Measuring bulk and surface acoustic modes in diamond by angle-resolved Brillouin spectroscopy

At a Glance

Metadata	Details
Publication Date	2021-07-01
Journal	Science China Physics Mechanics and Astronomy
Authors	Yaru Xie, Shu-Liang Ren, Yuanfei Gao, Xue‐Lu Liu, Ping‐Heng Tan
Institutions	Institute of Semiconductors, University of Chinese Academy of Sciences
Citations	11
Analysis	Full AI Review Included

Executive Summary

This study utilizes angle-resolved Brillouin Light Scattering (BLS) spectroscopy to characterize the acoustic modes in single-crystal CVD diamond, providing critical data for high-performance acoustic device engineering.

Core Achievement: Successfully measured and identified the velocities of Bulk Acoustic Waves (BAWs) and three distinct Surface Acoustic Waves (SAWs) on a (100)-oriented diamond surface.
High-Velocity Modes: Identified two high-velocity Surface Skimming Bulk Waves (SSBWs): the Surface Skimming Longitudinal Wave (SSLW) at 1.727 x 10⁶ cm/s and the Surface Skimming Transverse Wave (SSTW) at 1.277 x 10⁶ cm/s.
Engineering Advantage: The SSBW modes exhibit significantly higher propagation velocities than the traditional Rayleigh SAW (RSAW, 1.080 x 10⁶ cm/s), enabling the design of higher-frequency and temperature-stable diamond-based acoustic devices.
Methodological Advance: Developed a relationship (Equation 6) that connects the refractive index, incident angle, and BAW velocity, allowing for the calculation of acoustic properties along arbitrary crystal directions.
Material Basis: The research leverages diamond’s superior properties (superhigh elastic modulus, high thermal conductivity) for applications in high-frequency and high-power acoustic wave devices.
Quantum Relevance: The findings support the development of Quantum Acoustodynamics (QAD) cavities and hybrid quantum devices utilizing coherent interaction between SAWs and diamond spin centers (NV, SiV).

Technical Specifications

Parameter	Value	Unit	Context
Material Type	Type IIa Single Crystal	N/A	CVD synthesized diamond
Crystal Orientation	(100) surface	N/A	Measured face
Density (ρ)	3.515	g/cm³	Diamond parameter
Refractive Index (n)	2.426	N/A	Measured at λ = 532 nm
Incident Laser Wavelength (λ)	532	nm	BLS excitation source
Incident Laser Power	29	mW	Focused on diamond surface
SSLW (C Mode) Velocity	1.727 ± 0.010 x 10⁶	cm/s	Surface Skimming Longitudinal Wave
SSTW (A Mode) Velocity	1.277 ± 0.011 x 10⁶	cm/s	Surface Skimming Transverse Wave
RSAW (B Mode) Velocity	1.080 ± 0.009 x 10⁶	cm/s	Rayleigh Surface Acoustic Wave
LA BAW Velocity (Γ-X)	1.745 ± 0.0041 x 10⁶	cm/s	Bulk Longitudinal Acoustic Wave
TA BAW Velocity (Γ-X)	1.268 ± 0.0003 x 10⁶	cm/s	Bulk Transverse Acoustic Wave
BLS System Contrast	~10¹⁵	N/A	High-resolution measurement capability
Objective Lens NA	0.42	N/A	Numerical Aperture

Key Methodologies

Sample Preparation: A 3x3x0.25 mm³ Type IIa single-crystal diamond, (100) oriented with <100> edges, was polished to a roughness of less than 30 nm. The sample was mounted on a silicon wafer.
Angle-Resolved Setup: The diamond was fixed on a home-built angle-resolved holder, allowing rotation around the z-axis to adjust the incident angle (θ_i) with a rotation accuracy of 1°.
Brillouin Light Scattering (BLS): Spectra were acquired using a confocal microscopic BLS system in backscattering geometry, ensuring collected scattering information originated near the surface.
Interferometry: The system employed high-contrast (3+3)-pass tandem Fabry-Pérot interferometers (FPI) for high-resolution detection of acoustic phonons below 300 GHz.
Excitation Source: A 532 nm single longitudinal mode laser (29 mW) was used. The high thermal conductivity of diamond prevented observable laser heating effects.
Polarization Configurations: Measurements were performed under three configurations to isolate specific acoustic modes:
- Circular polarization (σ⁺σ^-).
- Parallel polarization (VV).
- Cross polarization (VH).
Acoustic Velocity Determination: The Brillouin shift frequency (f) was used to calculate acoustic velocity (v) via the dispersion relation f = qv. The surface wave vector (q^||) was varied proportionally to sin(θ_i) by changing the incident angle.
BAW Modeling: BAW velocities along arbitrary directions (Γ-A) were calculated using a vector sum method within the irreducible wedge (IW) of the Brillouin Zone, providing a concise method based on the incident angle and refractive index (Equation 6).

Commercial Applications

The characterization of high-velocity acoustic modes in diamond is crucial for several advanced engineering fields:

High-Frequency Communications:
- RF Filters and Resonators: Diamond’s exceptional elastic modulus and thermal stability enable the fabrication of high-power, high-frequency (GHz) acoustic wave devices essential for modern mobile communication systems (5G/6G).
- Miniaturization: The use of micro-acoustic devices, such as SAW MEMS, allows for significant shrinking of signal processors.
Quantum Technology and Sensing:
- Quantum Acoustodynamics (QAD): Diamond-based QAD cavities are foundational for developing hybrid quantum devices.
- Coherent Spin Interaction: SAWs are used to achieve coherent interaction with long-coherence-time spin defects in diamond, such as NV and SiV centers, critical for quantum sensing and computing.
High-Performance Substrates:
- Temperature-Stable Devices: The high propagation velocity and stability of Surface Skimming Bulk Waves (SSBWs) make diamond an ideal substrate for fabricating acoustic devices that must operate reliably under high-temperature or high-power conditions.
Fundamental Materials Engineering:
- Elasticity and Thermal Modeling: The precise measurement of acoustic velocities provides necessary input data for modeling the elasticity, electrostriction, and thermal capacity of diamond, supporting further material optimization.

Tech Support

Original Source

DOI: https://doi.org/10.1007/s11433-020-1710-6

References

2019 - 2019 20th International Conference on Solid-State Sensors, Actuators and Microsystems & Eurosensors XXXIII [Crossref]
2000 - Surface Acoustic Wave Devices in Telecommunications: Modelling and Simulation [Crossref]