Reflectometry in DANSE Paul Kienzle 1 and John F. Ankner 2 1 NIST Center for Neutron Research 2 Spallation Neutron Source, ORNL

Reflectometry in DANSE

Paul Kienzle1 and John F. Ankner2

1NIST Center for Neutron Research

2Spallation Neutron Source, ORNL

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

Reflectometry in DANSEAugust 15, 2006

Reflectometry

M1

M2

detector θ 2θ

Beam Image

apertures


3Reflectometry in DANSEAugust 15, 2006

Specular reflectivity layer models

ll

llll

lll

llll

lll

lllll

kk

kkF

dika

traR

FR

FRaR

1

1,1

2

,1

,1211

2/exp

/

1

.

.

.

r0

tL

Parratt recursionformula

lll

ll

vbn

knk

k

/1

/sin2

2

0

0



Challenge #1

Challenge: Fitting even a relatively simple specular reflectivity curve requires hours of effort by a skilled user

Solution: Direct methods and data inversion



Fitted Data

1e-08

1e-07

1e-06

1e-05

0.0001

0.001

0.01

0.1

1

10

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

Re

fle

ctivity

Q (inverse Angstroms)

data 0fit 0

0

2e-05

4e-05

6e-05

8e-05

0.0001

0.00012

-100 0 100 200 300 400 500 600 700 800

rho (nu

mber d

ensity)

Depth (Ang)



Landscape (d3 vs d2)



Challenge #2

Challenge: SNS data rates will exceed those of current instruments by factors of 20-100, enabling extensive parametric studies in both thermodynamic variables and time. We must self-consistently invert/model entire data sets.

Solution: Apply or develop appropriate multi-data-set minimization routines



Flexibility of DANSE framework

Model 1

Model 2

Model 3

. . .

Model k

Parameters

Sum X2

Nelder Mead Simplex

Levenberg Marquardt

Genetic Algorithms

Multiple data-set refinement



Challenge #3

Challenge: Improve “lines of communication” between simulation techniques (MD, micro-magnetics, etc.) and neutron scattering data

Solution: Develop the appropriate software



Molecular dynamics and reflectivity



Challenge #4

Challenge: SNS instruments will feature gnarly resolution functions

Solution: Fit/model data as it looks to the instrument. Don’t reduce data so much as simulate it. Possibly more natural way to incorporate MD simulation as well.



Wavelength vs. tof

det [n/(cm2-pulse-ster-Å)]

tdet (msec)

8 10 12 14 16 18 20 22 24

(Å

)

2

3

4

5

6

104

105

106

107

108

109

1010

Choppers set todeliver

2.5 Å < < 6 Å



Challenge #5

Challenge: Next-generation reflectometers will be capable of measuring an extensive off-specular Q range. We lack robust modeling capability for this type of data.

Solution: Adapt/develop (2+1)D modeling algorithms and make them user-friendly



Reflection geometries

Specularαi αf

θ 0

Off-Specularαi αf

θ 0

GISANSαi αf

αi , αf αc

θ 0

Specular: Q = 4πsinα λ



The SNS Liquids Reflectometer

[Manufactured by JJ X-Ray]

0 ≤ αliquid ≤ 5.5°0 ≤ 2α ≤ 90°0 ≤ 2θ ≤ 30°



Adapt NIST Reflpak to tof at SNS

Reduction

Analysis

Common Platform



Current Capabilities

Simulate

Reduce

Fit

Model

Analytic

FreeformUser



Planned Capabilities

Simulate

Reduce

Fit

Model

Analytic

Structural

FreeformUser

OOMMF

NAMD

GROMACS

Invert



Reflectometry DANSE project status• First SNS reflectometer beam July 2006

• Have initial data viewer for SURF

• First data October 2006

• Fit program already in use for TOF neutron and fixed- neutron and X-ray data

• Users include undergrads from NIST summer research program

• Current developers are UMD undergrads

• Will hire developer, postdoc and grad student in Y1



Interface Builder

ModelInterface

Text field

Graph

Button

Data

Title

CountsVector

MethodsTransformData

Component Network

...

...



Simulated SNS reflectometer performance

10 Å SiO2/Si

Q = 4π sinα / λ

Documents

Reflectometry in DANSE Paul Kienzle 1 and John F. Ankner 2 1 NIST Center for Neutron Research 2 Spallation Neutron Source, ORNL