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| {{Science with neutrons}}
| | Hello friend. Allow me introduce myself. I am Luther Aubrey. Some time in the past he selected to reside in Kansas. Meter studying is exactly where my main income comes from but quickly I'll be on my personal. Camping is something that I've done for years.<br><br>my web site: car warranty - [http://85.214.206.118/index.php?mod=users&action=view&id=3033 click through the up coming page], |
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| '''Neutron reflectometry''' is a [[neutron diffraction]] technique for measuring the structure of [[thin films]], similar to the often complementary techniques of [[X-ray reflectivity]] and [[ellipsometry]]. The technique provides valuable information over a wide variety of scientific and technological applications including chemical aggregation, [[polymer]] and [[surfactant]] [[adsorption]], structure of thin film magnetic systems, biological membranes, etc.
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| ==Technical details==
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| The technique involves shining a highly [[Collimator|collimated]] beam of [[neutrons]] onto an extremely flat surface and measuring the intensity of reflected radiation as a function of angle or neutron wavelength. The exact shape of the reflectivity profile provides detailed information about the structure of the surface, including the thickness, density, and roughness of any thin films layered on the substrate.
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| Neutron reflectometry is a [[specular reflection]] technique, where the angle of the incident beam is equal to the angle of the reflected beam. The reflection is usually described in terms of a [[momentum]] [[momentum transfer|transfer]] [[vector (geometric)|vector]], denoted <math>q_z</math>, which describes the change in momentum of a neutron after reflecting from the material. Conventionally the <math>z</math> direction is defined to be the film normal direction, and for specular reflection, the scattering vector has only a <math>z</math>-component. A typical neutron reflectometry plot displays the reflected intensity (relative to the incident beam) as a function of the scattering vector:
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| <math> q_z = \frac{4\pi}{\lambda}\sin ( \theta )</math>
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| where <math>\lambda</math> is the neutron [[wavelength]], and <math>\theta </math> is the angle of incidence. The [[Abeles matrix formalism]] or the Parratt recursion can be used to describe the specular signal arising from the interface. | |
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| The wavelength of the neutrons used for reflectivity are typically on the order of 0.2 to 1 [[Metre#SI_prefixed_forms_of_metre|nm]] (2 to 10 [[Ångström|Å]]). This technique requires a [[neutron source]], which may be either a [[research reactor]] or a [[spallation]] source (based on a [[particle accelerator]]). Like all [[neutron scattering]] techniques, neutron reflectometry is sensitive to contrast arising from different nuclei (as compared to electron density, which is measured in x-ray scattering). This allows the technique to differentiate between various [[isotopes]] of [[chemical element|elements]]. Neutron reflectometry measures the neutron ''scattering length density'' (SLD) and can be used to accurately calculate material [[density]] if the atomic composition is known.
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| ==Comparison to other reflectometry techniques==
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| Although other reflectivity techniques (in particular optical reflectivity, x-ray reflectometry) operate using the same general principles, neutron measurements are advantageous in a few significant ways. Most notably, since the technique probes nuclear contrast, rather than electron density, it is more sensitive for measuring some elements, especially lighter elements ([[hydrogen]], [[carbon]], [[nitrogen]], [[oxygen]], etc.). Sensitivity to isotopes also allows contrast to be greatly (and selectively) enhanced for some systems of interest using isotopic substitution, and multiple experiments that differ only by isotopic substitution can be used to resolve the [[phase problem]] that is general to scattering techniques. Finally, neutrons are highly penetrating and typically non-perturbing: which allows for great flexibility in sample environments, and the use of delicate sample materials (e.g., biological specimens). By contrast x-ray exposure may damage some materials, and [[laser]] light can modify some materials (e.g. [[photoresist]]s). Also, optical techniques may include ambiguity due to optical [[anisotropy]] ([[birefringence]]), which complementary neutron measurements can resolve. [[Dual polarisation interferometry]] is one optical method which provides analogous results to neutron reflectometry at comparable resolution although the underpinning mathematical model is somewhat simpler, i.e. it can only derive a thickness (or [[birefringence]]) for a uniform layer density.
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| Disadvantages of neutron reflectometry include the higher cost of the required infrastructure, the fact that some materials may become [[radioactive]] upon exposure to the beam, and insensitivity to the chemical state of constituent atoms. Moreover, the relatively lower flux and higher background of the technique (when compared to x-ray reflectivity) limit the maximum value of <math>q_z</math> that can be probed (and hence the measurement resolution).
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| ==Partial list of neutron reflectometers==
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| *[http://lansce.lanl.gov/lujan/instruments/Asterix/index.html ASTERIX] at the [[Los Alamos Neutron Science Center]] in [[Los Alamos National Laboratory]]
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| *[http://lansce.lanl.gov/lujan/instruments/SPEAR/index.html SPEAR] at the [[Los Alamos Neutron Science Center]] in [[Los Alamos National Laboratory]]
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| *[http://www.ansto.gov.au/bragg/facilities/instruments/platypus.html Platypus] at [[ANSTO]] in [[Sydney]], [[Australia]]
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| * [http://neutron.nrc-cnrc.gc.ca/c5gen_e.html C5 spectrometer] at [[National Research Council of Canada|NRC Canada]] [[Chalk River Laboratories|Chalk River Labs]] in [[Chalk River, Ontario|Chalk River]], [[Canada]]. ''Note: a new dedicated reflectometer (D3) was commissioned in 2006.''
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| * [http://neutron.nrc-cnrc.gc.ca/d3gen_e.html D3 reflectometer] at [[National Research Council of Canada|NRC Canada]] [[Chalk River Laboratories|Chalk River Labs]] in [[Chalk River, Ontario|Chalk River]], [[Canada]].
