Chemical Analysis of Buried Interface Using SERS Sensors

At a Glance

Metadata	Details
Publication Date	2016-01-01
Journal	Hyomen Kagaku
Authors	Masahiro Yanagisawa, Takayuki Homma
Institutions	Waseda University
Analysis	Full AI Review Included

6CCVD Technical Briefing: High-Resolution SERS Analysis of Buried Interfaces and Dynamic Temperature Profiling

This document analyzes recent advancements in Surface-Enhanced Raman Scattering (SERS) technology, focusing on atomic-scale depth profiling and in-situ temperature measurement for solid-state and liquid interfaces. These techniques demonstrate critical requirements for ultra-high purity, high-stability substrates and thin films, aligning directly with 6CCVD’s expertise in customized MPCVD diamond solutions.

Executive Summary

Core Achievement: Development of a highly sensitive SERS system capable of non-destructive chemical analysis of buried interfaces (solid/solid, liquid/solid).
Ultra-High Resolution: Achieves atomic-scale depth profiling with 0.1 nm resolution steps, revealing layered structures (e.g., 0.31 nm periodicity in HOPG) and precise interface thicknesses (e.g., 0.7 nm bonded lubricant layers).
High Sensitivity: System utilizes plasmonic sensors resulting in Raman signal enhancements exceeding 2000 times compared to conventional techniques, enabling analysis of ultra-thin (2 nm) films and trace contaminants.
In-Situ Temperature Mapping: Successfully measures localized sample temperature using the Anti-Stokes/Stokes ratio, confirming high temperatures up to 580 °C within 2 nm Diamond-Like Carbon (DLC) films during pulsed laser heating simulation (relevant to HAMR technology).
Dynamic Kinetics: Enables time-resolved observation of fast chemical processes (oxidation/decomposition) under pulsed laser irradiation, identifying critical pulse widths (250 µs) required to suppress thermal degradation.
Methodology: Integrates custom plasmonic sensors (Ag nanoparticles on quartz) with high-precision Z-stage mechanisms and pulsed excitation sources.

Technical Specifications

The following hard parameters were extracted from the SERS analysis and experimentation:

Parameter	Value	Unit	Context
SERS Enhancement Factor	> 2000	Times	Net peak height comparison vs. standard Raman measurement.
Depth Resolution (Z-Stage Step)	0.1	nm	Precision movement for interface depth profiling.
DLC Film Thickness (Example)	2	nm	Thickness of DLC layer analyzed on Si or CoPt disk.
Lubricant Bonded Layer Thickness	0.7	nm	Measured thickness of the strongly interacting (bonded) lubricant layer on DLC.
HOPG Layer Periodicity (Measured)	0.31	nm	Observed deep-layer structure periodicity.
Maximum Localized Temperature (DLC)	580	°C	Calculated temperature in the 2 nm DLC layer during high-power simulation.
Maximum Localized Temperature (Si Substrate)	250	°C	Calculated temperature of the Si substrate during laser heating.
Heating Laser Power	80	mW	Excitation laser power used for thermal analysis (on Si/DLC stack).
Critical Pulse Width (Oxidation Suppression)	250	µs	Calculated threshold for suppressing oxidation reaction kinetics.

Key Methodologies

The core research relied on integrating novel plasmonic sensors with advanced spectroscopic and mechanical control systems to achieve high spatial and thermal resolution:

Plasmonic Sensor Fabrication: Transmissive SERS probes were created by coating the convex surface of quartz glass lenses with high-purity Ag nanoparticles. These noble metal nanoparticles were applied using dry processes (sputtering/vapor deposition) to prevent contamination from solvents or dispersing agents, ensuring high purity interfaces.
High-Precision Interface Setup: The plasmonic sensor (Ag-coated convex lens) was placed in direct physical contact with the sample surface (e.g., DLC film). The exciting laser was focused through the sensor substrate onto the contact interface.
Atomic-Scale Depth Profiling (Z-Profiling): A high-precision piezo stage mechanism was utilized to move the focal point in the Z-direction (depth) in steps of 0.1 nm. Depth profiles were generated by recording the intensity and spectral shifts of Raman peaks (e.g., SiC at the DLC/Si interface).
In-Situ Thermal Monitoring: Sample temperature was simultaneously monitored by measuring the intensity ratio of the Anti-Stokes (IaSt) and Stokes (Ist) Raman peaks (IaSt/Ist = exp(-hν / kT)). The high SERS enhancement was critical to making the normally weak Anti-Stokes signal measurable.
Dynamic Reaction Analysis: Pulsed laser excitation was employed for rapid, controlled localized heating. The spectrometer detection was synchronized with the pulse excitation to perform time-resolved measurements and analyze chemical kinetic changes (e.g., the oxidation rate of DLC films as a function of irradiation time).

