Chemical nano-identification of a sample using normalized near-field spectroscopy

Patent metadata

Field	Value
Publication number	US-9846178-B2
Application number	US-201615241029-A
Country	US
Kind code	B2
Filing date	Aug 18, 2016
Priority date	Mar 15, 2013
Publication date	Dec 19, 2017
Grant date	Dec 19, 2017

Abstract

Apparatus and method for nano-identification a sample by measuring, with the use of evanescent waves, optical spectra of near-field interaction between the sample and optical nanoantenna oscillating at nano-distance above the sample and discriminating background backscattered radiation not sensitive to such near-field interaction. Discrimination may be effectuated by optical data acquisition at periodically repeated moments of nanoantenna oscillation without knowledge of distance separating nanoantenna and sample. Measurement includes chemical identification of sample on nano-scale, during which absolute value of phase corresponding to near-field radiation representing said interaction is measured directly, without offset. Calibration of apparatus and measurement is provided by performing, prior to sample measurement, a reference measurement of reference sample having known index of refraction. Nano-identification is realized with sub-50 nm resolution and, optionally, in the mid-infrared portion of the spectrum.

First claim

What is claimed is:

1. A method for optical characterization of a sample (SUT) using evanescent waves, the method comprising:
detecting, with an optical detector, an optical signal interferometrically formed by
(i) first electromagnetic radiation backscattered by a nanoantenna in response to being incident electromagnetic radiation, said nanoantenna being controllably movable above a surface of the SUT, and
(ii) second electromagnetic radiation representing a portion of said incident electromagnetic radiation, a phase-delay equal to a difference between a phase of the second electromagnetic radiation and a phase of the first electromagnetic radiation being variable;

 to form an optical data output;
processing said optical data output in time domain to extract a first portion of said optical data output that represents electromagnetic field caused by near-field interaction between the nanoantenna and the surface during a motion of the nanoantenna above the SUT, wherein the motion includes a recurring motion;

and
normalizing said first portion of the optical data output, by reference optical data that have been interferometrically acquired in a process of backscattering of said incident radiation by the nanoantenna moving above a surface of a reference sample, to determine at least one of real and imaginary parts of a complex-valued difference between first and second values of electric field characterizing said near-field interaction,
wherein the first and second values respectively correspond to first and second phases of the motion.

2. A method according to claim 1 , wherein said normalizing includes determining a spectral distribution of said at least one of real and imaginary parts to identify a component of a complex-valued permittivity of the SUT.

3. A method according to claim 2 , further comprising suppressing a contribution of background electromagnetic radiation to the first portion of the optical data output to obtain a second portion of the optical data output in which said contribution is reduced as compared to the first portion.

4. A method according to claim 3 , wherein said suppressing includes determining of the first portion of the optical data output at first, second, third and fourth phases of said motion as respective first, second, third, and fourth values, and further determining a difference between a sum of the first and third values and a sum of the second and fourth values.

5. A method according to claim 1 , further comprising determining at least one of real and imaginary parts of a complex-valued difference between first and second values of electric field that characterizes said near-field interaction to identify a component of a complex-valued permittivity of the SUT based on said complex-valued difference.

6. A method according to claim 1 , further comprising processing determining amplitude and phase of electric field representing said near-field interaction from first portion of said optical data to ascertain a dielectric constant parameter and an absorption parameter characterizing the SUT.

7. A method according to claim 1 , wherein said incident radiation includes a plurality of wavelengths while the phase of second electromagnetic radiation differs from the phase of the first electromagnetic radiation by an amount that is being modulated, and
further comprising analyzing data derived from the optical data output in the time domain with the use of spectral analysis to derive a spectrum representing an interferogram.

8. A method according to claim 7 , wherein the phase-delay is being continuously changed in a reference arm of an interferometer according to a periodic function characterized by a modulation frequency.

9. A method according to claim 8 , wherein said periodic function includes at least one of linear and sinusoidal functions.

10. A method for optical characterization of a sample (SUT) using evanescent waves, the method comprising:
detecting, with an optical detector, an optical signal interferometrically formed by
(i) first electromagnetic radiation backscattered by a nanoantenna in response to being incident electromagnetic radiation, said nanoantenna being controllably movable above a surface of the SUT, and
(ii) second electromagnetic radiation representing a portion of said incident electromagnetic radiation, a phase-delay equal to a difference between a phase of the second electromagnetic radiation and a phase of the first electromagnetic radiation being variable;

 to form an optical data output;
processing said optical data output in time domain to extract a first portion of said optical data output that represents electromagnetic field caused by near-field interaction between the nanoantenna and the surface during a motion of the nanoantenna above the SUT, wherein the motion includes a recurring motion;

and
normalizing said first portion of the optical data output, by reference optical data that have been interferometrically acquired in a process of backscattering of said incident radiation by the nanoantenna moving above a surface of a reference sample, to determine at least one of real and imaginary parts of a complex-valued difference between first and second values of electric field characterizing said near-field interaction,
wherein the first and second values respectively correspond to first and second phases of the motion, and
wherein said normalizing includes determining a spectral distribution of said at least one of real and imaginary parts to identify a component of a complex-valued permittivity of the SUT.

11. A method according to claim 10 , further comprising suppressing a contribution of background electromagnetic radiation to the first portion of the optical data output to obtain a second portion of the optical data output in which said contribution is reduced as compared to the first portion.

12. A method according to claim 11 , wherein said suppressing includes determining of the first portion of the optical data output at first, second, third and fourth phases of said motion as respective first, second, third, and fourth values, and further determining a difference between a sum of the first and third values and a sum of the second and fourth values.

13. A method according to claim 10 , further comprising determining at least one of real and imaginary parts of a complex-valued difference between first and second values of electric field that characterizes said near-field interaction to identify a component of a complex-valued permittivity of the SUT based on said complex-valued difference.

14. A method according to claim 10 , further comprising processing determining amplitude and phase of electric field representing said near-field interaction from the first portion of said optical data to ascertain a dielectric constant parameter and an absorption parameter characterizing the SUT.

15. A method according to claim 10 , wherein said incident radiation includes a plurality of wavelengths while the phase of second electromagnetic radiation differs from the phase of the first electromagnetic radiation by an amount that is being modulated, and
further comprising analyzing data derived from the optical data output in the time domain with the use of spectral analysis to derive a spectrum representing an interferogram.

16. A method according to claim 15 , wherein the phase-delay is being continuously changed in a reference arm of an interferometer according to a periodic function characterized by a modulation frequency.

Assignees

• Bruker Nano Inc

Inventors

• Andreev Gregory
• Osechinskiy Sergey
• Minne Stephen
• Su Chanmin

Classifications

• G01Q30/04 Primary

  Display or data processing devices · CPC title

• G01Q60/22

  Probes, their manufacture, or their related instrumentation, e.g. holders · CPC title

• G01Q20/02 Primary

  by optical means · CPC title

• G01Q60/18

  SNOM [Scanning Near-Field Optical Microscopy] or apparatus therefor, e.g. SNOM probes · CPC title