Patent Number: 
Section: claims

1. A device for characterizing surfaces, the device comprising:means for generating a beam of neutral atoms or molecules, the means being arranged to direct said beam towards a surface for characterizing; anddetector means that are sensitive to position for detecting the neutral atoms or molecules of said beam that have been diffused forwards by said surface for characterizing;wherein:said means for generating a beam of neutral atoms or molecules produces a beam having energy lying in the range 50 eV to 5 keV with divergence no greater than 0.05°; andsaid means for generating a beam of neutral atoms or molecules directs said beam towards said surface for characterizing at an angle of incidence no greater than 10° relative to the plane of said surface;in such a manner that a diffraction pattern of said neutral atoms or molecules diffused forwards by said surface for characterizing is detectable by said position-sensitive detector means. 2. A device according to claim 1, wherein said means for generating a beam of neutral atoms or molecules produces a beam having energy lying in the range 100 eV to 2 keV. 3. A device according to claim 1, wherein said means for generating a beam of neutral atoms or molecules produces a beam having energy lying in the range 100 eV to 1 keV. 4. A device according to claim 1, wherein said means for generating a beam of neutral atoms or molecules produces a beam having energy dispersion no greater than 5%. 5. A device according to claim 1, wherein said means for generating a beam of neutral atoms or molecules directs said beam towards said surface for characterizing with an angle of incidence lying in the range 0.5° to 3°. 6. A device according to claim 1, wherein the angle of incidence θinc and the energy E0 of said beam of atoms or molecules are selected such that E0 sin2 θinc≦1 eV. 7. A device according to claim 1, wherein said means for generating a beam of neutral atoms or molecules generates a beam constituted by particles having atomic mass lying in the range 1 au to 20 au. 8. A device according to claim 7, wherein said means for generating beam of neutral atoms or molecules generates a beam constituted by a chemical species selected from H, H2, and 3He, and isotopes thereof. 9. A device according to claim 1, wherein said means for generating a beam of neutral atoms or molecules comprise:means for generating a beam of atomic or molecular ions;means for neutralizing said beam of atomic or molecular ions; andmeans for collimating the beam of neutral atoms or molecules obtained by neutralizing said beam of atomic or molecular ions. 10. A device according to claim 9, wherein said means for generating a beam of neutral atoms or molecules also comprise means for filtering said atomic or molecular ions by mass. 11. A device according to claim 9, wherein said means for generating a beam of neutral atoms or molecules comprise chopper means for generating a pulsed beam. 12. A device according to claim 11, wherein said position-sensitive detector means also present time sensitivity, with resolution of not more than 50 ns, so as to determine the energy loss of the neutral atoms or molecules of said beam as a result of being diffused by said surface, by measuring flight time. 13. A device according to claim 12, wherein said position-sensitive detector means present time sensitivity, with resolution of not more than 10 ns. 14. A device according to claim 1, also comprising secondary detector means for detecting neutral or ionized atoms or molecules, said secondary detector means having time resolution no greater than 1 μs, and being arranged in such a manner as to detect neutral or ionized atoms or molecules that leave the surface for characterizing on a trajectory that forms relative to said surface an angle that is greater than the specular reflection angle of said beam of neutral atoms or molecules. 15. A machine for molecular jet epitaxy, the machine including a surface characterizing device according to claim 1, arranged to characterize the surface of a crystal that is being grown. 16. A method of characterizing surfaces, the method comprising the steps of:directing a beam of neutral atoms or molecules on the surface to be characterized; anddetecting in position-sensitive manner the neutral atoms or molecules of said beam that have been diffused forwards by said surface for characterizing;wherein:said beam of neutral atoms or molecules has energy lying in the range 50 eV to 5 keV, and divergence no greater than 0.05°; andthe angle of incidence of said beam on said surface for characterizing is no greater than 10° relative to the plane of said surface;in such a manner that at least some of said forwardly-diffused neutral atoms or molecules are diffracted by said surface for characterizing. 17. A method of characterizing surfaces according to claim 16, wherein said beam of neutral atoms or molecules presents energy lying in the range 100 eV to 2 keV. 18. A method of characterizing surfaces according to claim 17, wherein said beam of neutral atoms or molecules presents energy lying in the range 100 eV to 1 keV. 19. A method of characterizing surfaces according to claim 16, wherein said beam of neutral atoms or molecules presents energy dispersion no greater than 5%. 20. A method of characterizing surfaces according to claim 16, wherein the angle of incidence of said beam on said surface for characterizing lies in the range 0.5° to 3°. 21. A method of characterizing surfaces according claim 16, wherein the angle of incidence θinc and the energy E0 of said beam of atoms or molecules are selected such that E0 sin2 θinc<1 eV. 22. A method of characterizing surfaces according to claim 16, wherein said beam is constituted by particles presenting atomic mass lying in the range 1 au to 20 au. 23. A method of characterizing surfaces according to claim 22, wherein said beam is constituted by a chemical species selected from H, H2, and 3He, and isotopes thereof. 24. A method according to claim 16, also including a step for determining at least one crystallographic parameter of said surface for characterizing from a detected diffraction pattern of said neutral atoms or molecules diffused forwards by said surface for characterizing. 25. A method according to claim 24, implemented during fabrication of a crystal by molecular beam epitaxy, the method also including:a step of observing oscillatory behavior over time of said diffraction pattern; anda step of extracting information relating to the epitaxial growth of successive layers of atoms forming said crystal on the basis of said observation of oscillatory behavior over time of said diffraction pattern.