Periodic Reporting for period 4 - WIREDETECT (High resolution X-ray detectors based on nanowire arrays)
Berichtszeitraum: 2023-08-01 bis 2024-07-31
In this project we are developing ultra-high resolution X-ray detectors based on semiconductor nanowires, whose spatial resolution will be radically better than the current state of the art. In X-ray detectors the primary X-ray absorption induces a cascade of secondary electrons and photons which are measured at the front or back of the detector, but during the long transport to the point of detection these can spread orthogonally to the optical axis. This limits the resolution in present bulk detectors.
The concept of WIREDETECT is to create a nanostructured detector based on an array of semiconductor nanowires, which will confine and physically prevent spreading of the secondary electrons and photons. In a nanowire array, the pixel size is the diameter of the nanowire, which can be as low as 10 nm, while the nanowires can be as long as the X-ray absorption length. The very high aspect ratio of nanowires allows detectors with simultaneously very high spatial resolution and sensitivity. I will investigate both direct detectors and scintillators, in which the secondary electrons and photons are detected, respectively.
The objective is to create detectors based on arrays of 10 nm-diameter nanowires. Time- and temperature resolved measurements will be used to improve understanding of the X-ray physics in these nanodevices, with strong quantum confinement of electrons and phonons and high surface to volume ratio. I will test the detectors within an imaging project targeting the neural connectome, and compare the nanowire detectors with commercial ones.
The conclusion of the project was that we were able to build ultra-high resolution X-ray detectors based on semiconductor nanowires, both indirect and direct type detectors. We achieved record-high spatial resolutions, reaching 60 nm for the direct type and about 2 micron for the indirect type. We also made several unexpected discoveries regarding the crystal growth and crystal structure of perovskites.
The concept of WIREDETECT is to create a nanostructured detector based on an array of semiconductor nanowires, which will confine and physically prevent spreading of the secondary electrons and photons. In a nanowire array, the pixel size is the diameter of the nanowire, which can be as low as 10 nm, while the nanowires can be as long as the X-ray absorption length. The very high aspect ratio of nanowires allows detectors with simultaneously very high spatial resolution and sensitivity. I will investigate both direct detectors and scintillators, in which the secondary electrons and photons are detected, respectively.
The objective is to create detectors based on arrays of 10 nm-diameter nanowires. Time- and temperature resolved measurements will be used to improve understanding of the X-ray physics in these nanodevices, with strong quantum confinement of electrons and phonons and high surface to volume ratio. I will test the detectors within an imaging project targeting the neural connectome, and compare the nanowire detectors with commercial ones.
The conclusion of the project was that we were able to build ultra-high resolution X-ray detectors based on semiconductor nanowires, both indirect and direct type detectors. We achieved record-high spatial resolutions, reaching 60 nm for the direct type and about 2 micron for the indirect type. We also made several unexpected discoveries regarding the crystal growth and crystal structure of perovskites.
Most of the work has been devoted to making devices of the two types, direct detectors and scintillators. The direct detector subproject has made steady progress, focusing on the single-nanowire detector. In the end of 2019, we successfully made the first vertical nanowire detector. The device was tested at the NanoMax beamline, MAX IV synchrotron in Lund, Sweden. We demonstrated imaging using the 60 nm-diameter nanowire detector, with by far the best spatial resolution of any X-ray detector. The results were published in Nano Letters in 2020. The subproject has recently focused on optimization of the single-nanowire device and applications in the optical regime.
The scintillator subproject has also been successful. The first nanowire arrays were grown in 2020 and then optimized with respect to efficiency and resolution. These are some of the highest-resolution detectors ever reported for a perovskite detector. A significant amount of time and money has been spent on developing the X-ray detector lab. The original plan was to design a home-built system. However, we instead managed to find a very favourable solution from a supplier, that saved a lot of time. This system has been successfully used for measuring the spectra and spatial resolution of perovskite nanowire scintillators since the spring 2021. We have been able to use to scintillator detectors for high-resolution imaging in 2D and 3D.
The scintillator subproject has also been successful. The first nanowire arrays were grown in 2020 and then optimized with respect to efficiency and resolution. These are some of the highest-resolution detectors ever reported for a perovskite detector. A significant amount of time and money has been spent on developing the X-ray detector lab. The original plan was to design a home-built system. However, we instead managed to find a very favourable solution from a supplier, that saved a lot of time. This system has been successfully used for measuring the spectra and spatial resolution of perovskite nanowire scintillators since the spring 2021. We have been able to use to scintillator detectors for high-resolution imaging in 2D and 3D.
The project has made substantial progress beyond the state of the art. Some of the most interesting results were close to the original plan, while others were unexpected.
Some of the highlights which are in line with the proposal:
- We demonstrated imaging using a single 60 nm-diameter InP nanowire detector, with by far the best spatial resolution of any X-ray detector and about 1000 times better than commercial direct detectors.
- We have achieved some of the highest-resolution perovskite scintillator X-ray images
- We made the first high-resolution 3D X-ray images using a perovskite scintillator.
In addition, we have made some unexpected discoveries:
- We have done significant work on understanding the basic properties of the CsPbBr3 perovskite material. We have studied the ferroelastic domain dynamics using state of the X-ray methods, where we observe both reversible and irreversible processes.
- We have discovered a method to grow free-standing perovskite nanowires
- We have made substantial contributions to perovskite processing methods, with a new electron beam lithography process and a gas-phase ion exchange process to create heterostructures
Some of the highlights which are in line with the proposal:
- We demonstrated imaging using a single 60 nm-diameter InP nanowire detector, with by far the best spatial resolution of any X-ray detector and about 1000 times better than commercial direct detectors.
- We have achieved some of the highest-resolution perovskite scintillator X-ray images
- We made the first high-resolution 3D X-ray images using a perovskite scintillator.
In addition, we have made some unexpected discoveries:
- We have done significant work on understanding the basic properties of the CsPbBr3 perovskite material. We have studied the ferroelastic domain dynamics using state of the X-ray methods, where we observe both reversible and irreversible processes.
- We have discovered a method to grow free-standing perovskite nanowires
- We have made substantial contributions to perovskite processing methods, with a new electron beam lithography process and a gas-phase ion exchange process to create heterostructures