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Focused X-Ray Beams :
Generation and Applications
Advances in Science, Engineering and Technology Colloquium
[email protected]
X-ray Interaction with Matter
source: Spring-8 web site
Focused X-ray Beams
W.C. Roentgen : Refractive index of all materials ≈ unity
Difficult to make an x-ray lens.
With the recent availability of extremely bright x-ray sources
(synchrotron storage rings, x-ray free electron lasers, …),
R&D efforts towards focusing x-rays to smaller and smaller
size have become intense.
At present it is possible to generate focused x-ray beam of
<30 nm, using the reflection, diffraction and refraction
phenomena in the x-ray region.
Optics for X-ray (~10 keV)
 Complex refractive index: n=1-δ+iβ
 Refraction is small: Re(n)=1-δ with δ=10-6 ….10-5
 Focal length: f=R/2 (n-1) = R/2δ
 Absorption is high: absorption lengths 1μm … 10μm
 Figure of merit: β/δ = 10-5 (Li,Be) …10-3 (C,Al,Si) …10-1
(Au,Pt,W)
Dilemma
 smaller f
smaller R
 more flux
larger aperture
larger R
Why focus x-ray to sub micron size?
 X-ray microscopy: Most materials are heterogeneous at
length scale of micron to nm (transmission microscopy,
scanning microscopy…).
 Increased flux: Higher sensitivity due to reduced
background.
 Small samples or samples in different environment
(pressure, temperature, magnetic field …)
General Terminology in X-Ray Optics
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

Magnification
Numerical Aperture
Resolution
Depth of focus
Astigmatism
Chromatic Aberration
Ideal focusing lens: Converts plane wave
to a spherical wave, with the
conservation of the coherence
 In-coherent source
Geometric Optics
Refraction
1/F = (n-1) (1/Do + 1/Di)
 Coherent source
Wave Optics
Refraction
Phase shift along the optical path
Magnification: M=Di/Do
For generating x-ray micro/ nano focused beam M~10-2 to 10-4 in
synchrotron beamline.
Numerical Aperture
• Measure of light collection power
NA= n Sin θmax
NA ~ 0.5 (D/f)
NA is very closely related to performance of the
optics (e.g. depth of focus, diffraction limited
resolution, flux etc.). Low NA is one of the
major constraint for x-ray optics.
For high photon flux at the focus:
High brightness and large numerical
aperture
 Focusing increases the angular spread.
 Brightness: B= P/ (ΔAs . ΔΩs)
P : radiated power; ΔAs :source area ;
ΔΩs : source divergence
The photon flux at the focus is ~ B. 2 . NA2. η
 is spot size and η is the efficiency of the optics.
Thus the high photon flux at the focus requires
high source brightness and large numerical
aperture optics.
Rayleigh’s Criterion: Resolution Limit




Point sources are spatially coherent
Mutally incoherent
Intensities add
Rayleigh criterion (26.5% dip)
Conclusion : With spatially coherent illumination, objects are “just resolavable” when
source: D. Attwood
Resolution improves with smaller λ
Depth of focus
Where  is a spot size
source: Xradia
Astigmatism
Horizontal and vertical focusing
are separated at grazing incidence.
fm = (R Sin θ)/2
fs = R/(2Sinθ)
Source
Reflection Crossed mirror pair (Kirkpatrick-Baez system)
Focus
Synchrotron radiation sources
or
or
Chromatic aberration
Reflective Optics: Can focus pink beams using
grazing incidence optics. Grazing angles can be
higher by using x-ray multilayer reflector, but
at the cost of limited energy
Diffractive Optics : f ~ E , small NA
Refractive Optics : f ~ E2
X-ray Micro focussing optics
 Reflective optics
 Diffractive optics
 Refractive optics
X-ray Reflectivity: Single and Multilayer
Single Layer
Multilayer
Total external reflection
when θ<θc (a few mrad)
Large θ leads to larger acceptance
or shorter mirror length.
c = √2  = λ√Z
Spectral bandwidth ~ a few %
X-ray Multilayer Optics
Advantages
Layer
Can
thicknesses can be tailored
be deposited on figured surfaces
Reflective optics
 Schwarzschild objective
 Wolter microscope
 Capillary optics
 Kirkpatrick-Baez mirrors
Schwarzschild objective
 Near normal incidence with
multilayer coating (126 eV)
 N.A. > 0.1
 Imaging microscope
source: F. Cerrina (UW-Madison), J. Underwood (LBNL)
Wolter microscope
 Use 2 coaxial conical
mirrors with hyperbolic and
elliptical profile
 Imaging microscope
 Difficult to polish for the
right figures and roughness
Capillary optics
One-bounce capillary
Multi- bounce condensing
capillary
 Large working distance (cm)
 Easy to make with small
opening (submicron)
 Compact: may fit into space too
 small for K-B
 Nearly 100% transmission
 Short working distance (100 μm)
 Low transmission
 N.A. ~ 2-4 mrad (¡Ü 2θc)
 Difficult to make submicron spot
source: D. Bilderback (Cornell)
Kirkpatrick-Baez mirrors
A horizontal and a vertical mirror arranged to have a
common focus
 Achromatic: can focus pink beam (but not with
multilayer coating)
Can be used to produce ~ round focal spot
 Very popular for focusing in the 1-10 μm
APS 85x90 nm2 ESRF 45 nm, Spring8 25x30 nm2
(diffraction limit ~ 17 nm)

