View source for Grazing-incidence small-angle scattering

'''Grazing-incidence small-angle scattering''' ('''GISAS''') is a scattering technique used to study nanostructured surfaces and thin films. The scattered probe is either photons ('''grazing-incidence small-angle X-ray scattering''', '''GISAXS''') or neutrons ('''grazing-incidence small-angle neutron scattering''', '''GISANS'''). GISAS combines the accessible length scales of [[small-angle scattering]] (SAS: [[SAXS]] or [[Small-angle neutron scattering|SANS]]) and the surface sensitivity of [[grazing incidence diffraction]] (GID).

[[Image:GISAXS.png|300px|thumb|right|Geometry of a GISAS experiment. The incident beam strikes the sample under a small angle close to the critical angle of total external x-ray reflection. The intense reflected beam as well as the intense scattering in the incident plane are attenuated by a rod-shaped beam stop. The diffuse scattering from the sample (red arrow) is recorded with an area detector. As an example the scattering from a block copolymer film with perpendicular lamellae is shown in the detector plane. The two lobes of scattering correspond to the lateral lamellar period of about 80&nbsp;nm.
]]

==Applications==

A typical application of GISAS is the characterisation of [[self-assembly]] and [[self-organization]] on the [[Nanoscopic scale|nanoscale]] in thin films. Systems studied by GISAS include quantum dot arrays,<ref>{{cite journal | last1=Metzger | first1=T.H. | last2=Kegel | first2=I. | last3=Paniago | first3=R. | last4=Lorke | first4=A. | last5=Peisl | first5=J. | last6=Schulze | first6=J. | last7=Eisele | first7=I. | last8=Schittenhelm | first8=P. | last9=Abstreiter | first9=G. |display-authors=5| title=Shape, size, strain and correlations in quantum dot systems studied by grazing incidence X-ray scattering methods | journal=Thin Solid Films | publisher=Elsevier BV | volume=336 | issue=1–2 | year=1998 | issn=0040-6090 | doi=10.1016/s0040-6090(98)01290-5 | pages=1–8| bibcode=1998TSF...336....1M }}</ref>
growth instabilities formed during in-situ growth,<ref name="renaud">{{cite journal | last1=Renaud | first1=G. |first2=Rémi |last2=Lazzari|first3=Christine |last3=Revenant|first4= Antoine |last4=Barbier|first5=Marion |last5=Noblet|first6=Olivier |last6=Ulrich|first7=Frédéric |last7=Leroy|first8=Jacques |last8=Jupille|first9=Yves |last9=Borensztein|first10=Claude R. |last10=Henry| s2cid=7244337 |display-authors=5| title=Real-Time Monitoring of Growing Nanoparticles | journal=Science | publisher=American Association for the Advancement of Science (AAAS) | volume=300 | issue=5624 | date=2003-05-30 | issn=0036-8075 | doi=10.1126/science.1082146 | pmid=12775836 | pages=1416–1419| bibcode=2003Sci...300.1416R }}</ref>
self-organized nanostructures in thin films of [[block copolymers]],<ref name="smilgies">{{cite journal | last1=Smilgies | first1=Detlef‐M. | last2=Busch | first2=Peter | last3=Papadakis | first3=Christine M. | last4=Posselt | first4=Dorthe | title=Characterization of polymer thin films with small‐angle X‐ray scattering under grazing incidence (GISAXS) | journal=Synchrotron Radiation News | publisher=Informa UK Limited | volume=15 | issue=5 | year=2002 | issn=0894-0886 | doi=10.1080/08940880208602975 | pages=35–42| s2cid=122797468 }}</ref>
silica mesophases,<ref name="gibaud">{{cite journal | last1=Gibaud | first1=A. | last2=Grosso | first2=D. | last3=Smarsly | first3=B. | last4=Baptiste | first4=A. | last5=Bardeau | first5=J. F. | last6=Babonneau | first6=F. | last7=Doshi | first7=D. A. | last8=Chen | first8=Z. | last9=Brinker | first9=C. Jeffrey | last10=Sanchez | first10=C. | title=Evaporation-Controlled Self-Assembly of Silica Surfactant Mesophases | journal=The Journal of Physical Chemistry B | publisher=American Chemical Society (ACS) | volume=107 | issue=25 | year=2003 | issn=1520-6106 | doi=10.1021/jp027612l | pages=6114–6118}}</ref><ref name="Hazra3">{{cite journal | last1=Chatterjee | first1=P. | last2=Hazra | first2=S. | last3=Amenitsch | first3=H. | s2cid=98053328 | title=Substrate and drying effect in shape and ordering of micelles inside CTAB–silica mesostructured films | journal=Soft Matter | publisher=Royal Society of Chemistry (RSC) | volume=8 | issue=10 | year=2012 | issn=1744-683X | doi=10.1039/c2sm06982b | page=2956| bibcode=2012SMat....8.2956C }}</ref>
and [[nanoparticles]].<ref name=Hazra2>{{cite journal | last1=Hazra | first1=S. | last2=Gibaud | first2=A. | last3=Sella | first3=C. | title=Tunable absorption of Au–Al<sub>2</sub>O<sub>3</sub> nanocermet thin films and its morphology | journal=Applied Physics Letters | publisher=AIP Publishing | volume=85 | issue=3 | date=2004-07-19 | issn=0003-6951 | doi=10.1063/1.1774250 | pages=395–397| bibcode=2004ApPhL..85..395H }}</ref><ref>{{cite journal | last1=Saunders | first1=Aaron E. | last2=Ghezelbash | first2=Ali | last3=Smilgies | first3=Detlef-M. | last4=Sigman | first4=Michael B. | last5=Korgel | first5=Brian A. | title=Columnar Self-Assembly of Colloidal Nanodisks | journal=Nano Letters | publisher=American Chemical Society (ACS) | volume=6 | issue=12 | year=2006 | issn=1530-6984 | doi=10.1021/nl062419e | pmid=17163739 | pages=2959–2963| bibcode=2006NanoL...6.2959S }}</ref>

