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Jesper Wallentin

Our research concerns the intersection of nanoscience and X-ray science. We use X-rays to investigate nanostructured devices, and we develop nanostructures as X-ray detectors. We have a strong collaboration with the Nanomax beamline at MAX IV, and we also visit other synchrotrons for experiments. Most of the projects also involve colleagues in NanoLund, and we are frequent users of the Lund Nano Lab.

We can offer many kinds of different MSc and BSc thesis projects, focusing on X-ray analysis, data analysis or nanofabrication. Please contact Jesper for more information. You can find a non-exhaustive list of ideas for projects under the headline "Semiconductor nanostructure analysis" here.

Some ongoing research projects are described below:

 

Growth of metal halide perovskite nanowires for X-ray detection applications

 

CsPbBr3 metal halide perovskite nanowire X-ray detectors. Left: Cross-sectional SEM. Middle: Photoluminescence [Zhang 2021]. Right: X-ray image of test pattern with 2 micron lines[Zhang 2022].

Metal halide perovskites are most famous for their rapid development in solar cells, but they are also promising materials for X-ray scintillation detectors. We are synthesizing CsPbBr3 nanowire arrays using solution growth, by using anodized aluminum oxide nanopores as templates. Our first paper in this project  [Zhang 2021] showed that the nanowires have an impressive stability to air exposure, with samples exposed to air for 4 months still exhibiting comparable photoluminescence and UV stability to fresh samples. The second paper demonstrated high-resolution X-ray imaging using these structures [Zhang 2022], with excellent radiation stability.

Free-standing metal halide perovskite nanowires devices and heterostructures

Freestanding CsPbBr3 nanowires. Left: Cross-sectional SEM of as-grown nanowires. Middle: Cross-sectional optical microscopy (not false colored) of blue-green CsPbCl1.1Br1.9-CsPbBr3 heterostructured nanowires [Zhang 2022]. Single nanowire transistor [Lamers 2022].

We have discovered a method to grow free-standing vertically aligned CsPbBr3 metal halide perovskites [Zhang 2022]. Part of the nanowires can be converted to blue-emitting CsPbCl1.1Br1.9. MHPs are soluble in polar solvents, which makes normal lithography processing schemes difficult to use. However, we have found a method to perform electron beam lithography (EBL) using only non-polar solvents [Lamers 2022]

Nanostructured X-ray detectors and X-ray beam induced current (XBIC)

Left: The nanofocus at the NanoMax beamline, MAX IV, Lund [Chayanun 2020], imaged with a single nanowire. Right: X-ray beam induced current (XBIC) in a single nanowire [Chayanun 2019].

Traditional X-ray detectors use bulk crystals, which limits their resolution. In this project, financed by an ERC Starting Grant, we are developing vertical arrays of nanowires as high-resolution X-ray detectors. We have shown that X-rays can be detected by single nanowires, with much higher spatial resolution than commercial systems [Chayanun 2020].

X-rays that are absorbed in a semiconductor excite electrons over the bandgap, and in the presence of an internal or external electric field the electrons will generate a measurable current. With a nanofocused X-ray beam, we can locally probe the electronic properties of semiconductor devices. We have shown that X-rays can be used to image the carrier collection within single nanowire solar cells [Chayanun 2019].  We also demonstrated that scanning X-ray fluorescence can be used for mapping Zn dopants in InP nanowires with 50 nm resolution [Troian 2018].

 

Coherent X-ray diffraction of nanocrystals and nanoscale devices

          

3D strain simulation and measurement of axially heterostructured nanowire [Hammarberg 2020].

X-ray diffraction can be used to study strain, piezoelectricity and heating in crystalline samples. Modern X-ray optics can reach below 100 nm focus size, which we have used to study core-shell [Wallentin 2017] and axially hetereostructured nanowires [Hammarberg 2020]. We have shown that the shape of bent nanowires can be reconstructed in 3D with nanometre precision [Wallentin 2017]. Hard X-rays can penetrate through thick samples, allowing measurements of operational devices [Wallentin 2016]. The intensity of focused X-rays can lead to beam damage, and we have studied beam induced heating of nanostructured samples [Wallander 2017]. We are also developing novel methods for coherent diffraction methods, which use phase retrieval to overcome the limit of the focusing optics. Recently, we showed how the uncontrolled rotation of 60 nm nanoparticles could be used for 3D strain imaging [Björling 2020].

X-ray imaging of ferroelastic domains

Left: Imaging of ferroelastic domain dynamics in a CsPbBr3 perovskite nanowire as the temperature is ramped across a phase transition [Marcal 2020]. The Bragg peak and the domain pattern change as the temperature crosses the orthorhombic to tetragonal phase transition at 80C. Right: 3D reconstruction of two ferroelastic domains in a CsPbBr3 nanoparticle [Dzhigaev 2021]

We have recently shown that it is possible to image ferroelastic domains inside nanowires of the metal halide perovskite CsPbBr3 [Marcal 2020]. A presentation by Lucas Marcal on these results can be found here. Similar methods can be used to image ferrolastic domains induced by AFM [Marcal 2021]. Recently, we demonstrated 3D imaging of ferroelastic domains in CsPbBr3 nanoparticles [Dzhigaev 2021]. A presentation about these results can be found here. Dmitry Dzhigaev has also made a longer presentation about the method, Bragg Coherent Diffraction Imaging, found here.

