Sub-10 nm Precision Engineering of Solid-State Defects via Nanoscale Aperture Array Mask
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-02-08 |
| Journal | Nano Letters |
| Authors | Tae-Yeon Hwang, JungâHyun Lee, Seung-Woo Jeon, YongâSu Kim, YoungâWook Cho |
| Institutions | Hanyang University, Korea University of Science and Technology |
| Citations | 9 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research details a breakthrough method for engineering solid-state defects (Nitrogen Vacancy, NV centers) in diamond with sub-10 nm precision, crucial for scalable quantum systems.
- Core Innovation: A double-layered mask system combining Nanoscale Aperture Arrays (NAAs) and Electron Beam Lithography (EBL) is used for highly precise 14N+ ion implantation.
- Precision Record: The technique achieved the smallest reported single aperture mask opening area (28 nm2) and the closest center-to-center spin separation (approximately 10 nm).
- NAA Characteristics: The NAAs, derived from phase-separated eutectic Al-Si, exhibit a high aspect ratio (10) and an inherently uniform triangular lattice geometry, ensuring high scalability.
- Cluster Confinement: The method successfully confined small clusters of up to three NV spins within a 30 nm diameter EBL hole spot, verified by g(2) and ODMR measurements.
- Coupling Potential: The close proximity (~10 nm) achieved suggests the potential for strong NV-NV dipolar coupling, a prerequisite for realizing scalable quantum registers.
- Scalability: The NAA-EBL double-layer mask is robust for fabricating a large number of uniform, closely separated quantum nodes in a wide area.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| NV Positioning Precision (Area) | 28 | nm2 | Smallest single aperture mask opening area achieved. |
| Aperture Size (da) | 5.87 ± 0.82 | nm | Mean aperture size of optimized NAAs. |
| Aperture-to-Aperture Distance | 10.7 | nm | Center-to-center separation of NAAs. |
| NAA Aspect Ratio | 10 | Ratio | High aspect ratio achieved via Al-Si phase separation. |
| NAA Mask Thickness | 55 | nm | Sufficient to block 10 keV ions. |
| EBL Secondary Mask Diameter | ~30 (Measured 32.23) | nm | Confining cluster size (Sample A). |
| Ion Species | 14N+ | Ion | Implanted nitrogen source. |
| Implantation Energy | 10 | keV | Standard energy used for all samples. |
| Implantation Dose | 4 x 1013 | ions/cm2 | Total dose applied. |
| SRIM Projected Range (10 keV) | 30.1 | nm | Calculated projected range of 14N+ ions. |
| Single NV Coherence Time (T2,Hahn) | 4.5 | ”s | Average measured T2,Hahn for single NVs. |
| Maximum Single NV T2,Hahn | >16 | ”s | 10% of measured single NVs exceeded this value. |
| Strong Coupling Separation Target | ~10 | nm | Required separation for strong NV-NV dipolar coupling. |
| Confined NV Count | Up to 3 | NVs | Confirmed within a single 30 nm EBL spot. |
Key Methodologies
Section titled âKey MethodologiesâThe fabrication relies on a phase-separation technique combined with standard lithography and ion implantation:
- Diamond Cleaning: High-purity diamond substrate cleaned by tri-acid boiling (sulfuric, perchloric, nitric acid) for >1 h at 170 °C.
- Al-Si Thin Film Deposition: A 55 nm thick eutectic Al-Si phase-separated thin film deposited via RF sputtering (Ar pressure 0.3 mTorr, substrate temperature 100 °C, RF power 150W).
- NAA Formation (Selective Etching): Aluminum nanowires selectively etched by immersion in 5% phosphoric acid, leaving the NAA layer composed of amorphous silicon oxide with a mean aperture size of 5.87 nm.
- Secondary Mask Patterning: A secondary EBL mask (ZEP520a) with circular holes (~30 nm diameter, 200 nm thickness) applied onto the NAAs to define implantation spots.
- Ion Implantation: 14N+ ions implanted through the NAA-EBL double-layer mask at 10 keV with a dose of 4 x 1013/cm2.
- NV Generation (Annealing): Samples annealed sequentially at 800 °C for 8 h and 1100 °C for 2 h to generate NV centers.
- Surface Treatment: Additional O2 annealing performed at 450 °C for 4 h to induce oxygen termination, improving the spin coherence time of shallow NV centers.
- Measurement: Optical and spin properties verified using home-built confocal microscopy, second-order autocorrelation function (g(2)), and Optically Detected Magnetic Resonance (ODMR).
Commercial Applications
Section titled âCommercial ApplicationsâThis high-precision defect engineering technique is foundational for developing next-generation quantum technologies:
- Scalable Quantum Computing: Enables the fabrication of uniform, strongly coupled quasi-2D spin clusters, essential for constructing scalable solid-state qubit registers and quantum processors.
- High-Resolution Quantum Sensing: Facilitates the creation of dense, uniform arrays of NV spin sensors, significantly improving the spatial resolution and sensitivity of magnetic field imaging and other quantum sensing applications.
- Quantum Simulation Platforms: Provides a robust method for engineering strongly interacting electronic spin ensembles, serving as ideal platforms for studying complex quantum phenomena and many-body physics.
- Advanced Qubit Manufacturing: Offers a highly robust and scalable tool for deterministic positioning of solid-state defects, overcoming yield and uniformity challenges associated with previous nanoimplantation methods (e.g., AFM tip or single-layer EBL masks).
- Shallow NV Enhancement: The technique, when combined with post-processing methods like epitaxial overgrowth or microwave-assisted chemical vapor deposition (CVD), can lead to shallow NV centers with enhanced spin properties and longer coherence times.
View Original Abstract
Engineering a strongly interacting uniform qubit cluster would be a major step toward realizing a scalable quantum system for quantum sensing and a node-based qubit register. For a solid-state system that uses a defect as a qubit, various methods to precisely position defects have been developed, yet the large-scale fabrication of qubits within the strong coupling regime at room temperature continues to be a challenge. In this work, we generate nitrogen vacancy (NV) color centers in diamond with sub-10 nm scale precision using a combination of nanoscale aperture arrays (NAAs) with a high aspect ratio of 10 and a secondary E-beam hole pattern used as an ion-blocking mask. We perform optical and spin measurements on a cluster of NV spins and statistically investigate the effect of the NAAs during an ion-implantation process. We discuss how this technique is effective for constructing a scalable system.