The Transitional Wettability on Bamboo-Leaf-like Hierarchical-Structured Si Surface Fabricated by Microgrinding

At a Glance

Metadata	Details
Publication Date	2022-08-22
Journal	Nanomaterials
Authors	Ping Li, Jinxin Wang, Jiale Huang, Jianhua Xiang
Institutions	Guangzhou University
Citations	4
Analysis	Full AI Review Included

Technical Documentation & Analysis: Transitional Wettability on Hierarchical-Structured Surfaces

Executive Summary

This analysis focuses on the successful fabrication of stable, transitional hydrophobic surfaces on monocrystalline silicon (Si) using a single-step diamond microgrinding process. This research is highly relevant to 6CCVD’s core mission, demonstrating advanced surface engineering techniques applicable to hard and brittle materials, particularly diamond.

Core Achievement: Stable transitional wettability (hydrophilic to hydrophobic) was achieved on Si surfaces solely through mechanical texturing (Bamboo-Leaf-like Hierarchical Structures, BLHS), eliminating the need for unstable low-surface-energy coatings.
Fabrication Method: Hierarchical micro-nanostructures were created using one-step microgrinding with diamond grinding wheels (SD60 to SD3000 grain sizes).
Wetting Performance: Contact angles (CAs) were successfully increased from the intrinsic hydrophilic state (< 60°) to a stable hydrophobic range (77° to 97°).
Robustness Verified: The hydrophobic state proved highly stable, with CA reduction of only 2° after high-velocity droplet impact (Weber number We=21).
Advanced Characterization: Fractal theory (3D box-counting method) was utilized to accurately characterize the multi-scale complexity (Fractal Dimension D_β 2.06-2.54) of the BLHS morphology, proving superior to traditional roughness metrics (Sa).
Application Potential: The structured surfaces demonstrated excellent droplet manipulation capabilities, including 100% mass transfer and rapid self-suction into micro-tubes (0.1 s) when modified with low-energy coatings.
6CCVD Relevance: The methodology confirms that ultraprecision diamond machining is a viable, eco-efficient path for creating high-performance, bio-inspired functional surfaces on hard materials, directly translating to the superior properties of MPCVD diamond.

Technical Specifications

The following hard data points were extracted from the research paper detailing the material properties and performance metrics of the fabricated BLHS surfaces.

Parameter	Value	Unit	Context
Intrinsic Si Contact Angle (CA)	< 60	°	Bare Si (Hydrophilic)
Achieved BLHS Contact Angle (CA) Range	77 to 97	°	SD3000 (fine) to SD60 (coarse) grinding
Contact Angle Reduction Post-Impact	2	°	After droplet impact (v=1.0 m/s, We=21)
Solid-Surface Roughness (Sa) Range	0.6 to 7.2	µm	SD3000 (fine) to SD60 (coarse) grinding
Fractal Dimension (D_β) Range	2.06 to 2.54	N/A	SD60 to SD3000 grinding
Microstructure Depth Range (Micro)	0.1 to 5	µm	BLHS structures
Nanostructure Depth Range (Nano)	50 to 100	nm	BLHS structures
Grinding Wheel Speed (N)	3000	rpm	Microgrinding condition
Feed Speed (v_f)	2000	mm/min	Microgrinding condition
Droplet Volume Used for Testing	3	µL	DI water
Self-Suction Time (Coated BLHS)	0.1	s	Into hollow micro-tube (without external force)

Key Methodologies

The experiment successfully demonstrated the fabrication and characterization of hierarchical structures on hard, brittle Si using ultraprecision machining techniques.

Fabrication:
- Tooling: Diamond grinding plane wheels (Resin bonded) with grain sizes ranging from SD60 (coarse) to SD3000 (fine) were used.
- Workpiece: Monocrystalline silicon chips.
- Process: One-step microgrinding in the elastic-plastic removal region, utilizing a CNC grinder (SMART B818) at N = 3000 rpm and v_f = 2000 mm/min.
- Result: Creation of BLHS surfaces with microgrooves (0.1-5 µm depth) and random nanostructures (50-100 nm depth).
Wettability Testing:
- Measurement: Static contact angles (CAs) measured using a Dataphysics OCA40 Micro at 25 °C and 58% relative humidity.
- Stability Test: Droplet impact experiments (v=1.0 m/s, We=21) were conducted to assess wetting robustness.
- Manipulation Tests: Droplet splitting, transfer, and self-suction capabilities were tested on both bare and PFPE-coated BLHS surfaces.
Characterization:
- Morphology: White Light Interferometer (WLI: BMT SMS Expert 3D) for 3D topography and roughness (Sa, Rax, Raz).
- Microstructure Detail: Scanning Electron Microscopy (SEM: TESCAN MIRA4) and Environmental SEM (ESEM) for visual confirmation of hierarchical structures.
- Chemical Analysis: Energy-dispersive X-ray spectroscopy (EDS) confirmed Si as the only element present, verifying that the wetting transition was purely physical (structural), not chemical.
- Modeling: Abbott-Firestone curves and a 3D box-counting method were used to calculate the fractal dimension (D_β) to characterize multi-scalarity.

6CCVD Solutions & Capabilities

6CCVD specializes in MPCVD diamond, the hardest and most chemically inert material available, making it the ideal platform to replicate and significantly enhance the functional surfaces demonstrated in this research. The successful microgrinding of Si using diamond tools directly validates the potential for advanced structuring on diamond itself.

