characterization

Nanoscale resolved mapping of the dipole emission of hBN color centers with a scattering-type scanning near-field optical microscope

Color centers in hexagonal boron nitride (hBN) are promising candidates as quantum light sources for future technologies. *

In the article “Nanoscale resolved mapping of the dipole emission of hBN color centers with a scattering-type scanning near-field optical microscope “, Iris Niehues, Daniel Wigger, Korbinian Kaltenecker, Annika Klein-Hitpass , Philippe Roell, Aleksandra K. Dąbrowska, Katarzyna Ludwiczak, Piotr Tatarczak, Janne O. Becker , Robert Schmidt, Martin Schnell, Johannes Binder, Andrzej Wysmołek and Rainer Hillenbrand utilize a scattering-type near-field optical microscope (s-SNOM) to study the photoluminescence (PL) emission characteristics of such quantum emitters in metalorganic vapor phase epitaxy grown hBN. *

On the one hand, Iris Niehues et al. demonstrate direct near-field optical excitation and emission through interaction with the nanofocus of the AFM tip resulting in a subdiffraction limited tip-enhanced PL hotspot. *

On the other hand, the authors show that indirect excitation and emission via scattering from the AFM tip significantly increases the recorded PL intensity. This demonstrates that the tip-assisted PL (TAPL) process efficiently guides the generated light to the detector. *

Iris Niehues et al. apply the TAPL method to map the in-plane dipole orientations of the hBN color centers on the nanoscale. This work promotes the widely available s-SNOM approach to applications in the quantum domain including characterization and optical control. *

The investigation utilizes a scattering-type near-field optical microscope employing a metallized Arrow AFM tip ( NanoWorld Arrow-NCPt AFM probe) illuminated by monochromatic laser light. *

The AFM tip acts as an optical antenna, transforming the incident p-polarizedlight into a highly focused near field at the AFM tip apex, the so-called nanofocus. *

The nanofocus interacts with the sample leading to modified scattering from the AFM tip and encoding local sample properties.

In conventional s-SNOM operation, the elastically scattered light is recorded as function of sample position (note that the sample is scanned), yielding near-field optical images with a spatial resolution down to 10 nm. *

To supress background scattering, the AFM is operated in tapping mode and the detector signal is demodulated at a higher harmonic of the AFM tip’s oscillation frequency. *

In the article, Iris Niehues et al. use the s-SNOM instrument to study PL from individual hBN color centers. *

To that end, the inelastically tip-scattered light is recorded with a grating spectrometer coupled to a CCD camera. Note that signal demodulation has not been possible with the use of a CCD camera so far. It may be achieved employing a photomultiplier tube or similar. Importantly, the authors’ s-SNOM setup includes a high-quality, silver-protected off-axis parabolic mirror with a numerical aperture (NA) of 0.72, which optimizes the focusing and collection efficiency of the optical system and is crucial for the performed PL measurements. *

Characterization of photoluminescence mapping

In the specific experiments performed by “, Iris Niehues et al., the authors employ the near-field optical microscope in tapping mode, with low oscillation amplitudes between 20 nm and 30 nm, to detect PL signals influenced by the presence of the metallic AFM tip. *

They use standard metallic Arrow AFM tips (NanoWorld Arrow-NCPt) Throughout this study, Iris Niehues et al., use a 532 nm (2.33 eV) laser for the optical excitation of the hBN color centers. *

Figure 1 from Iris Niehues et al. 2025 “Nanoscale resolved mapping of the dipole emission of hBN color centers with a scattering-type scanning near-field optical microscope” :Photoluminescence (PL) measurement of a single color center taken with an AFM tip. The images are shown with the same color bar for better comparison of the observed PL intensities. (a) PL intensity map without the tip showing a diffraction limited emission spot. (b) PL spectrum of the studied emitter recorded with an extended integration time inside the arc in (c). The zero-phonon line (ZPL) and optical phonon sidebands (PSBs) of 160 meV are marked as well as the broad background PL (black line). (c) PL map of the same emitter with the AFM tip showing two subdiffraction limit features marked as “dot” and “arc.” (d) Lineprofiles along the dashed lines in (a) in black and (c) in red (dark measurement, bright Gaussian fits). The fitted full widths at half maximum (FWHM) are 110 nm (dot), 209 nm (arc), and 1,418 nm (w/o tip). (e) Schematic of the interference between direct and indirect excitation/emission of the color center via the AFM tip (TAPL). Inset shows the nanofocus interaction at the location of the color center explaining the dot (TEPL). (f) Analytical reproduction of the TAPL arc in (c) applying the model in (e). NanoWorld Arrow-NCPt AFM probes with a platinum iridium coating were used. — Figure 1 from Iris Niehues et al. 2025 “Nanoscale resolved mapping of the dipole emission of hBN color centers with a scattering-type scanning near-field optical microscope” :
Photoluminescence (PL) measurement of a single color center taken with an AFM tip. The images are shown with the same color bar for better comparison of the observed PL intensities. (a) PL intensity map without the tip showing a diffraction limited emission spot. (b) PL spectrum of the studied emitter recorded with an extended integration time inside the arc in (c). The zero-phonon line (ZPL) and optical phonon sidebands (PSBs) of 160 meV are marked as well as the broad background PL (black line). (c) PL map of the same emitter with the AFM tip showing two subdiffraction limit features marked as “dot” and “arc.” (d) Lineprofiles along the dashed lines in (a) in black and (c) in red (dark measurement, bright Gaussian fits). The fitted full widths at half maximum (FWHM) are 110 nm (dot), 209 nm (arc), and 1,418 nm (w/o tip). (e) Schematic of the interference between direct and indirect excitation/emission of the color center via the AFM tip (TAPL). Inset shows the nanofocus interaction at the location of the color center explaining the dot (TEPL). (f) Analytical reproduction of the TAPL arc in (c) applying the model in (e).

