reflectometry in danse paul kienzle 1 and john f. ankner 2 1 nist center for neutron research 2...
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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