CN105301287B - Radio frequency reflection type scanning tunneling microscope - Google Patents
Radio frequency reflection type scanning tunneling microscope Download PDFInfo
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- CN105301287B CN105301287B CN201410538330.6A CN201410538330A CN105301287B CN 105301287 B CN105301287 B CN 105301287B CN 201410538330 A CN201410538330 A CN 201410538330A CN 105301287 B CN105301287 B CN 105301287B
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Abstract
A radio frequency reflection type scanning tunneling microscope having a probe spaced from and disposed opposite to a sample to be measured for scanning the surface appearance of the sample to be measured, comprising: the radio frequency scanning resonance circuit comprises an inductor, a capacitor, a resistor and a tunneling resistor, wherein the capacitor, the resistor and the tunneling resistor are connected with one end of the inductor in parallel, the tunneling resistor is formed between a sample to be detected and a probe, a directional coupler is electrically coupled with the other end of the inductor, a radio frequency signal source which generates a radio frequency signal and outputs the radio frequency signal to the radio frequency scanning resonance circuit through the directional coupler, and a radio frequency signal measuring system which receives a radio frequency reflection signal transmitted by the radio frequency scanning resonance circuit through the directional coupler, so that the probe is controlled according to the radio frequency reflection signal in a feedback mode, and a scanning result related to the surface appearance of the sample to be detected is generated.
Description
Technical field
The present invention relates to a kind of tunneling microscopes, and tunneling microscope is scanned more particularly to a kind of radio frequency reflection formula.
Background technology
Existing tunneling microscope has following items limitation in use, and one be the sample to be tested need to be electrically conductive substance；
Two can be by the interference in multiple outfield electronics (stream) sources, the outfield electronics for the tunneling microscope of the existing constant current mode
(stream) source includes the incident electron that electron gun generates, secondary electron, Ou Jie electronics, and by light activated photoelectron etc.；Three are
The bandwidth of current-to-voltage convertor is limited within tens of KHz.It, should if the electron source is incident or leaves near a tunneling energy barrier
External electrical (son) is flowed can amplify via current-voltage converter together with tunnel current It, and then existing electric current is interfered to return
Infeed mechanism, cause can not scanning imagery the problem of.
After selection inductance L and capacitance C determines resonant frequency, tunneling resistor Rt to Rt ≈ L/ (C*Z0) are adjusted, are made
The impedance Z t=output impedances Z0 (50 nurse difficult to understand) of resonant circuit, can be obtained best impedance matching, resonant circuit can be intimate at this time
Fully absorb the radio frequency energy of input.
Such as shown in Fig. 3, when taking tunneling resistor Rt=0.15Mohm, good impedance matching can be obtained, return at this time
It is 45dB to lose (return loss).If probe 10, far from sample 20, tunneling resistor Rt increases, at this time because of resonant circuit
Impedance Z t is mismatched with output impedance Z0, and the reflected energy of radiofrequency signal will increase, and Fig. 3 is illustrated in different tunneling electricity
When hindering Rt values, the phenomenon that reflectivity increases sharply.And as seen from Figure 3 when tunneling resistor Rt fades to 0.4M by 0.15M ohm
When ohm, reflectance factor just becomes 15dB from 45dB, and when tunneling resistor Rt is 1M ohm, reflectance factor is 12dB, and when tunneling
Resistance Rt because the variation all too of reflectance factor is small, and all almost can not divide at 11dB between 10M ohm to 1G ohm
Come, why not same has so that being difficult handle seperately out tunneling resistor 10Mohm and 100M ohm in practical, and in practical application, wear
Often operation is in 10M ohm~1G ohm ranges by tunnel resistance Rt, so above-mentioned scan mode hardly results in useful signal.
In addition, as shown in Figure 4 it is found that between the above-mentioned scan mode radio frequency reflection rate intensity obtained and tunneling resistor Rt simultaneously
Non- list correspondence, that is to say, that same reflection rate intensity value can correspond to two tunneling resistor Rt values, this will cause scanning to control
Erroneous judgement of the circuit processed to scanning result, and if using the height of this reflectivity feedback control probe 10, will produce unstable
Situation.
Invention content
It is in single correspondence the purpose of the present invention is to provide a kind of radio frequency reflection rate intensity and tunneling resistor, and can operates
In appropriate tunneling resistor value and high bandwidth, the radio frequency reflection formula scanning without the interference by outfield electronics (stream) source is tunneling micro-
Mirror.
The radio frequency reflection formula of the present invention scans tunneling microscope, the spy for having one and one sample to be tested interval and being oppositely arranged
Needle, the surface complexion for scanning the sample to be tested, and include：One radio frequency reading resonant circuit, a directional coupler and one penetrate
Frequency Signal Measurement System, the radio frequency reading resonant circuit include the inductance with a first end and a second end, and with this
A capacitance, a resistance and a tunneling resistor for the first end parallel connection of inductance, the wherein tunneling resistor are formed in the sample to be tested
Between the probe；The second end electric coupling of direction coupler and the inductance of the radio frequency reading resonant circuit, and receive one
Radiofrequency signal, and the radiofrequency signal is exported to the radio frequency reading resonant circuit, and one is received via radio frequency reading resonance electricity
The radio frequency reflection signal passed back is reflected on road；It is anti-to receive the radio frequency that the radiofrequency signal measuring system is electrically connected direction coupler
Penetrate signal, and according to the radio frequency reflection signal feedback control probe, and it is related with the surface complexion of the sample to be tested to generate one
Scanning result.
Preferably, the radio frequency reading resonant circuit further includes an auxiliary capacitor in parallel with the second end of the inductance.
Preferably, the radio frequency reading resonant circuit further include one with the capacitance series and by one first applied voltage control,
Concatenated with the auxiliary capacitor with the first voltage controlled capacitor and one that adjust a resonant frequency of the radio frequency reading resonant circuit and by
One second applied voltage controls, with the second voltage controlled capacitor of determine the radio frequency reading resonant circuit one final impedance.
Preferably, the probe and the radio frequency reading resonant circuit are coated on wherein by the shield shell, to avoid the radio frequency
Signal is reflected to be interfered by a foreign current (son) field.
Preferably, the shield shell includes a notch, the notch is adjacent to the probe, for a bare front end of the probe.
Preferably, the radiofrequency signal measuring system is using the radio frequency reflection signal feedback control probe, and make the radio frequency
The energy intensity or phase for reflecting signal maintain an operation mode of certain value for certain radio frequency reading pattern.
Preferably, the radio frequency reflection formula scans tunneling microscope further includes one and the rf signal generator electric coupling 1
To 2 power dividers, which is divided into two, and exported respectively to direction coupler via two output ends and
The radiofrequency signal measuring system, and the radiofrequency signal measuring system further includes a reflection signal compensation circuit, by 1 couple, 2 work(
Its phase is suitably amplified and adjusted to the radiofrequency signal of rate distributor output, and the radio frequency reflection signal is suitably amplified, and makes this
Radiofrequency signal is identical as the amplitude of the part radiofrequency signal being contained in the radio frequency reflection signal and phase differs 180 degree, then
The two is added, to eliminate the radiofrequency signal composition in the radio frequency reflection signal.
Preferably, the reflection signal compensation circuit includes the first controllable gain amplifier of the amplification radiofrequency signal, one
Amplify the radio frequency reflection signal the second controllable gain amplifier, one adjust the radiofrequency signal phase, make and the radio frequency reflection
What adjustable phase shifter and one of the part radiofrequency signal with 180 degree phase difference in signal exported the adjustable phase shifter
The combiner that signal is added with the signal that second controllable gain amplifier exports.
Preferably, the radiofrequency signal measuring system further includes the adjustable phase shifter for being located at the RF compensation circuit and should
The radio frequency detecting unit that first direction coupler between one input terminal of combiner, one are electrically connected the reflection signal compensation circuit,
And one be electrically connected to feedback control unit between the radio frequency detecting unit and the sample to be tested, which receives by this
First direction coupler couples radiofrequency signal and the radio frequency reflection signal that the adjustable phase shifter is exported, and detects the radio frequency
One power level of a phase difference and the radio frequency reflection signal between signal and the radio frequency reflection signal, to obtain the instruction work(
The output of rate intensity, and the feedback control unit according to the output of the instruction power level from the radio frequency detecting unit come
Adjust the height of the probe.
