CN101363789B - Scanning-tunnelling microscope for vibrating example and measurement method thereof - Google Patents
Scanning-tunnelling microscope for vibrating example and measurement method thereof Download PDFInfo
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- CN101363789B CN101363789B CN2008101984784A CN200810198478A CN101363789B CN 101363789 B CN101363789 B CN 101363789B CN 2008101984784 A CN2008101984784 A CN 2008101984784A CN 200810198478 A CN200810198478 A CN 200810198478A CN 101363789 B CN101363789 B CN 101363789B
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Abstract
The invention provides a scanning tunneling microscope for a vibrating specimen and a measurement method thereof. The scanning tunneling microscope comprises a scanning head (1), a preamplifier (2) and a scanning tunneling microscope controller (4), wherein the scanning head (1) is provided with a probe (1-1), the preamplifier (2) is provided with a current/voltage converter (2-1), a low pass voltage amplifier (2-2) and a band pass voltage amplifier (2-3), a phase detector (3) is also arranged, and respectively connected with the band pass voltage amplifier (2-3) and the scanning tunneling microscope controller (4), and the phase detector (3) is also provided with a voltage signal generating device (3-1) which is connected with a piezoelectric vibration exciter (1-3) arranged under the probe (1-1). The invention provides a device for measuring the characteristics of nanometer or atom scale while measuring the tunneling current by applying light mechanical vibration to the detected specimen on the basis of STM, and a measurement method for realizing the recognition of the categories of atom or molecule or obtaining the physical properties of the material such as the micro-elasticity.
Description
Technical field
The invention belongs to the scanning probe microscopy technical field, particularly relate to a kind of scanning tunnel microscope that the atom or the molecular species of sample are discerned of realizing, and adopt this microscopical measuring method.
Technical background
Scanning probe microscopy (SPM) mainly comprises two major types: based on the scanning tunnel microscope (STM) of tunnel effect with based on the atomic force microscope (AFM) of acting force between atom.
Sample is normally fixed in STM.When the distance between metal probe and tested conducting sample is adjusted to nanoscale when following, the Dc bias that is applied causes having between probe and sample tunnel current to take place.By feedback circuit, when keeping distance constant (the permanent height pattern) scanning between probe and tested conducting sample, what obtain usually is the density of states two-dimensional image on sample surface; By feedback circuit, when keeping constant tunnelling current mode scanning (constant current mode), what obtain is the two-dimensional image of surface relief image-atomic arrangement.It is which kind of atom or molecule that existing scanning tunnel microscope can not be discerned what be observed.
STM surveys interatomic tunnelling current, has the resolution of atomic scale; And interatomic interaction force in most advanced and sophisticated atom of AFM exploratory probe and the measured object surface certain limit, its resolution is lower than STM usually.On the other hand, function and the measurement pattern of STM are less at present, have then developed many new functions and measurement pattern on the AFM basis, as mgnetic observations, electrostatic force measurement, piezoelectric response measurement pattern, sample vibration and acoustic mode etc.So on STM, realize among a kind of and the AFM the similarly metering system of vibrating example, with high resolving power measurements that utilizes STM obtain sample surfaces more, the characteristic details of nanometer or atomic scale, have great importance.
Summary of the invention
The objective of the invention is to overcome the deficiencies in the prior art, provide a kind of on the basis of common STM, by sample being applied small mechanical vibration, measuring samples is at the device of the characteristic of nanometer or atomic scale when measuring tunnel current.
Another object of the present invention is to provides a kind of species detecting that can realize the different composed atoms of sample surfaces when finishing conventional STM pattern scanning according to this device, or the reflection sample is in the method for the elastic property of nanoscale.
