ID10B Overview

Introduction

Troika II is a multi-purpose beamline for the study of liquid and solid interfaces, combining grazing-incidence diffraction (GID), x-ray reflectivity (XRR), and grazing-incidence small-angle scattering (GISAXS) techniques in a single instrument. Scattering experiments can be performed in both horizontal and in vertical scattering geometry. High-resolution studies are possible in both scattering geometries via the use of analyzer crystal stages in different orientations. A speciality of ID10B is the study of organic thin films on solid or liquid and fluid surfaces. With the techniques of GID, XRR and GISAXS, length scales from sub-nm to 100 nm, in some cases even up to 1000 nm, can be explored. This allows to investigate self-organization processes at surfaces, interfaces and in thin films.

Beamline Overview

Fig. 1: Schematic layout of the TROIKA beamline.

Click here to get detailed drawing of the Optics hutch (pdf format)
Click here to get detailed drawing of the Experimental hutch (pdf format)

The Troïka II beamline is the second branch of a high-brilliance multipurpose undulator beamline, sharing the source with Troïka I (ID10A) and Troïka III (ID10C). Independent operation of Troïka II branch from the other branches of ID10 is achieved by splitting the white beam from the undulators with an X-ray transparent monochromator crystal.

The schematic layout of the TROIKA beamline is shown in Figure 1. The front end (FE), located 26 m from the insertion devices (ID) interfaces the beamline to the storage ring and contains the main beam shutter, a diamond window (300 µm) and beryllium compound refractive lenses (CRL). The first safety hutch (Optics-Hutch) houses the primary slits (PS), a beam diagnostics device (BPM), the TROIKA II monochromator for the ID10B branch where the X-ray beam splits. The transmitted white beam passes in a shielded pipe through the TROIKA II experimental hutch and enters into the TROIKA I experimental station.

Fig. 2: Schematic layout of ID10B beamline (PS primary slits, M1, M2 first and second monochromator vessel, Mi double mirror, PhS beam shutter, D deflector, Diff diffractometer; source distances in m).

ID10B is equipped with a horizontal fixed-exit diamond (111) double-crystal monochromator (M1, M2) located in the common ID10 Optics Hutch which is tunable in the energy range from 8 keV to 13 keV. The first monochromator crystal (M1) splits the beam into a transmitted white beam and a monochromatic beam which by means of another Bragg reflection from a second diamond(111) crystal (M2) runs parallel to the white beam at a fixed distance of 850 mm. A separate (horizontally displaced) beam pipe contains the ID10B double mirror (Mi), diagnostics optics and secondary slits and guides the ID10B monochromatic beam via an independent beam shutter (PhS) into the TROIKA II experimental station.

The experimental hutch is equipped with a beam deflector stage (D), mainly used for experiments on liquid surfaces and multi-purpose 2+2 circle diffractometer (Diff) for surface/interface studies in soft- and hard condensed matter systems. In order to follow the deflected beam, the support of the diffractometer can be rotated around the deflector and its height can be adjusted. The diffractometer has a two-component detector arm and a combined scattering stage for both horizontal and vertical scattering geometries. The sample position on the diffractometer is at 40.88 m from the source.

Full energy tunability of both branches is ensured by three undulators with individually tunable gaps.

The Undulator Source

The beamline uses three undulator segments in series: one 27 mm undulator (U27), one 35 mm undulator (U35), and a revolver unit carrying both U27 and U35 undulators. Hence the source consists of either 2xU27+U35 or 2xU35+U27 depending on the energy requirements. All undulators are installed in series in the ID10 high- straight section. The source size (FWHM) for the 3.9 nm lattice and 1% coupling is 928 µm (horizontal) and 23 µm (vertical). The electron beam divergences are 24 µrad (h) and 9 µrad (v) . The divergence of the photon beam depends on the length of the undulator, the photon energy, the energy spread of the electron beam and the undulator tuning. Typical divergences (FWHM) at 10 keV are 28 µrad (h) and 17 µrad (v) implying a maximum beam size of 2 mm (h) x 0.8 mm (v) at the TROIKA I monochromator position (44.2 m from source). The total emitted power from a single undulator is 1.14/2.05 kW (U27/U35 @ 100 mA) and the maximum power density in the central cone at 27 m distance is 66 W/mm² for both undulators at 100mA ring current. Figure 3 shows undulator spectra taken with a Si monochromator crystal. The spectra have been corrected for absorption by Be and diamond windows. More details about the UNDULATOR SOURCE

Fig. 3: Flux spectra of the ID10 undulators tuned to produce 8 keV photons (U27: 1st harmonic, U35: 3rd harmonic). The spectra were recorded with a Si (111) crystal in symmetric Bragg scattering geometry.

Monochromator

The first single bounce monochromator crystal is a diamond (111) crystal of 120 µm thickness in symmetric Bragg geometry and acts as a beam splitter deflecting a narrow energy band of radiation (E/E = 6·10^-5) in horizontal geometry while the main part of the beam is transmitted downstream to the other Troika experimental stations (ID10A and ID10C). The transmission of the first crystal is between 40% to 70% for the transmitted beam depending on the Bragg angle of the crystal and yields about 65% for photons close to 9 keV. The crystal holder has two additional slots (vertically stacked on a common crystal mount) which can be translated into the white beam. A future option for additional monochromator crystals is diamond (220) (symmetric Bragg geometry).

Independent operation of ID10A/C and ID10B is guaranteed by three undulators in the ID10 common front-end which can be operated simultaneously. Depending on the energy requirements, three modes of operation are possible:

1. Each Troïka station runs on one of the undulators.
2. Both undulators are set to the same gap and the stations use different harmonics.
3. Both stations use the same undulator harmonic.