Preferably, the radio frequency detecting unit has a radio-frequency power amplifier, one first bandpass filter, 1 pair of 2 work(
Rate distributor, a radio-frequency power detector, one second bandpass filter, a phase difference detector and a display feedback circuit, should
Radio-frequency power amplifier receives the output of the combiner from the reflection signal compensation circuit, and is amplified into a compensation
Amplified signal；First bandpass filter is electrically connected the radio-frequency power amplifier to receive the compensation amplified signal, and by the benefit
Amplified signal is repaid to be filtered to obtain one first filtering signal；1 couple, 2 power divider is electrically connected first bandpass filter
To receive first filtering signal, and first filtering signal is divided into one first difference signal and one second difference signal, it should
First difference signal and the second difference signal are relevant to the radio frequency reflection signal；Radio-frequency power detector is electrically connected 1 couple, 2 work(
Rate distributor provides the output for indicating the power level to detect the power level of the first difference signal；Second band
Bandpass filter, which is electrically connected the reflection signal compensation circuit and couples the adjustable phase shifter to receive the first direction coupler, to be exported
The radiofrequency signal, and the radiofrequency signal is filtered to obtain second filtering signal；The phase difference detector is electrically connected
1 couple, 2 power divider and second bandpass filter are used with receiving the second difference signal and second filtering signal respectively
The phase difference between detecting the second difference signal and second filtering signal, and the output for indicating the phase difference is provided,
Second filtering signal is relevant to the radiofrequency signal；The display feedback circuit is electrically connected the radio-frequency power detector, the phase difference
Detector, to receive the output from the radio-frequency power detector and receive the output from the phase difference detector, and according to
The output of the instruction power level or phase value describe the surface complexion of the sample to be tested and show rendering results.
Preferably, the radio frequency detecting unit also has one to be set to 1 couple, 2 power divider and the radio-frequency power detector
Between a frequency modulation filter circuit, which there is one first mixer of a local oscillator and a third band logical to filter
Wave device, the local oscillator generate a local oscillated signal；First mixer is electrically connected 1 couple, 2 power divider and this
Ground oscillator carries out smear to receive the first difference signal and the local oscillated signal, and generates one first smear signal；
The third bandpass filter is electrically connected first mixer to receive the first smear signal, and the first smear signal is carried out
To obtain a third smear signal, which is relevant to the first difference signal, and is sent to the radio frequency work(for filtering
Rate detector.
It is also electrically connected in direction coupler, 1 couple comprising one preferably, the radio frequency reflection formula scans tunneling microscope
Optimization unit between 2 power dividers and the radiofrequency signal compensation circuit, the optimization unit include a local oscillator one second
Mixer, one first bandpass filter, a third mixer and one second bandpass filter, the local oscillator generate one
Ground oscillator signal；Second mixer is electrically connected to direction coupler and the local oscillator to receive the radio frequency reflection signal
With the local oscillated signal and carry out smear, and generate one second smear signal；First bandpass filter be electrically connected this second
The second smear signal is filtered to receive the second smear signal and generates one first smear filtering letter by mixer
Number, and the first smear filtering signal is sent to second controllable gain amplifier VGA；The third mixer is electrically connected to this
1 pair of 2 power divider and the local oscillator carry out smear to receive the reference signal and the local oscillated signal, and generate
One third smear signal；Second bandpass filter is electrically connected the third mixer to receive the third smear signal, and should
Third smear signal is filtered and generates one second smear filtering signal, and by the second smear filtering signal be sent to this
One controllable gain amplifier VGAR.And the radio frequency detecting unit has a radio-frequency power amplifier, one 1 couple of 2 power divider, one
Radio-frequency power detector, a phase difference detector and a display feedback circuit, the radio-frequency power amplifier are electrically connected the combiner
To receive the signal of combiner output, and amplified into a compensation amplified signal；1 couple, 2 power divider is electrically connected
The compensation amplified signal is divided into one first difference signal and one by the radio-frequency power amplifier to receive the compensation amplified signal
Second difference signal, the first difference signal and the second difference signal are relevant to the radio frequency reflection signal；The radio-frequency power is detectd
It surveys device and is electrically connected 1 couple, 2 power divider to detect the power level of the first difference signal, and provide one and indicate the power
The output of intensity；The phase difference detector be electrically connected 1 couple, 2 power divider and the first direction coupler with receive this second
The signal of difference signal and first direction coupler output, for detecting the second difference signal and the first direction coupler
The phase difference between the signal of output, and the output for indicating the phase difference is provided, the signal of first direction coupler output
It is relevant to the radiofrequency signal；The display feedback circuit receives the output from the radio-frequency power detector and comes from the phase with reception
The output of poor detector, and the surface complexion of the sample to be tested is described simultaneously according to the output of the instruction power level or phase value
Show rendering results.
Preferably, the radio frequency reflection formula scan tunneling microscope further include a current-voltage switching amplifier and one with should
The Bias-T circuits of directional coupler and the radio frequency reading resonant circuit electric coupling, the radiofrequency signal of direction coupler output
The radio frequency reading resonant circuit, and the radio frequency reflection letter that the radio frequency reading resonant circuit generates are inputted via the Bias-T circuits
Number via the Bias-T circuit outputs to direction coupler, and the tunnel current warp that the radio frequency reading resonant circuit generates
It is amplified by the Bias-T circuit outputs to the current-voltage switching amplifier, and this is inputted after being converted into an output voltage
Feedback control unit makes the feedback control unit according to the output voltage and the power level or the phase value feedback control spy
Needle.
Preferably, the feedback control unit includes one second feedback controller, a switching switch and one first feedback control
Device, second feedback controller receive the output voltage to generate a direct current output；Switching switch is by control to select to come from
The direct current output of second feedback controller or the output from the radio frequency detecting unit, as an output；This is first anti-
Feedback controller receives the output of switching switch to adjust the height of the probe.
Preferably, the sample to be tested is applied in a bias, and the probe is grounded so that close enough this of the probe waits for test sample
When the surface of product, the tunneling resistor is generated in formation tunneling effect between the two；Alternatively, the sample to be tested is grounded, and this is penetrated
Frequency scanning resonant circuit is applied in a bias via a high frequency choke coil, and being somebody's turn to do for the radio frequency reading resonant circuit is inputted with blocking
High-frequency signal influences the bias, and the resistance is also connected a barrier capacitance, with stop that the radio frequency reading resonant circuit generates one
Tunnel current flows through the resistance.
Preferably, the sample to be tested is grounded, and the radio frequency reading resonant circuit is applied in via a high frequency choke coil
One bias, the high-frequency signal of the radio frequency reading resonant circuit is inputted with blocking influences the bias, and the resistance also connect and one hindered
The barrier capacitance of stopping direct current, to stop the one of the radio frequency reading resonant circuit generation resistance for passing through the radio frequency reading resonant circuit
A DC current.
Effect of the present invention is：In addition to the tunneling electricity between probe and sample to be tested can be measured using radio frequency reflection signal
Inhibition effect, it may have measure the phase difference of radio frequency reflection signal to react the ability of the reactive effect on sample to be tested surface, and energy
It is not influenced by external electrical (stream) field and can have complete and uninterruptedly scanning result, actually reach the work(of the present invention
Effect.
