CN201041541Y - Tunnel current testing device of scanning tunnel microscope based on interconnected amplifier - Google Patents
Tunnel current testing device of scanning tunnel microscope based on interconnected amplifier Download PDFInfo
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- CN201041541Y CN201041541Y CNU2006200761145U CN200620076114U CN201041541Y CN 201041541 Y CN201041541 Y CN 201041541Y CN U2006200761145 U CNU2006200761145 U CN U2006200761145U CN 200620076114 U CN200620076114 U CN 200620076114U CN 201041541 Y CN201041541 Y CN 201041541Y
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Abstract
The utility model relates to a tunnel current measurement device based on the scanning tunneling microscope of a cross-correlation amplifier. The utility model is characterized in that the output terminals of two current-voltage conversion amplifiers are respectively connected with the two input terminals of a multiplier, and the output terminal of the multiplier is connected with the input terminal of an averager; the detection input terminals of the two current-voltage conversion amplifiers are connected with a probe frame or a sample frame after being connected with short circuit, and the two reference input terminals are adopted as reference input terminal after connected with short circuit; a probe is fixed on the probe frame in an electrical contacting way, the probe frame is fixed on the top end of a piezoelectric ceramic, the sample frame is fixed on a base plated pointed by the probe, and the other end of the piezoelectric ceramic is fixed on a rough adjustment driver in Z direction. The utility model greatly improves the speech noise ratio, the sensitivity, the resolving power and the measurement precision; and the function of the scanning tunneling microscope can be realized after applying a 3D scanning controller and a Z direction feedback controlling system, and particularly, thereby the constant current scanning mode can be realized through setting the tunnel current power.
Description
The technical field is as follows:
the utility model belongs to the technical field of scanning tunnel microscope, in particular to low noise high accuracy measuring device of tunnel current.
Background art:
the tunnel current measuring device is used for measuring the change of tunnel current between a certain point of a sample and a probe by utilizing the tunneling principle of quantum mechanics to research the property of the surface of the sample. The tunnel current signal is normally extremely weak (only 10) -12 On the order of amperes) and therefore very high requirements are placed on the preamplifier used for the measurement. The journal of scientific Instruments review (reviewof scientific Instruments, vol.69, 1998, P3529) reports a scanning tunneling microscope using single-channel amplification, but the quality of the imaged image is not good because the noise itself cannot be removed. The existing preamplifiers for measuring the tunnel current are all traditional single-channel amplifiers, namely, a one-channel amplifying circuit is used for amplifying a measured signal. Although shielding, grounding, etc. can reduce the external interference on the amplifier and the noise of the circuit itself to a low level, one of the inherent drawbacks of the single-channel amplifier is that the noise of the amplifier itself cannot be eliminated. In this case, the lowest noise level of a single-channel amplifier is the noise level of itself, which is the limit that this kind of amplifier can reach and is the key reason for limiting the resolution of a single-channel amplifier.
Intercorrelation amplifiers are reported in the journal of the Scientific Instrument Review (Review of Scientific Instruments, vol.70, 2002, P2520). The cross-correlated amplifier is able to cancel the noise of the amplifier itself, and thus has much higher noise performance, compared to a single-channel amplifier. However, its application in scanning tunneling microscopy has not been seen to date. If the existing cross-correlation amplification technology is applied to the field of tunnel current measurement, the method has many defects: according to the double-point measurement method, because input signals of two channels come from different points of a tested circuit or device, one is from a sample and the other is from a probe, tunnel current is generated only by applying bias voltage between the sample and the probe, the two channels work at different reference voltages, and the working points are not symmetrical any more; furthermore, the difference of the temperature, parasitic capacitance and the like between the probe and the sample can also cause asymmetry of the dual-channel working point; in addition, the separation of the two channels also does not facilitate integration and miniaturization. The above disadvantages all result in a reduction of the measurement accuracy.
