X. Yang
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1
Hexagonal boron nitride (hBN) has emerged as a unique platform for room temperature quantum photonics, yet translating its optically active defects into a practical single molecule sensing technology requires two stringent conditions: (i) deterministic and spatially controlled generation of emitters and (ii) engineering nanoscale confinement geometries that reliably bring labelled biomolecules in proximity to the hBN emitters while suppressing background fluorescence. This dissertation develops and connects these two capabilities through complementary routes based on optical and strain nano-engineering in layered hBN.
We initially establish a microsphere-assisted femtosecond-laser approach to enhance light–matter interaction during defect formation and readout. By exploiting the combination of photonic nanojets with whispering gallery mode-assisted signal collection, the method enables deterministic emitter generation with improved spatial confinement and higher collection efficiency compared to microsphere-free processing. Specifically, the approach reduces the emission area by a factor of five and increases fluorescence collection efficiency by approximately tenfold.
A second result is the generation and characterization of hBN wrinkle networks in multilayer hexagonal boron nitride,which form from thermal expansion coefficient mismatch with the substrate during annealing. We demonstrate that wrinkles function as planar nanoscale confinements, and can therefore be used as a feature rather than a limitation. Liquid infiltration and retention are validated by time dependent optical imaging, Raman mapping of the water OH stretch band, and capacitance gradient mapping, consistent with liquid retention exceeding 10 h. This self-assembly process provides a lithography-free route to obtain 1D nanochannels and multi-junctions directly on-chip.
For the purposes of biomolecule confinement and imaging, however, such confinements alone do not guarantee clear optical readouts because wide-field imaging remains limited by fluorescence background from surface adsorbed molecules. This shortcoming motivated a background suppression strategy that we implement via vertical hBN/graphene stacks. By using few-layer hBN as a precise physical spacer between biomolecules and graphene, non-radiative energy transfer can be tuned in a predictable manner. This yields a parameter i.e. spacer thickness, that can be exploited to control the degree of quenching and fluorescence recovery. In this way, graphene suppresses unwanted background fluorescence from molecules adsorbed on hBN wrinkles, while preserving the emission from molecules confined deeper inside the wrinkle volumes. As a result, the imaging contrast is starkly improved.
Overall, this dissertation demonstrates how hBN emitter engineering, strain defined confinement, and interface controlled background suppression can be combined into a framework for high-throughput, fluorescence based biosensing using hBN, forming the first steps towards optical protein fingerprinting at 2D material interfaces. ...
We initially establish a microsphere-assisted femtosecond-laser approach to enhance light–matter interaction during defect formation and readout. By exploiting the combination of photonic nanojets with whispering gallery mode-assisted signal collection, the method enables deterministic emitter generation with improved spatial confinement and higher collection efficiency compared to microsphere-free processing. Specifically, the approach reduces the emission area by a factor of five and increases fluorescence collection efficiency by approximately tenfold.
A second result is the generation and characterization of hBN wrinkle networks in multilayer hexagonal boron nitride,which form from thermal expansion coefficient mismatch with the substrate during annealing. We demonstrate that wrinkles function as planar nanoscale confinements, and can therefore be used as a feature rather than a limitation. Liquid infiltration and retention are validated by time dependent optical imaging, Raman mapping of the water OH stretch band, and capacitance gradient mapping, consistent with liquid retention exceeding 10 h. This self-assembly process provides a lithography-free route to obtain 1D nanochannels and multi-junctions directly on-chip.
For the purposes of biomolecule confinement and imaging, however, such confinements alone do not guarantee clear optical readouts because wide-field imaging remains limited by fluorescence background from surface adsorbed molecules. This shortcoming motivated a background suppression strategy that we implement via vertical hBN/graphene stacks. By using few-layer hBN as a precise physical spacer between biomolecules and graphene, non-radiative energy transfer can be tuned in a predictable manner. This yields a parameter i.e. spacer thickness, that can be exploited to control the degree of quenching and fluorescence recovery. In this way, graphene suppresses unwanted background fluorescence from molecules adsorbed on hBN wrinkles, while preserving the emission from molecules confined deeper inside the wrinkle volumes. As a result, the imaging contrast is starkly improved.