Description of the drawings
The other features and effect of the present invention, will clearly be presented in the embodiment with reference to schema, wherein：
Fig. 1 is a circuit diagram, illustrates a kind of existing tunneling microscope of radio frequency reading formula；
Fig. 2 is an equivalent circuit diagram, the tunneling microscopical LCR resonant circuits of 1 existing radio frequency reading formula of definition graph it is equivalent
Circuit；
Fig. 3 is a curve graph, illustrates the radio frequency reflection rate variation corresponding to different tunneling resistor values；
Fig. 4 is a curve graph, illustrate radio frequency reflection rate intensity that the tunneling microscope of existing radio frequency reading formula obtains with it is tunneling
Not single correspondence between resistance；
Fig. 5 is a circuit diagram, mainly illustrates the tunneling microscopical radio frequency reading resonance electricity of radio frequency reflection formula scanning of the present invention
Road；
Fig. 6 is an equivalent circuit diagram, the tunneling microscopical radio frequency reading resonant circuit of 5 radio frequency reading formula of definition graph it is equivalent
Circuit；
Fig. 7 is a double logarithmic chart, illustrates that the variable quantity of radio frequency reflection power Γ is presented single pair with tunneling resistor and should close
System；
Fig. 8 is an equivalent circuit diagram, illustrates that the present invention can also be in parallel in the second end of the inductance of radio frequency reading resonant circuit
One auxiliary capacitor；
Fig. 9 is an equivalent circuit diagram, illustrates that the present invention can respectively connect a voltage controlled capacitor again on capacitance and auxiliary capacitor,
And two voltage controlled capacitor is controlled respectively using two applied voltages；
Figure 10 is a circuit diagram, illustrates that radio frequency reflection formula of the present invention scans a tunneling microscopical first embodiment；
Figure 11 is a circuit diagram, illustrates one first aspect of the detecting unit of the present invention；
Figure 12 is a circuit diagram, illustrates one second aspect of the detecting unit of the present invention；
Figure 13 is a circuit diagram, illustrates a third aspect of the detecting unit of the invention；
Figure 14 is a statistical chart, illustrates that radio frequency reflection rate Г-tunneling resistor Rt-of the first embodiment of the present invention is tunneling
The statistical result of the measured data of electric current It and bias Vb；
Figure 15 is a curve graph, illustrates the radio frequency reflection signal difference Δ Г and tunnel current of the first embodiment of the present invention
It signals have very high consistency；
Figure 16 is a striograph, illustrate the present invention the first embodiment operation generated when determining radio frequency reading pattern wait for
Sample surface scan image；
Figure 17 is a striograph, and it is to be measured to illustrate that the first embodiment operation of the present invention is generated in current scanning pattern
Sample surfaces scan-image；
Figure 18 is a photo, and it is to be measured to illustrate that the first embodiment operation of the present invention is generated in constant current scan pattern
Sample surfaces scanned photograph；
Figure 19 is a photo, illustrates that the first embodiment of the present invention is operated when determining RF signal strength scan pattern formula
The sample to be tested surface scan photo of generation；
Figure 20 is a schematic diagram, illustrates that the probe of the first embodiment of the present invention moves closer to the height for generating tunnel current
When, the drive signal of 100MHz is sent into probe, the intensity of radio frequency reflection signal just has the variation of 100MHz；
Figure 21 is a schematic diagram, illustrates that the probe of the first embodiment of the present invention is pulled open to the height of not tunnel current
When, the intensity of radio frequency reflection signal is just fixed；
Figure 22 is a measured result figure, illustrates that the radiofrequency signal of the first embodiment of the present invention has high operation band
It is wide；
Figure 23 is an equivalent circuit diagram, illustrates that the first embodiment of the present invention applies a bias on sample to be tested, and
A kind of bias fashion for enabling probe be grounded；
Figure 24 is an equivalent circuit diagram, illustrates that the first embodiment of the present invention applies one on radio frequency reading resonant circuit
Bias, and another bias fashion for enabling sample to be tested be grounded；
Figure 25 is a circuit diagram, illustrates that radio frequency reflection formula of the present invention scans a tunneling microscopical second embodiment；
Figure 26 is a schematic diagram, illustrates that radio frequency reflection formula of the present invention scans a screen of the tunneling microscopical second embodiment
Cover body diagram；
Figure 27 is an equivalent circuit diagram, illustrates that the shield shell of the second embodiment of the present invention coats the probe, is somebody's turn to do
One schematic diagram of radio frequency reading resonant circuit, the Bias-T circuits and the current-voltage switching amplifier；
Figure 28 is a schematic diagram, and it is anti-to illustrate that the probe measuring one of the second embodiment of the present invention is placed in a liquid phase electrochemistry
Answer the sample to be tested of slot；
Figure 29 is a striograph, illustrates the extraneous electricity and the radio frequency reflection signal of the second embodiment of the present invention
Variation diagram；
Figure 30 is a curve graph, illustrates the second embodiment of the present invention when this determines radio frequency reading pattern, the probe
Height does not change with the variation of a totalling electric current；
Figure 31 is a curve graph, illustrates the second embodiment of the present invention in the constant current scan pattern, the probe
Height is significantly proportional to the integral of the totalling current square wave；
Figure 32 is a striograph, illustrates that an X-ray excitaton source of the second embodiment of the present invention is opened in a flash, should add
The variation of total current I；
Figure 33 is a striograph, illustrates that the X-ray excitaton source of the second embodiment of the present invention is adjusted to interact Push And Release
Become, the variation of totalling electric current I；
Figure 34 is a photo, illustrates that the second embodiment of the present invention operates under constant current scan pattern and without outer incoming call
The sample to be tested surface scan image of stream；
Figure 35 is a photo, illustrates that the second embodiment of the present invention operates in the case where determining radio frequency reading pattern and has outer incoming call
The sample to be tested surface scan image of stream；
Figure 36 is a photo, illustrates that the second embodiment of the present invention is operated and determines under radio frequency reading pattern and without external at this
The sample to be tested surface scan image of electric current；
Figure 37 is a photo, illustrates that the second embodiment operation of the present invention is determined under radio frequency reading pattern and had external at this
The sample to be tested surface scan image of electric current
Figure 38 is a photo, illustrates that the second embodiment of the present invention operates under the constant current scan pattern and has external
The sample to be tested surface scan image of electric current；And
Specific implementation mode
Shown in Figure 5, radio frequency reflection formula of the present invention scans a first embodiment of tunneling microscope 3, has one and one
The probe 10 that sample to be tested 20 is spaced and is oppositely arranged, the surface complexion for scanning sample to be tested 20, and include that a radio frequency is swept
Retouch resonant circuit 31, a directional coupler 32, a radio-frequency signal source 33 and a radiofrequency signal measuring system 4.Wherein radio frequency reading
Resonant circuit 31 includes the inductance L with a first end 34 and a second end 35, and in parallel with the first end 38 of inductance L
One capacitance Cp, a resistance Rp and a tunneling resistor Rt, wherein tunneling resistor Rt are formed between sample to be tested 20 and probe 10；And it wears
Tunnel resistance Rt is to apply a bias Vb by generating Times pressures between probe 10 and sample to be tested 20, such as in sample to be tested 20,
And probe 10 is allowed to be grounded, then when the surface of 10 close enough sample to be tested 20 of probe, it can form tunneling effect between the two and produce
Raw tunneling resistor Rt, and radio frequency reading resonant circuit 31 and the equivalent circuit of its front-end circuit are as shown in Figure 6.
In advance the value of inductance L, capacitance Cp and resistance Rp are adjusted to resonate again, resonant frequency can be determined by downlink formula：
The value of wherein R=Rt//Rp, and in practice, tunneling resistor Rt are in Ω to G Ω grades of M, and resistance Rp is about K Ω
Grade or so, therefore, Rt>>Rp.So when tunneling resistor Rt is infinitely great (when probe is far from sample to be tested 20), R=Rp,
Therefore the resonant frequency of radiofrequency signal, depending on making radio frequency reading resonant circuit 31 that there is optimum impedance matching in R=Rp, i.e.,
The impedance Z t=output impedances Z0 (50 nurse difficult to understand) of radioresonance circuit 31, radio frequency reflection rate Γ is minimum at this time.Then when probe 10 with
When the distance of sample to be tested 20 approaches and tunneling resistor Rt is made to become as low as finite value, then R is less than and is similar to Rp, and radio frequency reading is total
The impedance matching of circuit 31 of shaking can be deteriorated, and cause radio frequency reflection rate Γ to increase, whereby so that the variable quantity of radio frequency reflection rate Γ by
The impedance Z t decisions of radio frequency reading resonant circuit 31, i.e. Zt=L/ (Cp*R), that is to say, that when the micro changes of R, by micro change
Zt, and then micro change radio frequency reflection rate Γ.Therefore, pass through resistance Rp so that tunneling resistor Rt is generated with radio frequency reflection rate Γ
Relationship, and this relationship shows the variable quantity of radio frequency reflection rate Γ (S11) with tunneling resistor Rt in the double logarithmic chart of Fig. 7
And change, and tunneling resistor Rt is presented single pair with the variable quantity of radio frequency reflection rate Γ in a big variation range and answers and linearly
Aspect, solve existing radio frequency reflection formula scan tunneling microscope because of tunneling resistor Rt and radio frequency reflection rate Γ in pair corresponding and
The problem that scanning result caused by non-linear relation is judged by accident and feedback control is unstable.
Shown in Fig. 5, above-mentioned radiofrequency signal is to be generated by radio-frequency signal source 33, and 32 electric coupling of directional coupler exists
Between the second end 35 of the resonance inductor L of radio-frequency signal source 33 and radio frequency reading resonant circuit 31, for radio-frequency signal source 33 is defeated
The radiofrequency signal gone out is input to radio frequency reading resonant circuit 31 via an input path 321.Directional coupler 32 can also incite somebody to action simultaneously
Radiofrequency signal is input to by 31 reflected radio frequency reflection signal of radio frequency reading resonant circuit via a coupling path 322 to measure
System 4.Therefore, radiofrequency signal measuring system 4 receives the radio frequency that radio frequency reading resonant circuit 31 is transmitted via directional coupler 32
Signal is reflected, with according to the height of radio frequency reflection signal feedback control probe 10, and generates the table of one and sample to be tested 20 according to this
The related scanning result of face complexion.
In addition, to allow the reflection loss of radio frequency reading resonant circuit 31 (return loss) to maintain 20dB or more, and
Operation is in relatively high frequency (hundreds of MHz or more), then the value of inductance L and capacitance Cp are wanted small (referring to formula above), and resistance
Rp is enough big, because of the variable quantity of the radio frequency reflection rate Γ of radio frequency reading resonant circuit 31, depends on the residual quantity of Rp and Rp//Rt,
So the value of resistance Rp is bigger, the variable quantity of radio frequency reflection rate Γ is bigger.But since resistance Rp is equivalent to L/ (C*Zo),
Resistance Rp be difficult be set as larger value, even if capacitance Cp be only on printed circuit board stray capacitance (<1.0pF), resistance
It is all extremely difficult that Rp will be transferred to several K or more.