Phase contrast tomography


In this project, we have built a phase contrast X-ray tomograph based on a microfocus Cu source. Traditional X-ray imaging is based on absorption contrast, which has poor contrast for small and weakly absorbing samples. Much better contrast can be achieved using phase contrast. The system is based on a microfocus X-ray source with a Cu target, a high-resolution detector and a high-precision sample stage. It's capable of X-ray absorption contrast and phase contrast imaging at a spatial resolution of about 1 micrometer in 2D and 3D. The image above shows part of a blueberry seed. We have recently published our first results: [Dierks 2020]

Research group

 

Postdocs:
Zhaojun Zhang
Lucas Marcal
Dmitry Dzhigaev
PhD students:
Susanna Hammarberg
Hanna Dierks
Nils Lamers
Huaiyu Chen
Alumni:
Lert Chayanun, currently postdoc at Chalmers University

Publications

For an updated and complete list of publications, please see Google Scholar. A selected list of recent work:

  1. Z. Zhang, N. Lamers, C. Sun, C. Hetherington, I. G. Scheblykin, and J. Wallentin, "Free-Standing Metal Halide Perovskite Nanowire Arrays with Blue-Green Heterostructures"  Nano Lett. (2022) http://doi.org/10.1021/acs.nanolett.2c00137
  2. Z. Zhang, H. Dierks, N. Lamers, C. Sun, K. Nováková, C. Hetherington, I. G. Scheblykin, and J. Wallentin, "Single-Crystalline Perovskite Nanowire Arrays for Stable X-ray Scintillators with Micrometer Spatial Resolution"  ACS Applied Nano Materials 5 (1), 881 (2022) http://doi.org/10.1021/acsanm.1c03575
  3. D. Dzhigaev et al., "Three-dimensional coherent x-ray diffraction imaging of ferroelastic domains in single CsPbBr3 perovskite nanoparticles"  New J. Phys. 23 (6), 063035 (2021) http://doi.org/10.1088/1367-2630/ac02e0
  4. A. Björling,et al., "Three-Dimensional Coherent Bragg Imaging of Rotating Nanoparticles"  Phys. Rev. Lett. 125 (24), 246101 (2020) http://dx.doi.org/10.1103/PhysRevLett.125.246101
  5. L Chayanun et al., "Direct Three-Dimensional Imaging of an X-ray Nanofocus Using a Single 60 nm Diameter Nanowire Device" Nano Letters 20 (11) 8326 (2020) https://doi.org/10.1021/acs.nanolett.0c03477
  6. L. A. B. Marcal et al., "In Situ Imaging of Ferroelastic Domain Dynamics in CsPbBr3 Perovskite Nanowires by Nanofocused Scanning X-ray Diffraction" ACS Nano 14 (11), 15973 (2020)
    https://doi.org/10.1021/acsnano.0c07426
  7. H. Dierks and J. Wallentin, "Experimental optimization of X-ray propagation-based phase contrast imaging geometry"  Opt. Express 28 (20), 29562-29575 (2020) dx.doi.org/10.1364/OE.399819
  8. S Hammarberg et al., "High resolution strain mapping of a single axially heterostructured nanowire using scanning X-ray diffraction", Nano Res. 13 (9), 2460 (2020) http://doi.org/10.1007/s12274-020-2878-6
  9. L. Chayanun et al.: "Combining Nanofocused X-Rays with Electrical Measurements at the NanoMAX Beamline"  Crystals 9 (8), 432 (2019) http://dx.doi.org/10.3390/cryst9080432
  10. L Chayanun et al.: Nanoscale mapping of carrier collection in single nanowire solar cells using X-ray beam induced current J. Synchrotron Radiat. 26 (1) (2019) doi.org/10.1107/S1600577518015229
  11. A. Troian et al, Nanobeam X-ray fluorescence dopant mapping reveals dynamics of in situ Zn-doping in nanowires Nano Lett. 18 (10), 6461 (2018) dx.doi.org/10.1021/acs.nanolett.8b02957
  12. H. Wallander and J. Wallentin, Simulated sample heating from a nanofocused X-ray beam
    J. Synchrotron Radiat. 24 (5) (2017) doi.org/10.1107/S1600577517008712
  13. J. Wallentin et al., Bending and twisted lattice tilt in strained core-shell nanowires revealed by nanofocused X-ray diffraction Nano Lett. 17 (7) (2017) dx.doi.org/10.1021/acs.nanolett.7b00918
  14. J. Wallentin, M. Osterhoff, and T. Salditt, In operando X-ray diffraction reveals electrically induced strain and bending in single nanowire device Adv. Mater. 28 (9), 1788 (2016) http://dx.doi.org/10.1002/adma.201504188

Financing

  • European Research Council, ERC, Starting Grant WIREDETECT, 801847
  • Stiftelsen Olle Engkvist Byggmästare, Swedish Foundations' Starting Grant
  • Röntgen-Ångström Cluster grant, together with Tim Saditt in Göttingen, Germany, and Magnus Borgström in Lund
  • Swedish Research Council (VR)
  • Crafoord
  • NanoLund