probe and the tested nanometer functional material sample is 30-100 nm.
7. The apparatus according to any one of claims 2 to 6,
the working frequency range of the hot-pressing detection probe is 100Hz-10kHz, and the working current range is 1mA-100 mA.
8. The apparatus according to any one of claims 2 to 7,
the hot-pressing detection probe and the hot-pressing reference probe in the Wheatstone bridge are connected in a differential input mode to form a double-probe structure.
9. The device according to any one of claims 1 to 8,
the nanometer thermal-electromechanical signal in-situ detection platform comprises a front-end loop processing module, a phase-locked amplifier and a data processing and displaying module which are sequentially connected, so that in-situ real-time detection and processing of weak thermal signals and electrical signals are carried out, and imaging representation results of micro-area thermal conductivity and electric domain structures are displayed.
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