Using diamond (111) reflections, the monochromators of both Troïka stations can be tuned to the same undulator peak to within 20 eV. In the latter two modes the intensity at both stations is doubled.

The available energy range (either 8 keV-13 keV with diamond (111) or 13keV-22keV with diamond (220)) is given by the exit angle of the beryllium window (25° to 46°) of the first monochromator and the matching range of the translation stage of the second crystal in symmetric Bragg reflection. The second crystal is mounted on a high-resolution goniometer with the usual two rotations, two additional translations and a crystal exchanger. The second monochromator vessel is operated under helium atmosphere, whereas the first monochromator in the white beam is operated in ultra-high vacuum.

The diamond crystals (natural or synthetic) have typical dimensions of 8 x 6 mm² and are cut along the (111) face for one and along the (220) face for other type of crystals. The diamonds are close to perfect with a rocking width for the (111) reflection of typically 0.002° @ 8 keV and show no heat load induced broadening in the undulator beam.

Main mirrors

The Troika II beamline is equipped with a compact double-mirror setup for a strong suppression of higher harmonics. This is particularly important for background reduction in scattering experiments on liquid surfaces. The first mirror is a 300 mm silicon mirror with three strips (platinum, bare substrate, palladium) which adsorbs most of the higher harmonics passing the monochromator. The second mirror is a 300 mm Pyrex mirror with three corresponding stripes. The incidence angle for the mirrors are set typically to 80% of the critical angle of the respective stripe material yielding a suppression of more than 10^-4 of the intensity of third harmonic which is the most important high-energy contribution in the beam.

A ultra-high vacuum chamber houses both mirrors. Each mirror is actuated via bellows by three motorized high-precision jacks forming a kinematic mount. For controlling and aligning the mirrors the displacements of the jacks are converted into incident angle, sideways tilt, and height for both mirrors. The whole mirror assembly can be shifted sideways to choose the required strip material. At the end of the mirror chamber the beam position can be determined with a wire monitor.

In the standard geometry, the first mirror deflects the beam up and the second mirror reflects the beam back horizontally. Small downward deflections of the x-ray beam up to 2.5 mrad for liquid scattering experiments can be obtained by tilting the second mirror accordingly.

Deflector

The deflector stage is a flexible optical device at the entrance of the beam into the experimental hutch. Its primary function is to deflect the incident beam with respect to the horizontal plane for scattering experiments from liquid surfaces and self-organized molecular layers at the air-water interface. For large inclination angles between +60 mrad and -140 mrad the deflector goniometer can be equipped with a Ge(111) Bragg crystal. In this configuration the deflector crystal turn table sits on top of an arc with rotation axis parallel to the beam, so that the incident angle of the beam at the crystal stays fixed at the Bragg angle, while the deflected beam runs on the Scherrer cone. An alternate deflection device for deflection angles up to 20 mrad is a platinum coated Pyrex mirror. The deflector goniometer can be translated in three directions.

Fig. 4: ID10B deflector stage.

Technical Information

scientist in charge	Oleg Konovalov tel:+33 (0)4 76 88 27 31, fax: +33 (0)4 76 88 21 60,   Email
scientific applications	Open undulator beamline for surface diffraction from solids and liquids. /Reflectivity (XRR) , Grazing incidence diffraction (GID), Grazing incidence small angle diffraction (GISAXS), Asymptotic Bragg Diffraction (TRD)/
source parameters	high straight section; three undulator segments in series: U27, U35 and a U27/U35 revolver unit.
		U27 undulator		U35 undulator
	u	27 mm		35 mm
	Kmax	5.0		6.5
	field Bmax	2 T		2 T
	source size	928 x 23 µm2 (HxV) FWHM
	source divergence	28 x 17 µrad2 (HxV) FWHM @ 10keV
	peak brilliance	> 1020 ph s-1mrad-2mm-2 (0.1% bw, 100 mA @ 8 keV)
	power	1.14/2.05 kW @ 100mA ring current (single U27/U35)
	power density	33 W mm-2 (single U27 or U35) @ 27 m distance from source and at 8keV and 100 mA ring current
optics		primary slits	monochromator		mirrors
	distance from source:	27 m	30.5 m		34.5 m
	focusing:	horizontal in monochromatic beam (optional)
	beam size at sample:	< 1 x 0.5 mm2 (HxV) without focusing < 0.03 x 0.1 mm2 (HxV) with focusing
	intrinsic resolution E/E:	5.9 x 10-5 diamond (111)
	flux at sample:	1012 ph/s/mm2 (100 mA @ 9 keV)
detectors	Scintillation counters (Cyberstar)			Ø 10 or 25 mm
	Kapton detector (Kapton scatterer + Cyberstar)			Ø 10 mm
	Linear position sensitive gas detector (PSD)- 50 mm (MBraun)			50 x 10 mm2
	PSD - 150mm (Gabriel/EMBL)			150 x 10 mm2
analyzer crystals	Si(111)	170 x 40 mm2	only in horizontal scattering geometry
	Ge(111)	60 x 40 mm2	symmetric cut
	Si(111)	60 x 40 mm2	symmetric cut
	Si(111)	60 x 40 mm2	asymmetric cut, b=10 at 9 keV
	Si(111)	60 x 40 mm2	asymmetric cut, b=0.1 at 9 keV
	beamline control	Linux PC, SPEC control software
	auxiliary equipment	beam deflector using Si(111) Bragg crystal or Pt coated Pyrex mirrors, analyser, Soller collimator, temperature controller