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

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

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

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

4Reflectometry in DANSEAugust 15, 2006

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

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

Reflectometry in DANSEAugust 15, 2006

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)

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

Reflectometry in DANSEAugust 15, 2006

Landscape (d3 vs d2)

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

7Reflectometry in DANSEAugust 15, 2006

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

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

Reflectometry in DANSEAugust 15, 2006

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

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

9Reflectometry in DANSEAugust 15, 2006

Challenge #3

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

Solution: Develop the appropriate software

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

10Reflectometry in DANSEAugust 15, 2006

Molecular dynamics and reflectivity

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

11Reflectometry in DANSEAugust 15, 2006

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.

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

12Reflectometry in DANSEAugust 15, 2006

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

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

13Reflectometry in DANSEAugust 15, 2006

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

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

14Reflectometry in DANSEAugust 15, 2006

Reflection geometries

Specularαi αf

θ 0

Off-Specularαi αf

θ 0

GISANSαi αf

αi , αf αc

θ 0

Specular: Q = 4πsinα λ

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

15Reflectometry in DANSEAugust 15, 2006

The SNS Liquids Reflectometer

[Manufactured by JJ X-Ray]

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

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

16Reflectometry in DANSEAugust 15, 2006

Adapt NIST Reflpak to tof at SNS

Reduction

Analysis

Common Platform

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

Reflectometry in DANSEAugust 15, 2006

Current Capabilities

Simulate

Reduce

Fit

Model

Analytic

FreeformUser

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

Reflectometry in DANSEAugust 15, 2006

Planned Capabilities

Simulate

Reduce

Fit

Model

Analytic

Structural

FreeformUser

OOMMF

NAMD

GROMACS

Invert

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

Reflectometry in DANSEAugust 15, 2006

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

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

Reflectometry in DANSEAugust 15, 2006

Interface Builder

ModelInterface

Text field

Graph

Button

Data

Title

CountsVector

MethodsTransformData

Component Network

...

...

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

21Reflectometry in DANSEAugust 15, 2006

Simulated SNS reflectometer performance

10 Å SiO2/Si

Q = 4π sinα / λ