Methods and devices configured to operated scanning tunneling microscopes using out-of-bandwidth frequency components added to bias voltage and related software

Patent metadata

Field	Value
Publication number	US-11143671-B2
Application number	US-202017089214-A
Country	US
Kind code	B2
Filing date	Nov 4, 2020
Priority date	Nov 4, 2019
Publication date	Oct 12, 2021
Grant date	Oct 12, 2021

Abstract

In the system and method disclosed, an ultrahigh vacuum (UHV) scanning tunneling microscope (STM) tip is used to selectively desorb hydrogen atoms from the Si(100)-2X1:H surface by injecting electrons at a negative sample bias voltage. A new lithography method is disclosed that allows the STM to operate under imaging conditions and simultaneously desorb H atoms as required. A high frequency signal is added to the negative sample bias voltage to deliver the required energy for hydrogen removal. The resulted current at this frequency and its harmonics are filtered to minimize their effect on the operation of the STM's feedback loop. This approach offers a significant potential for controlled and precise removal of hydrogen atoms from a hydrogen-terminated silicon surface and thus may be used for the fabrication of practical silicon-based atomic-scale devices.

First claim

What is claimed:

1. A method of operating a scanning tunneling microscope (STM), the method comprising:
applying a time-varying voltage signal between a tip of the STM and a surface of a sample located beneath the tip, the time-varying voltage signal comprising a dc bias voltage modulated with a dither voltage signal having a dither frequency and dither amplitude;
receiving a time varying tip-sample current signal, including components at the dither frequency, tunneling between the tip and the sample; and
filtering the time varying tip-sample current signal to attenuate the components at the dither frequency to provide a filtered tip-sample current signal.

2. The method of claim 1 further comprising:
providing the filtered tip-sample current signal to a control feedback loop of the STM; and
adjusting a height of the tip relative to the surface responsive to a comparison of the filtered tip-sample current signal to a tunneling current setpoint.

3. The method of claim 2 wherein the control feedback loop has an associated operating bandwidth including an upper frequency limit that is less than the dither frequency.

4. The method of claim 3 wherein the associated bandwidth is defined from an input to the control feedback loop comprising the filtered tip-sample current signal to an output of the control feedback loop comprises adjusting the height of the tip of the STM relative to the surface.

5. The method of claim 2 wherein filtering comprises filtering the time varying tip-sample current signal with a notch filter configured to attenuate at least the components at the dither frequency included in the time varying tip-sample current signal to provide the filtered tip-sample current signal to the control feedback loop of the STM.

6. The method of claim 5 wherein the notch filter is further configured to attenuate harmonics of the dither frequency included in the time varying tip-sample current signal.

7. The method of claim 1 further comprising:
positioning the tip of the STM opposite a location on the surface of the sample;
monitoring operation of the STM for an indication of a change in height of the tip above the surface at the location; and
(a) incrementing a present value of the dither amplitude to ramp up the time-varying voltage signal applied between the tip and the sample at the location while monitoring operation of the STM for the indication of the change in height.

8. The method of claim 7 further comprising:
(b) indicating desorption of an atom terminating the surface at the location responsive to detecting the indication of the change in height being greater than a threshold value.

9. The method of claim 8 further comprising:
returning the dither amplitude to an initial value; and
positioning the tip of the STM opposite a next location on the surface of the sample responsive to determining that additional positions reaming to be processed by the STM.

10. The method of claim 8 further comprising:
(c) indicating lack of desorption of an atom terminating the surface at the location responsive to detecting the indication of the change in the height being less than the threshold value; and
performing operations (a)-(c) until the dither amplitude reaches a final value.

11. The method of claim 7 wherein the indication of the change in the height of the tip above the surface at the location comprises an increase in an ac current between the tip and the sample at the location that exceeds a threshold value.

12. The method of claim 7 wherein the indication of the change in the height of the tip above the surface at the location comprises an increase in a z position of the tip relative to the surface of the sample at the location that exceeds a threshold value.

13. One or more non-transitory processor-readable media storing processor-executable instructions for causing one or more processors to perform a method of operating a scanning tunneling microscope (STM), the method comprising:
applying a time-varying voltage signal between a tip of the STM and a surface of a sample located beneath the tip, the time-varying voltage signal comprising a dc bias voltage modulated with a dither voltage signal having a dither frequency and dither amplitude;
receiving a time varying tip-sample current signal, including components at the dither frequency, tunneling between the tip and the sample; and
filtering the time varying tip-sample current signal to attenuate the components at the dither frequency to provide a filtered tip-sample current signal.

14. The one or more non-transitory processor-readable media storing processor-executable instructions according to claim 13 further comprising:
providing the filtered tip-sample current signal to a control feedback loop of the STM; and
adjusting a height of the tip relative to the surface responsive to a comparison of the filtered tip-sample current signal to a tunneling current setpoint.

15. The one or more non-transitory processor-readable media storing processor-executable instructions according to claim 14 wherein the control feedback loop has an associated operating bandwidth including an upper frequency limit that is less than the dither frequency.

16. The one or more non-transitory processor-readable media storing processor-executable instructions according to claim 14 wherein filtering comprises filtering the time varying tip-sample current signal with a notch filter configured to attenuate at least the components at the dither frequency included in the time varying tip-sample current signal to provide the filtered tip-sample current signal to the control feedback loop of the STM.

17. A method of operating a scanning tunneling microscope (STM), the method comprising:
applying a time-varying voltage signal between a tip of the STM and a surface of a sample located beneath the tip, the time-varying voltage signal comprising a dc bias voltage modulated with a dither voltage signal having a dither frequency and dither amplitude;
receiving a time varying tip-sample current signal, including components at the dither frequency, tunneling between the tip and the sample;

filtering the time varying tip-sample current signal to attenuate the components at the dither frequency to provide a filtered tip-sample current signal to generate a topographical image data of the sample; and
applying the time varying tip-sample current signal to an input of a lock-in amplifier to generate an ac tunneling current by subtracting a capacitive current component from the time varying tip-sample current signal to provide spectroscopic data of the sample.

18. A method of operating a scanning tunneling microscope (STM), the method comprising:
applying a time-varying voltage signal between a tip of the STM and a surface of a sample located beneath the tip, the time-varying voltage signal comprising a dc bias voltage modulated with a dither voltage signal having a dither frequency and dither amplitude;
receiving a time varying tip-sample current signal, including components at the dither frequency, tunneling between the tip and the sample; and
applying the time varying tip-sample current signal to an input of a lock-in amplifier to subtract a capacitive current component from the time varying tip-sample current signal to provide magnitude of an ac component of tunneling current as an input to a control feedback loop of the STM.

19. The method of claim 18 further comprising:
filtering the time varying tip-sample current signal to attenuate the components at the dither frequency to

Assignees

• Univ Texas

Inventors

• Moheimani Seyed Omid Reza
• Alemansour Hamed

Classifications

• B82B3/0004 Primary

  Apparatus specially adapted for the manufacture or treatment of nanostructural devices or systems or methods for manufacturing the same · CPC title

• H01J2237/2818

  Scanning tunnelling microscopes · CPC title

• G01Q10/065 Primary

  Feedback mechanisms, i.e. wherein the signal for driving the probe is modified by a signal coming from the probe itself · CPC title

• H01J37/28

  with scanning beams {(H01J37/268, H01J37/292, H01J37/2955 take precedence)} · CPC title

• G01Q60/10

  STM [Scanning Tunnelling Microscopy] or apparatus therefor, e.g. STM probes · CPC title