In order to realize goal of the invention one, the technical scheme of employing is as follows:
A kind of scanning tunnel microscope of vibrating example, comprise scanner head, prime amplifier, scanning tunnel microscope controller, described scanner head is provided with the conducting metal probe, prime amplifier is provided with the logical voltage amplifier of current/voltage converter, low pass voltage amplifier and band, the present invention also is provided with phase detectors, described phase detectors are logical voltage amplifier of connecting band and scanning tunnel microscope controller respectively, and phase detectors also are provided with voltage signal generator, and voltage signal generator is connected with the piezoelectric vibration exciter that is arranged on the probe below.
The present invention does not influence original STM measurement function.When measuring, the voltage signal that voltage signal generator produces is applied on the piezoelectric vibration exciter, makes it to produce mechanical vibration.Piezoelectric vibration exciter and sample closely are bonded together, thereby can drive the sample vibration.The direction of vibration is the normal direction of sample surfaces, is the length direction of probe.The frequency of vibration is selected in more than the responsive bandwidth of common STM backfeed loop, and Oscillation Amplitude compares very for a short time with the tunnel junction spacing, and therefore, this vibration is to the not influence of conventional imaging of tunnel current.
In the technique scheme, the logical voltage amplifier parallel connection of described low pass voltage amplifier and band, its common input end connects the output terminal of current/voltage converter, and the output terminal of low pass voltage amplifier connects the scanning tunnel microscope controller, and the output terminal of the logical voltage amplifier of band connects phase detectors.Vibrate caused, small tunnel current AC compounent and measure by phase detectors, can measure its amplitude and phase place through current/voltage converter in the prime amplifier and the logical voltage amplifier amplification of band back.The local character of this amplitude and phase signal reflection sample on nanometer or atomic scale can be used for imaging.Therefore, in the single pass of probe, can obtain two-dimentional shape appearance figure, exchange current amplitude image and the phase diagram on measured object surface simultaneously.On exchange current amplitude image and phase diagram, can obtain the details of failing to demonstrate with two-dimentional shape appearance figure, these details can reflect the element kind difference of tested atom, can be used for the identification of atom or molecular species, or reflect the differences of physical properties of measured material in the nanometer microcell, as viscoelastic property.
In order to realize goal of the invention two, the technical scheme of employing is as follows:
A kind of measuring method of scanning tunnel microscope of vibrating example, adopt scanning tunnel microscope to measure the tunnel current of sample, the voltage signal that produces by voltage signal generator is applied on the piezoelectric vibration exciter simultaneously, make it to drive sample vibration, again by the amplitude and the phase place of the caused tunnel current AC compounent of phase detectors measuring vibrations.
The voltage signal that described voltage signal generator produces is applied on the piezoelectric vibration exciter, make it to produce mechanical vibration, the direction of vibration is the normal direction of the sample surfaces that closely is bonded together with piezoelectric vibration exciter, it also is the length direction of probe, the frequency of vibration is greater than the responsive bandwidth of scanning tunnel microscope backfeed loop, and Oscillation Amplitude is less than the tunnel junction spacing.
The present invention obtains two-dimentional shape appearance figure, exchange current amplitude image and the phase diagram on sample surface simultaneously by scanning tunnel microscope.
By exchange current amplitude image and the phase diagram that obtains, can reflect the element kind difference of sample atom, carry out the identification of atom or molecular species, or reflect the differences of physical properties of sample in the nanometer microcell.
The concrete operations of the identification that exchange current amplitude image that obtains and phase diagram carry out atom or molecular species are as follows:
At first according to tunnel current formula: I=I
0Exp (2 κ z), wherein κ is the attenuation constant of tunnel current, z is the tunnel junction spacing, establishes being changed to of the tunnel junction spacing that causes of vibration: z=z
0+ Acos (2 π ft), wherein A represents the mechanical vibration amplitude of sample, and f represents vibration frequency, and t is the time, and the logarithmic form that draws normallized current is: ln (I/I
0The 2 κ z of)=-
0-2 κ Acos (2 π ft).Because the alternating component I of tunnel current
AcTotal relatively tunnel current is very little, thereby can get: I
Ac∝ κ A.On two-dimensional distribution, exchange current component I
AcThe reflection of pairing image be the difference of space distribution of the attenuation constant κ of tunnel current.Because the κ value of different types of atom there are differences, thereby can distinguish or discern different element kinds.This operation is primarily aimed at sample combines very tight and sample with piezoelectric vibration exciter the little situation of mechanical property difference.
