1 / 23

Use of gratings in neutron instrumentation

Use of gratings in neutron instrumentation. F. Ott, A. Menelle, P. Humbert and C. Fermon Laboratoire Léon Brillouin CEA/CNRS Saclay. Objective. Study of the neutron diffraction on periodical gratings. (produced by lithographic techniques) .

fadhila
Download Presentation

Use of gratings in neutron instrumentation

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Use of gratings in neutron instrumentation F. Ott, A. Menelle, P. Humbert and C. Fermon Laboratoire Léon Brillouin CEA/CNRS Saclay

  2. Objective • Study of the neutron diffraction on periodical gratings.(produced by lithographic techniques). • Theoretical calculation of the diffraction intensities: • Born / DWBA approximation (fails for large diffraction intensities) • matrix formalism : full dynamical calculation. • Application of gratings in neutron optics. • Example: energy analyser for time of flight neutron reflectometer

  3. Outline • Theoretical background • Fabrication of gratings • Energy analysis on a reflectometer using gratings

  4. Off-specular diffraction geometry Side view Thin film plane + grating Diffraction condition

  5. Modelisation of the grating Medium - stratified along (Oz) - periodical of period d along (Ox) Þ it is possible to divide the grating in sub-layers in which the optical index varies as a rectangle function of period d

  6. Dynamical calculation : matrix formalism Continuity conditions at the interfaces

  7. Fabrication of gratings. • Fabrication of periodical gratings by optical U.V. lithography. • Periodicities from 2 to 50 µm, resolution of 1 µm • aspect ratio of the order of 1

  8. Etching techniques • Dry argon etching: not element specific • 8 inch etching plant (VEECO) • two small etching guns • Chemical etching: element specific • ex: Ni,Fe: FeCl3 • fast and cheap even over very large areas • Reactive ion etching: element specific • oxygen, SF6, CH4 • no good for multilayers (ex. Ni/Ti) • one vacuum chamber for samples of 50x50

  9. Etching examples Argon etch of a supermirror Chemical etching (Ni etched by FeCl3) Rie (SF6) of glass

  10. Deposition / Lithography facilities • Deposition: • Sputtering (3 inches) • MBE (limited areas) + sputtering (2 targets) • or use of standard supermirrors (e.g. Swiss Neutronics, Cilas) • Lithography: • clean room with U.V. lithography facilityBut limited area: 50x50mm² • electron beam lithography:very precise but limited in size too • Masks price: (ordered outside) from 1-2 k€

  11. Off-specular diffraction on a glass grating (periodicity 10 µm, lines width 7 µm) Measurement on the time of flight reflectometer EROS (LLB) Detector fixed at 1.5°, scan in the reciprocal space obtained by rocking curves around 0.75° Off-specular diffraction modes Specular reflection line

  12. Increase of the diffraction efficiencies • Increase of the contrast between the incidence medium and the diffraction grating. • Three possibilities : • grating made out of a high index material (Nickel) • incidence medium with an index >1 (Titanium) • use of materials with an «high artificial index» : supermirrors. • Results • under some conditions, efficiencies > 20% • increase of the “diffraction bandwidth”:- high efficiency for a wide wavelength spectrum- or for a large range of incidence angles.

  13. Glass grating with and without a Ni coating

  14. Titanium coating(1st order diffraction mode efficiencies)

  15. Supermirror gratings It is possible to obtain good diffraction efficiencies over a large qz range (0.3 - 0.6 nm-1) The diffracted beam is not much wider than the specular reflected beam

  16. Time of flight reflectivity Cu (30nm) sur Si Dq l = 2 - 0.2 nm 5 µs pulse Spatial spread

  17. Application in neutron instrumentation: Energy analysis. The diffraction direction is a function of the wavelength

  18. Application on a time of flight spectrometer for energy analysis.

  19. Detector view l 0.2 nm Mode 1 I 1.5 nm 200 mm Specular reflection 1.5 nm Mode -1 0.2 nm Sample horizon

  20. Intensity gain • Use of a white beam • a reflectivity curve in a single “shot”. • Study of the evolution of materials or liquids on a time scale of a few minutes • Examples: • liquid interfaces • diffusion, sticking, breaking

  21. Example: PS-PPMA di-block copolymers • Study of the ordering

  22. Techni project • Fabrication and tests of small prototypes (20x20mm²) • choice of materials, periodicities, shape of the grating • optimisation in the resolution, useful q range • Comparison with simulations • Extension to large surfaces (100x50mm²) • Integration on the EROS reflectometer for measurements on liquids • Data processing (deconvolution)

  23. Conclusion • Off-specular diffraction on grating: • We have shown that is is possible to produce grating which have diffraction efficiencies as high as 30% • The good diffraction efficiency can be obtained over a rather broad range of qz or incidence angles. • This suggests the possibility of building a neutron energy analyser by separating a white neutron beam by diffraction on a grating. • Next steps • Production of gratings over large surfaces • Obtain good diffraction resolutions • Use for the study of the reflectivity on liquids

More Related