Quantitative determination of the interaction potential between two surfaces using frequency-modulated atomic force microscopy
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-05-06 |
| Journal | Beilstein Journal of Nanotechnology |
| Authors | Nicholas Chan, Carrie Lin, Tevis D. B. Jacobs, Robert W. Carpick, Philip Egberts |
| Institutions | Mechanicsâ Institute, University of Pennsylvania |
| Citations | 6 |
| Analysis | Full AI Review Included |
Quantitative Determination of Interaction Potential Using MPCVD Diamond Substrates
Section titled âQuantitative Determination of Interaction Potential Using MPCVD Diamond SubstratesâThis technical documentation analyzes the research paper âQuantitative determination of the interaction potential between two surfaces using frequency-modulated atomic force microscopyâ to highlight the critical role of high-quality diamond substrates and demonstrate 6CCVDâs capabilities in supporting advanced nanoscale tribology and adhesion research.
Executive Summary
Section titled âExecutive Summaryâ- Advanced Methodology: A novel technique combining Frequency-Modulated Atomic Force Microscopy (FM-AFM) in Ultrahigh Vacuum (UHV) and Transmission Electron Microscopy (TEM) imaging was successfully used to quantitatively determine surface interaction potential parameters.
- Material System: The study focused on the interaction between a silicon AFM probe (with native oxide) and a highly stable, Single-Crystal Diamond (100) substrate, representing a critical hard engineering material pair.
- Key Parameters Extracted: Best-fit parameters for the 6-12 Lennard-Jones (LJ) potential were determined: Work of Adhesion ($W_{adh}$) = 80 ± 20 mJ/m2 and Range of Adhesion ($z_0$) = 0.6 ± 0.2 nm.
- Model Inadequacy Highlighted: The experimental results demonstrated a qualitative mismatch with the theoretical 6-12 LJ potential, suggesting that this standard model is insufficient for accurately characterizing repulsive forces in the silicon oxide-carbon system.
- Material Requirement Validation: The research underscores the necessity for ultra-low roughness ($R_{RMS}$ < 1 nm) and chemically stable diamond surfaces to minimize spatial variance in adhesion measurements and ensure high-fidelity data for validating empirical pair potentials.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the experimental section of the research paper:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Substrate Material | Single-Crystal Diamond | (100) Orientation | Nominally flat hard engineering material. |
| Operating Environment | 1 x 10-10 | Torr | Ultrahigh Vacuum (UHV) conditions. |
| Sample Preparation Bake | 120 | °C | Used to remove residual adsorbed moisture. |
| AFM Probe Material | Silicon (with native oxide) | PPP-NCL | Used for FM-AFM measurements. |
| Cantilever Spring Constant (k) | 30.5 | N/m | Calculated using the beam geometry method. |
| Cantilever Oscillation Amplitude (a) | 12 ± 1 | nm | Set amplitude for dynamic force spectroscopy. |
| Diamond Surface RMS Roughness | 0.78 | nm | Measured over a 500 nm x 500 nm area. |
| Average Work of Adhesion ($W_{adh}$) | 80 ± 20 | mJ/m2 | Best-fit parameter for SiOx-Diamond system. |
| Average Range of Adhesion ($z_0$) | 0.6 ± 0.2 | nm | Best-fit parameter for SiOx-Diamond system. |
Key Methodologies
Section titled âKey MethodologiesâThe experimental procedure relied on precise material preparation and advanced dynamic force spectroscopy techniques:
- Substrate Cleaning and Baking: Single-crystal diamond (100) samples were cleaned ultrasonically (acetone, then ethanol) and baked at 120 °C for 8 hours prior to UHV transfer.
- Pre-Experiment Tip Characterization: The AFM tip apex geometry was characterized using Transmission Electron Microscopy (TEM) before being mounted in the UHV AFM system.
- UHV Operation: All measurements were performed in a RHK 750 UHV-AFM system at 1 x 10-10 Torr and room temperature.
- Electrostatic Force Compensation: A DC bias was applied to the sample surface to compensate for the tip-sample contact potential difference, determined by measuring the probe frequency shift as a function of sample bias voltage.
- Dynamic Force Spectroscopy Acquisition: Frequency Modulation (FM) AFM was used to acquire $\Delta f-d$ curves (frequency shift vs. piezo displacement) across an 8 x 8 grid (500 nm x 500 nm2 scan area).