Diffractive optics
 Fresnel zone plates (FZP)
 Multilayer Laue Lens (MLL)
Fresnel zone plates
(Phase ZP and Amplitude ZP)
 Efficiency of an amplitude ZP with opaque zones ~ 10%
 Efficiency of a phase ZP with π-phase shift ~ 40%
Phase
For a phase shift of 
Fabrication Fresnel zone plates
E Anderson, A Liddle, W Chao, D Olynick and B Harteneck (LBNL)
Hard X-ray ZP: recently available
W. Yun (Xradia)
Δr = 24 nm, 300 nm thick, Aspect Ratio = 12.5 (Xradia)
Aspect ratio > 100 is probably difficult to achieve with lithographic zone plates!
Multilayer Laue Lens (MLL)
For high aspect ratio
Aspect ratio > 1000 (Δr = 5-10 nm, 10 μm thick) demonstrated
Source : A. Macrander (APS)
Refractive optics
 Compound refractive lens (CRL)
Small aperture
Small focusing strength
Strong absorption E>20keV
f = R/2N
R radius (~200 m)
N number of lenses (10 …300)
 real part of refractive index (10-5 to 10-6)
2R0  800 m -1000 m
d 10 m -50 m
Parabolic profile : No spherical aberration
Source : Achen Univ., APL 74, 3924 (1999)
What is Synchrotron Radiation?
Synchrotron radiation is emitted from an electron
traveling at almost the speed of light (0.99999999C) and
its path is bent by a magnetic field. It was first observed
in a synchrotron in 1947. Thus the name
"synchrotron radiation".
Generation of Synchrotron Radiation
Synchrotron radiation is emitted at a bending magnet
or at an insertion device. Corresponding to the weak
and strong magnetic field, there are two types of
insertion devices: an undulator and a wiggler.
General Properties of
Synchrotron Radiation
 Ultra-bright
 Highly directional
 Spectrally continuous (Bending Magnet /Wiggler)
or quasi-monochromatic (Undulator)
 Linearly or circularly polarized
 Pulsed with controlled intervals
 Temporally and spatially stable
Synchrotron Radiation Spectrum
Brightness of synchrotron sources
X-ray Sources: Peak Brilliance
Synchrotron Radiation(SR) Sources…
America:
Asia:
Europe:
Oceania:
18
25
22
1
IV generation light sources under construction/ planning stage.
A Typical Synchrotron Facility
Creating SR light
(3) Then they pass
into the booster ring
accelerated to   c
(4) And are finally
transferred into
the storage ring
(1) Electrons are
generated here
(2) Initially accelerated in the LINAC
A typical
Synchrotron source
With
BM and ID
Building a Synchrotron Source…
Magnets
Beam physics
Survey and alignment
Controls
LCW
UHV
Power supplies
Synchrotron
Health physics
Beam diagnostics
RF systems
Chemical Cleaning
Cryogenics
etc.
Fabrication and
metrology shop
Utilization of the properties of the SR
beam: A few examples
Microbeam: Diffractometry, microscopy
Pulsed Structure : Time-resolved experiments
Energy Tunability: Crystal structure analysis, anomalous
dispersion
High collimation: Various types of imaging techniques with high
spatial resolution
Linear / circular polarizion : Magnetic properties of materials.
High energy X-ray: High-Q experiments, Compton scattering,
Excitation of high-Z atoms
High spatial coherence: X-ray phase optics and X-ray
interferometry
Application of SR
Life Science
 Atomic structure analysis of protein macromolecules

