Shows 76% of WSe2 Monolayer Sites Yield Stable Single-Photon Emitters Via AFM Nanoindentation

Scientists are addressing a key challenge in quantum photonics by demonstrating a reliable method for creating single-photon emitters (SPEs) in monolayer tungsten diselenide (WSe2). Ajit Kumar Dash, Sanket Jugade, and Manavendra Pratap Singh, all from the Indian Institute of Science, alongside Tilly Guyot and Cora Crunteanu-Stanescu from Université de Toulouse, report a technique using atomic force microscope nanoindentation on rigid silicon dioxide/silicon substrates. This research is significant because it bridges a crucial technological gap, enabling the deterministic creation of SPEs directly on platforms compatible with integrated photonic circuits and cavities, paving the way for scalable quantum technologies.

This breakthrough addresses a critical technological gap in interfacing SPEs with photonic circuits and cavities, paving the way for scalable quantum technologies.

The team developed a displacement-controlled indentation process, achieving indent depths exceeding 150nm, necessary for SPE formation on the rigid substrate. Cryogenic (4K) photoluminescence (PL) spectra revealed sharp defect peaks, approximately 200 μeV wide, at the nanoindented sites, exhibiting stability up to 120K.
Experiments show that 0.76% of indented sites exhibit these sharp, defect-bound peaks, confirmed through power-dependent, temperature-dependent, and time-resolved PL (TRPL) measurements. AFM and PL mapping conclusively link these peaks to the periphery of the indentations, establishing a clear spatial correlation.

Notably, the observed peaks display sub-linewidth spectral jitter, a lack of blinking, and demonstrate single-photon characteristics in second-order autocorrelation measurements, confirming their potential as reliable SPEs. The research establishes electrical gating as a means to switch the SPEs on and off, and to suppress background emissions, offering precise control over emitter behaviour.

Gate-voltage dependent TRPL measurements indicate that SPE dynamics can be tuned, depending on the specific nature of the SPE, suggesting a pathway towards higher-purity emitters. This work is directly applicable to other 2D materials and rigid substrates compatible with photonic circuits and cavities, representing a significant advancement in scalable SPE technologies.

This displacement-controlled AFM nanoindentation method enables precise and consistent indentations with varying depths across multiple locations. Cryogenic PL spectra from indented sites with depths greater than 150nm reveal sharp bound-exciton peaks with widths less than a few hundred microelectronvolts.

The sharp peaks persist up to 120K, indicating excellent thermal stability and suitability for practical applications. Correlating PL maps with AFM images identifies the periphery of the nanoindent as the spatial origin of the sharp peaks, providing valuable insight into the formation mechanism.

Deterministic single-photon emitter creation via displacement-controlled nanoindentation of monolayer WSe2 is demonstrated

Scientists engineered a displacement-controlled nanoindentation process to deterministically create single-photon emitters (SPEs) in monolayer WSe2 directly on SiO2/Si substrates. This work addressed a critical technological gap for interfacing SPEs with photonic circuits and cavities. Researchers exfoliated WSe2 flakes onto SiO2/Si substrates using a PDMS-assisted blue tape technique, preparing the material for subsequent modification.

To overcome limitations of previous approaches using soft polymer substrates, the study pioneered the use of a sharp diamond tip with a 10nm radius mounted on a stiff cantilever of 350 N/m. Initial force-controlled nanoindentation experiments, applying a load of 20 μN, achieved depths up to 30nm but failed to produce sharp photoluminescence (PL) emission at cryogenic temperatures.

Consequently, the team adopted displacement control, precisely driving the AFM tip into the substrate to target depths using the Z-piezo. Calibration of the Z-piezo displacement was performed via indentation on bare SiO2/Si substrate to ensure accuracy. Systematic depth-dependent indentations revealed that depths exceeding 150nm were necessary for generating sharp defect peaks.

To demonstrate reproducibility, an array of 41 indentations was created with a target depth between 210 and 220nm, confirmed by high-resolution AFM imaging. Measurements across all sites yielded an average indent depth of 213.6nm with a standard deviation of only 3.4nm, highlighting the precision of the technique.

