Deterministic strain-induced arrays of quantum emitters in a two-dimensional semiconductor

At a Glance

Metadata	Details
Publication Date	2017-05-22
Journal	Nature Communications
Authors	Artur Branny, Santosh Kumar, Raphaël Proux, Brian D. Gerardot
Institutions	Heriot-Watt University
Citations	498
Analysis	Full AI Review Included

Technical Analysis and Documentation: Deterministic Strain Engineering for Quantum Emitters

Document Reference: Branny, A. et al. Deterministic strain-induced arrays of quantum emitters in a two-dimensional semiconductor. Nat. Commun. 8, 15053 (2017).

Executive Summary

This paper demonstrates a high-precision, scalable method for deterministically positioning single quantum emitters (SQEs) in atomically thin WSe₂ via nanoscale elastic strain engineering. This methodology provides a vital blueprint for the next generation of integrated quantum photonic devices, particularly those utilizing robust material platforms like MPCVD diamond.

Deterministic Placement: Achieved deterministic creation of SQE arrays by transferring monolayer/bilayer WSe₂ flakes onto a substrate patterned with dielectric nanopillars.
Near-Unity Yield: Demonstrated near-unity SQE creation probability, reaching up to 96% yield for optimized nanopillar geometries (Aspect Ratio h:w ≈ 0.3).
High Precision: Achieved a mean positioning accuracy of 120 ± 32 nm, with the potential for further refinement by optimizing substrate geometry.
Strain Magnitude: Local strain estimated to be up to 0.60%, resulting in significant band-gap modification (30.8 meV spectral shift), which efficiently funnels excitons.
Purity and Stability: Emitters show high-purity single-photon emission (g²(0) < 0.07 in 1L WSe₂) and exceptional optical stability over long measurement periods (20 h).
6CCVD Relevance: The strain engineering technique is directly applicable to creating ordered arrays of color centers (e.g., NV, SiV) in 6CCVD Single Crystal Diamond (SCD), critical for scalable quantum architectures.

Technical Specifications

Extracted quantitative data points illustrating the performance and parameters of the strain-induced quantum emitter platform.

Parameter	Value	Unit	Context
Substrate Lattice Pitch	4	µm	Square array of dielectric nanopillars
Emitter Positioning Accuracy (Mean)	120 ± 32	nm	Optimized nanopillar geometry (h:w ≈ 0.3)
Emitter Positioning Accuracy (Best Case)	30	nm	Highest precision achieved at specific location
Emitter Creation Probability	Up to 96	%	Yield of at least one quantum emitter per pillar (Rows 3, 4)
Maximum Estimated Strain	0.60	%	Corresponds to 30.8 meV spectral shift
Aspect Ratio (Height:Width, h:w) Range	0.15 to 0.59	N/A	Range tested for optimization
Operating Temperature	3.5	K	Closed-cycle cryostat for PL mapping
Monolayer PL Intensity Increase	50	x	Peak intensity increase at strained site vs. unstrained
Bilayer PL Intensity Increase	150	x	Peak intensity increase at strained site vs. unstrained
Single Photon Purity (1L WSe₂)	0.07 ± 0.04	g²(0)	High-purity antibunching
Single Photon Purity (2L WSe₂)	0.03 ± 0.02	g²(0)	Highly pure antibunching
Spectral Jitter (2L Emitter)	131	µeV FWHM	Jitter recorded over 20 h period

Key Methodologies

The experimental approach relies on precise nanofabrication of the straining substrate coupled with a specialized transfer technique to maximize strain perturbation and material conformity.