*Iris Niehues, Daniel Wigger, Korbinian Kaltenecker, Annika Klein-Hitpass , Philippe Roell, Aleksandra K. Dąbrowska, Katarzyna Ludwiczak, Piotr Tatarczak, Janne O. Becker , Robert Schmidt, Martin Schnell, Johannes Binder, Andrzej Wysmołek and Rainer Hillenbrand
Nanoscale resolved mapping of the dipole emission of hBN color centers with a scattering-type scanning near-field optical microscope
Nanophotonics, vol. 14, no. 3, 2025, pp. 335-342
DOI: https://doi.org/10.1515/nanoph-2024-0554

Open Access The article “Nanoscale resolved mapping of the dipole emission of hBN color centers with a scattering-type scanning near-field optical microscope” by Iris Niehues, Daniel Wigger, Korbinian Kaltenecker, Annika Klein-Hitpass , Philippe Roell, Aleksandra K. Dąbrowska, Katarzyna Ludwiczak, Piotr Tatarczak, Janne O. Becker , Robert Schmidt, Martin Schnell, Johannes Binder, Andrzej Wysmołek and Rainer Hillenbrand is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

NanoWorld at MRS Fall Meeting & Exhibit 2024 this week

NanoWorld CEO Manfred Detterbeck is in Boston for the MRS Fall 2024 Meeting & Exhibit this week.
You’ll meet him at some of the sessions or at NanoAndMore USA booth no. 402.

If you’re there too feel free to say hi and have a chat about #AFMprobes with him.

Happy to be at MRS Fall 2024. Hope to see many of you here.

Real-time multistep asymmetrical disassembly of nucleosomes and chromatosomes visualized by high-speed atomic force microscopy

During replication, expression, and repair of the eukaryotic genome, cellular machinery must access the DNA wrapped around histone proteins forming nucleosomes. These octameric protein·DNA complexes are modular, dynamic, and flexible and unwrap or disassemble either spontaneously or by the action of molecular motors. Thus, the mechanism of formation and regulation of subnucleosomal intermediates has gained attention genome-wide because it controls DNA accessibility.*

In the article “Real-Time Multistep Asymmetrical Disassembly of Nucleosomes and Chromatosomes Visualized by High-Speed Atomic Force Microscopy” Bibiana Onoa, César Díaz-Celis, Cristhian Cañari-Chumpitaz, Antony Lee and Carlos Bustamante describe how they imaged nucleosomes and their more compacted structure with the linker histone H1 (chromatosomes) using high-speed atomic force microscopy to visualize simultaneously the changes in the DNA and the histone core during their disassembly when deposited on mica.*

Furthermore, Bibiana Onoa et al. trained a neural network and developed an automatic algorithm to track molecular structural changes in real time. *

The authors’ results show that nucleosome disassembly is a sequential process involving asymmetrical stepwise dimer ejection events. The presence of H1 restricts DNA unwrapping, significantly increases the nucleosomal lifetime, and affects the pathway in which heterodimer asymmetrical dissociation occurs. *

Bibiana Onoa et al. observe that tetrasomes are resilient to disassembly and that the tetramer core (H3·H4)2 can diffuse along the nucleosome positioning sequence. Tetrasome mobility might be critical to the proper assembly of nucleosomes and can be relevant during nucleosomal transcription, as tetrasomes survive RNA polymerase passage. These findings are relevant to understanding nucleosome intrinsic dynamics and their modification by DNA-processing enzymes. *

To characterize the nucleosomes dynamics in 2D, individual molecules were observed in buffer using an Ando-type high speed atomic force microscope together with NanoWorld Ultra-Short Cantilevers for HS-AFM of the USC-F1.2-K0.15 AFM probe type ( typical spring constant 0.15 N/m, typical resonance frequency in air 1200 kHz, resonance frequency 500–600 kHz in liquid). *

The AFM data presented in the article allow the authors to directly visualize the dynamics of DNA and histones during nucleosome and chromatosome disassembly, providing a simultaneous observation of DNA unwrapping and histone dissociation. *

The experimental and analytical strategy presented shows that real-time HS-AFM is a robust and powerful tool for studying single nucleosomes and chromatin dynamics. *

graphical abstract from Bibiana Onoa et al 2024 "Real-Time Multistep Asymmetrical Disassembly of Nucleosomes and Chromatosomes Visualized by High-Speed Atomic Force Microscopy" - NanoWorld Ultra-Short Cantilevers of the USC-F1.2-k0.15 AFM probe type were used for the high-speed atomic force microscopy — graphical abstract from Bibiana Onoa et al 2024 “Real-Time Multistep Asymmetrical Disassembly of Nucleosomes and Chromatosomes Visualized by High-Speed Atomic Force Microscopy”

*Bibiana Onoa, César Díaz-Celis, Cristhian Cañari-Chumpitaz, Antony Lee and Carlos Bustamante
Real-Time Multistep Asymmetrical Disassembly of Nucleosomes and Chromatosomes Visualized by High-Speed Atomic Force Microscopy
ACS Central Science 2024, 10, 1, 122–137
DOI: https://doi.org/10.1021/acscentsci.3c00735

Open Access The article “Real-Time Multistep Asymmetrical Disassembly of Nucleosomes and Chromatosomes Visualized by High-Speed Atomic Force Microscopy” by Bibiana Onoa, César Díaz-Celis, Cristhian Cañari-Chumpitaz, Antony Lee and Carlos Bustamante is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.