Therefore, in order to achieve the above objectives, as shown in figure 8, the present invention can also be the inductance L's of radio frequency reading resonant circuit 31
35 one auxiliary capacitor Cpi of parallel connection of second end makes radio frequency reading resonant circuit 31 constitute a Π type circuit structures, and auxiliary capacitor
Cpi can use larger capacitance, and resistance Rp is allow to be transferred to larger value.And because of resonant frequency mainly still by inductance L
It is determined with capacitance Cp, so after setting resistance Rp and resonant frequency, so that it may to determine that the value of auxiliary capacitor Cpi (generally exists
Number pF is between tens of pF).And because of the opereating specification of tunneling resistor Rt about between tens of M Ω to 1G Ω, therefore resistance Rp's is upper
Limit can be set in about 1M Ω or so, make the variable quantity of radio frequency reflection rate Γ relative to same tunneling resistor Rt whereby, have compared with
Big response.
Furthermore the resonant circuit structure of this Π types also provides the feasibility in the online resonant frequency of adjustment in real time.Such as
Upper described, resonant frequency is decided by the part numerical value used in inside, once setting, just generates a specific resonant frequency,
Value is mainly determined by inductance L and capacitance Cp.And because resistance Rp not changes, thus change resonant frequency then need by capacitance Cp and
The adjustment of auxiliary capacitor Cpi, therefore as shown in figure 9, the present invention can series connection one be pressed respectively again on capacitance Cp and auxiliary capacitor Cpi
Control capacitance VCp and VCpi, and using two applied voltage Bias1 and Bias2 come control want generation equivalent capacitance Cp and
Auxiliary capacitor Cpi values.Wherein voltage Bias1 mainly controls resonant frequency, and voltage Bias2 then controls final impedance value.Whereby,
Radio frequency reading resonant circuit 31 can select the frequency of the radiofrequency signal to be detected in certain operational frequency range, to taste
The physics for trying different kenels measures.
The radiofrequency signal measuring system 4 of the present invention is basically according to the radio frequency reflection transmitted by directional coupler 32 again
Signal measures the radio frequency reflection rate Γ (S11) of radio frequency reading resonant circuit 31 and its variation corresponding with tunneling resistor Rt.So
And in reality, directional coupler 32 is simultaneously imperfect, because its directionality is the limited (left sides generally about 20~30dB
It is right), so it is sent in the signal of radiofrequency signal measuring system 4 by coupling path 322 other than radio frequency reflection signal itself
(also including the loss of coupling in the middle) further includes the radio frequency letter that coupling path 322 is leaked to by inputting path 321 of suitable composition
Number.If when larger by the RF signal strength that the input path 321 of directional coupler 32 inputs, via directional coupler
The RF signal strength of 32 leakages to coupling path 322 can even exceed in radio frequency reflection signal, then be supplied to radiofrequency signal to measure
In the measured signal of system 4 other than the radio frequency reflection signal of script, and by plus the radiofrequency signal for being equivalent to background signal, make
The variable quantity for the radio frequency reflection signal that the desired amount is surveyed is obtained, it is even more very little relative to measured signal itself, and radio frequency will be made
Reflecting the measurement of the variable quantity of signal becomes more difficult.
For example, if typical background signal (i.e. radiofrequency signal) intensity exported by directional coupler 32 is -40dbm
To -50dBm, and when 31 scanning of a surface of radio frequency reading resonant circuit has the sample 20 that atom rises and falls, the radio frequency reflection letter that generates
Even number variable quantity may be only lower in 0.01dB.Although this signal can be put with the radio frequency amplifier of low noise low distortion
Big extremely -10dBm or so, but the variable quantity (fluctuating gap) of signal remains as same 0.01dB.With power detector now
Ability, if thinking, direct measurement -10.000dBm and -10.01dBm or lower difference is very difficult, because of power detector
Even the noise level of output just approximate may surmount this numerical value.
Therefore, to solve the above problems, shown in Figure 10, the invention also includes one and 33 electric coupling of radio-frequency signal source
The radiofrequency signal of input can be divided into two by 1 pair of 2 power divider 36, and be exported respectively to direction via two output ends
Coupler 32 and radiofrequency signal measuring system 4, and radiofrequency signal measuring system 4 further includes a reflection signal compensation circuit 41,
In the first controllable gain amplifier VGAR comprising one with an output end electric coupling of power divider 36, one with the first controllable increasing
The adjustable phase shifter VPhase and one of beneficial amplifier VGAR electric couplings and 322 electric coupling of coupling path of directional coupler 32
Second controllable gain amplifier VGA.
And it is very big in tunneling resistor Rt, such as when 10G or bigger, radio-frequency signal source 33 is enabled to export RF signal, at this point, because
31 impedance matching of radio frequency reading resonant circuit is scanned the radiofrequency signal RF's of resonant circuit 31 by 32 input radio frequency of directional coupler
Change of reflection amount is extremely low, so visually being believed by the radio frequency reflection that directional coupler 32 is exported to the second controllable gain amplifier VGA
Number it is input path 321 leakage by directional coupler 32 to the radiofrequency signal of coupling path 322, background signal hereinafter referred to as, institute
To input the radiofrequency signal of the first controllable gain amplifier VGAR, reference signal Ref hereinafter referred to as can be controllable by adjusting first
The gain of gain amplifier VGAR and the phase of adjustable phase shifter VPhase make the reference letter exported by adjustable phase shifter VPhase
Number Ref is identical as the intensity of background signal and phase differs 180 degree, then the two is sent into a combiner 44 and is added, both allow because
Voltage be added and opposite in phase and cancel each other out so that the output of combiner 44 is zero or close to zero.Whereby, can to eliminate radio frequency anti-
Input path 321 leakage in signal RFr by directional coupler 32 is penetrated to the radiofrequency signal composition of coupling path 322 so that combination
The change in signal strength that device 44 exports can react the variable quantity that radiofrequency signal RF is generated by the variation of tunneling voltage Rt completely, and
After a radio-frequency power amplifier 45 (refering to fig. 1 1) amplification of this small variable quantity by radiofrequency signal measuring system 4, you can
Its power level variable quantity is easily measured by a radio-frequency power detector 46 of radiofrequency signal measuring system 4.Then, radio frequency is believed
One display feedback circuit 70 of number measuring system 4 is described the surface complexion of the sample to be tested 20 further according to the power level and is shown
Rendering results.
Furthermore, as shown in Figure 10, the embodiment of the present invention also includes the input path of one and directional coupler 32
321 and the Bias-T circuits 37 of 31 electric coupling of radio frequency reading resonant circuit and electric current-electricity of an electric coupling Bias-T circuits 37
Press switching amplifier 39.And Bias-T circuits 37 include electric coupling in the defeated of radio frequency reading resonant circuit 31 and directional coupler 32
The direct current isolation capacitance Cs and an electric coupling entered between path 321 is converted in radio frequency reading resonant circuit 31 and current-voltage
High frequency choke coil RFC between amplifier 39.The embodiment of the present invention is also electrically connected to 8 He of radio frequency detecting unit comprising one
Feedback control unit 9 between the sample to be tested, the feedback control list 9 is according to the power of the instruction from the radio frequency detecting unit 8
The output of intensity or phase difference adjust the height of the probe 10, which receives the current-voltage including one
One output voltage of switching amplifier 39 switches switches 92 with the second feedback controller 91, one for generating a direct current output,
By control to select the direct current output from second feedback controller or the output from the radio frequency detecting unit 8, as it
Output, which further includes first feedback controller 90, receives the output of the switching switch 92 to adjust this
The height of probe 10.And the present invention can first carry out an initial programming before being scanned to sample to be tested 20, that is to say, that
First probe 10 is placed in from sample to be tested 20 enough at a distance, and sets the frequency and amplitude of radiofrequency signal RF, then adjustment reflection
The gain of the first variable gain amplifier VGA in signal compensation circuit 41 makes output signal power reach one and makes by oneself just
Operational power range (such as -10dBm~-30dBm) is advised, then adjusts gain and the phase tune of the second variable gain amplifier VGAR
The phase of whole device Vphase, reference signal Ref is consistent with the intensity of background signal and reverse phase (difference 180 degree) to allow, then by two
Output makes the intensity of display output signal, then according to the back of the body to a spectrum analyzer (not shown) after person is added via combiner 44
The degree that scape signal eliminates, the output signal that can observe reflection signal compensation circuit 41 die down, such as by the first variable gain
The power of the normalized radio frequency reflection signal RFr of amplifier VGA is -10dBm, if through reflecting 41 compensation adjustment of signal compensation circuit
Output signal is -70dBm afterwards, then background cancellation amount is 60dB, therefore when completion initial programming, reflection signal compensation circuit 41
Output signal should level off to zero, if initial programming need to be finely tuned, can further with coarse adjustment stepwise operation by probe 10 close to waiting for test sample
Product 20 make generation tunnel current It is sent to current-voltage conversion via radio frequency reading resonant circuit 31 and Bias-T circuits 37 and put
Voltage is converted and zoomed into big device 39, then via second feedback controller 91 output to first feedback controller 90 to feed back
The height of probe 10 is controlled, until first feedback controller 90 judges that tunnel current It has reached a setting value, then by probe 10
After widening at a distance from sample to be tested 20, carry out can once eliminating such as above-mentioned initial programming once again because probe 10 is close to be measured
The capacitance variations that 20 surface of sample generates.
