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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.

Some ongoing projects below:

 X-ray beam induced current

X-ray beam induced current (XBIC) in a single nanowire

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].  Recently, 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

3D reconstruction of a single nanowire within a device

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 nanowires [Wallentin 2017]. We have shown that the shape of bent nanowires can be reconstructed in 3D with nanometre precision (Figure above). 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 developing novel methods for coherent diffraction methods, which use phase retrieval to overcome the limit of the focusing optics.

Nanostructured X-ray detectors

The nanofocus at the P10 beamline imaged with a single nanowire

Traditional X-ray detectors use bulk crystals, which limits their resolution. We have shown that X-rays can be detected by single nanowires, with a stronger response expected [Wallentin 2014]. In this project, financed by an ERC Starting Grant, we are developing vertical arrays of nanowires as high-resolution X-ray detectors.

Phase contrast imaging
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. In this project, we are building a phase contrast tomograph based on a microfocus Cu source. 

Page Manager:

Research group

 

Zhaojun Zhang, postdoc
Lucas Marcal, postdoc
Lert Chayanun, PhD student
Susanna Hammarberg, PhD student
Hanna Dierks, PhD student

 

 

Publications

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

  1. 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
  2. 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
  3. 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
  4. L. Chayanun et al, Spectrally resolved X-ray beam induced current in a single InGaP nanowire Nanotechnology 29, 454001 (2018) doi.org/10.1088/1361-6528/aadc76
  5. 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
  6. 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
  7. 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
  8. J. Wallentin et al, Hard X-ray detection using a single 100 nm-diameter nanowire Nano Lett. 14 (12), 7071 (2014) http://dx.doi.org/10.1021/nl5040545