6CCVD Solutions & Capabilities

The successful replication and expansion of this SERS technology require substrates and films characterized by extreme purity, thermal stability, and customizable surface properties—the core competencies of 6CCVD.

Applicable Materials

To replicate or extend research focused on high-stability interfaces, ultra-thin films, and high-temperature environments, 6CCVD recommends:

Optical Grade Single Crystal Diamond (SCD): Required for applications demanding the lowest defect density and high transparency across a wide spectrum.
- Application Focus: Ideal as a stable, ultra-low-noise substrate for advanced plasmonic sensor integration where thermal and chemical inertness are paramount.
- Thickness: 6CCVD offers SCD thickness control from 0.1 µm up to 500 µm.
High Purity Polycrystalline Diamond (PCD): Excellent thermal management and large-area solutions.
- Application Focus: Can serve as robust, large-area support wafers for fabricating complex sensor arrays or for studying large-format solid/solid interfaces. 6CCVD supplies wafers up to 125mm (PCD).
Boron-Doped Diamond (BDD): Essential for extending the electrochemical SERS analysis demonstrated in the paper (e.g., plating solution analysis on Cu).
- Application Focus: BDD films offer excellent electrochemical stability and conductivity, vital for the dynamic analysis of redox reactions at liquid/solid interfaces.

Customization Potential for Advanced SERS Research

Replicating the research, particularly the integration of metallic plasmonic structures or the analysis of customized film stacks (like DLC on Si), requires stringent control over material properties:

Required Capability	6CCVD Solution	Relevance to SERS Study
Surface Finish (Interface Quality)	Polishing: Ra < 1 nm (SCD), Ra < 5 nm (Inch-size PCD).	Crucial for maximizing the coupling efficiency of the plasmonic field and ensuring intimate contact between the sensor and the sample interface (key to 0.1 nm depth resolution).
Metalization Integration	Custom Thin Film Deposition: In-house capability for Au, Pt, Pd, Ti, W, Cu.	Required for fabricating plasmonic sensors (substituting Ag with Au/Pt for specific environments) or for creating custom electrical contacts needed for in-situ electrochemical studies.
Custom Geometry	Laser Cutting & Shaping: Custom dimensions and precise edge finishing.	Essential for fitting diamond substrates or films into complex spectroscopic stages or micro-mechanical setups (e.g., integrating with the piezo Z-stage).
Thermal Stability	CVD Diamond Substrates: Maximum stability and heat spreading.	Necessary for high-power, dynamic studies where localized laser heating generates temperatures up to 580 °C, ensuring the substrate integrity remains unchanged.

Engineering Support

6CCVD’s in-house PhD engineering team specializes in material science and CVD growth optimization. We can assist researchers and technical engineers in selecting the optimal diamond morphology (SCD vs. PCD) and surface finish required for complex Buried Interface Analysis and Dynamic Thermal Mapping projects.

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

View Original Abstract

New technique for analyzing buried interface has developed based on surface-enhanced Raman scattering spectroscopy. It consists of plasmonic sensors and spectrometer equipped with high precision mechanisms. Performance of the system involves in-situ measurement of interfaces, i.e. liquid/solid or solid/solid, with high sensitivity and high depth resolution on a variety of samples. Additional functions are in-situ temperature measurement by anti-Stokes/Stokes ratio, simultaneous acquisition with laser heating, time-resolved measurement, and pulsed laser Raman spectroscopy. A depth profile of layered ultra-thin films, i.e. diamond-like carbon (DLC) or highly oriented pyrolytic graphite (HOPG), was analyzed in atomic scale resolution at solid/solid interface. Molecular configuration and bonding feature of liquid organic molecules, i.e. lubricants for magnetic disks or reducing agents for a plating, were analyzed at liquid/solid interface. Oxidation process or decomposition process of ultra-thin DLC films was analyzed for a variety of DLC films. Spectral change with irradiation time by pulsed laser heating exhibited a kinetic change of molecular structures in a chemical reaction with in-situ heating temperature measurement.

Tech Support

Original Source

DOI: https://doi.org/10.1380/jsssj.37.435