And above-mentioned first variable gain amplifier (VGA), the second variable gain amplifier VGAR and adjustable phase shifter
VPhase, which is substantially all, to be controlled by computer 70, can also be manually operated.Because when compensation referential RF signal with
Anti- RF signal accurately could will compensate background signal very with amplitude and 180 degree difference, so second voltage controlled gain amplifies
Device VGA, the first controllable gain amplifier VGAR and adjustable phase shifter Vphase will have good resolution ratio and stability
Most background signal could be removed.
In addition, since above-mentioned compensating operation only can be effective to single-frequency, so the higher hamonic wave in reflection signal RFr
Deng can all leave.And since the radio-frequency power detector 46 is using the power detector for being operable in broadband, so radio frequency is anti-
The higher hamonic wave signal penetrated in signal RFr can all become the signal-to-noise ratio for effectively exporting and reducing radio frequency reflection signal RFr.
Therefore, while refering to fig. 11, the radiofrequency signal measuring system 4 of the present embodiment also includes one to be electrically connected the reflection signal
The radio frequency detecting unit 8 of compensation circuit 41, the first aspect of the radio frequency detecting unit 8 are to be electrically connected the reflection signal with one to mend
Circuit 41 is repaid to receive the signal exported by the combiner 44, and is amplified the radio-frequency power into a compensation amplified signal
Amplifier 45, one is electrically connected the power amplifier 45 to receive the compensation amplified signal and be filtered, to obtain one first
First bandpass filter 471, one of filtering signal is electrically connected first bandpass filter 471 to receive first filtering signal
1 couple, 2 power divider 49 and generate respectively with the relevant first difference signal of the radio frequency reflection signal and one second difference
Signal, and the radio frequency detecting unit 8 is also with electrical connection 1 couple, 2 power divider 49 to detect one first difference signal
The power level, and provide and indicate that the radio-frequency power detector 46, one of power level output is electrically connected the reflection signal compensation
Circuit 41 couples the radiofrequency signal that adjustable phase shifter VPhase is exported to receive the first direction coupler 42, and should
Radiofrequency signal is filtered receives second difference letter to obtain the second bandpass filter 472, one of second filtering signal
Number and second filtering signal, and detect the second difference signal and the phase difference of second filtering signal, and provide a finger
Show the phase difference detector 72 of the output of the phase difference, and is electrically connected the radio-frequency power detector 46, the phase difference detector 72
The display feedback circuit 70 between the feedback control unit 9.And first bandpass filter 471 only passes through respective frequencies (work
Working frequency), to reduce the higher hamonic wave composition in radio frequency reflection signal RFr.And if signal-to-noise ratio is important consideration, the first band logical
The high crystal filter of Q values or surface acoustic wave filter (SAW filter) can be selected in filter 471, this is because the filter
The bandwidth of wave device is narrow, can improve the signal-to-noise ratio of radio frequency reflection signal RFr.But such product currently on the market is designed to quotient
Industry uses frequency range, not necessarily meets the setpoint frequency and bandwidth of the present invention.
Therefore, as shown in figure 12, the radio frequency detecting unit 8 of the present embodiment also have one second aspect, second aspect with
First aspect is similar, and difference is in is electrically connected to 1 couple, 2 power divider 49 and the radio-frequency power detector 46 in setting one
Between a frequency modulation filter circuit 81, which, which can be directed to, measures the radio-frequency power and makees the excellent of a frequency and filtering
Change, therefore the frequency modulation filter circuit 81 also has one can generate the local oscillator LO of a local oscillated signal, an electrical connection
1 couple, 2 power divider 49 and local oscillator LO are carried out with receiving the first difference signal and the local oscillated signal
Smear, and one first mixer 50, one for generating first smear signal be electrically connected first mixer 50 with receive this
One smear signal to obtain the third bandpass filter 48 of a third smear signal, for radio frequency believe by the frequency of the local oscillated signal
The resonant frequency of number RF with it is the working frequency of third bandpass filter 48 and/or poor, such as by taking resonant frequency 820MHz as an example,
If using the commercial third bandpass filter 48 that working frequency is 374MHz, local oscillating frequency can be set as 820-374=
446MHz or 820+374=1194MHz.Then again by first mixer (Mixer) 50 by the first difference signal with this
Ground oscillator signal mixing, makes the working frequency that radio frequency reflection signal is moved to commercial third bandpass filter 48, the third smear
Signal is relevant to the first difference signal, then third bandpass filter 48 is filtered out the third smear signal come and is sent to radio-frequency power
Detector 46, you can greatly improve the signal-to-noise ratio of radio frequency reflection signal.
Can also be that the radio frequency is detectd such as Figure 13 if wanting compensator optimization in the frequency of a specific commercial high q-factor filter
The third aspect of unit 8 is surveyed, which is similar to first aspect, and difference is in by the first band of first aspect
Before bandpass filter 471 and second bandpass filter 472 move to the radiofrequency signal compensation circuit 41, that is to say, that the radiofrequency signal
Measuring system 4 further include one be electrically connected to direction coupler 32,1 couple, 2 power divider 36 and the radiofrequency signal compensation electricity
Optimization unit 89 between road 41, the optimization unit 89 include one second mixer 473 and a third mixer 47, second smear
Device 473 and the third mixer 47 distinctly receive radio frequency reflection signal and 1 couple, 2 power distribution from direction coupler 32
The reference signal of device 36 simultaneously carries out smear, second mixer 473 and the third mixer 47 with the local oscillated signal respectively
Respectively by after smear one second smear signal and a third smear signal be sent to first bandpass filter 471 and this second
Bandpass filter 472 is filtered, and one first smear filtering signal and one second smear filtering signal are supplied the radio frequency after filtering
Signal compensation circuit 41 receives, thus, which operating frequency can be moved to first to first bandpass filter 471 of high q-factor together
With the working frequency where second bandpass filter 472, and to second voltage control Amplifier VGA, this first controllable increases
The design of beneficial amplifier VGAR and adjustable phase shifter VPhase etc. all be directed to this working frequency optimize, it is possible thereby to power with
The best signal-to-noise ratio of phase.
Furthermore the present embodiment radio frequency reflection formula scans the intensity of radio frequency reflection signal RFr caused by tunneling microscope only
It is related with tunneling resistor Rt.That is, radio frequency reflection rate Г-tunneling resistor Rt-tunnel current It as shown in figure 14 with partially
The statistical result for pressing the measured data of Vb, can be clearly seen that at different tunnel current It and bias Vb, if keeping wearing
Tunnel resistance Rt is fixed, then radio frequency reflection rate Г (being represented with gray scale color) is also kept fixed.Since tunneling resistor Rt is decided by wait for
The electron configuration on the surface and probe 10 of sample 20 is tangible close so the radio frequency reflection rate Г variation that we measure
Effect in field (i.e. nanometer distance).
Moreover, in order to prove that the radio frequency reflection rate Г variations of the present invention can be consistent with tunnel current It, the present embodiment is with stone
Sample is made on black surface, while obtaining the radio frequency reflection signal variable quantity and tunnel current It of a scan line, obtains such as Figure 15
As a result.Each fluctuating of curve represents the signal of a carbon atom in Figure 15, it can be seen that radio frequency reflection signal difference Δ
The consistency of Г and tunnel current It signals are very high, and when probe 10 departs slightly from, tunnel current It disappears, while radio frequency reflection
Signal also no longer changes, this means that the variation of leading radio frequency reflection signal RFr is near-field effect.
