Nexray: Network of integrated miniaturized X-ray systems operating in complex environments

Pierangelo Gröning of EMPA Thun/Schutz, expert in plasma deposition of organic molecules

Hans von Kaenel of ETHZ/D-PHYS/SOLID/Physics of New Materials, expert in low-dimensional magnetism. liquid crystals. semiconductor photoelectro-chemistry. epitaxial interfaces and surfaces. scanning probe techniques. epitaxial growth

This project targets at the development of novel pocket X-ray sources and X-ray direct detectors that will be combined in a distributed network to solve important tasks. The miniaturised X-ray sources are based on multi-wall carbon nanotube (CNT) cold electron emitters and advanced microsystems technology. The electron field emission properties of CNTs with their high current densities make them prime candidates for cold emitter cathodes. Due to their small (nanometer) diameter and large aspect ratio, CNTs show a large electrical field enhancement factor and consequently a low threshold voltage for electron extraction. With using CNT cold electron emitters it will be possible to miniaturise the whole X-ray source. Additionally as opposed to classical thermionic emission, field electron emission of the CNT is voltage controlled which allows for high modulation frequencies up to GHz level. For modulations in the GHz level a additional grid will be required.

The X-ray direct detectors in turn are based on crystalline Germanium absorption layers grown directly on a CMOS sensor chip yielding high resolution and high sensitivity X-ray detectors. Single photon detection will allow for a significant improvement of contrast for applications in security, health care and non destructive testing. Moreover, the direct integration of germanium absorption layers into CMOS sensors results in on-pixel signal pre-processing capabilities which can be exploited for various application. 

Radical new approaches to X-ray imaging will be addressed and demonstrated, including:

X-ray time-of-flight (xTOF) measurements to probe the depth inside objects. This calls for an intensity modulated X-ray signal in the MHz range which is not possible with conventional X-ray sources but can be achieved with CNT based cold emitters, for which modulation frequencies up to the GHz level were already reported. In combination with dedicated CMOS image sensors and data-pre-processing already at the pixel level, potentially new 3D X-ray imaging instruments can be realised.

Tomographic imaging that make use of the fact that both the X-ray source and the X-ray detector are pixelated: the fact that a X-ray source is built as a matrix of micro X-ray sources that also can be addressed and controlled individually is very novel and the combination of pixelated X- ray sources and detectors brings up completely new imaging capabilities, in particular the possibility to do static tomographic imaging and reduce therefore costs or increase throughput. This project is expected to set a novel technological base and platform which will lead to high benefits notably in the fields of security and health care, contributing thus to the well being of humans.

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