The utility model has the following contents:
the utility model aims at providing a scanning tunnel microscope's tunnel current measuring device based on correlation amplifier to reduce the noise that is introduced by preamplifier in tunnel current measurement by a great extent, thereby improve measurement SNR, sensitivity, resolution ratio and measurement accuracy by a great extent.
The utility model discloses scanning tunnel microscope's tunnel current measuring device based on correlation amplifier, including the probe frame, the probe, the sample frame, Z direction coarse adjusting driver and Z direction piezoceramics, its characterized in that two current-voltage conversion amplifier's output links to each other with two inputs of multiplier respectively, the output of multiplier links to each other with the input of averager, constitute the correlation amplifier from this, the detection input (sense input) of these two current-voltage conversion amplifiers is two input short circuits of correlation amplifier promptly and is back connected with probe frame or sample frame, regard as the reference input of correlation amplifier after the reference input (reference input) short circuit of these two current-voltage conversion amplifiers;
the probe is fixed on a probe frame in an electric contact manner, the probe frame is fixed at the top end of piezoelectric ceramic, the sample frame is fixed on a base pointed by the probe, the other top end of the piezoelectric ceramic is fixed on a Z-direction coarse adjustment driver, and the output end of an averager, namely the output end of a cross-correlation amplifier, is a signal output interface; or, the sample frame is fixed on the top end of the piezoelectric ceramic, the other top end of the piezoelectric ceramic is fixed on the Z-direction coarse adjustment driver, the probe frame is fixed on the base opposite to the sample frame, and the probe is fixed on the probe frame in an electric contact manner; the output end of the correlated amplifier is a signal output interface.
Because the amplifier in each passageway in the correlation amplifier is current-voltage conversion amplifier, and its output signal is the power of tunnel current signal, so make according to above-mentioned scheme the utility model discloses what tunnel current measuring device measured is the power spectrum of tunnel current.
The square-off operator can be added on the basis of the scheme of the utility model, the input end of the square-off operator is connected with the output end of the correlated amplifier to form the square-off correlated amplifier, and the output end of the square-off operator is the output end of the square-off correlated amplifier and is used as a signal output interface; or, a square-open arithmetic unit is connected between the multiplier and the averager of the cross-correlation amplifier, the input end of the square-open arithmetic unit is connected with the output end of the multiplier, the output end of the square-open arithmetic unit is connected with the input end of the averager, thereby forming the cross-correlation amplifier with square opening, and the output end of the averager, namely the output end of the cross-correlation amplifier with square opening, is used as a signal output interface; the squaring operator performs squaring operation on the power signal of the tunnel current to reduce the power signal into a voltage signal proportional to the tunnel current.
The three-dimensional scanning controller made of piezoceramic materials can be used for replacing the Z-direction piezoceramics in the scheme of the utility model, thereby realizing three-dimensional scanning; on the basis, a Z-direction feedback control system can be added between the output end of the correlated amplifier or squarer and the three-dimensional scanning controller to realize the functions of constant current scanning and constant height scanning of the scanning tunnel microscope.
It is also possible to connect an analog-to-digital converter before the two input terminals of the multiplier of the correlated amplifier, the input terminal of the analog-to-digital converter is connected to the input terminal of the current-to-voltage conversion amplifier in the channel, the output terminal of the analog-to-digital converter is connected to one of the input terminals of the multiplier, and the multiplier, the corresponding averager and the corresponding squaring operator are replaced by a digital multiplier, a digital averager and a digital squaring operator, respectively. Adopt this digital correlation amplifier and with the follow-up components and parts replacement for corresponding digital components and parts after, the utility model discloses a tunnel current measuring device just can digital work.
