US5672830A
Expired / Lapsed
US
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Measuring anisotropic mechanical properties of thin films
Assignee: Massachusetts Institute of Technology
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Filing: 1996-12-11
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Granted: 1997-09-30
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Expires: 2016-12-11
Abstract
Abstract Anisotropic mechanical properties of thin films are measured by exciting time-dependent waveguide acoustic modes in the thin film sample with a pair of excitation pulses from an excitation laser. The waveguide acoustic modes are then optically detected by diffracting a probe laser beam off the excited modes. The probe beam is detected to generate an electronic signal. The anisotropic moduli and related properties in the film are determined by analyzing the electronic signal using a mathematical inversion procedure.
Inventors
- 👤 John A. Rogers
- 👤 Keith A. Nelson
- 👤 Lisa Dhar
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 22:14
CPC Classifications
G; G01; G01N; G01N29/00; G01N29/44; G01N29/52; G01N29/22; G01N29/24; G01N29/2418; G01N2291/00; G01N2291/01; G01N2291/011; G01N2291/012; G01N2291/02; G01N2291/023; G01N2291/0237; G01N2291/04; G01N2291/042; G01N2291/0422
Claims Analysis
Total Claims: 21
Claim 1
Independent Claim
218 words
A method for determining the anisotropy between an out-of-plane and an in-plane material property of a thin sample, wherein an exposed surface of said thin sample extends substantially along said plane, comprising: exciting time-dependent waveguide acoustic modes in the sample by directing two time-coincident laser pulses onto the sample so that they overlap in an excitation region and interfere to form an excitation field having a known wavevector, detecting said waveguide acoustic modes by directing a probe beam onto the excitation region so that it is diffracted, said probe beam having a temporal width that is comparable to the detectable presence of said waveguide acoustic modes; analyzing the diffracted probe beam to measure phase velocities of said waveguide acoustic modes, and determining the anisotropy between the out-of-plane and the in-plane mechanical property of said sample by: proposing stiffness tensors in directions of interest, calculating phase velocities based on said proposed stiffness tensors, comparing said calculated phase velocities to said measured phase velocities, repeating said proposing, calculating, and comparing until said calculated phase velocities match said measured phase velocities to a desired degree, and determining the anisotropy between the out-of-plane and the in-plane mechanical property in the direction of interest from the stiffness tensors for which the calculated phase velocities match the measured phase velocities to said desired degree.
Claim 2
Independent Claim
218 words
A method for determining the anisotropy between an out-of-plane and an in-plane material property of a thin sample, wherein an exposed surface of said thin sample extends substantially along said plane, comprising: exciting time-dependent waveguide acoustic modes in the sample by directing two time-coincident laser pulses onto the sample so that they overlap in an excitation region and interfere to form an excitation field having a known wavevector, detecting said waveguide acoustic modes by directing a probe beam onto the excitation region so that it is diffracted, said probe beam having a temporal width that is comparable to the detectable presence of said waveguide acoustic modes; analyzing the diffracted probe beam to measure phase velocities of said waveguide acoustic modes, and determining the anisotropy between the out-of-plane and the in-plane mechanical property of said sample by: proposing stiffness tensors in directions of interest, calculating phase velocities based on said proposed stiffness tensors, comparing said calculated phase velocities to said measured phase velocities, repeating said proposing, calculating, and comparing until said calculated phase velocities match said measured phase velocities to a desired degree, and determining the anisotropy between the out-of-plane and the in-plane mechanical property in the direction of interest from the stiffness tensors for which the calculated phase velocities match the measured phase velocities to said desired degree.
Claim 3
Dependent Claim
57 words
The method of claim 1 wherein said probe beam has a small dimension compared to said excitation region and the equations of motion for said sample are described by ##EQU5## where ρ is the density, μ is the displacement, c is the stiffness tensor, and the coordinate system is defined with the wavevector in the z direction.
Claim 4
Dependent Claim
30 words
The method of claim 2 wherein said excitation pulses are cylindrically focused to form an elliptical spot with the major axis of said elliptical spot being in the z direction.
Claim 5
Dependent Claim
23 words
The method of claim 2 wherein the probe pulse has a dimension of about an order of magnitude smaller than said excitation region.
Claim 6
Dependent Claim
34 words
The method of claim 1, wherein said laser pulses are selected to maximize the number of waveguide modes excited in said sample by having a wavelength at which the sample is about 20-80% absorbant.
Claim 7
Dependent Claim
13 words
The method of claim 1 wherein the wavevector-thickness product is between about 2-6.
Claim 8
Dependent Claim
20 words
The method of claim 1, wherein said probe beam is generated by temporally modulating an output of a cw laser.