Cryogenic (4 K) PL spectra acquired from indented sites with depths greater than 150nm exhibited sharp bound-exciton peaks with widths less than 200 μeV. These peaks persisted up to 120 K, demonstrating excellent thermal stability. Cryogenic PL mapping correlated with AFM images, identifying the periphery of the nanoindent as the spatial origin of the sharp peaks.

Power-dependent PL and time-resolved PL (TRPL) experiments confirmed the bound nature of the exciton peaks, while second-order autocorrelation measurements verified the single-photon nature of the emission. Finally, fabricated gated devices enabled electrical switching of the emitters, suppression of background PL, and tuning of SPE dynamics via TRPL measurements, paving the way for high-purity SPEs in 2D materials.

Deterministic single-photon emitters created via nanoscale indentation of monolayer tungsten diselenide exhibit promising coherence properties

Scientists achieved deterministic creation of single-photon emitters (SPEs) in monolayer WSe2 on SiO2/Si substrates using a sharp diamond atomic force microscope (AFM) tip. A displacement-controlled indentation process was developed, enabling indent depths exceeding 150nm, crucial for SPE formation and interfacing with photonic circuits.

Experiments revealed sharp defect peaks, with linewidths as narrow as 0.2 meV, observed in cryogenic (4K) photoluminescence (PL) spectra at nanoindented sites, demonstrating stable emission up to approximately 120K. Data shows that 0.76% of indented sites exhibited sharp defect-bound peaks, confirmed through power-dependent, temperature-dependent, and time-resolved PL (TRPL) measurements.

AFM and PL mapping linked these peaks to the periphery of the indentations, establishing a clear correlation between the physical indentation and the resulting SPEs. Measurements confirm sub-linewidth spectral jitter and the absence of blinking, indicating high-quality single-photon emission. The team measured that the extracted linewidth of the zero-phonon line (ZPL) was approximately 0.5 meV and 0.9 meV for two distinct spectra, with the ZPL accounting for the majority of emission intensity, suggesting low inhomogeneous broadening.

Cryogenic (4K) PL mapping revealed bright spots corresponding to Xd peaks around some indented sites, with the PL map in the 1.63-1.68 eV range clearly showing these bright spots. Systematic depth-dependent indentations demonstrated that indent depths greater than 150nm are required to create these sharp defect peaks.

Tests prove that SPEs can be switched on and off, and background emissions suppressed, using electrical gating. Gate-voltage dependent TRPL indicate that SPE dynamics can be tuned, depending on the nature of the SPE, pointing towards the development of higher-purity SPEs. An array of 41 indentations created with a target depth between 210 and 220nm yielded an average indent depth of 213.6nm with a standard deviation of 3.4nm, highlighting the precision and repeatability of the technique. This work is directly applicable to other 2D materials and rigid substrates, representing a significant step towards scalable SPE technologies.

Deterministic single-photon sources created within monolayer tungsten diselenide via nanoindentation offer promising avenues for quantum technologies

Scientists have demonstrated a method for deterministically creating single-photon emitters (SPEs) in monolayer tungsten diselenide (WSe2) directly on silicon dioxide/silicon substrates. This achievement addresses a key technological challenge in interfacing SPEs with photonic circuits and cavities, utilising a displacement-controlled nanoindentation process with an atomic force microscope (AFM) tip to achieve indent depths exceeding 150nm.

Cryogenic photoluminescence (PL) mapping revealed a high yield of SPE formation, with approximately 76% of indented sites exhibiting sharp defect-bound peaks, confirming the reproducibility of the technique. These SPEs, originating from the periphery of the indent, displayed notable characteristics including minimal spectral jitter, the absence of blinking, and confirmed single-photon behaviour via second-order autocorrelation measurements.

Furthermore, the researchers found that electrical gating could be used to switch the SPEs on and off, and to tune their dynamics, suggesting a pathway towards higher-purity emitters. The authors acknowledge that some SPEs exhibit anomalous behaviour at certain gate voltages due to background doping, representing a limitation to be addressed.

Future work could extend this technique to other two-dimensional semiconductors, magnetic materials for chiral SPEs, and incorporate ferroelectric tunability using materials like hafnium oxide. This work establishes a robust platform for scalable SPE fabrication with tuneable properties, potentially advancing quantum technologies.