PROJECT Multifunctional neutron reflectometer GRAINS with horizontal sample plane at the IBR-2M reactor Spokesmen from JINR Dr. V.V.Lauter-Pasyuk, Dr. M.V.Avdeev Co-spokesman from Germany Dr. H. Lauter (ILL) Period of realization 2007÷2011 Outline 1. Scientific background 1.1. Interface science in modern soft matter physics, biology and chemistry. Applications of neutron reflectometry 1.2. Modern tendencies in synthesis of layered nanostructures. Applications of neutron off-specular scattering and GISANS. Kinetics of interface formation. 1.3. New trends in development of reflectometry with polarized neutrons Off-specular scattering GISANS Angular encoding 1.4. Selected basic scientific directions for the new reflectometer 1.5. The IBR-2M reactor. New parameters and possibilities 2. General overview of the reflectometer 2.1. Specific features 2.2. Principle scheme 2.2.1. Cold moderator and head part 2.2.2 Beam formation system, polarisation devices and deflectors 2.2.4 Around the sample position 2.2.5 Control system and DAQS 3. Team 4. Budget 5. References 1. Scientific background 1.1. Interface science in modern soft matter physics, biology and chemistry. Applications of neutron reflectometry The interface science today is an important area of soft matter physics, biology, chemistry and pharmacy. Due to widespread applications in practical and functional systems the knowledge about formation, stability and breakdown of different kinds of interfaces including liquid-solid, liquid-air and liquid-liquid interfaces is of a great importance. The mentioned types of interfaces are essential constituents of biological systems, polymer multilayers and blends, polyelectrolytes, and mixed surfactant layers. Due to the continuing development of neutron reflectometry over the past decades, major advances have been made into the investigation of the structure of surfaces and interfaces [Pen1, Bow1]. In comparison with other methods dealing with interfaces one can enumerate several advantages using neutrons. First, the neutrons scattering is a weak interaction and the samples are not destroyed or even influenced by neutrons. Second, the contrast variation using isotopic substitution hydrogen/deuterium allows in particular in fluid or biological samples to create contrasts between selected parts of the sample. Third, the possibility to probe rather easily magnetic structures of or in mono or multilayers due to the magnetic moment of neutrons is an enormous advantage. The important feature of the modern neutron reflectometry is the development of instruments with horizontal sample plane for studying fluid-containing interfaces with high resolution. Neutron reflectometry for the interface science in modern soft matter physics is applied in different fields. The neutron reflectivity is very sensitive to the nanoscaled inhomogeneities at the interfaces with liquids. The number of important parameters can be obtained including the width of interface and its mean density. The direct modeling of interface profiles allows one to find out the molecule distribution over the depth of the interface, which makes it possible to follow the interface phase diagrams by varying different conditions (temperature, concentration) [Gru1]. A progress in this field both for comparatively simple and complex liquids can be seen [Bow1, Zar1, Zar2, Bow3, Bow4, Bow5, Sch1]. The neutron reflectivity is a suitable method for studying adsorption and structural organization of nanoscaled organic molecules and colloidal particles adsorbed to functionalized aqueous interfaces [Loes1]. Reflectometry experiments on organization of membrane protein assemblies [Hol1, Reu1] and structure of the HIV-1 accessory protein Vpu in Langmuir monolayers [Zhe1] were successfully performed. For the given class of systems the full/partial deuteration of both liquids and molecules is a quite developed technique, which determines the active use of the contrast variation method in investigations of such type of interfaces. Numerous examples cover adsorption of elongated organic molecules [Zar3, Bow6], block copolymers [Bow1, Bow2] and polyelectrolites [Ste1] at liquid-liquid, liquid-solid and liquid-air interfaces. The important direction connected with the adsorption of biological molecules at such interfaces is intensively developed including phospholipid bilayers [Gut2, Del1] and vesicles [Gut1], as well as proteins [Hen1, Jac1, Jac2, Cze1]. Magnetic fluids (fine liquid dispersions of magnetic nanoparticles caoted by surfactants) represent a special class. The liquid-solid interface with magnetic fluids can be studied by conventional reflectometry [Vor1, Vor3] to obtain the information about atomic structure of the interface, while the reflectometry of polarized neutrons [Vor2] reveals features of magnetic organization of the interface. In addition, magnetic fluids show some interesting free surface phenomena. One of them concerns instabilities at the interface fluid-air when a perpendicular magnetic field is applied. As it was shown [Vor4], the formation of these instabilities can be seen at the nanoscale by means of neutron reflectometry and analysis of off-specular scattering. It should be pointed out that the neutron reflectometry for analysis of interfaces with absorbed nanoparticles is, in fact, a special method, which allows one to obtain the information about the inner structure of the particles themselves. It can be considered as a method complimentary to those dealing with particles in bulk, such as smallangle scattering. 