Substrate Preparation: Silicon (Si) or Si/SiO₂ (285 nm SiO₂) wafers were coated with negative resist (AZ 2070, ~200 nm thickness).
Pattern Generation: Electron Beam Lithography (EBL) was employed (using Raith Pioneer) to define a 4 µm pitch square lattice of nanopillars, with pillar dimensions varied to control the aspect ratio (h:w 0.15 to 0.59).
WSe₂ Exfoliation: Mono-layer (1L) and bi-layer (2L) WSe₂ flakes were obtained via standard mechanical exfoliation.
All-Dry Viscoelastic Stamping: A specialized all-dry transfer technique was used to place the WSe₂ flakes onto the patterned nanopillar array. Van der Waals forces ensured the 2D flake conformed to the topography, inducing point-like elastic strain.
Characterization and Testing: Substrate topography was mapped via Atomic Force Microscopy (AFM). Quantum emission characteristics were measured using low-temperature confocal photoluminescence (T = 3.5 K) coupled with a fiber-based Hanbury-Brown and Twiss interferometer for second-order correlation measurements.
Positioning Determination: Emitter locations were distilled from peak intensity maps and compared to nanopillar centers, which were determined by spectral weighted averaging (WA) fits.

6CCVD Solutions & Capabilities

The successful deterministic patterning demonstrated in this research hinges on precision substrate engineering. While the study focuses on WSe₂, the technique is foundational for addressing the challenge of scalability in established quantum platforms, particularly diamond. 6CCVD provides the necessary high-quality diamond materials and precision engineering services required to replicate and significantly advance this research paradigm within a robust, integrated quantum architecture.

Applicable Materials

To replicate the structural precision and mechanical stability required for deterministic strain engineering, 6CCVD recommends the following materials:

6CCVD Material	Description & Application	Benefit over Current Material (AZ 2070 Resist)
Optical Grade SCD Wafers	SCD plates up to 500 µm thickness and 5x5 mm dimensions. Ideal for creating strain-inducing nanopillars or mesas directly on the diamond substrate.	Superior thermal stability, chemical inertness, and exceptional mechanical robustness for repeatable strain cycles. Low fluorescence background.
High Uniformity PCD Substrates	PCD wafers up to 125 mm diameter, ideal for large-scale production of integrated devices where the diamond substrate serves as a stable, high-surface-quality base.	Excellent base for EBL patterning. Enables high-throughput fabrication necessary for scalable quantum arrays.

Customization Potential for Integrated Quantum Devices

The paper utilizes polymeric resist nanopillars, which limits temperature stability and long-term mechanical resilience. 6CCVD offers solutions to transition this technology to a superior, integrated diamond platform.

Precision Substrates: 6CCVD supplies SCD and PCD substrates up to 125 mm with sub-nanometer surface roughness (Ra < 1 nm for SCD, Ra < 5 nm for inch-size PCD). This surface quality is essential for the reliable Van der Waals transfer required to induce uniform strain.
Custom Microstructure Replication: Leveraging our expertise in diamond etching, we can fabricate high aspect ratio diamond nanopillars or strained membranes directly into the MPCVD material, replacing the unstable polymeric resist structures used in this study. This enables the direct integration of stress-inducing elements with quantum emitters (e.g., NV/SiV centers) generated within the diamond lattice.
Patterning Services: 6CCVD offers custom laser cutting and shaping services to produce geometrically specific, strain-engineered microstructures suitable for focused ion beam (FIB) implantation or EBL patterning for deterministic creation of color center arrays.
Metalization Capability: While not the focus of the strain engineering, 6CCVD offers in-house metalization (Au, Pt, Ti, W, Cu) for creating integrated contacts or alignment marks, supporting the construction of electrically driven quantum devices analogous to the light-emitting diodes referenced in the paper.

Engineering Support

The success of deterministic strain-induced quantum emitters depends heavily on precise material geometry and structural quality. 6CCVD’s in-house PhD team provides expert consultation on material specifications, advising on optimal SCD crystal orientation and defect density necessary to maximize color center coherence while ensuring the mechanical integrity required for nanoscale strain application. We specialize in tailoring diamond material parameters to meet the specific requirements of advanced quantum photonics applications like those detailed in this research.

Call to Action: For custom specifications or material consultation related to deterministic strain engineering in diamond or other quantum platforms, visit 6ccvd.com or contact our engineering team directly.

Tech Support

Original Source

DOI: https://doi.org/10.1038/ncomms15053