And when the range of scanning extended to face by line, scanning result can be obtained shows the radio frequency of Figure 16 such as in a manner of 3D and sweep
The current scanning image of shading picture and Figure 17.It can see that apparent high correlation is presented in the two from two figures, and independent
Many atoms can clearly distinguish that and in comparison, the signal-to-noise ratio of the radio frequency reading image of Figure 16 is even than Figure 17's
Current scanning image will also be got well.Therefore, because radio frequency reflection signal difference Δ Г and tunnel current It has very high consistency, so
The former may replace the latter as feedback mechanism, allow probe 10 can be with morphologic prominence.Such as constant current mode, if radio frequency is anti-
It penetrates signal RFr intensity to fix, i.e., fixed tunneling resistor Rt, then the height of probe 10 can also fix.Such as the present embodiment is to be measured
The same area of sample 20 using constant current mode and is determined RF signal strength pattern and is scanned respectively, can measure two respectively
Person's photo such as Figure 18 and Figure 19.This test is to be carried out under air and room temperature, and can be seen that two kinds are returned from Figure 18 and Figure 19
Feedback pattern achieves very consistent surface landforms.
Again because the present embodiment will be compared with existing tunneling microscopical tunnel current It signals, above test is
It is carried out under relatively low sweep speed, but the present embodiment is still because it can be with using a main cause of radiofrequency signal RF
Operation is in high bandwidth, so as shown in figure 20, the present embodiment uses one to be set to the Z axis 51 of probe 10 to control the height of probe 10
Piezoceramics crystal (PZT) 52, and after the tunneling distance for setting probe 10, utilize a high voltage capacitance (not shown)
One small modulated signal (driving voltage ,~mV grades) is sent into the PZT driving circuits 53 of Z axis 51, because PZT52 is moved
It is dynamic apart from very little, so probe 10 can be on Z axis 51The quick up-down vibration of amplitude, it is sufficient to make the tunneling electricity of direct current
The intensity for flowing It signals and radio frequency reflection signal RFr generates variation, while the also further variation of verification radio frequency reflection signal RFr
It is near-field effect.Such as shown in Figure 20, when probe 10 is moved closer to the height for generating tunnel current It, the driving of 100MHz is believed
Number feeding probe 10, the intensity of radio frequency reflection signal RFr just have the variation of 100MHz, and if as shown in figure 21, probe 10 is drawn
When opening to the height of no tunnel current It, the intensity of radio frequency reflection signal RFr just secures, even if this phenomenon can verify that spy
For needle 10 under the high-speed motion of 100MHz, the present embodiment still can effectively measure the radio frequency reflection change in signal strength near field.
Therefore, the present embodiment can compare the bandwidth with dc sweeps and radio frequency reading with above method, that is,
It says and gradually increases the frequency of drive signal, while measuring shaking for tunnel current It and the changed power of radio frequency reflection signal RFr
Width, using the two the starting of low frequency end amplitude as reference value, then increase frequency and compare the oscillation wave amplitude of low frequency and high frequency
Ratio, and make the bandwidth value that amplitude reduces 3dB, then it is found by the measured result of Figure 22, drive signal is increased to by 100Hz
When 500MHz, the amplitude of direct current tunnel current It is begun to decline at 10KHz, and relative intensity is that -7dB (is about when arriving 100KHz
Originally the 1/6 of intensity).And the amplitude of radio frequency reflection signal is until 500MHz (limit of test scope) is flat and nothing
Significant decline, and it is such detecting bandwidth considerably beyond existing any scanning probe microscopy bandwidth of operation.
Furthermore first feedback controller 90 of the present embodiment can simultaneously according to the margin of error of direct current tunnel current It with
Two parts of margin of error Δ Г of radio frequency reflection signal RFr are done to generate the feedback signal of control 10 start of probe in fact
There can be several kinds of combinations, such as individually use the error of radio frequency reflection signal RFr using the margin of error of tunnel current It, individually
Measure Δ Г or both dual-purpose.And since the bandwidth of radiofrequency signal RF is higher, so there is its advantage in feedback control.
In addition, it is noted that as shown in figure 23, when generating tunneling effect between probe 10 and sample to be tested 20, removing
Tool is there are one outside equivalent tunneling resistor Rt between probe 10 and sample to be tested 20, actually in probe 10 and sample to be tested 20
Between there is also a tunneling energy barrier capacitance Ct.And in order to allow tunneling resistor Rt to be formed, radio frequency reading resonant circuit 31
It is required close enough between probe 10 and sample to be tested 20, the present embodiment can by applying a bias Vb on sample to be tested 20, and
The ground connection of probe 10 is enabled to reach to detect tunnel current It.And the tunnel current It generated on radio frequency reading resonant circuit 31 will
It is exported to current-voltage switching amplifier 39 via the high frequency choke coil RFC of Bias-T circuits 37.Therefore, if sample to be tested
20 be the good material of an electric conductivity, then tunneling resistor Rt can be the primary variables for influencing radio frequency reflection signal strength, wear at this time
The value of tunnel energy barrier capacitance Ct generally in af (10-18F) following level, has little effect radio frequency reading resonant circuit 31.And
Above-described embodiment is to be scanned to sample to be tested 20 under the conditions of such a.
On the contrary, if sample to be tested 20 is an inclined dielectric material, insulating properties is good, even if then probe 10 is very close to waiting for test sample
20 surface of product, tunneling resistor Rt between the two are still very big so that and influences of the tunneling resistor Rt to radio frequency reflection signal strength is small,
At this point, tunneling energy barrier capacitance Ct will change with the variation of probe 10 and 20 surface distance of sample to be tested.Therefore, such as Figure 10 and
Shown in Figure 11, an Adjustable Phase Shift for being located at RF compensation circuit 41 is also may include in the radiofrequency signal measuring system 4 of the present embodiment
First direction coupler 42 between device VPhase and an input terminal of combiner 44.And the phase difference detector 72 can then detect by
The reference signal Ref and the phase between the first difference signal that the first direction coupler 42 couples adjustable phase shifter VPhase outputs
Potential difference, and the phase difference has reacted the reactive effect of tunneling energy barrier, that is to say, that the dielectric property of sample to be tested 20, so this is aobvious
Show that feedback circuit 70 can also change according to the phase difference that phase difference detector 72 measures, the corresponding surface for depicting sample to be tested 20
Complexion.Therefore, the present embodiment also can measure 20 surface of sample to be tested by detecting the phase difference variation of radio frequency reflection signal RFr
Reactive effect, and higher space and temporal resolution can be obtained.
Moreover, being another mode for generating Times pressures between probe 10 and sample to be tested 20 as shown in figure 24, that is to say, that
It allows sample to be tested 20 to be grounded, and high frequencies of the bias Vb via Bias-T circuits 37 is provided by current-voltage switching amplifier 39
Choking-winding RFC is added on radio frequency reading resonant circuit 31, to allow entire radio frequency reading resonant circuit 31 to float on bias Vb.And
If using this bias fashion, because to measure the amount for the tunnel current It for flowing through tunneling resistor Rt, to avoid flowing through resistance
Rp(Rp<<Rt electric current) is much larger than the electric current for flowing through tunneling resistor Rt, so resistance Rp must be allowed, which to connect one, obstructs capacitance Cb
To stop that electric current flows through resistance Rp.Because if the capacitance of barrier capacitance Cb is very big (tens of nF grades or more), hundreds of MHz are grasped
It is equivalent to short circuit for the radiofrequency signal of working frequency, but open circuit is then equivalent to for DC current, whereby, allows tunnel current It energy
Enough flow completely through tunneling resistor Rt.
Refering to Figure 25, radio frequency reflection formula of the present invention scans a second embodiment of tunneling microscope 3, with first implementation
The circuit of example is identical, and is in the difference of the first embodiment and scans tunneling microscope 3 also comprising one in the radio frequency reflection formula
The probe 10 and the radio frequency reading resonant circuit 31 are coated on wherein by shield shell 5 (as shown in figure 26), the shield shell 5,
And include one for the probe 10 the exposed notch in a front end 100, to protect the radio frequency reading resonant circuit 31 not by outside one
Electronics (stream) field of rather low-frequency, generated extraneous electricity interference, external electrical (stream) field can be that an electron gun generates
Multiple incident electrons, secondary electron, Ou Jie electronics, or for by light activated multiple photoelectrons or electrochemical reaction institute
The faradic currents generated.More preferably, while refering to Figure 27, which can also coat the Bias-T circuits 37 and should
Current-voltage switching amplifier 39 makes the probe 10, the radio frequency reading resonant circuit 31, the Bias-T circuits 37 and the electric current-
Voltage converting amplifiers 39 can obtain a good shielding.
The radio frequency reflection formula of the present embodiment scans tunneling microscope 3 other than increasing this newly and determining radio frequency reading pattern, also has
Retain existing tunneling microscopical constant current scan pattern.One when the probe 10 and the sample to be tested 20 measures at environment
In in external electrical (stream) field (or the probe 10 under the liquid phase environment just like Figure 28 caused by the faradic currents
), the extraneous electricity (not shown) come with external electrical (stream) field can all add tunnel current It and be added up into one
Electric current I, and amplified by the current-voltage switching amplifier 39, and existing current feedback mechanism is interfered, it causes not scanning
The problem of imaging.