1.2. Modern tendencies in synthesis of layered nanostructures. Applications of neutron off-specular scattering and GISANS. Kinetics of interface formation. Aligned two- and three-dimensional films with templated lateral and transverse structure are of particular interest for creation of functional materials. The developments of the advanced methods for thin films preparation created an avalanche of demand for the characterization of thin films properties. Specular reflection delivers information about the depth profile of the mean scattering length density (SLD) averaged over the whole sample surface. However, in reality pure specular reflection does not exist, because real surfaces or interfaces are not ideal and cannot be atomically flat. Therefore, specular reflection is always accompanied by offspecular scattering. The full range of off-specular scattered intensity, accompanying the specular reflection, became accessible mainly due to the use of multidetectors. Off-specular scattering probes the lateral structure (lateral form factor, structure factor or the roughness) at surfaces and interfaces in films or multilayers. Thus, the most exhaustive and detailed information on the 3-dimensional structure (transverse and lateral) of thin films and multilayers can be gained using grazing incidence neutron techniques, comprising reflectometry and off-specular scattering. The state of the art in surface preparation and analysis has made it feasible to produce new types of materials that are structured on the nanometer scale. For design of biosensors based on membrane receptors the development of biocompatible interfaces plays an important role [Sac1]. Small unilamellar phospholipid vesicles are basic elements in the design of biophysical model systems for studying the interaction of biomolecules with membrane surfaces [Wag1]. Neutron reflectometry was used to study in situ phospholipids bilayer formation [Gut1]. Lamellar vesicles are of particular interest in biochemical field for drug delivery, they can be also used as biological membrane models [Nel1, Su1]. Recent advances in novel drug delivery systems focused on alternate surfactant systems, which can also produce similar structures [Beu1]. Thus the systems containing mixtures of cationic and anionic surfactants or single-chain nonionic surfactants can form vesicular solutions. The ordered lamellar structure and stability of dichain cationic surfactants was studied by neutron reflectometry. The interfacial structure of aggregates was examined by off-specular scattering [McGil1]. Only a few limited methods are currently available to determine the fundamental smectic length scale or the bilayer bending rigidity. Using off-specular neutron scattering from aligned phases the bilayer structure and fluctuations is accessible over a wide range both for relatively stiff and for soft systems, covering length scales from the molecular scale up to a few hundreds nm. Thermal fluctuations of lipid membrane phases reflect fundamental physical properties of the lipid bilayer, related to thermodynamic stability, elasticity, interaction potentials, and phase transitions. From the experiments on the investigation of thermal fluctuations of oriented lipid membranes using the neutron off-specular scattering the smectic penetration depth was determined [Sal1]. The grazing incidence small angle neutron scattering (GISANS) is complementary to offspecular scattering and reveals information about the lateral structure, ordering and preferential orientations of surfaces and interfaces which measures structures at the 1 to 80 nm length [Mue1, Wol1]. Using this technique, the lateral structure of surfactant layer adsorbed at a hydrophyllic solid/liquid interface was studied with temperature [Ste2]. Finally, kinetics of the interface formation is of current interest. In this connection the employment of neutron time-of-flight instruments is the most effective and useful. This allowed for a monitoring kinetic processes in polymer solutions [Wan1] and investigation of growth of polymer brush [Him1]. 