Scanning diamond NV center probes compatible with conventional AFM technology

At a Glance

Metadata	Details
Publication Date	2017-10-16
Journal	Applied Physics Letters
Authors	Tony Zhou, Rainer Stöhr, Amir Yacoby
Citations	1
Analysis	Full AI Review Included

Technical Documentation & Analysis: Scanning Diamond NV Center Probes

This document analyzes the fabrication requirements and performance metrics detailed in the research paper, “Scanning Diamond NV Center Probes Compatible with Conventional AFM Technology,” and maps them directly to the advanced material and processing capabilities offered by 6CCVD.

Executive Summary

The research successfully demonstrates a robust and scalable method for creating monolithic diamond scanning probes integrated with RF micro-antennas, enabling high-performance NV center magnetometry compatible with standard AFM platforms.

High-Purity Material Requirement: Fabrication relies on ultra-pure, electronic-grade, (100)-oriented Single Crystal Diamond (SCD) substrates, polished to an exceptional surface roughness (Ra < 1 nm).
Quantum Performance: Achieved high-quality NV centers via Nitrogen 15 implantation (6 keV), resulting in an average T₂ coherence time of 61 µs and single NV count rates up to 500 x 10³ per second.
Monolithic Integration: The probes feature integrated nanophotonic structures (nanopillars, ~350 nm diameter) and are defined as detachable 125 µm x 50 µm x 50 µm cubes.
Advanced Processing: The fabrication sequence requires deep Reactive Ion Etching (RIE) through 50 µm of diamond and precise photolithography aligned to sub-micron features.
RF Control: Successful integration of a Titanium (Ti) micro-antenna structure allows for efficient NV spin manipulation, achieving Rabi frequencies up to 4.8 MHz.
AFM Compatibility: The final probes are designed for reliable integration onto commercial tipless AFM cantilevers and quartz tuning fork sensors, broadening accessibility for quantum sensing applications.

Technical Specifications

The following table extracts key material and performance data points critical for replicating or extending this NV center magnetometry research.

Parameter	Value	Unit	Context
Initial Substrate Material	SCD (100)-oriented	N/A	Ultrapure electronic grade, ¹³C natural abundance
Initial Substrate Thickness	50	µm	Required starting thickness for deep RIE
Initial Surface Roughness (Ra)	~1	nm	RMS, achieved via high-quality polishing
Probe Dimensions (L x W x T)	125 x 50 x 50	µm	Final dimensions of the detachable diamond sensor
Nanopillar Diameter	~350	nm	Nanophotonic structure for enhanced photon collection
Nanopillar Length	~3.5	µm	Optimized length via etching time
Nitrogen Implantation Energy	6	keV	Used to create shallow NV centers
Average Coherence Time (T₂)	61	µs	Key metric for quantum sensing performance
Single NV Count Rate	200-500 x 10³	per second	Usable range for scanning applications
Etch Mask Material	Titanium (Ti)	N/A	Used as hard mask for deep RIE
Etch Mask Thickness	400	nm	Thickness of thermally evaporated Ti layer
Maximum Rabi Frequency	4.8	MHz	Achieved at 1.75 GHz RF, 35 dBm input power
NV Center to Sample Distance	20	nm	Minimum distance achieved, controlled by implantation energy

Key Methodologies

The fabrication process is complex, requiring precise control over material quality, etching depth, and surface preparation.

Material Preparation and Polishing: Start with ultra-pure, (100)-oriented CVD diamond polished to 50 µm thickness with Ra < 1 nm.
Defect Etching: Oxygen RIE is used to etch approximately 5 µm from one surface to remove polishing-induced strain and defects, ensuring optimal crystal quality near the NV centers.
NV Center Formation: Nitrogen 15 ions are implanted at 6 keV into the etched surface, followed by high-temperature thermal annealing to activate the NV centers.
Nanopillar Definition: Lithography and RIE are used to define 350 nm diameter nanopillars (~3.5 µm length) on the implanted side, acting as nanophotonic waveguides.
Probe Shape Definition: Photolithography is performed on the opposite side, precisely aligning the mask to the nanopillars to define the 125 µm x 50 µm x 50 µm probe shape.
Metal Etch Mask: A 400 nm Titanium (Ti) layer is thermally evaporated and patterned via lift-off to serve as a robust mask for the subsequent deep etch.
Deep Diamond Etching: Oxygen RIE is used to etch through the entire 50 µm thickness, creating an array of individual diamond probes connected by weak joints to the substrate frame.
Final Cleaning and Termination: The entire substrate undergoes a boiling acid clean (sulfuric, nitric, perchloric acid) to remove metallic and organic contaminants and oxygen terminate the surface.
Sensor Integration: Individual probes are detached by breaking the weak joints and glued onto commercial tipless AFM cantilevers or quartz tuning forks.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the foundational materials and advanced processing services required to replicate and scale this high-impact NV center magnetometry research. Our capabilities directly address the challenges of material purity, dimensional control, and complex metalization detailed in the paper.