- Analytical Force Conversion: Experimental $\Delta f-d$ curves were converted into interaction force-displacement curves, $F(z)$, using the analytical inversion method developed by Sader and Jarvis.
- Regression Analysis: Theoretical Lennard-Jones $F(z)$ curves, generated using the TEM-derived tip geometry, were compared to experimental $F(z)$ curves via least squares regression to determine the best-fit $W_{adh}$ and $z_0$ parameters.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research paper demonstrates the critical need for high-quality, precisely characterized diamond materials to advance nanoscale tribology. 6CCVD is uniquely positioned to supply the necessary MPCVD diamond substrates and customization services required to replicate and extend this high-level research.
| Requirement from Research Paper | 6CCVD Solution & Capability | Technical Advantage |
|---|---|---|
| High-Purity Diamond Substrates | Optical Grade Single Crystal Diamond (SCD) wafers, available in (100) orientation (as used in the study) or (111) orientation. | Provides the ultra-high mechanical stiffness, chemical inertness, and stability essential for UHV-AFM measurements of fundamental interaction potentials. |
| Ultra-Low Surface Roughness | Precision Polishing Service: SCD wafers polished to achieve surface roughness $R_a < 1$ nm. Inch-size Polycrystalline Diamond (PCD) available with $R_a < 5$ nm. | Directly addresses the paperâs conclusion that localized roughness significantly impacts $W_{adh}$ variance, enabling researchers to achieve higher fidelity, spatially consistent adhesion data. |
| Custom Sample Dimensions | Custom Dimensions and Thickness: SCD plates available from 0.1 ”m up to 500 ”m thick. PCD plates up to 125 mm diameter. Substrates available up to 10 mm thick. | Supports the creation of custom AFM probe holders, punches, or specialized sample geometries required for combined TEM/AFM or in situ force measurements. |
| Surface Chemistry Control | Custom Surface Termination: We offer SCD/PCD with specific terminations (e.g., Hydrogen or Oxygen) to control surface energy and chemical stability, mitigating variations in $W_{adh}$ caused by chemical aging. | Essential for future studies aiming to isolate the effects of interaction potential modeling from surface chemistry variations, as recommended by the authors. |
| Conductive Interface Studies | In-House Metalization: We offer custom metal layers (Au, Pt, Pd, Ti, W, Cu) for creating conductive diamond tips or substrates. | Enables researchers to extend this methodology to conductive AFM techniques (like FIM or APT) or to study complex metal-diamond interfaces relevant to microelectromechanical systems (MEMS). |
Engineering Support: 6CCVDâs in-house PhD team can assist with material selection and optimization of surface properties (roughness, termination, and doping) for similar nanoscale tribology and adhesion projects, ensuring the highest material fidelity for validating empirical pair potentials.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
The interaction potential between two surfaces determines the adhesive and repulsive forces between them. It also determines interfacial properties, such as adhesion and friction, and is a key input into mechanics models and atomistic simulations of contacts. We have developed a novel methodology to experimentally determine interaction potential parameters, given a particular potential form, using frequency-modulated atomic force microscopy (AFM). Furthermore, this technique can be extended to the experimental verification of potential forms for any given material pair. Specifically, interaction forces are determined between an AFM tip apex and a nominally flat substrate using dynamic force spectroscopy measurements in an ultrahigh vacuum (UHV) environment. The tip geometry, which is initially unknown and potentially irregularly shaped, is determined using transmission electron microscopy (TEM) imaging. It is then used to generate theoretical interaction force-displacement relations, which are then compared to experimental results. The method is demonstrated here using a silicon AFM probe with its native oxide and a diamond sample. Assuming the 6-12 Lennard-Jones potential form, best-fit values for the work of adhesion ( W adh ) and range of adhesion ( z 0 ) parameters were determined to be 80 ± 20 mJ/m 2 and 0.6 ± 0.2 nm, respectively. Furthermore, the shape of the experimentally extracted force curves was shown to deviate from that calculated using the 6-12 Lennard-Jones potential, having weaker attraction at larger tip-sample separation distances and weaker repulsion at smaller tip-sample separation distances. This methodology represents the first experimental technique in which material interaction potential parameters were verified over a range of tip-sample separation distances for a tip apex of arbitrary geometry.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 1998 - Annual Proceedings - Reliability Physics (Symposium)