1.3. New trends in development of reflectometry with polarized neutrons: Off-specular scattering, GISANS, Angular encoding At present the majority of published data in reflectometry concerns specular reflection, from which the structural information perpendicular to the surface of a sample is obtained. For this purpose, the Qz vector is scanned as a function of the incoming scattering angle in the monochromatic (MC) mode or the wavelength in time-of-flight (TOF) as schematically shown in fig.1. A further step in the sample characterisation is to obtain information about the lateral structure of surfaces and interfaces from off-specular scattering. Off-specular scattering appears in the same scattering plane and gives structural information along the surface in Qx-direction on the scale of a few 10 nm to a few 100μm. GISANS probes the correlations along the sample surface in Qy-direction perpendicular to Qx on a length scale from less than 10nm to a few 100nm, which is similar to the one of small-angle scattering. A combined measurement of specular reflection, offspecular and GISANS, called complete reflectometry [Lau1], probes lateral correlations in a depth sensitive way providing a 3-dimensional (3-D) structural analysis. In complete reflectometry the detailed neutron wave field along the surface normal created by dynamical scattering is taken into account. Thus assembling the scattering mechanisms leads to a 3-D structural information of layered sample [Lau1]. These recent developments are taken into account in the lay-out of the new horizontal reflectometer. A flexible collimation system allows to install a slit-shaped incoming beam for the set-up of specular reflection with offspecular scattering and a pencil-shaped incoming beam for the set-up of complete reflectometry. In particular a good resolution along Qz, which is the necessary base for the depth sensitivity of off-specular scattering and GISANS, is guarantied. Magnetic GISANS measurements including the polarisation analysis of specular together with off-specular scattering following Ref.[Lau1] is taken into account in the lay-out of the Qz Off-specular scattering - Qx Specular reflection - Qz GISANS - Qy Qx Qy Fig.1: Scheme of specular reflection (blue) along Qz, off-specular scattering (green) along Qx and GISANS (black) along Qy in reciprocal space. The incoming wave vector along “transmitted beam” is not shown. The final wave vectors are shown in the colour of the scattering/reflection process as well as the momentum transfers belonging to them. (The background scheme shows the scattering from a grating as example.) new horizontal reflectometer. At present the detailed treatment of magnetic specular reflection and off-specular scattering in a broad range of momentum transfer can be performed [Top1, Lau2, Lau3]. Further development in handling the complexity of scattering mechanisms including GISANS (particularly in magnetic case) will be done. For this purpose also the implication of Larmor-precession (see following paragraphs) in the measuring magnetic GISANS is foreseen. Magnetic and non-magnetic GISANS implies, as already mentioned, a pencil-shaped collimation of the incident beam. A considerable decrease of the flux on the sample is the consequence. This decrease of flux will be counterbalanced by the application of angular encoding with Larmor precession. If the incoming scattering angle is encoded its angular divergence can be enlarged and thus flux on the sample is increased. The method, we will apply, is different from SESANS in reflection or SERGIS, for which spin-echo technique is employed. Here we will use one Larmor precession field as explained in the following. A pilot experiment on the TOF-reflectometer REMUR has been performed [Lau4]. The encoding of the wavelength visible by intensity oscillations in TOF is shown in fig.2 and is obtained by a Larmor n CS2 Reflected beam CS1 HH Direct beam Det. Analyzer Sample LP-device Res. spin flipper Fig.2: Wavelength encoded intensity map of direct beam (lower trace) and reflected beam (upper trace) in TOF of a Polymer-multilayer [Lau4] in the right lower intensity map. No encoding is seen with switched off current-sheets in the left lower intensity map. The experimental set-up with two current-sheets (CS1 and CS2) defining the extent of the Larmor-precession (LP)-device is shown in the top of the figure. precession field using two current sheets followed by spin analysis of transmitted and scattered intensity. Turning the current-sheets with respect to the neutron beam provides different path lengths for neutrons coming under different angles, which results in angular encoding. Thus, a broad angular encoded incoming beam can be used and the high resolution scattered intensity can be reconstructed by Fourier analysis with the known encoding code. With this method a factor >5 (for magnetic scattering a factor >10) in intensity can be gained being particularly valuable for GISANS. Further, by scanning one of the Larmor-precession parameters the angular encoding can be refined [Lau5]. A second important application of Larmor precession is 3-dimensional analysis of magnetisation distribution in layered magnetic samples. In standard experiments the external magnetic field and the neutron magnetic moment are oriented parallel to