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	Chinese Academy of Sciences, University of Chinese Academy of Sciences
Citations	11
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Velocity Acoustic Modes in Diamond

Executive Summary

This research successfully characterizes the acoustic properties of single crystal diamond (SCD) using angle-resolved Brillouin Light Scattering (BLS), providing critical data for advanced device engineering.

Core Achievement: Precise measurement of Bulk Acoustic Waves (BAWs) and Surface Acoustic Waves (SAWs) in (100)-oriented CVD Single Crystal Diamond.
Key Modes Identified: Three distinct surface acoustic modes were detected: Rayleigh SAW (RSAW), Surface Skimming Transverse Wave (SSTW), and Surface Skimming Longitudinal Wave (SSLW).
High Velocity Confirmation: The SSLW mode exhibited an extremely high velocity of 1.727 x 10⁶ cm/s, confirming diamond’s superior potential for high-frequency and high-power acoustic devices.
Material Requirement: The study relied on a high-quality, Type IIa SCD sample (3x3x0.25 mm³) with a polished surface roughness Ra < 30 nm.
Device Relevance: The findings are directly applicable to the design of high-performance micro-acoustic devices (RF filters, MEMS) and emerging Quantum Acoustodynamics (QAD) systems utilizing NV/SiV centers.
Methodology: Angle-resolved BLS allowed for the determination of acoustic velocity dependence on incident angle and crystal direction, providing comprehensive dispersion data.

Technical Specifications

The following hard data points were extracted from the experimental results and material characterization:

Parameter	Value	Unit	Context
Material Used	Type IIa SCD	N/A	CVD synthesized single crystal diamond
Sample Dimensions	3 x 3 x 0.25	mm³	Plate size used for BLS measurements
Surface Orientation	(100)	N/A	Polished surface orientation
Surface Roughness (Ra)	< 30	nm	Polishing specification of the sample
Density (ρ)	3.515	g/cm³	Material density used for calculations
Refractive Index (n)	2.426	N/A	Measured at λ = 532 nm
Laser Wavelength (λ)	532	nm	Incident light source
SSLW Velocity (V_C)	1.727 ± 0.010 x 10⁶	cm/s	Surface Skimming Longitudinal Wave
SSTW Velocity (V_A)	1.277 ± 0.011 x 10⁶	cm/s	Surface Skimming Transverse Wave
RSAW Velocity (V_B)	1.080 ± 0.009 x 10⁶	cm/s	Rayleigh Surface Acoustic Wave
LA Velocity ([100] Γ-X)	1.745 ± 0.0041 x 10⁶	cm/s	Bulk Longitudinal Acoustic Wave
TA Velocity ([100] Γ-X)	1.268 ± 0.0003 x 10⁶	cm/s	Bulk Transverse Acoustic Wave

Key Methodologies

The acoustic modes were measured using a highly sensitive, angle-resolved Brillouin Light Scattering (BLS) system in a backscattering geometry.

Spectroscopy Setup: A confocal microscopic BLS system was employed, featuring high-contrast (3+3)-pass tandem Fabry-Pérot interferometers (FPI).
Sample Preparation: A Type IIa SCD plate, (100) oriented, was placed on a pristine (111) silicon wafer and mounted on a home-built angle-resolved holder.
Angle Resolution: The incident angle (θ_i) was adjusted by rotating the diamond sample around the z-axis with a rotation accuracy of 1°.
Excitation Source: A single longitudinal mode laser (λ = 532 nm) with 29 mW power was focused onto the diamond surface.
Polarization Control: Measurements were performed under three distinct polarization configurations to isolate specific acoustic modes:
- Circular Polarization (σ⁺σ^-)
- Parallel Polarization (VV)
- Cross Polarization (VH)
Data Analysis: Acoustic velocities were calculated from the measured Brillouin shift (frequency, f) using the dispersion relation f = qv, where q is the wave vector magnitude.

6CCVD Solutions & Capabilities

The successful replication and extension of this high-frequency acoustic research require ultra-high quality, precisely engineered diamond substrates. 6CCVD is uniquely positioned to supply the necessary materials and customization services.

Applicable Materials for Acoustic Research

To replicate the high-performance Type IIa diamond used in this study and to advance research into QAD and high-frequency devices, 6CCVD recommends:

Optical Grade Single Crystal Diamond (SCD): Our highest purity SCD material, ideal for minimizing defects (like NV or SiV precursors) when studying intrinsic acoustic properties and maximizing coherence time in QAD applications.
- Orientation Control: Available in precise (100) orientation, matching the experimental requirement, as well as (110) and (111) for exploring anisotropic acoustic propagation.
Custom Thickness SCD: We supply SCD plates from 0.1 µm up to 500 µm thick, allowing researchers to investigate the thickness dependence of Surface Skimming Bulk Waves (SSBWs) and other pseudo-surface acoustic modes.

Customization Potential for Device Engineering

The performance of SAWs and SSBWs is highly sensitive to surface quality and geometry. 6CCVD offers capabilities that exceed the specifications of the reported study:

Requirement from Paper	6CCVD Capability	Technical Advantage
Surface Roughness (Ra < 30 nm)	Ultra-Smooth Polishing: Ra < 1 nm (SCD)	Essential for minimizing the “surface ripple” mechanism and reducing scattering losses, thereby improving SAW coherence and device Q-factor.
Dimensions (3x3 mm²)	Large Area Plates: Up to 125 mm diameter (PCD) or custom SCD plates.	Enables scaling up research to commercial-sized acoustic filters and MEMS resonators.
Orientation ((100) miscut < 3°)	Precision Orientation: Guaranteed crystal orientation and low miscut angles.	Critical for controlling the propagation direction of BAWs and SAWs along high-symmetry axes (Γ-X, Γ-K).
Metalization (N/A in paper)	In-House Metalization: Au, Pt, Pd, Ti, W, Cu.	Necessary for fabricating Interdigital Transducers (IDTs) directly onto the diamond surface for active SAW/SSBW device testing.

Engineering Support

6CCVD’s in-house PhD team can assist with material selection for similar High-Frequency Acoustic Wave Device and Quantum Acoustodynamics (QAD) projects. We provide consultation on:

Optimizing crystal orientation to maximize specific acoustic velocities (e.g., V_LA or V_SSBW).
Selecting the appropriate SCD purity grade for minimizing background noise or maximizing the performance of integrated color centers (NV, SiV).
Designing custom polishing and metalization schemes for integrated acoustic resonators and filters.

Global Logistics

6CCVD ensures reliable, global shipping (DDU default, DDP available) to deliver high-quality MPCVD diamond materials directly to your lab or fabrication facility worldwide.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

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]