The exchange current amplitude image and the phase diagram that obtain reflect that the differences of physical properties concrete operations of sample in the nanometer microcell are as follows:
At first according to tunnel current formula: I=I
0(2Kz), wherein κ is the attenuation constant of tunnel current to exp, and z is the tunnel junction spacing, establishes being changed to of the tunnel junction spacing that causes of vibration: z=z
0+ Acos (2 π ft), wherein A represents the mechanical vibration amplitude of sample, and f represents vibration frequency, and t is the time, and the logarithmic form that draws normallized current is: ln (I/I
0The 2 κ z of)=-
0-2 κ Acos (2 π ft).On two-dimensional distribution, exchange current component I
AcPairing image will reflect the space distribution of effective Oscillation Amplitude A.Because effectively Oscillation Amplitude A is main relevant with the physical property of material, thereby can be used for characterizing physical characteristics.There is the situation of bigger difference in the microcosmic mechanical property that this operation is primarily aimed at sample.
The present invention carries out small mechanical vibration to sample and excites and can not influence original STM measurement function in the STM device.By applying amplitude and the phase place that this excited and measured simultaneously the respective quadrature flow component in the tunnel current, can obtain the more nanometer relevant or the information of atom microcell with material behavior.In concrete application example, with the method for sample vibration realized different elements distinguish with the heterogeneous alloy material in out of phase resolution.
Description of drawings
Fig. 1 is a structure principle chart of the present invention;
Fig. 2 is the amplitude of alternation response signal and the phase place curve map with frequency change;
Fig. 3 is the figure as a result of embodiment one;
Fig. 4 is the figure as a result of embodiment two.
Embodiment
The present invention is described further below in conjunction with accompanying drawing.
Structural representation of the present invention as shown in Figure 1, comprise the scanner head 1 that is provided with probe 1-1, be provided with current/voltage converter 2-1, low pass voltage amplifier 2-2, the prime amplifier 2 of the logical voltage amplifier 2-3 of band, phase detectors 3, and scanning tunnel microscope controller 4, the logical voltage amplifier 2-3 parallel connection of described low pass voltage amplifier 2-2 and band, its common input end connects the output terminal of current/voltage converter 2-1, the output terminal of low pass voltage amplifier 2-2 connects scanning tunnel microscope controller 4, the output terminal of the logical voltage amplifier 2-3 of band connects phase detectors 3, phase detectors 3 also are provided with voltage signal generator 3-1, voltage signal generator 3-1 is connected with the piezoelectric vibration exciter 1-3 that is arranged on probe 1-1 below, and sample 1-2 and piezoelectric vibration exciter 1-3 fit tightly together.
Measuring method of the present invention is as follows:
With platinumiridio (Pt-Ir) probe and golden platinum (Au-Pt) film sample is that example is made an explanation.
Piezoelectric vibration exciter adopts single crystal quartz sheet (x cuts); The probe that uses is Pt-Ir probe (being to obtain with mechanical shearing method on 0.25 millimeter the Pt80/Ir20 alloy threadlet from diameter); Sample has been part sputter proof gold (Au) surface of platinum (Pt).Sample bias is set at 0.1V, and tunnel current is set at 0.8nA.
Concrete measuring method is:
1, at first the distance adjustment of probe and sample is made to nanoscale and produce stable tunnel current with the method for STM, when applying alternation exciting voltage, obtain the amplitude of alternation response signal and phase place relation curve with frequency sweeping, as shown in Figure 2 with frequency change at fixed position.
