High-accuracy [R, T] optical characterization of small-area diamond samples via a custom dual-beam sample holder.

Area of Science:

• Materials Science
• Optical Physics
• Nanotechnology

Background:

• Accurate optical characterization of small, high-optical density materials like diamond is challenging.
• Existing methods often rely on indirect measurements or curve-fitting, limiting precision and physical insight.
• Dual-beam spectrophotometry requires specialized setups for high-fidelity measurements on micro-scale samples.

Purpose of the Study:

• To develop a custom sample holder system (SHS) for high-fidelity reflectance and transmittance ([R, T]) measurements of small diamond samples.
• To enable direct optical retrieval of material properties without reliance on curve-fitting.
• To demonstrate the system's capability for non-destructive analysis of growth physics and material quality.

Main Methods:

• A custom sample holder system (SHS) was designed for precision alignment and distortion cancellation in dual-beam spectrophotometry.
• Sub-percent absolute photometric accuracy was achieved using reference materials and aperture correction.
• A Newton-Raphson (N-R) method was employed for direct inversion of [R, T] data to extract optical constants [n, k] and physical parameters.
• Analysis of fringe behavior, including p- and m-branch crossings, was used to determine thickness, roughness, and non-uniformity.

Main Results:

• The SHS achieved sub-percent photometric accuracy for [R, T] measurements of 3-7 mm diamond samples.
• Direct inversion of optical constants [n, k] was performed without curve-fitting.
• Thickness variance in boron-doped diamond (BDD) films was reduced by over 3× compared to mass-gain measurements.
• Carrier density gradients and ripple-like discontinuities in [n, k] were identified, correlating with growth physics and enabling retrieval of effective hole mass, carrier lifetime, and doping profiles.

Conclusions:

• The developed SHS and inversion method provide a powerful tool for non-destructive, nanoscale characterization of small, high-optical density materials.
• The approach reveals hidden growth physics encoded in optical data, moving beyond passive measurement to active material analysis.
• This inversion-aware metrology enhances structural verification, diagnostic clarity, and process insight for advanced material systems.