Applicable Materials

To achieve the reported T₂ coherence times and high photon collection efficiency, the highest quality SCD is essential.

6CCVD Material Solution	Specification Match	Application Relevance
Optical Grade SCD (100)	Ultra-pure, low strain, high crystal quality.	Essential for long T₂ coherence times (61 µs) and minimizing decoherence sources (e.g., paramagnetic surface spins).
Custom Thickness SCD	50 µm thickness requirement.	We provide SCD wafers/plates from 0.1 µm up to 500 µm, allowing precise control over the starting material thickness for deep RIE.
High-Purity Polishing	Ra < 1 nm RMS surface roughness.	Our standard SCD polishing achieves Ra < 1 nm, minimizing surface defects that require extensive pre-etching.

Customization Potential

The success of this probe design hinges on precise dimensional control and integrated metal layers. 6CCVD offers comprehensive services to meet these exact specifications.

Research Requirement	6CCVD Capability	Value Proposition
Custom Probe Dimensions	Plates/wafers up to 125 mm; custom laser cutting.	We can supply the initial 2x4 mm² substrates or larger wafers up to 125 mm (PCD) and perform precision laser cutting to define the final 125 µm x 50 µm probes, ensuring high yield and consistency.
Deep RIE Etching	Substrate thickness up to 500 µm (SCD/PCD).	We provide expert RIE services capable of etching through 50 µm of SCD with high aspect ratios, crucial for defining the nanopillars and the final probe shape.
Integrated Metalization	Au, Pt, Pd, Ti, W, Cu (Internal capability).	The paper used a 400 nm Titanium (Ti) layer for the etch mask and potentially for the RF antenna. 6CCVD offers custom Ti deposition and patterning services, simplifying the fabrication workflow.
Implantation Control	Material preparation for ion implantation.	We supply substrates optimized for subsequent ion implantation, ensuring the required (100) orientation and low defect density necessary for precise NV center depth control (e.g., 6 keV implantation).

Engineering Support

The complexity of NV center fabrication—combining quantum material science with nanophotonics and micro-electromechanical systems (MEMS)—requires specialized expertise.

Material Selection for Quantum Sensing: 6CCVD’s in-house PhD team specializes in CVD diamond growth and processing for quantum applications. We can assist researchers in selecting the optimal SCD grade (e.g., isotopic purity, nitrogen concentration) to maximize T₂ coherence times for similar NV center magnetometry projects.
Process Optimization: We offer consultation on RIE recipe development and metal hard mask selection (e.g., Ti, W) to ensure high-yield fabrication of complex nanostructures like the 350 nm diameter nanopillars.
Global Logistics: We ensure reliable, global shipping (DDU default, DDP available) of sensitive, high-value diamond materials, supporting international research collaborations.

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

View Original Abstract

Scanning probe microscopy using nitrogen vacancy (NV) centers in diamond has become a versatile tool with applications in physics, chemistry, life sciences, and earth and planetary sciences. However, the fabrication of diamond scanning probes with high photon collection efficiency, NV centers with long coherence times, and integrated radio frequency (RF) remains challenging due to the small physical dimensions of the probes and the complexity of the fabrication techniques. In this work, we present a simple and robust method to reliably fabricate probes that can be integrated with conventional quartz tuning fork based sensors as well as commercial silicon AFM cantilevers. An integrated RF micro-antenna for NV center spin manipulation is directly fabricated onto the probe making the design versatile and compatible with virtually all AFM instruments. This integration marks a complete sensor package for NV center-based magnetometry and opens up this scanning probe technique to the broader scientific community.