GISAXS was introduced by Levine and Cohen<ref>{{cite journal | last1=Levine | first1=J. R. | last2=Cohen | first2=J. B. | last3=Chung | first3=Y. W. | last4=Georgopoulos | first4=P. | title=Grazing-incidence small-angle X-ray scattering: new tool for studying thin film growth | journal=Journal of Applied Crystallography | publisher=International Union of Crystallography (IUCr) | volume=22 | issue=6 | date=1989-12-01 | issn=0021-8898 | doi=10.1107/s002188988900717x | pages=528–532}}</ref> to study the dewetting of gold deposited on a glass surface. The technique was further developed by Naudon<ref>A. Naudon in H. Brumberger (ed.): "Modern Aspects of Small-Angle Scattering", (Kluwer Academic Publishers, Amsterdam, 1995), p. 191.</ref> and coworkers to study metal agglomerates on surfaces and in buried interfaces.<ref name=Hazra1>{{cite journal | last1=Hazra | first1=S | last2=Gibaud | first2=A | last3=Désert | first3=A | last4=Sella | first4=C | last5=Naudon | first5=A | title=Morphology of nanocermet thin films: X-ray scattering study | journal=Physica B: Condensed Matter | publisher=Elsevier BV | volume=283 | issue=1–3 | year=2000 | issn=0921-4526 | doi=10.1016/s0921-4526(99)01899-2 | pages=97–102| bibcode=2000PhyB..283...97H }}</ref> With the advent of [[nanoscience]] other applications evolved quickly, first in hard matter such as the characterization of [[quantum dots]] on semiconductor surfaces and the in-situ characterization of metal deposits on oxide surfaces. This was soon to be followed by [[soft matter]] systems such as ultrathin [[polymer]] films,<ref>{{cite journal | last1=Gutmann | first1=J.S. | last2=Müller-Buschbaum | first2=P. | last3=Schubert | first3=D.W. | last4=Stribeck | first4=N. | last5=Smilgies | first5=D. | last6=Stamm | first6=M. | title=Roughness correlations in ultra-thin polymer blend films | journal=Physica B: Condensed Matter | publisher=Elsevier BV | volume=283 | issue=1–3 | year=2000 | issn=0921-4526 | doi=10.1016/s0921-4526(99)01888-8 | pages=40–44| bibcode=2000PhyB..283...40G }}(Proceedings of SXNS–6)</ref> polymer blends, [[block copolymer]] films and other self-organized nanostructured thin films that have become indispensable for nanoscience and technology. Future challenges of GISAS may lie in biological applications, such as [[proteins]], [[peptides]], or [[viruses]] attached to surfaces or in lipid layers.