The utility model discloses scanning tunnel microscope's tunnel current measuring device based on correlation amplifier measures the rationale of tunnel current as follows: a reference voltage is added between a reference input end of a cross-correlation amplifier and a sample frame, so that a bias voltage is generated between a sample and a probe, the piezoelectric ceramic is driven to move slightly in the Z direction by applying a voltage on the piezoelectric ceramic in the Z direction, so that the distance between the sample and the needle point can be adjusted to generate a tunnel current, the tunnel current is input into the cross-correlation amplifier through the probe and then divided into two equal parts, the two parts of current are respectively input into two channels of the cross-correlation amplifier, the two parts of current are amplified through an amplifier in the channel and then output to a multiplier in the form of a voltage signal, the multiplier multiplies the two voltage signals, then inputs the two voltage signals into an inverse averager for averaging operation, and finally the two voltage signals are output from a signal output interface in the form of the power of the tunnel current. In the whole process, the noise of the amplifiers in the two channels is superimposed on the signals related to the tunnel current in the respective channels. Because the noises of the amplifiers in the two channels are random signals which are not correlated, the output signals of the two channels of signals after passing through the multiplier and the averager in the correlated amplifier are the power of the tunnel current after the noises of the amplifiers are eliminated. To this end, the set of devices measures the power of the tunnel current, which is a power output not available in the prior art.
If a squaring operator is added after the cross-correlation amplifier, the output signal of the cross-correlation amplifier is subjected to squaring operation and then becomes a voltage signal which is in direct proportion to the tunnel current; or, a squarer is added between the multiplier and the averager of the cross-correlation amplifier, thereby forming a square cross-correlation amplifier, so that the signal output by the square cross-correlation amplifier is a voltage signal proportional to the tunnel current. This corresponds to the voltage output in the prior art, but since the noise of the amplifier itself is suppressed, its signal-to-noise ratio, resolution, measurement accuracy, sensitivity, etc. are greatly superior to the prior art.
The utility model discloses scanning tunnel microscope's tunnel current measuring device based on correlation amplifier has two kinds of working patterns: one is to keep the bias voltage between the probe and the sample constant, and measure the tunnel spectrum by adjusting the distance between the probe and the sample, i.e. constant voltage mode; the other is to keep the distance between the probe tip and the sample constant, and measure the tunnel spectrum by adjusting the magnitude of the bias voltage between the probe and the sample, i.e. constant high mode. Applying a bias voltage between the probe and the sample, adjusting the distance between the probe tip and the sample by roughly adjusting the driver and the piezoelectric ceramic to generate a tunnel current between the probe tip and the sample, adjusting the moving distance of the piezoelectric ceramic in the Z direction under a constant voltage mode, inputting the tunnel current between the probe and the sample along with the change, amplifying the tunnel current into a cross-correlation amplifier and converting the tunnel current into a voltage signal, and finally obtaining a curve of the tunnel current along with the change of the tunneling distance, namely a relation curve of the tunnel current and the probe-sample distance; under the constant height mode, the distance between the needle tip and the sample is kept unchanged, the magnitude of bias voltage applied between the sample and the probe is changed, the tunnel current is changed accordingly, the tunnel current is input into the correlated amplifier for amplification and is converted into a voltage signal, and finally a curve of the tunnel current changing along with the bias voltage, namely a relation curve of the tunnel current and the voltage between the probe and the sample is obtained.
The tunnel current measuring device of the scanning tunnel microscope based on the correlated amplifier can work in an on-line scanning mode or a surface scanning mode after using the three-dimensional scanning controller made of the piezoceramic material; if a Z-direction feedback control system is added between the input end of the correlated amplifier or squarer and the three-dimensional scanning controller, the novel device can realize the function of a scanning tunnel microscope in two working modes of constant current or constant height; if do not add Z direction feedback control system, then the utility model discloses can realize the function of scanning tunnel microscope with the mode of invariable height. When not adding the square operator, the utility model discloses the device realizes the scanning mode of constant current under the circumstances of setting for the power value of tunnel current, and this constant current's that realizes when setting for the voltage value directly proportional with the size of tunnel current under the single channel amplification condition scanning mode has higher sensitivity than.
