This project targets 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, for example in the field of security, by ensuring reliable and real-time monitoring of failure sensitive parts in large manufacturing plants or in public transportation.
The miniaturized 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. Using CNT cold electron emitters will make it possible to miniaturize 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. 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 nondestructive testing.
1. Nexray A. Dommann A , H. von Känel C , P. Gröning B , N. Blanc A , C. A. Bosshard A , A. D. Brenzikofer A , S. Giudice A , R. Jose James A , R. Kaufmann A , C. Kottler A , C. Lotto A , A. Neels A , P. Niedermann A , P. Seitz A , G. Spinola Durante A , C. Urban A , H.R. Elsener B , O. Gröning B , B. Batlogg C , C.V. Falub C , K. Mattenberger C , E. Müller C , P. Wägli C Bern, 13. 5. 2011 A: CSEM; B: EMPA, C: ETHZ Network of integrated miniaturized X-ray systems operating in complex environments
2. A system approach Source Sample Detector Contrast mechanism Resolution, Size, Efficiency Spectrum, power, Coherence, Size Miniaturized, fast and programmable X-ray sources Phase contrast X-ray imaging Direct X-ray detectors Breakthroughs in all key building blocks of X-ray systems: Sources, Contrast mechanism and Detectors
3. Network of integrated miniaturized X-ray systems operating in complex environments Single-photon solid-state X-ray detection Si-Ge layers for high-energy X-ray detection Phase contrast X-ray imaging Miniaturized, fast and programmable X-ray sources
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7. A system approach Source Sample Detector Contrast mechanism Resolution, Size, Efficiency Spectrum, power, Coherence, Size Miniaturized, fast and programmable X-ray sources Phase contrast X-ray imaging Direct X-ray detectors
9. Plasma Enhanced-CVD growth of CNTs Utilization of a Plasma during deposition allows the growth of vertically oriented CNTs Ni dot of Da = 70 nm -> catalyst for growth of straight CNTs TiN for homogenisation of CNTs electron emission
15. Emission characteristics: longtime-stability Applied elec. field 20, 100, 500 µA Longtime measurement: 13 h Distance: 20 µm Emission current: 50 µA (constant) I-V measurement after longtime test
16. A system approach Source Sample Detector Contrast mechanism Resolution, Size, Efficiency Spectrum, power, Coherence, Size Miniaturized, fast and programmable X-ray sources Phase contrast X-ray imaging Direct X-ray detectors
17. Low-Energy Plasma-Enhanced CVD (LEPECVD) • Electrons emitted by a hot filament sustain a DC plasma • Low (~10eV) ion energy – no ion damage • Discharge confined by a magnetic field (~1 mT) • Deposition rates 0.01-10nm/s depending on gas flow and plasma density • Gas phase precursors: SiH 4 , GeH 4
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21. INNOVATION: Self-aligned epitaxial Ge crystals Micromachined Si pillars Epitaxial Ge pillars on Si Ge Si 5 m Ge ~30 m No limitation for layer thickness!
22. INNOVATION: Selective Epitaxy on pre-patterned Si Ge fully relaxed Ge partially strained (0.14%) Perfect crystal structure despite lattice strain! Perfect basic understanding of the growth morphology Simulations Experiment
25. SiGe Pillars RSMs on Ge/Si(004) and Ge/Si(115) – measured on patterned part of the wafer Relaxed Ge (115) (004) Si-Substrate Patterned: Very small mosaicity. No tilt compared to #56558.