Claim 9
Dependent Claim
14 words
The method of claim 7, wherein said probe beam has a square temporal profile.
Claim 10
Dependent Claim
34 words
The method of claim 1 further comprising comparing the determined anisotropic material properties of the thin sample with at least one previously determined property to allow the quality of the film to be monitored.
Claim 11
Dependent Claim
13 words
The method of claim 9, wherein the anisotropic property is a sound velocity.
Claim 12
Independent Claim
149 words
A method for determining the anisotropy between an out-of-plane and an in-plane mechanical property of a thin sample, wherein an exposed surface of said thin sample extends substantially along said plane, comprising: exciting time-dependent waveguide acoustic modes in the sample by directing two time-coincident laser pulses onto the sample so that they overlap in an excitation region and interfere to form an excitation field having a known wavevector, detecting said waveguide acoustic modes by directing a probe beam onto the excitation region so that it is diffracted, said probe beam having a temporal width that is comparable to the detectable presence of said waveguide acoustic mode; measuring a phase velocity or frequency of said waveguide acoustic modes from said diffracted probe beam; and analyzing the phase velocity or frequency of said acoustic waveguide modes to determine the anisotropy between the out-of-plane and the in-plane mechanical property of said sample.
Claim 13
Independent Claim
149 words
A method for determining the anisotropy between an out-of-plane and an in-plane mechanical property of a thin sample, wherein an exposed surface of said thin sample extends substantially along said plane, comprising: exciting time-dependent waveguide acoustic modes in the sample by directing two time-coincident laser pulses onto the sample so that they overlap in an excitation region and interfere to form an excitation field having a known wavevector, detecting said waveguide acoustic modes by directing a probe beam onto the excitation region so that it is diffracted, said probe beam having a temporal width that is comparable to the detectable presence of said waveguide acoustic mode; measuring a phase velocity or frequency of said waveguide acoustic modes from said diffracted probe beam; and analyzing the phase velocity or frequency of said acoustic waveguide modes to determine the anisotropy between the out-of-plane and the in-plane mechanical property of said sample.
Claim 14
Independent Claim
125 words
A method for determining an out-of-plane mechanical property of a thin sample, comprising: exciting time-dependent waveguide acoustic modes in the sample by directing two time-coincident laser pulses onto the sample so that they overlap in an excitation region and interfere to form an excitation field having a known wavevector; detecting the waveguide acoustic modes by directing a probe beam onto the excitation region so that it is diffracted, with the probe beam having a temporal width that is comparable to the detectable presence of the waveguide acoustic modes; measuring a phase velocity or frequency of the waveguide acoustic modes from the diffracted probe beam; and analyzing the phase velocity or frequency of the waveguide acoustic modes to determine the out-of-plane mechanical property of the sample.
Claim 15
Independent Claim
125 words
A method for determining an out-of-plane mechanical property of a thin sample, comprising: exciting time-dependent waveguide acoustic modes in the sample by directing two time-coincident laser pulses onto the sample so that they overlap in an excitation region and interfere to form an excitation field having a known wavevector; detecting the waveguide acoustic modes by directing a probe beam onto the excitation region so that it is diffracted, with the probe beam having a temporal width that is comparable to the detectable presence of the waveguide acoustic modes; measuring a phase velocity or frequency of the waveguide acoustic modes from the diffracted probe beam; and analyzing the phase velocity or frequency of the waveguide acoustic modes to determine the out-of-plane mechanical property of the sample.
Claim 16
Dependent Claim
19 words
The method of claim 12, wherein the waveguide acoustic modes compress and expand the thin sample along its thickness.
Claim 17
Dependent Claim
19 words
The method of claim 13, wherein the out-of-plane mechanical property is calculated along the thickness of the thin sample.
Claim 18
Dependent Claim
19 words
The method of claim 14, wherein the mechanical property is the stiffness or elastic moduli of the thin sample.
Claim 19
Dependent Claim
23 words
The method of claim 12, wherein during said determining an anisotropy between the out-of-plane mechanical property and an in-plane mechanical property is determined.
Claim 20
Dependent Claim
19 words
The method of claim 11, wherein the waveguide acoustic modes compress and expand the thin sample along its thickness.
Claim 21
Dependent Claim
16 words
The method of claim 17, wherein the mechanical property is the stiffness of the thin sample.
References Cited (Backward Citations)
US4710030A
Cited
US4728165A
Cited
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| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
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| 3.5 Years (Year 4) | 2000-09-29 | 2001-03-31 | 2001-09-30 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2004-09-29 | 2005-03-31 | 2005-09-30 | $3760.00 | Window Closed / Lapsed |
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