X-Ray Spectroscopy of NiO and Nanodiamond at SSRL

At a Glance

Metadata	Details
Publication Date	2018-01-01
Journal	DigitalCommons (California Polytechnic State University)
Authors	Jackson Earl
Analysis	Full AI Review Included

Technical Analysis and Material Solutions: X-Ray Spectroscopy of Nanodiamond for Biosensing

Executive Summary

This research focuses on utilizing X-ray Absorption Spectroscopy (XAS) to advance two key areas: the surface chemistry of nanodiamonds (ND) for biosensing applications and the refinement of XAS measurement techniques. The core value propositions and findings are summarized below:

Quantum Sensing Foundation: Investigation focuses on high-purity HPHT nanodiamonds utilized for electric field biosensing based on the Nitrogen Vacancy (NV) center, leveraging its fluorescent and spin-sensitive properties.
NV Center Functionality: The NV center is confirmed as the basis for magnetic sensing, utilizing optical pumping (green excitation) to polarize the electronic spin and detecting fluorescence at 637 nm, corresponding to the 2.87 GHz transition frequency.
Nanomaterial Purification: HPHT nanodiamonds, milled down to the 25-43 nm size regime, were purified via aerobic oxidation in a tube furnace (475 °C to 575 °C for 2 hours) resulting in high purity (95% diamond content).
Surface Functionalization: A protocol for functionalizing the oxidized nanodiamond surface with amino (-NH₂) groups using ammonia gas under high heat is proposed, enabling targeted chemical bonding for biosensing applications.
XAS Technique Advancement: NiO/graphite samples were analyzed at varying probing angles (30°, 55°, 85°) and dilutions to systematically quantify and correct “saturation effects” common in Fluorescence Yield (FY) XAS measurements of concentrated bulk samples.
Engineering Outcome: This work provides critical material parameters and spectroscopic corrections necessary for the successful development of nanodiamond-based quantum sensors for medical and applied physics research.

Technical Specifications

Hard data points extracted from the research poster concerning material properties and experimental parameters.

Parameter	Value	Unit	Context
NV Center Ground State	³A₂	N/A	Lowest energy triplet state in diamond lattice
NV Center Emission	637	nm	Fluorescence detection wavelength
Magnetic Transition Frequency	2.87	GHz	Used for magnetic spin-sensitive detection
Oxidation Temperature Range	475 - 575	°C	Aerobic purification range for HPHT NDs
Oxidation Duration	2	hours	Time required to achieve high purity
Final Diamond Purity	95	%	Diamond content post-aerobic oxidation
Nanodiamond Size (TEM)	10 - 40	nm	Range of dimensions via High-Resolution TEM
Nanodiamond Size (DLS Average)	43 ± 17	nm	Average diameter measured by Dynamic Light Scattering
NiO XAS Probing Angles	30, 55, 85	°	Geometries used for saturation study
NiO Concentrations Tested	0.1, 1.0, 10.0, 100	%	Dilution levels in graphite matrix
Ni2p_3/2 XAS Peak Energy	853.7	eV	Multiplet-split peak observed in the NiO spectra

Key Methodologies

The experimental procedures focused on material purification and spectroscopic data correction essential for advanced quantum material characterization.

Nanodiamond Synthesis and Size Reduction: HPHT macroscopic single crystals were subjected to ball milling, reducing the material to the 20-50 nm nanodiamond (ND) size regime, characterized by irregular shapes.
Aerobic Purification: The raw ND material was purified through controlled aerobic oxidation conducted in a tube furnace at temperatures between 475 °C and 575 °C for 2 hours to remove non-diamond carbon content and achieve 95% purity.
Surface Chemistry Modification (Proposed): The purified and oxidized ND surface (saturated with hydroxyl groups) is reacted with NH₃ gas under high heat to attach amino (-NH₂) groups to the α carbon, enabling surface functionalization for biosensing.
X-Ray Absorption Spectroscopy (XAS) Detection: XAS measurements were primarily performed using Fluorescence Yield (FY) detection via a Transition Edge Spectrometer (TES) to overcome depth limitations inherent to Electron Yield (EY) detection, allowing for more representative bulk property analysis.
Saturation Effect Investigation: Nickel Oxide (NiO) was mixed with graphite at varying dilutions (0.1% to 100%) and measured at different probing angles (30°, 55°, 85°) to characterize how sample concentration and geometry distort the true absorption spectra due to saturation effects.
Computational Goal: Density Functional Theory (DFT) calculations using StoBe software are planned for the nanodiamond work, aiming to generate local density approximations for theoretical verification of the observed experimental chemistry.