the sample surface. From such experiment one gets information about the depth distribution of the mean value of in-plane magnetic moments. The off-specular magnetic scattering probes the magnetic fluctuations along the surface plane and gives information about their magnetisation state through spin-flip or non-spin flip scattering. However, a full 3-D analysis is only obtained if the polarisation of incoming neutron can be adjusted with respect to the magnetisation directions in the sample. In reflectometry this effect can be obtained if the neutron performs Reflected beam Sample HH Direct beam Det. Analyzer LP-device Res. spin flipper Fig.3: Wavelength encoded intensity map of direct beam (lower trace) and reflected beam (upper trace) in TOF of a Fe/Cr multilayer. Note the intensity modulations around the critical scattering (around 5Å) and the π-shift of the stripes in off-specular scattering above 2 Å due to spin-flip scattering [Lau3]. The experimental set-up with two current-sheets defining the extent of the Larmor-precession (LP)-device is shown in the top of the figure. Larmor precession with the plane of its magnetisation rotation perpendicular to the external field [Lau3]. Like this missing matrix elements in the magnetic interactions are measured in an elegant way in TOF. For this purpose a weak magnetic Larmor-precession field around the sample position is contained in the lay-out of the new horizontal reflectometer. In conclusion full 3-D non-magnetic and magnetic information of layered structures is only accessible by a detailed study of the combination of specular reflection, off-specular scattering and GISANS with the additional option of Larmor-precession. These new developments in neutron reflectometry are contained in the lay-out of the new horizontal reflectometer and will be explored in detail. 1.4. Selected basic scientific directions for the new reflectometer From the overview of the modern trends in soft matter physics, biology and chemistry, as well as in the synthesis of layered nanostructures, one can conclude that the indicated fields are actively developing at present. The important fact is their tight connection with the life sciences and real technical and industrial applications. On the other hand, last developments in the neutron scattering, which, in particular, employ new techniques in the polarization analysis, should be effectively adopted and used in the practice. From these points the scientific program on the new instrument, where complete neutron reflectometry can provide unique information, is seen as following. Biological systems The actual progress in the investigation of supported oriented phospholipids bilayer structures demonstrated that they provide realistic models for cell membranes. Therefore the study of ion transport channels as well as adsorption of proteins in these systems will be relevant for the development of new drug delivery systems and for the investigation of transport mechanisms. The size, distribution, physical and chemical behaviour of oriented lipid membranes is important to investigate. This information will be accessible through experiments on oriented lipid or synthetic membranes in different environments. The transverse and lateral structure and composition and their fluctuations will be investigated via real time studies based on TOF specular reflectometry with off-specular scattering and GISANS over a range of length scales from tens of nanometer in the case of ion transport channels, to microns for the membrane structure. Polymer and composite systems The phenomenon of self-organization is one of the most promising for engineering of new complex nano-composite materials with requested physical properties. Depending on the symmetry and molecular weight of self-assembled block-copolymer one can tailor cylindrical, spherical or lamellar polymer. The details of the internal structure of copolymer films with different architecture will be investigated. In-situ TOF experiments will be performed to obtain the structural modification of the self-organization process during annealing. A challenge in the production of composite films with complicated morphology is to control their internal structure. The polymeric matrix are used to re-print corresponding nano-particle structures and to bring them into a defined array on nanometer scale in a controlled way. Induced order in nano-particle ensemble is achieved by coating them with one or the other species of copolymer chain and hence providing the affinity of nano-particles to selected lamellae of the self-assembling multilayer film. The interaction of nano-particles with the host matrix and between the nanoparticles themselves is tuned by their density and size and reflects in the modification of the internal structure. Deuteration of the selected blocks of copolymer chains dramatically enhances the scattering contrast between two polymers. Thus using off-specular scattering we trace the modification