Overall, this dissertation demonstrates how hBN emitter engineering, strain defined confinement, and interface controlled background suppression can be combined into a framework for high-throughput, fluorescence based biosensing using hBN, forming the first steps towards optical protein fingerprinting at 2D material interfaces. ...
Hexagonal boron nitride (hBN) has emerged as a unique platform for room temperature quantum photonics, yet translating its optically active defects into a practical single molecule sensing technology requires two stringent conditions: (i) deterministic and spatially controlled generation of emitters and (ii) engineering nanoscale confinement geometries that reliably bring labelled biomolecules in proximity to the hBN emitters while suppressing background fluorescence. This dissertation develops and connects these two capabilities through complementary routes based on optical and strain nano-engineering in layered hBN.
We initially establish a microsphere-assisted femtosecond-laser approach to enhance light–matter interaction during defect formation and readout. By exploiting the combination of photonic nanojets with whispering gallery mode-assisted signal collection, the method enables deterministic emitter generation with improved spatial confinement and higher collection efficiency compared to microsphere-free processing. Specifically, the approach reduces the emission area by a factor of five and increases fluorescence collection efficiency by approximately tenfold.
A second result is the generation and characterization of hBN wrinkle networks in multilayer hexagonal boron nitride,which form from thermal expansion coefficient mismatch with the substrate during annealing. We demonstrate that wrinkles function as planar nanoscale confinements, and can therefore be used as a feature rather than a limitation. Liquid infiltration and retention are validated by time dependent optical imaging, Raman mapping of the water OH stretch band, and capacitance gradient mapping, consistent with liquid retention exceeding 10 h. This self-assembly process provides a lithography-free route to obtain 1D nanochannels and multi-junctions directly on-chip.
For the purposes of biomolecule confinement and imaging, however, such confinements alone do not guarantee clear optical readouts because wide-field imaging remains limited by fluorescence background from surface adsorbed molecules. This shortcoming motivated a background suppression strategy that we implement via vertical hBN/graphene stacks. By using few-layer hBN as a precise physical spacer between biomolecules and graphene, non-radiative energy transfer can be tuned in a predictable manner. This yields a parameter i.e. spacer thickness, that can be exploited to control the degree of quenching and fluorescence recovery. In this way, graphene suppresses unwanted background fluorescence from molecules adsorbed on hBN wrinkles, while preserving the emission from molecules confined deeper inside the wrinkle volumes. As a result, the imaging contrast is starkly improved.
Overall, this dissertation demonstrates how hBN emitter engineering, strain defined confinement, and interface controlled background suppression can be combined into a framework for high-throughput, fluorescence based biosensing using hBN, forming the first steps towards optical protein fingerprinting at 2D material interfaces.
We initially establish a microsphere-assisted femtosecond-laser approach to enhance light–matter interaction during defect formation and readout. By exploiting the combination of photonic nanojets with whispering gallery mode-assisted signal collection, the method enables deterministic emitter generation with improved spatial confinement and higher collection efficiency compared to microsphere-free processing. Specifically, the approach reduces the emission area by a factor of five and increases fluorescence collection efficiency by approximately tenfold.
A second result is the generation and characterization of hBN wrinkle networks in multilayer hexagonal boron nitride,which form from thermal expansion coefficient mismatch with the substrate during annealing. We demonstrate that wrinkles function as planar nanoscale confinements, and can therefore be used as a feature rather than a limitation. Liquid infiltration and retention are validated by time dependent optical imaging, Raman mapping of the water OH stretch band, and capacitance gradient mapping, consistent with liquid retention exceeding 10 h. This self-assembly process provides a lithography-free route to obtain 1D nanochannels and multi-junctions directly on-chip.
For the purposes of biomolecule confinement and imaging, however, such confinements alone do not guarantee clear optical readouts because wide-field imaging remains limited by fluorescence background from surface adsorbed molecules. This shortcoming motivated a background suppression strategy that we implement via vertical hBN/graphene stacks. By using few-layer hBN as a precise physical spacer between biomolecules and graphene, non-radiative energy transfer can be tuned in a predictable manner. This yields a parameter i.e. spacer thickness, that can be exploited to control the degree of quenching and fluorescence recovery. In this way, graphene suppresses unwanted background fluorescence from molecules adsorbed on hBN wrinkles, while preserving the emission from molecules confined deeper inside the wrinkle volumes. As a result, the imaging contrast is starkly improved.
