Fluorescent Nanodiamond Integrated Into Polymer Structures Advances Photonics and Quantum Computing

Nanodiamonds have emerged as promising applications for semiconductors and tool surface modification. Recent advancements in nanotechnology have enabled researchers to embed these materials within polymer microstructures, opening up possibilities for enhanced quantum computing and biological studies.

Limitations in Diamond Structures

Diamond is the only gem composed of a single element, carbon, surrounded by other carbon atoms linked together by covalent bonds. It also has both crystallographic and cubic structures.

The crystal structure of a diamond has a defect known as the nitrogen-vacancy (NV) center. Under this condition, a carbon atom is replaced by a nitrogen atom, leaving the diamond lattice's neighboring site vacant.

Such limitations and other fluorescent defects in diamonds, called color centers, have gained the attention of researchers due to their unique quantum properties. This is responsible for single photon emission at room temperature and with long coherence time.

NV center is an up-and-coming platform for various applications because of its favorable features like photostability and spin state that can be set and read out optically. Other applications include quantum information encoding and processing and cell marking in biological research.

Much effort has been made to incorporate color centers in photonic devices like resonant cavities, waveguides, and photonic crystals. One alternative is fabricating the photonic structures directly within bulk diamonds and carefully placing the NV center at desired positions. However, this process is limited by the strong bond between the carbon atoms, making this gem one of the hardest materials available.

Microfabrication in diamonds has been a difficult task. Experts embed custom-designed structures into nanodiamonds with color centers to integrate the quantum emitters into photonic devices. This method was established by a group of scientists at the University of São Paulo's São Carlos Institute of Physics (IFSC-USP) in Brazil.

Nanodiamond Integration for Enhanced Application

The research team, led by Professor Cleber Mendonça, demonstrated a method of embedding fluorescent nanodiamonds in microstructures designed for microfabrication. They investigated the ideal nanodiamond concentration in achieving a structure with at least one fluorescent nitrogen-vacancy center with good structural and optical quality.

The experts focused on photoresist, a light-sensitive material used in fabrication methods, especially when transferring nanoscale patterns to the substrate. They have extensively used two-photon polymerization (2PP) in fabricating three-dimensional microstructures. The 2PP process is a direct laser writing technique in which a high-intensity laser beam is focused on a light-sensitive polymer resin that has not yet solidified to produce the microstructure under study.

The study added a mixture of monomers that makes the photoresist to a nanodiamond solution in deionized water. After completing all the requisite physicochemical procedures, the researchers performed microfabrication by submitting the sample to pulses from a powerful titanium-sapphire laser. In defining the exact coordinates of the beam, a dedicated software program was used to control the laser.

Mendonça and his colleagues confirmed the presence and location of the nanodiamonds using fluorescence and Raman spectroscopy. Meanwhile, the scattering losses at higher concentrations were assessed through absorbance measurements. The study's findings demonstrated that fabricating microstructures integrating fluorescent nanodiamonds using 2PP can have potential applications in photonics and quantum technologies.