of buried copolymer interfaces and individual lamellar thickness, lateral and transverse conformity of interfacial roughness, and also position and distribution of nanoparticles within each lamellae. This approach can be applied to a broad variety of composites using other copolymer architectures including linear, di-, tri- and multiblock copolymer, heteroarm stars or Y structures. Magnetic nanoparticles give an additional aspect of magnetic ordering in a magnetic field and magnetic self-ordering. Polymer blends at liquid-liquid and liquid-air interfaces will be also investigated, as well as polyelectrolyte multilayers at the solid/liquid interfaces. Magnetic fluids The stability of magnetic fluids at the liquid-solid interface will be studied by complete reflectometry to obtain structural information near and at the interface. Application of polarized neutrons will reveal the kind of magnetic organization with depth sensitivity. Phenomena at the free surface include the formation of instabilities in a perpendicular magnetic field to be studied with complete reflectometry. Real time experiments on the growth of surface magnetic heterostructures are in particular suited for TOF reflectometry. Near surface SANS performed under grazing incidence conditions at the liquid-air or liquidsolid interfaces of bulk systems will be applied to reveal the inner structure of the particles themselves. Surfactant systems Mixed surfactant systems can form lamellar and micellar sytuctures at the air-solid and air-liquid interfaces. Polymer surfactant mixtures can exhibit in-plane structure in the form of ripple phases and other forms of correlated roughness. The behaviour of such systems depending on temperature, pH, ionic concentration and solution with additional possibility of time-resolved measurements will be studied. Special equipment For sample preparation Langmuir-Blodgett trough and spin-coating devices are foreseen. A vacuum furnace is available. For sample environment on the reflectometer are foreseen: humidity chamber, variable temperature device for 100K<T<400K, turning electromagnet with H<1.5T and active anti-vibrational table. 1.5. The IBR-2M reactor. New parameters and possibilities The IBR-2M reactor is a high flux long-pulse neutron source with optimal repetition rate. Such a source provides ideal conditions for reflectometry. The reactor renewal program is already running and e.g. the new fuel elements have been produced. An important part, the rotating reflectors, were already successfully exchanged. The renewed reactor will restart in Spring 2010. Until this date the spectrometer park will be upgraded and new spectrometers will be built. The very important new element in particular for reflectometry will be the installation of cold moderators. The cold moderators will be under-moderated and produce a broad wavelength band combined with the gain for cold neutrons. This is demonstrated in fig.4, in which the gain factor in flux is shown for the new water/mesithylene moderator. On the present reflectometer REMUR already a wavelength band from 1 to 14Å was available on the thermal source. The shown gain factor of 10 at 10 Å lets assume that the available wavelength band will be considerably extended to 25 Å. So a unique momentum transfer band with a width of a factor 25 will be available. The immense advantage is that most of the Fig.4: Gain factor of a new cold moderator (water/mesithylene) on the IBR-2M reactor [Sha1]. experiments can be performed in TOF in one shot without changing the incoming scattering angle. This removes difficulties in fitting the reflected and off-specular scattered intensity measured in several steps in Q-space with different resolution in the overlap regions. At this point it is worth to point out again, that the IBR-2M reactor will have the characteristics of the long pulse part of the ESS. The pulse width of the IBR-2M reactor of ~340μs with a flight path of 20m for a wave length band from 1 Å to 25 Å provides a resolution in δλ/λ from 7% to 0.3%. The angular resolution can be adjusted from <1% to 10%. An advantage of the new site on the 10th beam on the IBR-2M reactor will be the wide area of cold moderator of the 10th beam of 20cm x 20cm and a 20m flight-pass allows to optimise the intensity yield for the various focussing possibilities in complete reflectometry. Neutrons from a stripe of 20cm width in horizontal direction and a height of 2cm of the cold moderator are used for specular reflection and off-specular scattering from a horizontal sample. Adding GISANS leads to an area of 2cm x 2cm due to the necessary additional collimation. However, angular encoding, as described before, allows for an opening of the incoming beam in the vertical direction. The angular encoding in vertical direction will be performed to preserve the depth sensitivity in complete reflectometry with high resolution. Also a vaste space around the new reflectometer is a not negligible advantage in order