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| *[http://www.ill.eu/instruments-support/instruments-groups/instruments/d17/ D17], [http://www.ill.eu/instruments-support/instruments-groups/instruments/superadam/ SuperADAM] and [http://www.ill.eu/instruments-support/instruments-groups/instruments/figaro/ Figaro] at the [[Institut Laue-Langevin]] ([http://www.ill.eu/ ILL]) in [[Grenoble]], [[France]]
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| * [http://www-llb.cea.fr/spectros/pdf/eros-llb.pdf EROS] and [http://www-llb.cea.fr/spectros/pdf/prism-llb.pdf PRISM] ([http://www-llb.cea.fr/prism/PRISM.html alternate]) at [[Commissariat à l'énergie atomique|CEA]] [[Laboratoire Léon Brillouin]] ([http://www-llb.cea.fr/index_e.html LLB]) in [[Saclay]], [[France]]
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| * [http://www.frm2.tum.de/wissenschaft/diffraktometer/n-rex/index.html N-REX+], [http://www.frm2.tum.de/wissenschaft/diffraktometer/mira/index.html MIRA], [http://www.frm2.tum.de/wissenschaft/index.html TREFF@NoSpec], [http://www.hzg.de/central_departments/genf/branch/frm/005265/index_0005265.html REFSANS] and [http://www.jcns.info/jcns_maria/ MARIA] at the [[FRM II|Forschungsneutronenquelle Heinz Maier-Leibnitz]] ([http://www.frm2.tum.de FRM II]) in [[Garching]], [[Germany]]
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| * [http://www.gkss.de/central_departments/genf/instruments/003142/index_0003142.html.en NeRo] and [http://www.gkss.de/central_departments/genf/instruments/003138/index_0003138.html.de PNR] at the [[GKSS|GKSS Research Centre]] ([http://www.gkss.de GKSS]) in [[Geesthacht]], [[Germany]]
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| * [http://www.hmi.de/bensc/instrumentation/instrumente/v6/v6_en.htm V6 reflectometer] at [[Hahn-Meitner-Institut]] ([http://www.hmi.de/index_en.html HMI]) in [[Berlin]], [[Germany]]
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| * [http://www.fz-juelich.de/iff/wns_hadas/ HADAS] at [[Forschungszentrum Jülich]] in [[Jülich]], [[Germany]]
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| * PNR at the [[Dhruva reactor]], [[Bhabha Atomic Research Centre]] in [[Mumbai]], [[India]]
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| * [http://flnp.jinr.ru/140 REFLEX] and [http://flnp.jinr.ru/139/ REMUR] at [[Joint Institute for Nuclear Research]] IBR-2 in [[Dubna]], [[Russia]]
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| * [http://kur.web.psi.ch/amor/ AMOR] at the [[Paul Scherrer Institute]] ([http://www.psi.ch PSI]) in [[Villigen]], [[Switzerland]]
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| *[http://www.isis.rl.ac.uk/largescale/surf/surf.htm SURF], [http://www.isis.rl.ac.uk/largescale/surf/crisp.htm CRISP], [http://ts-2.isis.rl.ac.uk/instruments/inter/ INTER], [http://ts-2.isis.rl.ac.uk/instruments/offspec/ Offspec] and [http://ts-2.isis.rl.ac.uk/instruments/polref/ polREF] at the [[ISIS neutron source]] ([http://www.isis.rl.ac.uk/ ISIS]) in [[Oxfordshire]], [[United Kingdom]]
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| *[http://www.ncnr.nist.gov/instruments/ng1refl/ NG1], [http://www.ncnr.nist.gov/instruments/ng7refl/ NG7] and [http://www.ncnr.nist.gov/programs/reflect/ANDR/ AND/R] at the [[NIST Center for Neutron Research]] ([http://www.ncnr.nist.gov NCNR]) in [[Gaithersburg, Maryland]], [[United States]]
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| *[http://neutrons.ornl.gov/instrument_systems/beamline_04b_lr/index.shtml Liquids] and [http://neutrons.ornl.gov/instrument_systems/beamline_04a_mr/index.shtml Magnetic] at the [[Spallation Neutron Source]] ([http://neutrons.ornl.gov/ ORNL]) in [[Oak Ridge, Tennessee]], [[United States]]
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| * Neutron Reflectometer at the [http://www.murr.missouri.edu/rd_material_sciences_instrumentation_gans.php University of Missouri Research Reactor], in [[Columbia, Missouri]]
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| ==Partial list of neutron reflectometry software== | |
| *[http://www.ncnr.nist.gov/programs/reflect/data_reduction/software/reflred.html Reflred] and [http://www.ncnr.nist.gov/programs/reflect/data_reduction/software/reflfit.html reflfit] ([http://www.ncnr.nist.gov/programs/reflect/data_reduction/software/index.html NIST Center for Neutron Research])
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| *[http://motofit.sourceforge.net Motofit]
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| *[http://www.hmi.de/bensc/instrumentation/instrumente/v6/refl/parratt_en.htm Parratt32] ([[Hahn-Meitner-Institut|HMI]])
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| *[http://www.physics.brocku.ca/~tharroun/yanera Yanera] ([[Brock University]])
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| *[http://stochfit.sourceforge.net StochFit]
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| *[http://www.fs.kfki.hu FitSuite]
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| *[http://genx.sf.net GenX]
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| *[http://smmb.usc.es/sangra/sangra.php SANGRA] (web application, no local installation required)
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| [[Category:Neutron scattering]]
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Hello friend. Allow me introduce myself. I am Luther Aubrey. Some time in the past he selected to reside in Kansas. Meter studying is exactly where my main income comes from but quickly I'll be on my personal. Camping is something that I've done for years.
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