==Interpretation==

As a hybrid technique, GISAS combines concepts from transmission small-angle scattering (SAS), from grazing-incidence diffraction (GID), and from diffuse reflectometry. From SAS it uses the form factors and structure factors. From GID it uses the scattering geometry close to the critical angles of substrate and film, and the two-dimensional character of the scattering, giving rise to diffuse rods of scattering intensity perpendicular to the surface. With diffuse (off-specular) reflectometry it shares phenomena like the Yoneda/Vinyard peak at the critical angle of the sample, and the scattering theory, the [[distorted wave Born approximation]] (DWBA).<ref>{{cite journal | last1=Sinha | first1=S. K. | last2=Sirota | first2=E. B. | last3=Garoff | first3=S.|author3-link=Stephen Garoff | last4=Stanley | first4=H. B. | title=X-ray and neutron scattering from rough surfaces | journal=Physical Review B | publisher=American Physical Society (APS) | volume=38 | issue=4 | date=1988-08-01 | issn=0163-1829 | doi=10.1103/physrevb.38.2297 | pmid=9946532 | pages=2297–2311| bibcode=1988PhRvB..38.2297S }}</ref><ref>{{cite journal | last1=Rauscher | first1=M. | last2=Salditt | first2=T. | last3=Spohn | first3=H. | title=Small-angle x-ray scattering under grazing incidence: The cross section in the distorted-wave Born approximation | journal=Physical Review B | publisher=American Physical Society (APS) | volume=52 | issue=23 | date=1995-12-15 | issn=0163-1829 | doi=10.1103/physrevb.52.16855 | pages=16855–16863| pmid=9981092 | bibcode=1995PhRvB..5216855R }}</ref><ref>{{cite journal | last=Lazzari | first=Rémi | title=IsGISAXS: a program for grazing-incidence small-angle X-ray scattering analysis of supported islands | journal=Journal of Applied Crystallography | publisher=International Union of Crystallography (IUCr) | volume=35 | issue=4 | date=2002-07-18 | issn=0021-8898 | doi=10.1107/s0021889802006088 | pages=406–421| doi-access= }}</ref> However, while diffuse reflectivity remains confined to the incident plane (the plane given by the incident beam and the surface normal), GISAS explores the whole scattering from the surface in all directions, typically utilizing an area detector. Thus GISAS gains access to a wider range of lateral and vertical structures and, in particular, is sensitive to the morphology and [[preferential alignment]] of nanoscale objects at the surface or inside the thin film.

As a particular consequence of the DWBA, the refraction of x-rays or neutrons has to be always taken into account in the case of thin film studies,<ref>{{cite journal | last1=Lee | first1=Byeongdu | last2=Park | first2=Insun | last3=Yoon | first3=Jinhwan | last4=Park | first4=Soojin | last5=Kim | first5=Jehan | last6=Kim | first6=Kwang-Woo | last7=Chang | first7=Taihyun | last8=Ree | first8=Moonhor | title=Structural Analysis of Block Copolymer Thin Films with Grazing Incidence Small-Angle X-ray Scattering | journal=Macromolecules | publisher=American Chemical Society (ACS) | volume=38 | issue=10 | year=2005 | issn=0024-9297 | doi=10.1021/ma047562d | pages=4311–4323| bibcode=2005MaMol..38.4311L }}</ref><ref name="busch">{{cite journal | last1=Busch | first1=P. | last2=Rauscher | first2=M. | last3=Smilgies | first3=D.-M. | last4=Posselt | first4=D. | last5=Papadakis | first5=C. M. | title=Grazing-incidence small-angle X-ray scattering from thin polymer films with lamellar structures – the scattering cross section in the distorted-wave Born approximation | journal=Journal of Applied Crystallography | publisher=International Union of Crystallography (IUCr) | volume=39 | issue=3 | date=2006-05-10 | issn=0021-8898 | doi=10.1107/s0021889806012337 | pages=433–442}}</ref> due to the fact that scattering angles are small, often less than 1 deg. The refraction correction applies to the perpendicular component of the scattering vector with respect to the substrate while the parallel component is unaffected. Thus parallel scattering can often be interpreted within the kinematic theory of SAS, while refractive corrections apply to the scattering along perpendicular cuts of the scattering image, for instance along a scattering rod.

