Strain Mapping of Single Nanowires using Nano X-ray Diffraction
Author
Summary, in English
Nanowires are explored as basic components for a large range of electronic devices. The nanowire format offers
several benefits, including reduced material consumption and increased potential for combining materials to form
new novel heterostructures. Several factors, such as mechanical stress from contacting or a lattice mismatch in a
heterostructure, can strain and change the lattice tilt. The strain is often intertwined with small gradients of
composition. The strain relaxation can differ significantly from bulk due to the small diameters, but the mechanisms
are not fully comprehended. X-rays have a penetrating power that makes it possible to investigate embedded
samples without preparation or slicing. The high flux of coherent X-ray beams from synchrotron radiation facilities,
combined with the nano-focus capabilities developed in recent years, have made it possible to probe nano-crystals.
The 4th generation of synchrotrons, including MAX IV in Lund, Sweden, has even higher brilliance than previous
sources. Diffraction imaging techniques using synchrotron radiation can reveal small strains down to 10-4-10-5. The
field of coherent imaging pushes the limits of resolutions below the size of the focus. With Bragg ptychography, the
displacement field in a crystal can be probed with resolution beyond the probe focus by numerically reconstructing
the phase.
This thesis includes the development of X-ray nano-diffraction methods for the characterizing of nanowires, including
GaInP/InP barcode nanowires, p-i-n InP nanowire devices and metal halide perovskite CsPbBr3 nanowires. It
includes a theoretical background of the scattering mechanisms in Thomson scattering in nano-crystals, goes
through the formalism for coherent diffraction imaging, crystal structure and deformation in nanoobjects and the
technical aspects of the experimental setup and measurement. Moreover, theoretical modelling of elastic strain
relaxation in these nanowires was performed with finite element modelling.
Single III-V nanowire heterostructures and III-V nanowire devices were probed with scanning XRD and Bragg
projection ptychography (BPP). How the techniques compare to each other and how the results are affected by the
different approximations that are made in the respective technique was explored. Finite element simulations
combined with nano-diffraction revealed that the lattice mismatch of 1.5% could be relaxed elastically for the
diameter of 180 nm. From the strain mapping of the nanowire device, we found how the contacting of the nanowire
bends the nanowire resulting in a tilt normal to the substrate.
Single perovskite metal-halide perovskite CsPb(Br(1-x)Clx)3 nanowire heterostructures were characterized with
scanning nano-XRD and XRF, which showed that the lattice spacing was affected by composition and strain.
Composition gradients revealed that Cl diffusion had taken place within the heterostructure. Furthermore, extracting
the lattice tilts from shifts of the Bragg peak revealed a ferroelastic domain structure with simultaneously existing
lattice tilts. These findings are beneficial for the further development of MHP nanowires devices.
several benefits, including reduced material consumption and increased potential for combining materials to form
new novel heterostructures. Several factors, such as mechanical stress from contacting or a lattice mismatch in a
heterostructure, can strain and change the lattice tilt. The strain is often intertwined with small gradients of
composition. The strain relaxation can differ significantly from bulk due to the small diameters, but the mechanisms
are not fully comprehended. X-rays have a penetrating power that makes it possible to investigate embedded
samples without preparation or slicing. The high flux of coherent X-ray beams from synchrotron radiation facilities,
combined with the nano-focus capabilities developed in recent years, have made it possible to probe nano-crystals.
The 4th generation of synchrotrons, including MAX IV in Lund, Sweden, has even higher brilliance than previous
sources. Diffraction imaging techniques using synchrotron radiation can reveal small strains down to 10-4-10-5. The
field of coherent imaging pushes the limits of resolutions below the size of the focus. With Bragg ptychography, the
displacement field in a crystal can be probed with resolution beyond the probe focus by numerically reconstructing
the phase.
This thesis includes the development of X-ray nano-diffraction methods for the characterizing of nanowires, including
GaInP/InP barcode nanowires, p-i-n InP nanowire devices and metal halide perovskite CsPbBr3 nanowires. It
includes a theoretical background of the scattering mechanisms in Thomson scattering in nano-crystals, goes
through the formalism for coherent diffraction imaging, crystal structure and deformation in nanoobjects and the
technical aspects of the experimental setup and measurement. Moreover, theoretical modelling of elastic strain
relaxation in these nanowires was performed with finite element modelling.
Single III-V nanowire heterostructures and III-V nanowire devices were probed with scanning XRD and Bragg
projection ptychography (BPP). How the techniques compare to each other and how the results are affected by the
different approximations that are made in the respective technique was explored. Finite element simulations
combined with nano-diffraction revealed that the lattice mismatch of 1.5% could be relaxed elastically for the
diameter of 180 nm. From the strain mapping of the nanowire device, we found how the contacting of the nanowire
bends the nanowire resulting in a tilt normal to the substrate.
Single perovskite metal-halide perovskite CsPb(Br(1-x)Clx)3 nanowire heterostructures were characterized with
scanning nano-XRD and XRF, which showed that the lattice spacing was affected by composition and strain.
Composition gradients revealed that Cl diffusion had taken place within the heterostructure. Furthermore, extracting
the lattice tilts from shifts of the Bragg peak revealed a ferroelastic domain structure with simultaneously existing
lattice tilts. These findings are beneficial for the further development of MHP nanowires devices.
Publishing year
2023
Language
English
Full text
Document type
Dissertation
Publisher
Lund University
Topic
- Condensed Matter Physics
- Accelerator Physics and Instrumentation
Keywords
- Nanotrådar
- X-ray Diffraction
- Strain mapping
- XRF
- III-V nanowire
- perovskite nanowires
- Diffraction
- Nanowires
- Strain mapping
- XRD
- XRF
- MAX IV
Status
Published
Project
- Strain Mapping of Single Nanowires using Nano X-ray Diffraction
Supervisor
- Jesper Wallentin
- Anders Mikkelsen
- Alexander Björling
ISBN/ISSN/Other
- ISBN: 978-91-8039-654-7
- ISBN: 978-91-8039-653-0
Defence date
2 June 2023
Defence time
09:15
Defence place
Rydbergsalen
Opponent
- Thomas Cornelius (Dr)