And if the radio frequency reflection formula of the present embodiment is scanned into tunneling microscope 3 and is operated under the radio frequency reading pattern, by
In the masking of the shield shell 5, make radio frequency reflection signal RFr will not be by the interference of external electrical (stream) field, such as Figure 29 institutes
Show, it can be seen that when there is extraneous electricity addition, the totalling electric current I detected increases to 80nA by 40nA, radio frequency at this time
Reflection signal RFr does not change, therefore the height Z of the probe 10 will not be varied from, so, if being believed using the radio frequency reflection
Number to control the height Z of the probe 10, the radio frequency reflection formula can be reached scan tunneling microscope 3 and not done by the extraneous electricity
The effect of disturbing.
Further by the present embodiment, the radio frequency reflection formula scans tunneling microscope 3 respectively with constant current scanning herein
Pattern and the relationship for determining the feedback method under radio frequency reading pattern to inquire into the extraneous electricity and 10 height Z of the probe.
Refering to Figure 30 and Figure 31, extraneous electricity caused by external electrical (stream) field is tuned as square wave, and then influence
The current waveform of totalling electric current I is as shown in the figure, it can be seen that this of Figure 30 determines the probe 10 under radio frequency reading pattern feedback mode
Height Z only have because of thermal drift and slightly change, and had no to the extraneous electricity significant related；And Figure 31 this is fixed
The height Z of probe 10 under current scanning pattern feedback mode is significantly proportional to the integral of the totalling electric current I square waves, therefrom
Know that the height Z of the probe 10 under the constant current scan pattern feedback mode is influenced to determine radio frequency reading more than this by the extraneous electricity
The height Z of probe 10 under pattern feedback mode comes big.
And then extraneous electricity caused by foreign electron (stream) field is changed to the photoelectric current that an X-ray excitaton source is excited,
Relationship to test the totalling electric current I and the probe 10 in this under determining in a manner of radio frequency reading pattern feedback, when the X-ray excitaton source
Open in a flash, totalling electric current I i.e. be in a stepped variation, as shown in figure 32, but the radio frequency reflection signal RFr and should
The height Z of probe 10 has no corresponding change；In the same manner, when the X-ray excitaton source does modulation to interact Push And Release, such as Figure 33 institutes
Show, then totalling electric current I then has with the Push And Release modulation of the X-ray excitaton source and significantly changes, but the radio frequency reflection signal RFr and
The height Z of the probe 10 is also without corresponding change, that is to say, that determines the radio frequency under radio frequency reading pattern feedback mode at this
Radio frequency reflection signal RFr of the tunneling microscope of the reflective scanning mode 3 and height Z of the probe 10 can't with the extraneous electricity and
It changes.
It, can be clearly from Figure 34 and Figure 35 to prove that the radio frequency reflection formula of the invention scans the validity of tunneling microscope 3
It compares and the radio frequency reflection formula is whether scanned into tunneling microscope 3 operates in one without extraneous electricity and scan mould for the constant current
Formula one has extraneous electricity and determines radio frequency reading pattern for this, and the sample to be tested 20 observed is (in a stepped phlogopite
Piece) surface topography all have consistent correspondence.
Further the radio frequency reflection formula of the invention is scanned tunneling microscope 3 and operated and determines radio frequency reading pattern at this,
And the probe 10 and the sample to be tested 20 are in a measurement without extraneous electricity or the extraneous electricity for there are a 12Hz modulations respectively
Environment, to compare surface scan image of the sample to be tested 20 under the measurement environment, it may be clearly seen that without the outer incoming call
The surface scan image (Figure 36) of stream and there is the image of both the surface scan image (Figure 37) of the extraneous electricity that effect is presented to be
It is identical.The of the invention radio frequency reflection formula is scanned into tunneling microscope 3 again change and operates in the constant current scan pattern and carry out table
The scanning of Surface scan image, such as Figure 38, it is to be scanned to one third position when, that is, an extraneous electricity is added, observable, which goes out this, to be waited for
One surface scan image of sample 20 is when being added the extraneous electricity by serious influence.If that is, this is penetrated
Tunneling microscope 3 operation of frequency reflective scanning mode in constant current scan pattern, then the radio frequency reflection formula scan tunneling microscope 3 easily by
The influence of the extraneous electricity, that is to say, that as long as the radio frequency reflection formula, which is scanned the tunneling operation of microscope 3, is determining radio frequency reading mould
Formula whether has the interference of the extraneous electricity, does not all interfere with the work that the radio frequency reflection formula of the invention scans tunneling microscope 3
Industry.
Therefore, the present invention radio frequency reflection formula scan tunneling microscope 3 can be in the case where contemplating that extraneous electricity, directly
Make the probe 10 close to the sample to be tested 20 to the tunneling effect using a radio frequency reflection energy intensity of the radio frequency reading pattern
The region that should occur and the radio frequency reflection formula can be made to scan tunneling microscope 3 also can be to be measured by this in the case where there is extraneous electricity
The surface complexion of sample 20 is clearly described；But the operation that the present invention radio frequency reflection formula scans tunneling microscope 3 also can first exist
Do not have first to allow the probe 10 close to the tunneling effect of the sample to be tested 20 to one with the constant current scan pattern in the case of extraneous electricity
The region that should occur, then the radio frequency reflection formula is scanned into tunneling microscope 3 and is changed to determine radio frequency reading pattern with this to operate, this
When the height Z of probe 10 would not be influenced because of the extraneous electricity, and can be by the surface complexion of the sample to be tested 20
Clearly describe.
To sum up explanation is it is found that the present invention has the following advantages：
1. the present invention using radio frequency reflection signal come the tunneling resistor Rt measured between probe 10 and sample to be tested 20 in addition to being imitated
It answers, it may have measure the phase difference of radio frequency reflection signal to react the ability of the reactive effect on 20 surface of sample to be tested.
2. by the protection of the shield shell 5, radio frequency reflection formula scanning of the operation under the radio frequency reading pattern is made to wear
Tunnel microscope 3 can not be influenced by the extraneous electricity of external electrical (stream) field, and can reach under the constant current scan pattern and
The same effect of 20 surface topography of sample to be tested acquired by the interference of no external electrical (stream) field.
3. before the optimization unit 89 is placed in the reflection signal compensation circuit 41, its signal-to-noise ratio can be so promoted, so, really
Star is to the purpose of the present invention and effect.
As described above, only the embodiment of the present invention is when cannot be limited the scope of implementation of the present invention with this, i.e., all
According to simple equivalent changes and modifications made by claims of the present invention and description, all still belong to the scope of the present invention.
Claims (15)
1. a kind of radio frequency reflection formula scans tunneling microscope, tool there are one with a sample to be tested interval and the spy that is oppositely arranged
Needle, the surface complexion for scanning the sample to be tested, it is characterised in that：And include：
One radio frequency reading resonant circuit, including there are one an inductance of first end and a second end for tool, and with the inductance
One capacitance of first end parallel connection, an auxiliary capacitor in parallel with the second end of the inductance, a resistance and one wear
Tunnel resistance, the wherein tunneling resistor are formed between the sample to be tested and the probe；
One directional coupler, the second end electric coupling with the inductance of the radio frequency reading resonant circuit, and receive one and penetrate
Frequency signal, and the radiofrequency signal is exported to the radio frequency reading resonant circuit, and one is received via radio frequency reading resonance electricity
The radio frequency reflection signal passed back is reflected on road；And
One radiofrequency signal measuring system is electrically connected direction coupler to receive the radio frequency reflection signal, and according to the radio frequency
Reflection signal feedback control probe, to generate a scanning result related with the surface complexion of the sample to be tested.
2. radio frequency reflection formula according to claim 1 scans tunneling microscope, it is characterised in that：Radio frequency reading resonance electricity
Road further includes one and is controlled with the capacitance series and by first applied voltage, to adjust the one of the radio frequency reading resonant circuit
First voltage controlled capacitor of a resonant frequency and one concatenate with the auxiliary capacitor and are controlled by second applied voltage, with
Determine the second voltage controlled capacitor of a final impedance of the radio frequency reading resonant circuit.
3. radio frequency reflection formula according to claim 1 scans tunneling microscope, it is characterised in that：Also include：
The probe and the radio frequency reading resonant circuit are coated on wherein, to avoid the radio frequency reflection signal by one shield shell
It is interfered by an external electrical flow field or electron field.
4. radio frequency reflection formula according to claim 3 scans tunneling microscope, it is characterised in that：The shield shell includes：
One notch, neighbouring probe, for one end bare front end of the probe.
5. radio frequency reflection formula according to claim 4 scans tunneling microscope, it is characterised in that：The radiofrequency signal measures system
System makes the energy intensity of the radio frequency reflection signal or phase remain certain using the radio frequency reflection signal feedback control probe
One operation mode of value is certain radio frequency reading pattern.