The utility model discloses scanning tunnel microscope's tunnel current measuring device based on correlation amplifier proposes for the first time and adopts the associated amplification technique of two-channel to measure tunnel current to be applied to it for the first time in scanning tunnel microscope field, have pioneering nature. When the existing cross-correlation amplification technology is applied, input signals of two channels come from different points of a circuit or a device to be tested, namely, two-point measurement. The method applied to the field of tunnel current measurement has a plurality of defects: according to the two-point measurement method, the input signals of two channels are one from the sample and one from the probe; since tunnel current is generated only by applying bias voltage between the sample and the probe, the two channels will operate at different reference voltages, and the operating points are no longer symmetrical, which is the key to the correlation amplification technique; furthermore, the difference of the temperature, parasitic capacitance and the like between the probe and the sample can also cause asymmetry of the dual-channel working point; in addition, the separation of the two channels also does not facilitate integration and miniaturization. The above disadvantages all result in a reduction of the measurement accuracy. This is also an improvement of the present invention. And the utility model discloses the device adopts single-point measurement's mode, links to each other with the probe after the input short circuit of two passageways that are about to cross correlation amplifier again, because the signal in two passageways this moment comes from the same point of by-pass circuit or device, has just so overcome a series of shortcomings of current two-point measurement method, has guaranteed the strict symmetry of the tunnel current signal in two passageways.
The utility model discloses scanning tunnel microscope's tunnel current measuring device based on correlation amplifier has eliminated the noise of amplifier itself owing to adopted the correlation amplification technique of bi-channel, therefore compares with the tunnel current measuring device who adopts the single channel amplification technique that has higher SNR, sensitivity, resolution ratio and measurement accuracy. After the squaring arithmetic unit is added, the device can be used for measuring the power spectrum of the tunnel current and can also be used for directly measuring a voltage signal which is in direct proportion to the tunnel current. The utility model discloses a tunnel current measuring device applies to behind the scanning tunnel microscope, can increase substantially the resolution ratio and the sensitivity of microscope. In particular, the scanning tunnel microscope equipped with the device of the invention can realize the scanning mode of constant current under the condition of setting the power of tunnel current; since the power of the tunnel current is quadratic in relation to the tunnel current, the change of the tunnel current can be reflected more sensitively, and thus the scan mode of the constant current implemented in the case of setting the power value has higher sensitivity than the scan mode of the constant current implemented by setting the voltage value proportional to the magnitude of the tunnel current. Therefore, the scanning tunneling microscope equipped with the tunnel current measuring device of the present invention has a greater advantage in sample imaging and analysis than the existing scanning tunneling microscope.
Description of the drawings:
fig. 1 is a schematic diagram of the structural principle of the fixed sample mode of the tunnel current measuring device of the scanning tunnel microscope based on the correlated amplifier of the present invention.
Fig. 2 is a schematic structural diagram of the fixed probe mode of the tunnel current measuring device of the scanning tunnel microscope based on the correlated amplifier of the present invention.
Fig. 3 is a schematic diagram of a sample-fixing structure of the scanning tunneling microscope with the feedback control system added to fig. 1.
Fig. 4 is a schematic diagram of a probe-fixed type structure of a scanning tunneling microscope to which a feedback control system is added to fig. 2.
Fig. 5 is a schematic view of the structural principle of a fixed sample system of the tunnel current measuring apparatus to which a square-cut operator is added on the basis of fig. 1.
Fig. 6 is a schematic diagram showing a probe-fixed type structure of the tunnel current measuring apparatus to which a square-cut calculator is added in addition to fig. 2.
Fig. 7 is a schematic diagram of a sample-fixing system of the scanning tunneling microscope to which the feedback control system is added to fig. 5.
Fig. 8 is a schematic diagram of a fixed probe system of the scanning tunneling microscope to which the feedback control system is added to fig. 6.
Fig. 9 is a schematic diagram of a tunnel current measuring device operating in a digital mode.
