Nanodiamonds enable femtosecond-processed ultrathin glass as a hybrid quantum sensor

At a Glance

Metadata	Details
Publication Date	2023-04-18
Journal	Scientific Reports
Authors	Bhavesh Kumar Dadhich, Biswajit Panda, Mehra S. Sidhu, Kamal P. Singh
Institutions	Indian Institute of Science Education and Research Mohali
Citations	5
Analysis	Full AI Review Included

Executive Summary

This research demonstrates a novel method for creating highly sensitive, multifunctional hybrid quantum sensors by combining fluorescent nanodiamonds (NV centers) with ultra-thin (UT) flexible glass substrates using femtosecond (fs) laser processing.

Core Achievement: Successful fabrication of cantilever-based Hybrid Nanomechanical Quantum (HNQ) sensors using 30 µm thick UT-glass, shaped with nanoscale precision via fs laser ablation.
Quantum Property Preservation: The NV centers retained stable optical and quantum properties post-fabrication, exhibiting characteristic zero-phonon lines (ZPLs) and Optically Detected Magnetic Resonance (ODMR) near 2.87 GHz.
Multifunctional Sensing: The NV-UT cantilever was proven capable of sensing three distinct physical parameters simultaneously: acoustic pulses, external magnetic fields, and local heating.
Magnetic Sensitivity: Achieved quantitative magnetic field sensing via Zeeman splitting, demonstrating a sensitivity of 20 ± 2 MHz/Gauss.
Thermal Sensing: Demonstrated local thermometry by measuring the thermal shift of ODMR lines, achieving a sensitivity of 1.3 MHz/K.
Mechanical Response: The cantilever exhibited a clear nanomechanical response to acoustic impulses, measured with a quality factor of approximately 40 in air.
Versatile Substrate: The work establishes fs-processed fluorescent UT-glass as a new, versatile substrate suitable for the mass production of affordable, multifunctional quantum devices.

Technical Specifications

Parameter	Value	Unit	Context
UT-Glass Thickness	30	µm	Substrate material
UT-Glass Young’s Modulus	72.9	kN/mm²	Mechanical property
UT-Glass Bending Radius	< 1	mm	Flexibility specification
Nanodiamond Size (Average)	120	nm	Particle diameter
NV Coating Thickness (Average)	1000 to 2	nm/µm	For 1 mg/mL solution
ODMR Resonance Frequency	2.87	GHz	NV center quantum property
ODMR Linewidth (FWHM)	83	MHz	At 2.87 GHz, zero field
NV^-1 Zero-Phonon Line (ZPL)	637	nm	Optical readout wavelength
Magnetic Field Sensitivity	20 ± 2	MHz/Gauss	Measured via Zeeman splitting
Thermal Sensitivity (ODMR Shift)	1.3	MHz/K	Measured using CW blue laser heating
fs Laser Pulse Duration	25	fs	Fabrication parameter
fs Laser Wavelength (Central)	800	nm	Fabrication parameter (AIR)
fs Laser Repetition Rate	1	kHz	Fabrication parameter
fs Laser Ablation Threshold	> 0.5	mJ	Minimum pulse energy for cutting
Acoustic Vibration Quality Factor	~40	-	Measured in air
External Magnetic Field Range	0 to 22.5	G	Range used for Zeeman splitting measurements