When 2, selecting different measurement points, the position that the peak value on the frequency curve occurs may be different.The frequency of operation of the frequency of can be therein selecting steep place on a frequency peak or the curve on curve during as two-dimensional scan; Also can select a plurality of frequencies to scan simultaneously to obtain more information simultaneously as frequency of operation.
3, under vibrating example and normal STM image-forming condition, in single pass, obtain the amplitude image and the phase diagram of STM surface topography map, exchange current simultaneously.
Embodiment one: the realization atom is distinguished
In this sweep limit, the microcell that sample surfaces exists platinum and two kinds of elements of gold to form probably simultaneously.From shape appearance figure, can see a lot of crystal grain, but can't tell this two kinds of zones that element is formed.But on current amplitude figure and phase diagram, have two kinds of visibly different zones, the less zone of zone that current amplitude is less and phase place is corresponding.The mechanical property of platinum and gold is close, and the intensity of the effective accumulation signal in the microcell that two kinds of atoms are formed should be close.The exchange current image difference reflected should be the difference of space distribution of the attenuation constant κ of tunnel current, i.e. the difference of the work function of platinum and gold, or in the difference of each regional inner tunnel junction barrier height.Therefore, the presentation of results of Fig. 3 can be in the scanning of STM pattern with the method for vibrating example, and the different elements that pick out in each microcell are formed, and have the application prospect of atom or molecular recognition.
Embodiment two: differentiate the heterogeneous alloy material:
Leypewter is typical two-phase coexistent alloy material.From shape appearance figure, there are a lot of crystal grain, but can't tell this two kinds of out of phase zones.But on current amplitude figure and phase diagram, have two kinds of visibly different zones, the less zone of zone that current amplitude is less and phase place is corresponding; In the dark areas in the lower left corner, a little light tone zone has also appearred.In these two mutually pairing microcells, there is bigger difference in its elasticity, and therefore effectively Oscillation Amplitude differs bigger.That is to say, the exchange current image difference reflected should be the difference of the microcell elastic property of material.The difference in these two kinds of zones that shown in the accompanying drawing 4 and the character of nested feature and this material thereof match.Therefore, the presentation of results of accompanying drawing 4 can be in the scanning of STM pattern with the method for vibrating example, and the differences of physical properties such as elasticity of reflection material in each microcell is for the sign of material microscopic characteristics provides new method.
Claims (8)
1. the scanning tunnel microscope of a vibrating example, comprise scanner head (1), prime amplifier (2), scanning tunnel microscope controller (4), described scanner head (1) is provided with probe (1-1), prime amplifier (2) is provided with current/voltage converter (2-1), the logical voltage amplifier (2-3) of low pass voltage amplifier (2-2) and band, it is characterized in that also being provided with phase detectors (3), described phase detectors (3) are logical voltage amplifier (2-3) of connecting band and scanning tunnel microscope controller (4) respectively, and phase detectors (3) also are provided with voltage signal generator (3-1), voltage signal generator (3-1) is connected with the piezoelectric vibration exciter (1-3) that is arranged on probe (1-1) below, logical voltage amplifier (2-3) parallel connection of described low pass voltage amplifier (2-2) and band, its common input end connects the output terminal of current/voltage converter (2-1), the output terminal of low pass voltage amplifier (2-2) connects scanning tunnel microscope controller (4), and the output terminal of the logical voltage amplifier (2-3) of band connects phase detectors (3).
2. the scanning tunnel microscope of vibrating example according to claim 1 is characterized in that described probe (1-1) adopts the conducting metal probe.
3. the measuring method of the scanning tunnel microscope of a vibrating example, it is characterized in that adopting the scanning tunnel microscope of claim 1 to measure the tunnel current of sample, the voltage signal that produces by voltage signal generator is applied on the piezoelectric vibration exciter simultaneously, make it to drive sample vibration, again by the amplitude and the phase place of the caused tunnel current AC compounent of phase detectors measuring vibrations.