Overall, this dissertation demonstrates how hBN emitter engineering, strain defined confinement, and interface controlled background suppression can be combined into a framework for high-throughput, fluorescence based biosensing using hBN, forming the first steps towards optical protein fingerprinting at 2D material interfaces.
Journal article
(2025)
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Hande N. Açıkgöz, Dong Hoon Shin, Inge C. van der Knijff, Allard J. Katan, Xiliang Yang, Peter G. Steeneken, Gerard J. Verbiest, Sabina Caneva
High-frequency acoustic devices based on two-dimensional (2D) materials are emerging platforms to design and manipulate the spatiotemporal response of acoustic waves for next-generation sensing and contactless actuation applications. Conventional actuation methods, however, cannot be applied to all 2D materials, are frequency-limited or influenced by substrate interactions. Therefore, a universal, high-frequency, on-chip actuation technique is needed. Here, we demonstrate that surface acoustic waves (SAWs) can efficiently actuate suspended 2D materials by exciting suspended graphene membranes with high-frequency (375 MHz) Rayleigh waves and mapping the resulting vibration field with atomic force acoustic microscopy (AFAM), enabling direct visualization of wave propagation without substrate interference. Acoustic waves traveling from supported to suspended graphene experience a reduction in acoustic wavelength from 10 μm to ∼2 μm due to the decrease in effective bending rigidity, leading to a decrease in wave velocity on suspended graphene. By varying the excitation frequency through laser photothermal actuation (0-100 MHz) and SAW excitation (375 MHz), we observed a phase velocity change from ∼160 m/s to ∼700 m/s. This behavior is consistent with the nonlinear dispersion of acoustic waves, as predicted by plate theory, in suspended graphene membranes. The geometry and bending rigidity of the membrane thus play key roles in modulating the acoustic wave pattern and wavelength. This combined SAW actuation and AFAM visualization scheme advances the understanding of acoustic transport at the nanoscale limit and provides a route toward the manipulation of localized wavefields for on-chip patterning and transport over 2D materials surfaces.
...
High-frequency acoustic devices based on two-dimensional (2D) materials are emerging platforms to design and manipulate the spatiotemporal response of acoustic waves for next-generation sensing and contactless actuation applications. Conventional actuation methods, however, cannot be applied to all 2D materials, are frequency-limited or influenced by substrate interactions. Therefore, a universal, high-frequency, on-chip actuation technique is needed. Here, we demonstrate that surface acoustic waves (SAWs) can efficiently actuate suspended 2D materials by exciting suspended graphene membranes with high-frequency (375 MHz) Rayleigh waves and mapping the resulting vibration field with atomic force acoustic microscopy (AFAM), enabling direct visualization of wave propagation without substrate interference. Acoustic waves traveling from supported to suspended graphene experience a reduction in acoustic wavelength from 10 μm to ∼2 μm due to the decrease in effective bending rigidity, leading to a decrease in wave velocity on suspended graphene. By varying the excitation frequency through laser photothermal actuation (0-100 MHz) and SAW excitation (375 MHz), we observed a phase velocity change from ∼160 m/s to ∼700 m/s. This behavior is consistent with the nonlinear dispersion of acoustic waves, as predicted by plate theory, in suspended graphene membranes. The geometry and bending rigidity of the membrane thus play key roles in modulating the acoustic wave pattern and wavelength. This combined SAW actuation and AFAM visualization scheme advances the understanding of acoustic transport at the nanoscale limit and provides a route toward the manipulation of localized wavefields for on-chip patterning and transport over 2D materials surfaces.
Journal article
(2025)
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X. Yang, Dong Hoon Shin, Kenji Watanabe, Takashi Taniguchi, P.G. Steeneken, S. Caneva
Crystal defects in hexagonal boron nitride (hBN) are emerging as versatile nanoscale optical probes with a wide application profile, spanning the fields of nanophotonics, biosensing, bioimaging, and quantum information processing. However, generating these crystal defects as reliable optical emitters remains challenging due to the need for deterministic defect placement and precise control of the emission area. Here, we demonstrate an approach that integrates microspheres with hBN crystal lattices to enhance both hBN defect generation and optical signal readout. This technique harnesses microspheres to amplify light–matter interactions at the nanoscale through two mechanisms: focused femtosecond (fs) laser irradiation into a photonic nanojet (PNJ) for highly localized defect generation and enhanced light collection via the whispering gallery mode (WGM) effect. Our microsphere-assisted defect generation method reduces the emission area by a factor of 5 and increases the fluorescence collection efficiency by approximately 10 times compared to microsphere-free samples. These advancements in defect generation precision and signal collection efficiency open new possibilities for optical emitter manipulation in hBN, with potential applications in quantum technologies and nanoscale sensing.