Applicable Materials

The stability and robustness achieved on Si can be dramatically improved by utilizing 6CCVD’s superior diamond materials, which offer unmatched thermal, mechanical, and chemical resistance, crucial for extreme environments (boiling, condensing, acid/alkali) where Si coatings fail.

6CCVD Material	Recommended Grade	Application Relevance
Single Crystal Diamond (SCD)	Optical or Electronic Grade	Ideal for high-precision, low-roughness (Ra < 1nm) structuring where precise control over micro-groove geometry is critical for optical or quantum sensing applications.
Polycrystalline Diamond (PCD)	Mechanical or Thermal Grade	Suitable for large-area functional surfaces (up to 125mm wafers) requiring high robustness, extreme hardness, and superior thermal management (e.g., heat transfer enhancement).
Boron-Doped Diamond (BDD)	Heavy Boron Doped	Excellent for extending this research into electrochemical sensors or microfluidic devices where the structured surface requires simultaneous electrical conductivity and extreme chemical inertness.

Customization Potential

The research highlights the need for precise control over surface morphology (roughness Sa, fractal dimension D_β) to achieve specific wetting states. 6CCVD is uniquely positioned to support the next generation of this research:

Custom Dimensions: While the paper used Si chips, 6CCVD offers custom diamond plates and wafers up to 125mm (PCD), enabling scale-up of functional surfaces for industrial applications.
Precision Structuring: We provide diamond substrates with thicknesses ranging from 0.1µm to 500µm (SCD/PCD) and custom substrates up to 10mm. Our ultra-low roughness polishing (Ra < 1nm for SCD) provides the perfect starting point for controlled micro-texturing.
Advanced Metalization: If the research requires subsequent modification (like the PFPE coating used for self-suction), 6CCVD offers in-house metalization services (Au, Pt, Pd, Ti, W, Cu) for creating integrated microfluidic or electronic components directly on the structured diamond surface.

Engineering Support

The transition from Si to diamond for functional surfaces requires specialized expertise. 6CCVD’s in-house PhD team provides comprehensive engineering support:

Material Selection: Assistance in selecting the optimal diamond grade (SCD vs. PCD vs. BDD) based on required mechanical robustness, thermal conductivity, and target application (e.g., microfluidics, anti-condensation, or intelligent sensors).
Process Optimization: Consultation on adapting microgrinding or alternative structuring techniques (e.g., laser ablation, etching) to achieve desired fractal dimensions and roughness profiles (Sa 0.6 µm to 7.2 µm range) on diamond.
Application Extension: Support for similar Droplet Manipulation and Heat Transfer projects, leveraging diamond’s extreme properties to create surfaces that maintain stable wettability under high temperature or corrosive conditions far beyond the limits of silicon.

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

View Original Abstract

Stabilizing the hydrophobic wetting state on a surface is essential in heat transfer and microfluidics. However, most hydrophobic surfaces of Si are primarily achieved through microtexturing with subsequent coating or modification of low surface energy materials. The coatings make the hydrophobic surface unstable and impractical in many industrial applications. In this work, the Si chips’ wettability transitions are yielded from the original hydrophilic state to a stable transitional hydrophobic state by texturing bamboo-leaf-like hierarchical structures (BLHSs) through a diamond grinding wheel with one-step forming. Experiments showed that the contact angles (CAs) on the BLHS surfaces increased to 97° and only reduced by 2% after droplet impacts. This is unmatched by the current texturing surface without modification. Moreover, the droplets can be split up and transferred by the BLHS surfaces with their 100% mass. When the BLHS surfaces are modified by the low surface energy materials’ coating, the hydrophobic BLHS surfaces are upgraded to be superhydrophobic (CA > 135°). More interestingly, the droplet can be completely self-sucked into a hollow micro-tube within 0.1 s without applying external forces. A new wetting model for BLHS surfaces based on the fractal theory is determined by comparing simulated values with the measured static contact angle of the droplets. The successful preparation of the bamboo-leaf-like Si confirmed that transitional wettability surfaces could be achieved by the micromachining of grinding on the hard and brittle materials. Additionally, this may expand the application potential of the key semiconductor material of Si.

Tech Support

Original Source

DOI: https://doi.org/10.3390/nano12162888

References

2020 - Designing “Supermetalphobic” Surfaces that Greatly Repel Liquid Metal by Femtosecond Laser Processing: Does the Surface Chemistry or Microstructure Play a Crucial Role? [Crossref]
2017 - Rapid fabrication of bio-inspired nanostructure with hydrophobicity and antireflectivity on polystyrene surface replicating from cicada wings [Crossref]
2021 - A Unique Bamboo Leaf-Like Nanostructure Based Gas Sensor and Its Potential Application in Indoor Formaldehyde Monitor [Crossref]
2021 - Three-dimensional capillary ratchet-induced liquid directional steering [Crossref]
2014 - Fabrication of superhydrophobic surface with hierarchical multi-scale structure on copper foil [Crossref]
2017 - A lotus-leaf-like SiO2 superhydrophobic bamboo surface based on soft lithography. Colloids Surfaces A: Physicochem [Crossref]
2017 - Durable, high conductivity, superhydrophobicity bamboo timber surface for nanoimprint stamps [Crossref]
2008 - Petal Effect: A Superhydrophobic State with High Adhesive Force [Crossref]
2001 - Mechanisms for the surface colour protection of bamboo treated with chromated phosphate [Crossref]