A recent research paper has addressed a significant challenge for scientists working with diamonds by developing a new method to bond diamonds directly to materials that can seamlessly integrate with both quantum and conventional electronic systems. By applying this technique, the team successfully fused diamonds with various materials such as silicon, fused silica, sapphire, thermal oxide, and lithium niobate, eliminating the need for an intermediary ‘glue.’ Unlike the typical bulk diamonds used in quantum qubit studies, which can be several hundred microns thick, they bonded exceptionally thin crystalline membranes, measuring just 100 nanometers, while preserving adequate spin coherence for advanced quantum technologies.
Synthetic diamond is known for its durability, chemical stability, rigidity, excellent thermal conductivity, and overall favorable characteristics—making it a premium material for both quantum and traditional electronics. However, there’s a challenge: diamond prefers to bond only with other diamonds.
This preference, known as homoepitaxy, means that diamond will only grow on other diamond surfaces. Consequently, incorporating diamonds into quantum or traditional computers, quantum sensors, cellphones, or other technologies often leads to compromises in the diamond’s properties or necessitates the use of large, costly pieces of this precious material.
“Diamond is unparalleled in terms of its material features for electronics, with its wide bandgap, exceptional thermal conductivity, and remarkable dielectric strength, and for quantum applications, it contains nitrogen vacancy centers that are considered the gold standard for room-temperature quantum sensing,” stated Alex High, an assistant professor at the University of Chicago’s Pritzker School of Molecular Engineering (PME). “Nevertheless, as a platform, it’s quite challenging to work with.”
A paper published in Nature Communications by the High Lab at UChicago PME and Argonne National Laboratory has found a groundbreaking solution to this challenge by introducing a new method to bond diamonds directly to materials that work well with both quantum and conventional electronic systems.
“We treat the surfaces of both the diamonds and their supporting substrates to enhance their attraction to one another. By ensuring a pristine surface smoothness, these two flat surfaces can bond effectively,” explained Xinghan Guo, the first author who completed his PhD at UChicago PME in the spring. “An annealing process reinforces the bond, making it significantly robust. This capability allows our diamond to endure various nanofabrication operations, distinguishing our method from merely placing diamond atop other materials.”
Using this innovative approach, the team directly bonded diamonds with materials like silicon, fused silica, sapphire, thermal oxide, and lithium niobate without needing a ‘glue’ type intermediary.
Rather than relying on the bulky diamonds typically used for quantum qubit research, the team was able to bond ultra-thin crystalline membranes, just 100 nanometers thick, while retaining adequate spin coherence needed for advanced quantum applications.
Perfect Defects
In contrast to jewelers, quantum researchers value slightly imperfect diamonds. By intentionally engineering defects in the crystal structure, researchers can create robust qubits that are ideal for quantum computing, sensing, and other uses.
“Diamond is a wide bandgap material; it’s also inert, meaning it behaves exceptionally well and possesses excellent thermal and electronic properties,” remarked co-author F. Joseph Heremans from UChicago PME and Argonne. “Its inherent physical properties have many advantages across various fields, yet integrating it with dissimilar materials has been quite challenging—until now.”
Previously, the difficulty in utilizing thin diamond membranes limited integration directly into devices, requiring larger, albeit microscopic, portions of the material. Co-author Avery Linder, a fourth-year student in UChicago Engineering, likened constructing sensitive quantum devices from these diamonds to trying to make a grilled cheese sandwich with an entire block of cheddar.
UChicago PME Assistant Professor Peter Maurer, also a co-author of the paper, specializes in quantum bio-sensing. He applies revolutionary quantum techniques to obtain enhanced and more precise measurements of biological processes at the micro and nanoscale.
“While we have addressed various challenges associated with interfacing intact biological targets with diamond-based quantum sensors, integrating them into operational measurement devices, such as commercial microscopes or diagnostic equipment, without compromising readout efficiency, has remained a significant hurdle,” Maurer added. “This new advancement with diamond membrane bonding led by Alex’s lab has resolved many of these issues and brings us closer to practical applications.”
Sticky Diamonds
In diamonds, each carbon atom connects with four neighboring carbon atoms through shared electrons, forming strong bonds known as covalent bonds, which give diamonds their remarkable structural integrity.
However, if nearby carbon bonds are absent, “dangling bonds” occur on isolated atoms eager for bonding. Creating a diamond surface saturated with these dangling bonds enabled the team to directly bond the nanometer-scale diamond wafers to other surfaces.
“You can think of it like a sticky surface, as it desires to bond with something else,” Linder noted. “Essentially, we’re creating these ‘sticky’ surfaces and bringing them together.”
The researchers have secured a patent for this process and are working on commercializing it through the University of Chicago’s Polsky Center for Entrepreneurship and Innovation.
“This groundbreaking technique could significantly change how we approach manufacturing in quantum technology as well as in mobile phones or computers,” Linder remarked.
High compared this new diamond technology to the evolution seen in complementary metal-oxide semiconductors (CMOS) over the decades, which evolved from bulky individual transistors in labs during the 1940s to today’s powerful miniaturized integrated circuits used in computers and mobile devices.
“We hope that our ability to produce these ultra-thin films and integrate them in a scalable manner can trigger a CMOS-style revolution for diamond-based quantum technologies,” he concluded.
Funding: This research was supported by the U.S. Department of Energy Office of Science National Quantum Information Science Research Centers as part of the Q-NEXT center. The work on membrane bonding was backed by NSF award AM-2240399.