The specific implementation mode is as follows:
example 1: the utility model discloses a basic structure of scanning tunnel microscope's tunnel current measuring device based on correlation amplifier
In the embodiment, the sample is fixed, and the distance between the probe and the sample is adjusted by moving the probe. Fig. 1 shows a schematic diagram of the structural principle of the tunnel current measuring device of the scanning tunnel microscope based on the correlated amplifier in the embodiment: two input terminals 6g and 6h of the cross-correlation amplifier 6 are short-circuited and connected to a probe holder 3, a sample is fixed to the sample holder 1, a probe 2 is fixed to the probe holder 3 in electrical contact, the probe holder 3 is fixed to a tip of a piezoelectric ceramic 4, and a reference voltage V is applied between a reference input terminal 6e of the cross-correlation amplifier 6 and the sample holder 1 B Thereby contacting the probe 2 with the sampleGenerating a bias voltage between the product frame 1, primarily adjusting the distance between the probe 2 and the sample by a coarse adjustment driver 5, adjusting the distance between the probe 2 and the sample by slightly moving the piezoelectric ceramic 4 in the Z direction to generate a tunnel current, dividing the tunnel current into two equal parts after passing through a detection input end 6f of a cross-correlation amplifier 6, respectively inputting the two equal parts into two symmetrical channels of an upper channel and a lower channel in the cross-correlation amplifier, amplifying the two equal parts by a first current-voltage conversion amplifier 6a and a second current-voltage conversion amplifier 6b in the upper channel and the lower channel to become positive to the tunnel currentCompared voltage signals, two paths of voltage signals are input into a multiplier 6c, are input into an averager 6d for average operation after multiplication operation, and finally output signals are power corresponding to tunnel current.
The tunneling current measuring device can work under two modes of constant bias voltage and constant tunneling distance. In a first working mode, namely a constant bias mode, keeping the bias between the sample and the probe constant, and obtaining a relation curve between the tunnel current and the probe-sample distance by adjusting the distance between the probe 2 and the sample, wherein the relation curve can be realized by adjusting the micro movement of the piezoelectric ceramic 4 in the Z direction, and a tunnel spectrogram obtained in the working mode reflects the relation between the tunnel current and the tunneling distance; in a second operation mode, namely a constant tunneling distance mode, the distance between the probe 2 and the sample is kept constant, and the bias voltage between the sample and the probe is changed by changing the reference voltage connected between the reference input end 6e of the correlated amplifier and the sample holder 1, so that a relation curve of the tunnel current and the probe-sample voltage is obtained.
Tunnel current measuring device's probe frame 3 and probe 2 are made with good conductor, and probe 2 can be changed, is the electrical contact between probe 2 and the probe frame 3. The probe 2 may be fabricated by a fabrication process for fabricating a scanning tunneling microscope probe, including mechanical machining or chemical etching.
Example 2: another basic structure of the device of the utility model
In the embodiment 1, a fixed sample is adopted, and a tunnel current signal is obtained by adjusting the distance between the sample and a probe through moving the probe; in this embodiment, a fixed probe is adopted, and the distance between the sample and the probe is adjusted by moving the sample to obtain a tunnel current signal. Fig. 2 shows a schematic structural diagram of a probe fixing manner of the tunnel current measuring apparatus of the present embodiment: the sample holder 1 is fixed on the top of the piezoelectric ceramic 4, the probes 2 are fixed on the probe holder 3 in electric contact, and pass through the probe holderA reference voltage V is connected between a reference input 6e of the associated amplifier 6 and the sample holder 1 B So that a bias voltage is generated between the probe 2 and the sample holder 1, the distance between the probe 2 and the sample is preliminarily adjusted through the rough adjusting driver 5, the distance between the probe 2 and the sample is adjusted through adjusting the piezoelectric ceramic 4 to slightly move in the Z direction so as to generate a tunnel current, the tunnel current becomes a power signal corresponding to the tunnel current after being amplified by the cross-correlation amplifier 6, and finally the power signal is input to a device for recording and displaying a tunnel spectrum. The present embodiment can realize two operation modes, namely two modes of constant bias voltage and constant tunneling distance, as in embodiment 1, and the specific operation mode is the same as that in embodiment 1.
