Integration of Fluorescent, NV-Rich Nanodiamond Particles with AFM Cantilevers by Focused Ion Beam for Hybrid Optical and Micromechanical Devices

At a Glance

Metadata	Details
Publication Date	2021-10-29
Journal	Coatings
Authors	Mateusz Ficek, Maciej J. Głowacki, Krzysztof Gajewski, Piotr Kunicki, Ewelina Gacka
Institutions	Jagiellonian University, Wrocław University of Science and Technology
Citations	8
Analysis	Full AI Review Included

Executive Summary

The research details a novel fabrication technology for creating hybrid Atomic Force Microscopy (AFM) probes by integrating Nitrogen-Vacancy (NV)-rich nanodiamond (NV-ND) particles onto standard AFM cantilevers.

Core Value Proposition: Combines the nanometric spatial resolution of AFM scanning with the high magnetic sensitivity of NV color centers via Optically Detected Magnetic Resonance (ODMR).
Fabrication Method: Utilizes high-precision nanomanipulation combined with Focused Ion Beam (FIB) milling (for tip slot preparation) and Focused Electron Beam-Induced Deposition (FEBID) using a Platinum-Carbon (Pt(C)) precursor for permanent particle fixation.
Material Pre-processing: Ultrasonic disintegration of commercial NV-NDs (initial size ~1 µm) was successfully employed to reduce particle size to 500 nm or less, achieving the sharp, tip-like geometry required for high-resolution scanning.
Imaging Performance: The NV-ND integrated tip demonstrated superior scanning performance on Highly Oriented Pyrolytic Graphite (HOPG), yielding a Root Mean Square (RMS) roughness of 2.23 nm, significantly better than the 3.47 nm achieved by a standard platinum-coated tip.
Quantum Functionality: ODMR measurements confirmed the functionality of the NV ensemble, achieving a maximum contrast of 0.7% at zero magnetic field.
Thermal Challenge: Significant laser-induced heating was observed, estimated at approximately 300 °C at 50 mW excitation power, indicating a need for improved thermal management or lower-power detection systems.

Technical Specifications

Parameter	Value	Unit	Context
Initial Nanodiamond Size (Average)	~1	µm	Commercially sourced NV-rich particles
Optimal Nanodiamond Size (Target)	500 or less	nm	Required for high aspect ratio and small tip radius
FIB Milling Voltage	30	kV	Used for etching the mechanical slot in the AFM tip
FEBID Deposition Voltage	2	kV	Used for depositing Pt(C) material for particle fixation
Laser Excitation Wavelength	532	nm	Green laser source (Nd: YAG SHG)
Estimated Tip Heating (at 50 mW)	~300	°C	Calculated from the spectral shift of the NV Zero-Phonon Line (ZPL)
ODMR Contrast (0 G field)	0.7	%	Maximum contrast observed from the NV ensemble
ODMR Contrast (Applied field)	0.35	%	Contrast reduction observed under magnetic field
MW Frequency (ODMR)	2.87	GHz	Microwave signal frequency for electron spin resonance
NV-ND Tip RMS Roughness (HOPG)	2.23	nm	Measured during AFM scanning (demonstrates high resolution)
Standard Tip RMS Roughness (HOPG)	3.47	nm	Reference value for conventional platinum-coated tip
Maximum Resonant Frequency Shift	-57	Hz	Largest recorded shift in AFM cantilever frequency post-experiment

Key Methodologies

The fabrication and testing process involved precise material preparation, nanoscale manipulation, and multi-modal characterization:

Nanodiamond Fragmentation:
- NV-rich nanodiamonds (10 mg) were suspended in 10 mL Isopropyl Alcohol (IPA).
- Ultrasonic disintegration was performed in a pulsed mode (0.5 s work, 0.5 s idle) for durations up to 60 minutes.
- The 60-minute sonication yielded the highest fraction of desired 500 nm particles, eliminating particles > 1.5 µm.
AFM Tip Slot Preparation:
- A standard platinum-coated AFM cantilever was placed in a Helios NanoLab 600i SEM/FIB system.
- A slot was milled into the cantilever apex using a Gallium ion source (30 kV) to provide mechanical stability for the NV-ND particle.
Nanodiamond Transfer and Positioning:
- A suitable NV-ND particle (< 500 nm, sharp edges) was selected from the prepared suspension deposits.
- A nano-manipulator was used to attach and transfer the particle into the prepared slot on the AFM tip.
Particle Fixation (FEBID):
- The particle was permanently fixed using Focused Electron Beam-Induced Deposition (FEBID).
- The precursor MeCpPtMe₃ was used to deposit Platinum-Carbon (Pt(C)) material around the particle base using a 2 kV electron beam.
ODMR Characterization:
- Fluorescence spectra and ODMR signals were collected using a confocal microscope setup (532 nm laser, 40× objective, dichroic mirror, long-pass filter).
- Microwave signals (2.87 GHz) were delivered via a stripline antenna to excite the NV electron spins.
AFM Performance Testing:
- The fabricated hybrid probes were tested by imaging Highly Oriented Pyrolytic Graphite (HOPG) in tapping mode.
- Performance metrics included RMS roughness and monitoring the cantilever resonant frequency shift before and after scanning.

Commercial Applications

This technology is foundational for advanced metrology and quantum sensing applications, leveraging the unique properties of NV centers integrated into high-resolution scanning probes.

Quantum Sensing and Metrology: Enables the development of highly sensitive, nanoscale magnetometers for measuring weak magnetic fields, crucial for quantum computing hardware characterization and fundamental physics research.
Spintronics and Magnetic Materials Research: Provides the capability to quantitatively map stray magnetic fields and detect weak perturbations of magnetic textures in novel spintronic devices and magnetic storage media with nanometric resolution.
Bio-Magnetometry: Applicable in biological systems for nanoscale magnetometry in liquid environments, allowing for the study of magnetic fields generated by biological molecules, organelles, and living cells.
Advanced Microscopy Probes: The use of durable nanodiamond material results in AFM tips with high abrasion resistance, promising longer operational lifetimes and higher resolution imaging compared to conventional tips.
Hybrid Device Manufacturing: Establishes a robust, repeatable method (FIB/FEBID integration) for combining optical functionality (ODMR) directly onto standard MEMS/AFM platforms, paving the way for integrated multi-modal sensor arrays.

View Original Abstract

In this paper, a novel fabrication technology of atomic force microscopy (AFM) probes integrating cantilever tips with an NV-rich diamond particle is presented. Nanomanipulation techniques combined with the focused electron beam-induced deposition (FEBID) procedure were applied to position the NV-rich diamond particle on an AFM cantilever tip. Ultrasonic treatment of nanodiamond suspension was applied to reduce the size of diamond particles for proper geometry and symmetry. The fabricated AFM probes were tested utilizing measurements of the electrical resistance at highly oriented pyrolytic graphite (HOPG) and compared with a standard AFM cantilever performance. The results showed novel perspectives arising from combining the functionalities of a scanning AFM with optically detected magnetic resonance (ODMR). In particular, it offers enhanced magnetometric sensitivity and the nanometric resolution.

Tech Support

Original Source

DOI: https://doi.org/10.3390/coatings11111332

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