to be flexible in the set-up. 2. General overview of the reflectometer 2.1.Specific features Taking into account the fact that a number of scientific problems connected with the characterization of the interface containing liquids are continuously increasing the new reflectometer is planned for liquid samples. This feature determines the basic principle of the reflectometer construction, namely its horizontal sample plane (vertical scattering plane). Consequently, all set-up elements will be adopted and optimized for such geometry. The new reflectometer installed at the pulsed IBR-2M reactor will operate in the time-of-flight regime, which makes the technical realisation of the measuring procedure over a wide range of momentum transfer (see 1.5) much easier in comparison to the case of constant wavelength, because of a fixed sample position. Nevertheless two limiting incident angles are planned to satisfy studies at momentum transfers ranging from 2 10-3 Å-1 to 0.3 Å–1. Off-specular scattering and GISANS are measured simultaneously in TOF with a 2dimensional detector . Angular encoding is provided with a Larmor precession region limited by current sheets in front of the sample. 3-D polarimetry in reflection is provided by a Larmor precession region around the sample position. 2.2 Principle scheme The reflectometer is suggested to be installed at the 10th beam line of the IBR-2M facing the cold moderator. The principle scheme of the reflectometer is presented in Fig.5. Fig.5: Principle scheme of the horizontal reflectometer in top view (upper scheme) and side view (lower scheme). The length from moderator to detector of 30m is an upper length limit. (the Larmor-precession device will have two positions, before the sample and around the sample and is not shown for simplicity; “Polarizing mirror” stands for a stack of adjustable mirrors for polarizing and non-polarizing mode.) 2.2.1. Cold moderator and head part The head part contains the vacuum system starting at the cold moderator and extending towards the ring-corridor with the background chopper. The background chopper opens only during the neutron pulse. 2.2.2 Beam formation system, polarisation devices and deflectors - - After the head part the vacuum system (with a diameter ~80cm) continues up to close to the sample position extending through the first resonant spin flipper. The beam forming system consists of B4C containing polyethylene in particular in front and behind the background chopper and in front of the deflector/polarizing mirror. Flexible slit-collimators serve to tailor the beam shape for different applications: specular reflection with off-specular scattering (horizontal slit geometry) GISANS/complete reflectometry (pencil geometry along the beam) complete reflectometry with angular encoding (vertical slit geometry). The multi-channel mirror deflector and the multi-channel mirror polarizing mirror are exchangeable units in vacuum being composed of a stack of adjustable mirrors. With deflector or polarizing mirror the direct view from the sample position to the cold moderator is prohibited. A change of the reflection angle requires also a translation of the deflector/ polarizing mirror. 2.2.3 Analysing and detecting system - vacuum system after the sample resonant spin flipper after the sample multi-channel mirror analyser in front of position sensitive detector 2-dimensional position sensitive detector with adjustment system 2.2.4 Around the sample position - a slit system in front of the sample 2 goniometers and a rotation table under the sample active antivibration table 2.2.5 Control system and DAQS - VME-electronic for TOF, computers, power supplies for motors and interfaces etc. 3. Team ILL - Dr. H.Lauter FLNP JINR - Dr. V.V.Lauter-Pasyuk, Dr. M.V.Avdeev, Dr. V.I.Bodnarchuk, Prof. V.L.Aksenov, M.N.Jernenkov, S.P.Yaradaykin PNPI RAS - Dr.V.A.Ul’yanov, Prof.V.A.Trounov, S.V.Kalinin, Dr. A.P.Bulkin, Dr. V.A.Kudryashev 3. Budget Cost estimate, kEU External 2007 2008 2009 2010 2011 source 1- Background chopper 10 2- Vacuum system in front and after sample 40 3- Collimating system 5 4- Flexible slit-collimators 5 5- multi-channel mirror polarizer 50 6- multi-channel mirror deflector 40 7- Mechanics for adjustment and exchange of polarizer and deflector 60 7- Resonant spin-flippers 10 8- multi-channel mirror analyser 50 9- 2D Position Sensitive Detector 80 10- Slit system in front of sample 10 11- Goniometers and turn table 80 12- Sample holders with antivibrational table 13- Sample environment 40 20 14- Larmor precession device 30 30 30 50 20 15- Electromagnet 50 16- Electronics and DAQS 35 17- Control system 15 40 18- Subsidiary equipment 30 20 BMBF contribution 135 135 135 135 130 JINR contribution 40 40 40 40 40 external contribution 180 TOTAL: 1050 5. References [Beu1] S. Beugin, K. Edwards, G. Karlsson M. Ollivon, S. Lesieur, Biophys J 74, 3198 (1998) [Bou1] W.G. Bouwman, R. Pynn , T. 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