Active noise isolation for tunneling applications (ANITA)
An active noise isolation apparatus and method for cancelling vibration noise from the probe signal of a scanning tunneling microscope by generating a correction signal by convolution based on the probe signal and the sensor signal, which is based on the ambient vibration that adds noise to the probe signal.
1. A scanning probe microscope, comprising:
an existing scanning probe microscope (SPM) including:
a sample holder for holding a sample with a surface;
a probe operable to provide a probe signal based on the surface of the sample disposed on the sample holder;
a sensor external to the existing SPM generating a sensor signal based on an ambient vibration, the sensor and probe signals being dimensionally-distinct physical quantities, the ambient vibration creating a relative motion between the probe and the sample surface, the relative motion due to the ambient vibration adding noise to the probe signal; and
a processing unit generating a correction signal by convolution involving dimensioned parameters to account for the sensor and probe being the dimensionally-distinct physical quantities and determining a relationship between the sensor signal and a displacement of the probe based on the probe signal and the sensor signal, the processing unit removing noise from the probe signal by applying the correction signal to the probe signal.
2. The scanning probe microscope of claim 1 , wherein the sensor comprises a plurality of sensors.
3. The scanning probe microscope of claim 1 , wherein the sensor is selected from a group of an accelerometer, velocity sensor, proximity sensor and laser displacement sensor.
4. The scanning probe microscope of claim 1 , wherein the sensor is disposed at a location that is spaced from a location of the probe, sample holder and/or the surface of the sample.
5. The scanning probe microscope of claim 1 , wherein the sensor is not physically attached or connected with the probe, sample holder and/or the surface of the sample.
6. The scanning probe microscope of claim 1 , wherein the sensor generates the sensor signal based on the ambient vibration having a variable frequency and/or amplitude.
7. The scanning probe microscope of claim 1 , wherein the scanning probe microscope includes a constant tip-current or constant tip-height based scanning probe microscope, and the processing unit, respectively, generates the correction signal for the constant tip-current or constant tip-height based scanning probe microscope.
8. The scanning probe microscope of claim 1 , wherein the sensor detects a highest frequency of the ambient vibration and the processing unit generates the correction signal using a discrete algorithm that is run by the processing unit at a frequency that is at least twice the highest frequency of the ambient vibration.
9. The scanning probe microscope of claim 1 , wherein the ambient vibration comprises a plurality of frequencies and amplitudes, and the sensor generates the sensor signal based on the ambient vibration comprising the plurality of frequencies and amplitudes.
10. The scanning probe microscope of claim 9 , wherein the processing unit generates the correction signal by simultaneously convolving the sensor signal comprising the plurality of frequencies and amplitudes of the ambient vibration.
11. The scanning probe microscope of claim 1 , wherein the processing unit removes noise of the ambient vibration corresponding to a plurality of axes along the probe, sample holder and/or the surface of the sample.
12. The scanning probe microscope of claim 1 , wherein the processing unit generates the correction signal using digital signal processing.
13. The scanning probe microscope of claim 1 , wherein the processing unit does not generate the correction signal using analog signal processing.
14. A method of active noise isolation for a scanning probe microscope, comprising the steps:
providing a scanning probe microscope;
providing the probe signal from the probe based on the surface of the sample disposed on the sample holder;
providing an external sensor external to the existing SPM generating a sensor signal based on an ambient vibration, the sensor and probe signals being dimensionally-distinct physical quantities;
generating the sensor signal from the sensor based on the ambient vibration, the ambient vibration creating the relative motion between the probe and the sample surface, and the relative motion due to the ambient vibration adding noise to the probe signal;
generating the correction signal from the processing unit by convolution involving dimensioned parameters to account for the sensor and probe being the dimensionally-distinct physical quantities and determining a relationship between the sensor signal and a displacement of the probe based on the probe signal and the sensor signal; and
removing the noise of the ambient vibration from the probe signal using the processing unit by applying the correction signal to the probe signal.
15. The method of claim 14 , wherein the step of generating the correction signal comprises continuous or periodical monitoring of an amplitude and/or frequency of the ambient vibration to remove the noise.
16. The method of claim 14 , wherein the step of generating the sensor signal is based on the ambient vibration having a plurality of frequencies and amplitudes.
17. The method of claim 16 , wherein during the step of generating the correction signal the processing unit simultaneously convolves/convolutes the plurality of frequencies and amplitudes of the ambient vibration.
18. The method of claim 14 , further comprising a step of detecting a highest frequency of the ambient vibration, wherein the step of generating the correction signal comprises running a discrete algorithm at a frequency that is at least twice the highest frequency of the ambient vibration.
19. The method of claim 14 , wherein the step of providing the scanning probe microscope includes providing the sensor comprising a plurality of sensors.
20. The method of claim 14 , wherein the step of generating the correction signal comprises generating one or more kernels for each frequency in the ambient vibration for convolution.