4. the measuring method of the scanning tunnel microscope of vibrating example according to claim 3, it is characterized in that the voltage signal that described voltage signal generator produces is applied on the piezoelectric vibration exciter, make it to produce mechanical vibration, the direction of vibration is the normal direction of the sample surfaces that closely is bonded together with piezoelectric vibration exciter, it also is the length direction of probe, the frequency of vibration is greater than the responsive bandwidth of scanning tunnel microscope backfeed loop, and Oscillation Amplitude is less than the tunnel junction spacing.
5. according to the measuring method of the scanning tunnel microscope of claim 3 or 4 described vibrating examples, it is characterized in that obtaining simultaneously two-dimentional shape appearance figure, exchange current amplitude image and the phase diagram on sample surface by scanning tunnel microscope.
6. the measuring method of the scanning tunnel microscope of vibrating example according to claim 5, it is characterized in that exchange current amplitude image and phase diagram by obtaining, the element kind difference that can reflect the sample atom, carry out the identification of atom or molecular species, or reflect the differences of physical properties of sample in the nanometer microcell.
7. the measuring method of the scanning tunnel microscope of vibrating example according to claim 6, the concrete operations of the identification that it is characterized in that carrying out atom or molecular species by the exchange current amplitude image that obtains and phase diagram are as follows:
At first according to tunnel current formula: I=I
0Exp (2 κ z), wherein κ is the attenuation constant of tunnel current, z is the tunnel junction spacing, I
0Current value when being zero for the tunnel junction spacing;
If being changed to of the tunnel junction spacing that vibration causes: z=z
0+ Acos (2 π ft), wherein A represents the mechanical vibration amplitude of sample, and f represents vibration frequency, and t is the time, z
0Be the mean value of probe-sample interval, the logarithmic form that draws normallized current is: ln (I/I
0The 2 κ z of)=-
0-2 κ Acos (2 π ft) are because the alternating component I of tunnel current
AcTotal relatively tunnel current is very little, thereby can get: I
Ac∝ κ A, on two-dimensional distribution, exchange current component I
AcThe reflection of pairing image be the difference of space distribution of the attenuation constant κ of tunnel current, because the κ value of different types of atom there are differences, thereby can distinguish or discern different element kinds, this operation is primarily aimed at sample combines very tight and sample with piezoelectric vibration exciter the little situation of mechanical property difference.
8. the measuring method of the scanning tunnel microscope of vibrating example according to claim 6 is characterized in that reflecting that by the exchange current amplitude image and the phase diagram that obtain the differences of physical properties concrete operations of sample in the nanometer microcell are as follows:
At first according to tunnel current formula: I=I
0Exp (2 κ z), wherein κ is the attenuation constant of tunnel current, z is the tunnel junction spacing, I
0Current value when being zero for the tunnel junction spacing;
If being changed to of the tunnel junction spacing that vibration causes: z=z
0+ Acos (2 π ft), wherein A represents the mechanical vibration amplitude of sample, and f represents vibration frequency, and t is the time, z
0Be the mean value of probe-sample interval, the logarithmic form that draws normallized current is: 1n (I/I
0The 2 κ z of)=-
0-2 κ Acos (2 π ft), on two-dimensional distribution, exchange current component I
AcPairing image will reflect the space distribution of mechanical vibration amplitude A, because the mechanical vibration amplitude A is main relevant with the physical property of material, thereby can be used for characterizing physical characteristics, there is the situation of bigger difference in the microcosmic mechanical property that this operation is primarily aimed at sample.
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| CN104142410A (en) * | 2013-05-06 | 2014-11-12 | 中国科学院物理研究所 | Scanning head of scanning tunneling microscope |
| CN105510639B (en) * | 2014-09-24 | 2018-10-19 | 中国科学院宁波材料技术与工程研究所 | Probe, preparation method and detection method in a kind of scanning probe microscopy |
| CN108414176B (en) * | 2018-03-05 | 2020-01-31 | 山东理工大学 | Nano-beam vibration control device based on tunnel effect |
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