In the interpretation of GISAS images some complication arises in the scattering from low-Z films e.g. organic materials on silicon wafers, when the incident angle is in between the critical angles of the film and the substrate. In this case, the reflected beam from the substrate has a similar strength as the incident beam and thus the scattering from the reflected beam from the film structure can give rise to a doubling of scattering features in the perpendicular direction. This as well as interference between the scattering from the direct and the reflected beam can be fully accounted for by the DWBA scattering theory.<ref name="busch"/>

These complications are often more than offset by the fact that the dynamic enhancement of the scattering intensity is significant.  In combination with the straightforward scattering geometry, where all relevant information is contained in a single scattering image, in-situ and real-time experiments are facilitated. Specifically self-organization during MBE growth<ref name="renaud"/> and re-organization processes in block copolymer films under the influence of solvent vapor<ref name="smilgies"/> have been characterized on the relevant timescales ranging from seconds to minutes. Ultimately the time resolution is limited by the x-ray flux on the samples necessary to collect an image and the read-out time of the area detector.

==Experimental practice==

Dedicated or partially dedicated GISAXS beamlines exist at most [[synchrotron light sources]] (for instance Advanced Light Source (ALS), Australian Synchrotron, [[Advanced Photon Source|APS]], ELETTRA (Italy), Diamond (UK), [[European Synchrotron Radiation Facility|ESRF]], National Synchrotron Light Source II (NSLS-II), Pohang Light Source (South Korea), SOLEIL (France), Shanghai Synchrotron (PR China), [[Stanford Synchrotron Radiation Lightsource|SSRL]]

At [[neutron research facility|neutron research facilities]], GISANS is increasingly used, typically on small-angle (SANS) instruments or on [[neutron reflectometer|reflectometers]].

GISAS does not require any specific sample preparation other than thin film deposition techniques. Film thicknesses may range from a few nm to several 100&nbsp;nm, and such thin films are still fully penetrated by the x-ray beam. The film surface, the film interior, as well as the substrate-film interface are all accessible. By varying the incidence angle the various contributions can be identified.

==References==
{{Reflist}}

==External links==

* [https://smilgies.github.io/dms79/gisaxs/GISAXS.html GISAXS and GIWAXS tutorial] by Detlef Smilgies - Updated Link!
* [http://gisaxs.com/index.php/GISAXS GISAXS wiki] by Kevin Yager
* [https://web.archive.org/web/20100715231021/http://ln-www.insp.upmc.fr/axe4/Oxydes/IsGISAXS/isgisaxs.htm isGISAXS] modelling/fitting software by Rémi Lazzari
* [https://web.archive.org/web/20150924080820/http://www.pprime.fr/?q=fr%2Fbabonneau-david FitGISAXS] modelling/fitting software by David Babonneau
* [http://www.bornagainproject.org/ BornAgain] modelling and fitting software by Scientific Computing Group of MLZ Garching
* [http://portal.nersc.gov/project/als/hipgisaxs HiPGISAXS] Massively Parallel GISAXS simulation code by [[LBNL]]

{{X-ray science}}
{{DEFAULTSORT:Grazing-Incidence Small-Angle X-Ray Scattering}}
[[Category:X-rays]]
[[Category:Scattering]]
[[Category:Synchrotron-related techniques]]
[[Category:Scientific techniques]]
[[Category:Neutron scattering]]
[[Category:Nanotechnology]]