Example 3: feedback control system in the utility model
Tunnel current measuring device, the scanning device of adoption be Z direction piezoceramics, and this piezoceramics can be slice, column or any shape that can realize Z direction scanning other, can only realize Z direction scanning under this condition, can only adjust the size of tunneling distance promptly. The utility model discloses can also use the three-dimensional scan controller who makes with piezoceramics material to realize three-dimensional space's scanning, can realize the scanning and the formation of image to the sample under the invariable high mode under this condition. After the device is provided with a feedback control system in the Z direction, the sample can be scanned and imaged in two modes of constant height and constant current, and the function of a scanning tunneling microscope is realized. In the present embodiment, a feedback control system is applied, and referring to fig. 3 and 4: fig. 3 is a schematic diagram of a sample fixing mode of the tunnel current measuring device of the present embodiment to which the feedback control system 8 is added on the basis of fig. 1; fig. 4 is a schematic diagram of a probe-fixed type structure of the tunnel current measuring apparatus to which the feedback control system 8 is added in addition to fig. 2: the power of the tunnel current between the sample and the probe 2 is preset, and then the distance between the probe 2 and the sample is adjusted by controlling the piezoelectric ceramic 4 to slightly stretch in the Z direction through a feedback control system in the scanning process, so that the power of the tunnel current is kept constant. The change of the voltage signal outputted by the feedback control system 8 for controlling the piezoelectric ceramic 4 to slightly expand and contract in the Z direction reflects the roughness of the sample surface, and thus can be used for imaging, and the image formed at this time is the appearance image of the sample surface. Since the constant-current scan mode realized at this time is realized in the case of setting the power of the tunnel current, it is much more sensitive to set the tunnel current value than in the case of single-channel amplification.
Example 4: squaring device and method for making same
In the above embodiment, the signal output by the correlated amplifier 6 is the product of the voltage signals in the two channels, and thus is the power spectral density related to the tunnel current rather than the voltage signal proportional to the tunnel current, and when calculating the magnitude of the tunnel current, the output signal of the amplifier needs to be squared, and the actual magnitude of the tunnel current should be:
where i is the tunnel current, S is the power of the output signal of the correlated amplifier, and a is the amplification factor of the amplifier employed in the channel of the correlated amplifier. The factor 2 in the above equation indicates that the tunnel current is divided into two parts at the input end of the correlated amplifier, and the two parts are respectively input into the upper and lower channels of the correlated amplifier, so that the signal obtained after the square-open operation is a voltage signal which can monotonously reflect the change of the tunnel current in real time and is in proportion to the tunnel current.
To achieve the above object, it is necessary to connect a squaring operator 7 to the output of the correlated amplifier 6, see fig. 5 and 6: in this embodiment, the input terminal of the squaring operator 7 is connected to the output terminal of the correlated amplifier 6 to form a squared correlated amplifier, and the output terminal of the squaring operator 7, i.e. the output terminal of the squared correlated amplifier, is used as a signal output interface, so that the power signal output by the correlated amplifier and corresponding to the tunnel current becomes a voltage signal proportional to the tunnel current after the squaring operation of the squaring operator 7; or, a squaring operator 7 is added between the multiplier 6c and the averager 6d of the correlated amplifier 6, thereby forming an open-flat correlated amplifier, and the output terminal of the averager 6d, i.e. the output terminal of the open-square correlated amplifier, is used as the output interface of the signal, so that the power signal output by the open-flat correlated amplifier is the voltage signal proportional to the tunnel current.