6. the radio frequency reflection formula according to claim 1 to 5 any of which scans tunneling microscope, it is characterised in that：Also wrap
1 couple, 2 power divider with a radio-frequency signal source electric coupling is included, which is divided into two, and via two
A output end is exported respectively to direction coupler and the radiofrequency signal measuring system, and the radiofrequency signal measuring system further includes
One reflection signal compensation circuit, the radiofrequency signal that 1 couple, 2 power divider exports suitably is amplified and adjusts its phase
Position, and the radio frequency reflection signal is suitably amplified, and making the radiofrequency signal and the part that is contained in the radio frequency reflection signal, this is penetrated
The amplitude of frequency signal is identical and phase differs 180 degree, then the two is added, to eliminate the letter of the radio frequency in the radio frequency reflection signal
Number composition.
7. radio frequency reflection formula according to claim 6 scans tunneling microscope, it is characterised in that：The reflection signal compensation electricity
Road include one amplify the first controllable gain amplifier of the radiofrequency signal, one amplify the second controllable of the radio frequency reflection signal
Gain amplifier, a phase for adjusting the radiofrequency signal make to have with part radiofrequency signal in the radio frequency reflection signal
The adjustable phase shifter of 180 degree phase difference and a signal for exporting the adjustable phase shifter amplify with second controllable gain
The combiner that the signal of device output is added.
8. radio frequency reflection formula according to claim 7 scans tunneling microscope, it is characterised in that：The radiofrequency signal measures system
System further includes first between the adjustable phase shifter for being located at the reflection signal compensation circuit and an input terminal of the combiner
Directional coupler, a radio frequency detecting unit for being electrically connected the reflection signal compensation circuit and one are electrically connected to the radio frequency and detect
The feedback control unit between unit and the sample to be tested is surveyed,
The radio frequency detecting unit receive by the first direction coupler couple the radiofrequency signal that the adjustable phase shifter is exported and
The radio frequency reflection signal, and detect the phase difference between the radiofrequency signal and the radio frequency reflection signal and the radio frequency reflection signal
One power level, to obtain the output for indicating the power level,
And the feedback control unit according to the output or phase difference of the instruction power level from the radio frequency detecting unit come
Adjust the height of the probe.
9. radio frequency reflection formula according to claim 8 scans tunneling microscope, it is characterised in that：The radio frequency detecting unit has
Have
One radio-frequency power amplifier, receives the output of the combiner from the reflection signal compensation circuit, and is amplified
Amplified signal is compensated into one,
One the first bandpass filter is electrically connected the radio-frequency power amplifier to receive the compensation amplified signal, and by the compensation
Amplified signal is filtered to obtain first filtering signal,
One 1 pair of 2 power divider is electrically connected first bandpass filter to receive first filtering signal, and by this first
Filtering signal is divided into a first difference signal and a second difference signal, the first difference signal and the second difference signal
It is relevant to the radio frequency reflection signal,
One radio-frequency power detector, the power for being electrically connected 1 couple, 2 power divider to detect the first difference signal are strong
Degree, and the output for indicating the power level is provided,
One the second bandpass filter, be electrically connected the reflection signal compensation circuit with receive the first direction coupler couple this can
The radiofrequency signal for adjusting phase shifter to be exported, and the radiofrequency signal is filtered to obtain one second filtering signal,
One phase difference detector is electrically connected 1 couple, 2 power divider and second bandpass filter to receive this second point respectively
Qi signal and second filtering signal, for detecting the phase difference between the second difference signal and second filtering signal, and
One output for indicating the phase difference is provided, which is relevant to the radiofrequency signal, and
One display feedback circuit is electrically connected the radio-frequency power detector, the phase difference detector, and the radio frequency work(is come to receive
The output of rate detector with receive the output from the phase difference detector, and according to the defeated of the instruction power level or phase
Go out to describe the surface complexion of the sample to be tested and shows rendering results.
10. radio frequency reflection formula according to claim 9 scans tunneling microscope, it is characterised in that：The radio frequency detecting unit
Also there are one a frequency modulation filter circuit being set between 1 couple, 2 power divider and the radio-frequency power detector, the frequency modulation for tool
Filter circuit has
One local oscillator generates a local oscillated signal,
One the first mixer, be electrically connected 1 couple, 2 power divider and the local oscillator with receive the first difference signal and
The local oscillated signal and carry out smear, and generate a first smear signal, and
One third bandpass filter is electrically connected first mixer to receive the first smear signal, and by first smear
Signal is filtered to obtain a third smear signal, which is relevant to the first difference signal, and is sent to
The radio-frequency power detector.
11. radio frequency reflection formula according to claim 8 scans tunneling microscope, it is characterised in that：Also it is electrically connected comprising one
The optimization unit being connected between direction coupler, 1 couple, 2 power divider and the reflection signal compensation circuit, the optimization list
Member includes
One local oscillator generates a local oscillated signal,
One the second mixer is electrically connected to direction coupler and the local oscillator to receive the radio frequency reflection signal and be somebody's turn to do
Local oscillated signal and carry out smear, and generate a second smear signal,
One the first bandpass filter is electrically connected second mixer to receive the second smear signal, and by second smear
Signal is filtered and generates a first smear filtering signal, and it is second controllable that the first smear filtering signal is sent to this
Gain amplifier,
One third mixer is electrically connected to 1 couple, 2 power divider and the local oscillator to receive the radiofrequency signal and be somebody's turn to do
Local oscillated signal and carry out smear, and generate a third smear signal, and
One the second bandpass filter is electrically connected the third mixer to receive the third smear signal, and by the third smear
Signal is filtered and generates one second smear filtering signal, and the second smear filtering signal is sent to the first controllable increasing
Beneficial amplifier,
Wherein, which has
One radio-frequency power amplifier is electrically connected the combiner to receive the signal of combiner output, and is amplified
One compensation amplified signal,
One 1 pair of 2 power divider is electrically connected the radio-frequency power amplifier to receive the compensation amplified signal, and by the compensation
Amplified signal is divided into a first difference signal and a second difference signal, the first difference signal and the second difference signal
It is relevant to the radio frequency reflection signal,
One radio-frequency power detector, the power for being electrically connected 1 couple, 2 power divider to detect the first difference signal are strong
Degree, and the output for indicating the power level is provided,
One phase difference detector is electrically connected 1 couple, 2 power divider and the first direction coupler to receive second difference
The signal of signal and first direction coupler output, for detecting the second difference signal and first direction coupler output
Signal between the phase difference, and provide the output for indicating the phase difference, the first direction coupler output signal phase
About the radiofrequency signal, and
One display feedback circuit receives the output from the radio-frequency power detector with reception from the phase difference detector
Output, and the surface complexion of the sample to be tested is described according to the output of the instruction power level or phase value and shows description knot
Fruit.
12. radio frequency reflection formula according to claim 8 scans tunneling microscope, it is characterised in that：It further include an electric current-
The Bias-T circuits of voltage converting amplifiers and one and direction coupler and the radio frequency reading resonant circuit electric coupling, should
The radiofrequency signal of directional coupler output inputs the radio frequency reading resonant circuit, and the radio frequency reading via the Bias-T circuits
The radio frequency reflection signal that resonant circuit generates via the Bias-T circuit outputs to direction coupler, and the radio frequency reading
The tunnel current that resonant circuit generates is put via the Bias-T circuit outputs to the current-voltage switching amplifier
Greatly, and after being converted into an output voltage input the feedback control unit, make the feedback control unit according to the output voltage and
The power level feedback control probe.
13. radio frequency reflection formula according to claim 12 scans tunneling microscope, it is characterised in that：The feedback control unit
Including
One the second feedback controller, receives the output voltage to generate a direct current output, a switching switch, by control with
The direct current output from second feedback controller or the output from the radio frequency detecting unit are selected, it is defeated as one
Go out, and
One the first feedback controller receives the output of switching switch to adjust the height of the probe.
14. radio frequency reflection formula according to claim 1 scans tunneling microscope, it is characterised in that：The sample to be tested is applied
Add a bias, and the probe is grounded so that when the surface of the close enough sample to be tested of the probe, in forming tunneling effect between the two
It answers and generates the tunneling resistor.
15. radio frequency reflection formula according to claim 1 scans tunneling microscope, it is characterised in that：The sample to be tested is connect
Ground, and the radio frequency reading resonant circuit is applied in a bias via a high frequency choke coil, and the radio frequency reading is inputted with blocking
One high-frequency signal of resonant circuit influences the bias, and the resistance is also connected the barrier capacitance of a barrier direct current, to stop that this is penetrated
The one of frequency scanning resonant circuit generation passes through the DC current of the resistance of the radio frequency reading resonant circuit.
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| TW103124553A TWI504900B (en) | 2013-07-18 | 2014-07-17 | Radio-frequency reflectometry scanning tunneling microscope |
| TW103124553 | 2014-07-17 |
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