6CCVD Solutions & Capabilities

6CCVD provides the high-purity, custom-engineered diamond materials required to replicate and scale the successful quantum and surface chemistry studies outlined in this research, specifically leveraging the superior control of the MPCVD process over NV center incorporation.

Applicable Materials

To transition this proof-of-concept research into robust engineering applications, 6CCVD recommends materials optimized for precise NV center control and high surface uniformity:

Quantum Grade Single Crystal Diamond (SCD):
- Application Match: Ideal substrate for near-surface NV center creation and high-coherence quantum sensing applications (2.87 GHz magnetic sensing).
- Purity Advantage: Our SCD material offers ultra-low intrinsic defect density, allowing researchers to precisely control the introduction of NV centers via post-growth implantation and annealing, crucial for maximizing coherence time.
High Purity Polycrystalline Diamond (PCD):
- Application Match: Suitable for large-area diamond electrodes or substrates where uniform, high-surface-area films are required for efficient chemical functionalization or biosensing array development.
- Size Capability: 6CCVD can deliver PCD plates/wafers up to 125mm in diameter.
Material Form Factors: We supply both SCD and PCD with custom thicknesses ranging from 0.1 µm to 500 µm, allowing fine-tuning for surface-specific (thin film) or bulk-property investigations.

Customization Potential

The research highlights the importance of highly controlled geometry and chemistry. 6CCVD’s in-house capabilities directly address these requirements:

Precision Polishing: Achieving reproducible surface chemistry, as required for the proposed amination reaction, necessitates a highly uniform starting surface. 6CCVD provides:
- SCD polishing to Ra < 1nm.
- Inch-size PCD polishing to Ra < 5nm.
Advanced Metalization Services: For integrating quantum sensors into electrical or microwave circuits (necessary for controlling the 2.87 GHz spin state), 6CCVD offers custom internal metalization layers, including Au, Pt, Pd, Ti, W, and Cu.
Custom Dimensions and Etching: While this paper utilizes nanoparticles, 6CCVD can supply bulk wafers that can be laser-cut or micro-machined to create specific micro-structures or platforms for NV center studies, providing superior handling and uniformity compared to milled powder.

Engineering Support

6CCVD’s in-house PhD team provides specialized consultation to bridge the gap between materials science research and applied engineering needs.

We offer support for projects focused on near-surface NV center creation and optimizing material properties for applications related to electric field detection and nanoscale magnetic sensing.
Our experts can assist in selecting the optimal SCD or PCD grade to ensure compatibility with high-temperature chemical modification protocols (such as the 475 °C to 575 °C oxidation and subsequent high-heat amination).

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

View Original Abstract

The first aspect of this research project focuses on investigating the surface chemistry of high pressure high temperature (HPHT) nanodiamond by using X-ray spectroscopy techniques at the Stanford Synchrotron Radiation Lightsource (SSRL). HPHT nanodiamond is being examined as a biosensing tool for electric field detection based on the fluorescent nitrogen vacancy center hosted within diamond. With use of the transition edge spectrometer (TES), a state-of-the-art X-ray fluorescence detector, we are able to probe the surface and bulk properties of diamond. Preliminary work using density functional theory (DFT) has been done, offering insight into ground state energies and electronic structure. DFT will be used to perform future calculations. The second aspect of this research project investigates effects like saturation which distorts the true X-ray fluorescence-yield absorption spectrum, as well as various probing geometries with attention directed towards dilute samples of nickel oxide mixed with graphite. A typical method used to analyze the electronic structure of materials is electron yield detection. However, due to limitations in the escape depth of the electrons in such a method, the overall electron yield spectra is unrepresentative of bulk properties. Thus, we shift techniques to that of florescence yield detection. These two research endeavors serve to improve XAS techniques and advance nanodiamond for medical applications.

Tech Support

Original Source

DOI: None