Example 5: the utility model discloses several kinds of mode of tunnel current measuring device
A: on the basis of embodiment 4, the utility model discloses the size of measurement tunnel current that tunnel current measuring device has been can be accurate, and uses three-dimensional scanning controller 4 and feedback control system 8 just can realize the function of the constant current scanning of scanning tunnel microscope on this basis. See fig. 7 and 8: in this embodiment, a feedback control system 8 is connected between the squaring operator 7 and the three-dimensional scanning controller 4, an input end of the feedback control system 8 is connected with an output end of the squaring operator 7, an output end of the feedback control system 8 is connected with the three-dimensional scanning controller, since the magnitude of the tunnel current can be accurately measured, the magnitude of the tunnel current between the sample and the needle tip can be preset, then the feedback control system 8 controls the three-dimensional scanning controller 4 to slightly extend and retract in the Z direction during the scanning process to control the distance between the probe 2 and the sample so as to keep the tunnel current between the two constant (equal to the preset tunnel current), and a signal for controlling the piezoelectric ceramic 4 to slightly extend and retract in the Z direction output by the feedback control system 8 reflects the roughness of the sample surface, so that the signal can be used for imaging, and the image formed at this time is the image of the topography of the sample surface.
B: on the basis of the embodiment 4, the scanning mode with the constant height of the scanning tunnel microscope can be realized by only using the three-dimensional scanning controller 4 without using the feedback control system 8. See fig. 5 and 6: in the embodiment, the output end of the correlated amplifier 6 is connected with the input end of the squaring arithmetic unit 7, and the output end of the squaring arithmetic unit 7 is used as a signal output interface; or, a squaring operational amplifier 7 is added between the multiplier 6c and the averager 6d of the correlated amplifier, the output end of the averager 6d is used as an output interface of a signal, the three-dimensional scanning controller 4 is driven to scan the sample surface in the X and Y directions by an external voltage, no response is made in the Z direction of the three-dimensional scanning controller 4, the roughness of the sample surface is directly reflected by the measured tunnel current, and the image formed by directly utilizing the measured tunnel current is the appearance image of the sample surface.
Of course, the above two cases can be realized in the same system, i.e. in a complete large system equipped with the three-dimensional scan controller 4, the feedback control system 8 and the squaring operator 7. When the piezoelectric ceramic 4 is scanned, if the feedback control system 8 responds to make the measured tunnel current be a constant value, the constant current working mode of the scanning tunnel microscope can be realized; in this mode, if the square-on calculator 7 does not respond, it can be realized by setting the power of the tunnel current; if the squaring operator 7 responds, the tunnel current can be set directly; if the feedback control system 8 does not respond, the constant-height working mode of the scanning tunnel microscope can be realized; in this mode, if the square-on operator 7 does not respond, the image formed is a power spectrum image related to the tunnel current; if the squaring operator 7 responds, a voltage signal proportional to the tunnel current is measured, and the resulting image is a voltage spectrum image proportional to the tunnel current.
Example 6: digital tunnel current measuring device
The above embodiments all work in an analog state, and the present embodiment is a tunnel current measuring device working in a digital manner, see fig. 8: an analog-to-digital converter 6i, 6j is connected before each of the two input terminals of the multiplier 6c of the cross-correlation amplifier 6, the input terminals of the analog-to-digital converters are connected to the output terminal of the current-voltage conversion amplifier, the output terminal of the analog-to-digital converter is connected to one of the input terminals of the multiplier, and the subsequent multipliers and the subsequent averagers are replaced by digital multipliers and averagers, thereby forming the digital cross-correlation amplifier. When a digital open-square operator is connected to the output of the digital cross-correlation amplifier 6, a digital open-square cross-correlation amplifier is formed; alternatively, a digital squaring operator 7 is added between the multiplier 6c and the averager 6d of the digital cross-correlation amplifier 6, thereby forming a square-open digital cross-correlation amplifier. After using this digital correlation amplifier and replacing follow-up components and parts for corresponding digital components and parts, the utility model discloses a tunnel current measuring device just can work under digital mode.
