Detector Needs of Spectroscopy

Transcription

1 Detector Needs of Spectroscopy Klaus Attenkofer Inner Shell Spectroscopy Group (NSLS-2) 1 BROOKHAVEN SCIENCE ASSOCIATES

2 RELEVANCE TO DOE MISSION Electro catalysis Environmental sciences: uptake of nutrition Uptake of heavy metals Co 2 -binding in Rocks Oil from oil-shale.. 2 BROOKHAVEN SCIENCE ASSOCIATES

3 The Target Scientific Goal: Investigating correlations between structure, chemical composition and functionality in Real Worlds Materials and Under Realistic Environment Experimental Challenge: 1. Complex multiphase materials with partial/none long range order 2. In-operando conditions are different from steady-state 3. Satisfying both communities: DOI: /chem Applied/industrial and basic sciences community The Approach: 1. Increase the detection limit to 1µmol/L (ppb-level) 2. Develop and provide spectroscopic tools with increased chemical sensitivity 3. Increase throughput to serve not only a large community but also to allow combinatorial approaches 3 BROOKHAVEN SCIENCE ASSOCIATES

4 Spectroscopy Digital Zoom for Microscopy Imaging on the micrometer scale with sub-a resolution Combining microscopic and spectroscopic techniques Hem-Fe in a cell Information content: Micrometer-/nanometer scale elemental maps Chemical bonds of absorber atom (can distinguish between Fe-O,Fe-C., Fe-N ) 4 BROOKHAVEN SCIENCE ASSOCIATES

5 HOW DOES IT WORK: XPS WITH PHOTONS Relaxation from valence states (instead of core levels) relatively easy to calculate by DFT Unprecedented visualization (for an x-ray probe) of chemical environment Similar information to optical RAMAN- Spectroscopy Fe(IV)-O Some literature: J. AM. CHEM. SOC. 2010, 132, Kyle M. Lancaster et al. Science 334, 974 (2011) Inorg. Chem. 2011, 50, Fe(IV)-OH 5 BROOKHAVEN SCIENCE ASSOCIATES

6 DETECTION REQUIREMENT: A good spectrometer will fit all needs! Additional challenges: Compatible with exotic sample environments (especially temperature) High reliability and easy to handle (don t make the spectrometer to the experiment!) Count rates up to photons/s in the full detection system 6 BROOKHAVEN SCIENCE ASSOCIATES

7 ENERGY RESOLUTION AND DETECTION LIMIT Limit for 6 hour scan Signal to Background ratio has to be in the order of 1 Can be achieved by: Energy resolution Filtering (z-1 or crystals) Model: 1µmol/L (ppb-level) Sample, 1% collection efficiency & Photons/s incident However: Principle limits of electronic resolution Fundamental limit is: Material dependent limits: for Si ~135eV Collection efficiency (dependent on shaping time, material quality, geometry) creates tail on the low energy side Electronic noise makes increased baseline level Compton scattering background Excellent detector ~10-2 (would result in ~1000s/point or 11 days for a scan 7 BROOKHAVEN SCIENCE ASSOCIATES

8 X-RAY OPTICS MAY HELP Specifications of the system Energy resolution of about 10keV About 3eV 10KeV Energy scan (within ~40eV) by rocking the crystal without moving the detector arm 8 BROOKHAVEN SCIENCE ASSOCIATES

9 MODULAR SYSTEMS Focusing polycapillary Integration of Sample environment Focusing unit (poly capillary) Spectrometers Benefit: Alignment is not necessary (however, it has to be well engineered) Automatic match of source size and spectrometer focal spot Capillaries are cooled by exchange gas (high temperature environment) Market out side the synchrotron: Electron microscopy (SEM) Lab-based spectroscopy (white beam applications) 9 BROOKHAVEN SCIENCE ASSOCIATES

10 Vendors: MPO Poli-capillary Optics Mechanics Electronics Photonis INCOM Huber RMD SPECTROMETER: THE CONSORTIUM Open Source Development Concept: Poli-capillary Optics: Spectrometer design: In general: Risk Management Carolyn MacDonald (University of Albany) Pieter Glatzel (ESRF) Katarina Noren (MAX-LAB) concept review : BAT-meeting and discussions with community (conferences) Intermediate review: next BAT meeting External design review: end of final design review Support material: design functionality tests of individual units Alternative approach: Spherical Backscattering Analyzer with poly capillary focusing optics (currently developed by ESRF) 10 BROOKHAVEN SCIENCE ASSOCIATES

11 CONCLUSION Spectroscopy is a perfect probe for complex heterogeneous systems Compatible with in-operando conditions Compatible with scanning microscopy: digital zoom to see the chemistry of absorber Main requirements for the detector system: High count rate capability: up to the Photons/s Large solid angle: >π Required energy resolution: ~ KeV Energy range: 4-30keV (fast to change energy range [1-10s]) Compatible to sample environment What can we get? Required system does not exist Will require out-of-the-box-thinking Where are the potential partners: Industry (technology, production management, product development and marketing ) Astro-physics community HEP community 11 BROOKHAVEN SCIENCE ASSOCIATES