Key Methodologies

Substrate Preparation and Coating:
- Commercially available 30 µm thick UT-glass sheets were cleaned using acetone and methanol in an ultrasonic bath.
- Nanodiamond colloidal solution (120 nm particles, 1 mg/mL or 0.5 mg/mL concentration) was drop-cast and spin-coated (3000 rpm for 20 s) onto the glass surface.
- The coated substrate was dried in a desiccator for approximately 24 hours, resulting in a nanodiamond layer thickness of 500 nm to 2 µm.
Femtosecond (fs) Laser Fabrication:
- A custom fs nano-processing setup was employed, utilizing a commercial laser system (FEMTOLASERS).
- Laser parameters: 25 fs pulse duration, 800 nm central wavelength, 1 kHz repetition rate.
- The intense fs pulses were tightly focused onto the coated glass using a 10X objective (0.25 NA).
- Ablation: The pulse energy was systematically varied; cutting was achieved at energies > 0.5 mJ. Cantilevers were cut in real-time by raster scanning the fs-beam (1 mm/s speed) in the desired pattern.
Optical and Quantum Characterization Setup:
- A custom-built optical fluorescence microscope was used for imaging, spectroscopy, and ODMR.
- Excitation: A 532 nm CW green laser was used for NV center excitation (power varied from 6 µW to 20 µW for ODMR).
- Detection: Fluorescence was collected via a 40X objective (0.75 NA) and detected using an Avalanche Photodiode (APD) or an EMCCD camera.
ODMR and Sensing Implementation:
- Microwave Delivery: A single Cu wire resonator (10 µm radius) on a printed circuit board was used to deliver the microwave magnetic field.
- ODMR Scan: Microwave frequency was scanned from 1.35 to 3.1 GHz (1 MHz step) using a signal generator and a 30 dB amplifier.
- Magnetometry: An external magnetic field (B_ex) was generated by a solenoid placed under the resonator and varied from 0 to 22.5 G to measure Zeeman splitting.
- Thermometry: Local heating was induced at the cantilever tip using a 445 nm CW blue laser to measure the thermal shift of the ODMR resonance (1.3 MHz/K).
- Acoustic Sensing: The cantilever was excited with an acoustic impulse (160 Hz) in ambient conditions, and the resulting tip displacement was monitored via fluorescence modulation.

Commercial Applications

The integration of flexible UT-glass with quantum-enabled nanodiamonds via precision fs laser processing opens avenues for several high-tech engineering and commercial applications:

Quantum Sensing and Metrology:
- Flexible Quantum Sensors: Development of robust, flexible, and potentially wearable sensors for magnetic fields, temperature, and strain, suitable for complex or non-rigid surfaces.
- Multifunctional Probes: Creation of single-chip devices capable of simultaneous, localized measurement of multiple physical parameters (e.g., thermal and magnetic fields).
Biomedical and Nanoscale Imaging:
- In Vivo Thermometry: Use of NV-functionalized tips for highly localized, non-invasive temperature sensing (microkelvin resolution) within living cells and biological systems.
- Magnetic Field Mapping: Nanoscale scanning probes for mapping magnetic fields generated by biological processes or integrated circuits.
Optomechanics and Photonics:
- Precision Optomechanical Tests: Fabrication of UT-glass devices that can be coupled with optical cavities for advanced quantum optomechanical experiments.
- Flexible Photonics: Utilizing the high optical transparency and flexibility of UT-glass for flexible electronic and photonic devices, including stable attosecond delay-lines.
Micro-Electro-Mechanical Systems (MEMS) and Actuators:
- High-Speed Actuators: Development of high-speed, lightweight cantilevers for use in AFM or high-frequency mechanical systems.
- Acoustic and Vibration Sensors: Highly sensitive acoustic sensors leveraging the mechanical responsiveness and low mass of the UT-glass cantilever structure.

View Original Abstract

Abstract The quantum properties of fluorescent nanodiamonds offer great promise for fabricating quantum-enabled devices for physical applications. However, the nanodiamonds need to be suitably combined with a substrate to exploit their properties. Here, we show that ultrathin and flexible glass (thickness 30 microns) can be functionalized by nanodiamonds and nano-shaped using intense femtosecond pulses to design cantilever-based nanomechanical hybrid quantum sensors. Thus fabricated ultrathin glass cantilevers show stable optical, electronic, and magnetic properties of nitrogen-vacancy centers, including well-defined fluorescence with zero-phonon lines and optically detected magnetic resonance (ODMR) near 2.87 GHz. We demonstrate several sensing applications of the fluorescent ultrathin glass cantilever by measuring acoustic pulses, external magnetic field using Zeeman splitting of the NV centers, or CW laser-induced heating by measuring thermal shifting of ODMR lines. This work demonstrates the suitability of the femtosecond-processed fluorescent ultrathin glass as a new versatile substrate for multifunctional quantum devices.

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41598-023-30689-7