Claims (7)
1. A tunnel current measuring device of a scanning tunnel microscope based on a correlated amplifier comprises a probe frame, a probe, a sample frame, a Z-direction coarse adjustment driver and Z-direction piezoelectric ceramics, and is characterized in that output ends of two current-voltage conversion amplifiers are respectively connected with two input ends of a multiplier, an output end of the multiplier is connected with an input end of an averager, so that the correlated amplifier is formed, detection input ends of the two current-voltage conversion amplifiers, namely the two input ends of the correlated amplifier, are connected with the probe frame or the sample frame after being in short circuit, and reference input ends of the two current-voltage conversion amplifiers are used as reference input ends of the correlated amplifier after being in short circuit;
the probe is fixed on a probe frame in an electric contact manner, the probe frame is fixed at the top end of the piezoelectric ceramic, the sample frame is fixed on a base pointed by the probe, the other top end of the piezoelectric ceramic is fixed on a Z-direction coarse adjustment driver, and the output end of the averager, namely the output end of the cross-correlation amplifier, is a signal output interface; or the sample frame is fixed at the top end of the piezoelectric ceramic, the other top end of the piezoelectric ceramic is fixed on the Z-direction coarse adjustment driver, the probe frame is fixed on the base opposite to the sample frame, and the probe is fixed on the probe frame in an electric contact manner; the output end of the correlated amplifier is a signal output interface.
2. The tunneling current measuring apparatus according to claim 1, wherein the input of a squaring operator is connected to the output of the cross-correlation amplifier to form a squared cross-correlation amplifier, and the output of the squaring operator, i.e., the output of the squared cross-correlation amplifier, is used as the signal output interface.
3. The tunneling current measuring device of the correlated amplifier-based scanning tunneling microscope according to claim 1, wherein a square-on operator is connected between the multiplier and the averager of the correlated amplifier to form a square-on correlated amplifier, and the output terminal of the averager, i.e. the output terminal of the square-on correlated amplifier, is used as the signal output interface.
4. The tunneling current measuring apparatus for a scanning tunneling microscope based on correlated amplifier according to claim 1, 2 or 3, characterized in that said piezoelectric ceramic in Z direction is replaced with a three-dimensional scanning controller made of piezoelectric ceramic material.
5. Tunnel current measuring device according to claim 4, characterized in that a feedback control system in the Z-direction is added between the outputs of the correlated amplifiers and the three-dimensional scan controller.
6. Tunnel current measuring device according to claim 4, characterized in that a Z-direction feedback control system is added between the output of the squarer and the three-dimensional scan controller.
7. A tunneling current measuring device according to claim 1, 2, 3, 4, 5 or 6, characterized in that an analog-to-digital converter is added before each of the two inputs of the multiplier, and the multiplier and the corresponding averager and squarer are respectively replaced by a digital multiplier, a digital averager and a digital squarer.
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| CN101324785B (en) * | 2008-07-17 | 2010-06-09 | 浙江大学 | Pure tungsten material micro-nano probe preparation control system for scanning tunnel microscope |
| CN104880578A (en) * | 2015-06-17 | 2015-09-02 | 扬州大学 | Device for measuring micro-nano metal fiber surface topography, and use method thereof, and method for measuring driver moving distance in device |
| CN104880578B (en) * | 2015-06-17 | 2017-06-16 | 扬州大学 | The measuring method of driver move distance in a kind of device and its application method and the device for measuring micro-nano metallic fiber surface topography |
| CN106783656A (en) * | 2016-12-05 | 2017-05-31 | 武汉新芯集成电路制造有限公司 | A kind of probe structure for WAT detection machines |
| CN106783656B (en) * | 2016-12-05 | 2019-11-29 | 武汉新芯集成电路制造有限公司 | A kind of probe structure for WAT detection machine |
| CN110082568A (en) * | 2019-04-28 | 2019-08-02 | 广州大学 | A kind of scan-type electrochemical microscope and its bearing calibration |
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