...
Crystal defects in hexagonal boron nitride (hBN) are emerging as versatile nanoscale optical probes with a wide application profile, spanning the fields of nanophotonics, biosensing, bioimaging, and quantum information processing. However, generating these crystal defects as reliable optical emitters remains challenging due to the need for deterministic defect placement and precise control of the emission area. Here, we demonstrate an approach that integrates microspheres with hBN crystal lattices to enhance both hBN defect generation and optical signal readout. This technique harnesses microspheres to amplify light–matter interactions at the nanoscale through two mechanisms: focused femtosecond (fs) laser irradiation into a photonic nanojet (PNJ) for highly localized defect generation and enhanced light collection via the whispering gallery mode (WGM) effect. Our microsphere-assisted defect generation method reduces the emission area by a factor of 5 and increases the fluorescence collection efficiency by approximately 10 times compared to microsphere-free samples. These advancements in defect generation precision and signal collection efficiency open new possibilities for optical emitter manipulation in hBN, with potential applications in quantum technologies and nanoscale sensing.
Journal article
(2024)
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Xiliang Yang, Dong Hoon Shin, Ze Yu, Kenji Watanabe, Takashi Taniguchi, Vitaliy Babenko, Stephan Hofmann, Sabina Caneva
Fluorescence imaging is an invaluable tool to investigate biomolecular dynamics, mechanics, and interactions in aqueous environments. Two-dimensional materials offer large-area, atomically smooth surfaces for wide-field biomolecule imaging. Despite the success of graphene for on-chip biosensing and biomolecule manipulation, its strong fluorescence-quenching properties pose a challenge for biomolecular investigations that are based on direct optical readouts. Here, we employ few-layer hexagonal boron nitride (hBN) as a precisely tailorable fluorescence spacer between labelled lipid membranes and graphene substrates. By stacking high-quality hBN crystals in the 10–20 nm thickness range on monolayer graphene, we observe distance-dependent fluorescence intensity variations. Remarkably, with hBN spacers as thin as 20 nm, the fluorescence intensity is comparable to bare SiO2/Si substrates, while the intensity was reduced to 60 % and 80 % with ~10 nm and ~16 nm hBN thicknesses respectively. We confirm that pre-determined hBN thicknesses can be employed to control the non-radiative energy transfer properties of graphene, with fluorescence quenching following a d−4 distance-dependent behaviour. This seamless integration of electronically active and dielectric van der Waals materials into vertical heterostructures enables multifunctional platforms addressing the manipulation, localization, and visualization of biomolecules for fundamental biophysics and biosensing applications.
...
Fluorescence imaging is an invaluable tool to investigate biomolecular dynamics, mechanics, and interactions in aqueous environments. Two-dimensional materials offer large-area, atomically smooth surfaces for wide-field biomolecule imaging. Despite the success of graphene for on-chip biosensing and biomolecule manipulation, its strong fluorescence-quenching properties pose a challenge for biomolecular investigations that are based on direct optical readouts. Here, we employ few-layer hexagonal boron nitride (hBN) as a precisely tailorable fluorescence spacer between labelled lipid membranes and graphene substrates. By stacking high-quality hBN crystals in the 10–20 nm thickness range on monolayer graphene, we observe distance-dependent fluorescence intensity variations. Remarkably, with hBN spacers as thin as 20 nm, the fluorescence intensity is comparable to bare SiO2/Si substrates, while the intensity was reduced to 60 % and 80 % with ~10 nm and ~16 nm hBN thicknesses respectively. We confirm that pre-determined hBN thicknesses can be employed to control the non-radiative energy transfer properties of graphene, with fluorescence quenching following a d−4 distance-dependent behaviour. This seamless integration of electronically active and dielectric van der Waals materials into vertical heterostructures enables multifunctional platforms addressing the manipulation, localization, and visualization of biomolecules for fundamental biophysics and biosensing applications.