The neutron reflectometer ROG

The neutron reflectometer ROG can measure multiple layer thicknesses up to a total thickness of 300 nm with a 1 nm resolution.

In the ROG a narrowly collimated (polarised) neutron beam illuminates a flat sample at small glancing angles (of the order of a degree). Information on the structure perpendicular to the surface is obtained from the wavelength dependent intensity of the specularly reflected beam.

Information on the magnetic structure is obtained from the dependence on the direction of the polarization of the neutron beam (perpendicular to the beam), parallel or anti-parallel to the in-plane magnetisation of the sample. A polarized beam is obtained by reflection from a magnetised mirror.

A polarization turner is used to select the parallel or anti-parallel mode. The wavelength of a reflected neutron is determined from the time the neutron needs to travel the distance from the chopper at the entrance of the instrument to the detector. The use of a position-sensitive detector gives the possibility to determine the off-specular reflectivity, which yields information on in-plane structure. The twenty one position settings are computer controlled.

Contact person: Dr.Ir. Ad van Well

Measured quantity

Polarization dependent neutron reflectivity R+(q0) and R-(q0) as a function of the perpendicular component of the incoming wave- vector q0 = 2pq0/l.

From these reflectivities information is obtained on the nuclear and magnetic structure as a function of depth (from approximately 1 to 300 nm) perpendicular to the surface as a function of external parameters (e.g. H, T, time).

Applications

surface chemistry and physics:
density profiles at liquid/vapour interfaces
adsorption of surfactants or polymers at liquid/vapour,
liquid/liquid, and liquid/solid interfaces
Langmuir-Blodgett films and multilayers
magnetism:
magnetic structure at interfaces
magnetic structure in thin films and multilayers
magnetic recording materials

Details of the ROG Neutron Reflectometer

The neutron beam is parallel to both frames, at fixed distance. Modes of operation: · Straight beam. Angle with horizon: between 30 mradians downwards and 5 mradians upwards.

 

The beam can be deflected upwards or downwards with super mirror (polarized beam possible).

 

 

Instrument details:

 

 

 

Beam tube

 

left Stacked Neutron Guide

 

Beam width

 

30 mm

 

Distance from chopper to

 

monitor: 4075 mm

sample: 4415 mm

detector: 5415 - 6415 mm

 

Distance between slit diaphragms

 

3000 mm

 

Polarisation magnetised

 

CoTi supermirror

 

Double-disk chopper

 

2% or 4% TOF-resolution for all wavelengths frequency @ 6000 rpm

 

Monitor

 

9% efficiency at λ = 0.18 nm

 

Detectors

 

3He detector, 20 cm ´ Æ 2.5 cm

2-dim position sensitive scintillator detector,

Æ 10 cm, ~ 1 mm resolution

 

Wavelength range

 

0.1 < λ < 1.5 nm

 

Glancing angle

 

5 < q0 < 42 mrad for liquids from top

5 < q0 < 17 mrad for liquids from bottom

5 < q0 < 140 mrad for solids

 

Wavevector transfer

 

0.06 < 2q0 < 4.5 nm-1 for liquids from top

0.06 < 2q0 < 1.5 nm-1 for liquids from bottom

0.06 < 2q0 < 17.5 nm-1 for solids

 

Auxilary equipment

 

Magnet (B up to 0.8 T)

Vibration isolation system (JRS)

Closed teflon trough for liquids

 

Transnational Access

This instrument can be used with European funding.

 

Name author: M.Blaauw
© 2017 TU Delft

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