Elucidation of biological functions
Materials Science
 Precise electron distribution in inorganic crystals
 Structural phase transition
 Atomic and electronic structure of advanced materials
superconductors, highly correlated electron systems
and magnetic substances
 Local atomic structure of amorphous solids, liquids
and melts
Chemical Science
 Dynamic behaviors of catalytic reactions
 X-ray photochemical process at surface
 Atomic and molecular spectroscopy
 Analysis of ultra-trace elements and their chemical
states
 Archeological studies
Earth and Planetary Science
 In situ X-ray observation of phase transformation of
earth materials at high pressure and high temperature
 Mechanism of earthquakes
 Structure of meteorites and interplanetary dusts
Environmental Science
 Analysis of toxic heavy atoms contained in biomaterials

Development of novel catalysts for purifying
pollutants in exhaust gases
 Development of high quality batteries and hydrogen
storage alloys
Industrial Application
 Characterization of microelectronic devices and
nanometer-scale quantum devices
 Analysis of chemical composition and chemical state
of trace elements
 X-ray imaging of materials
 Residual stress analysis of industrial products
 Pharmaceutical drug design
Medical Application
 Application of high spatial resolution imaging
techniques to medical diagnosis of cancers
SR Based Research Methods
 X-ray Diffraction and Scattering
 Spectroscopy and Spectrochemical Analysis
 X-ray Imaging
 Radiation Effects
Indus building complex
Synchrotron Complex at RRCAT
housing Indus-1 and Indus-2
Schematic View of Indus Complex
Booster Synchrotron
(700 MeV)
TL-1
(Started in 1995)
Microtron
(20 MeV)
(Started in 1992)
TL-2
TL-3
Indus-1
(450 MeV, 100 mA)
(Working since 1999)
Indus-2, 2.5 GeV SR
Trials to store the beam began in
December 2005
Indus-1 Storage Ring
Schematic representation of
experimental hall
Five beamlines have
been operational.
Several publications
(~50) have resulted
from utilization of these
beamlines.
Beamlines operational on Indus-1
λ/Δλ
Experimental station
1.4 m TGM with
three gratings
~400
Reflectometer and time
of flight mass
spectrometer
Pt coated Toroidal
2.6 m TGM with
three gratings
~600
Hemi-spherical analyzer
(HSA)
4-100
Pt coated Toroidal
1.4 m TGM with
three gratings
~400
Angle resolved HSA
electron analyzer
Photo Physics
(BARC)
50-250
Au coated Toroidal
1 m Seya-Nomioka
~1000
Absorption cell , sample
manipulator
High resolution
VUV (BARC)
70-200
Au coated cylindrical
6.65 m off plane
Eagle mount
spectrometer
~70000 High temperature
furnace, absorption cell
Beamline
Range
(nm)
Beamline Optics
Pre and Post mirror
Reflectivity
(RRCAT)
4-100
Au coated Toroidal
Angle
Integrated PES
(UGC-DAECSR)
6-160
Angle Resolved
PES (BARC)
Monochromator
Recent studies using Indus -1
 Reflectivity near absorption edge energies
 Hydrogen bond braking near absorption edge
energies
 Interface studies
 Photo dissociation spectroscopy
 X-ray multilayer optics and optical response in soft
x-ray region
 X-ray Telescope Calibration
Indus-2 beamlines
BM Beamlines
ADXRD
(commissioned)
BL#
Groups
BL-12
RRCAT
EDXRD
(commissioned)
BL-11
BARC
EXAFS
(commissioned)
BL- 8
BARC
GIMS ( being installed)
Bl-13
SINP
PES (being installed)
BL-14
BARC
BM MCD/PES
BL-1
UGC-DAE-CSR
Imaging
BL-4
BARC +
UGC-DAE-CSR
ARPES/PEEM
BL-6
BARC
White-beam lithography
BL-7
RRCAT
Scanning EXAFS
BL-9
BARC
XRF-microprobe
BL-16
RRCAT
SWAXS
BL-18
BARC
Protein Crystallography
BL-21
BARC
X-ray diagnostics
BL-23
RRCAT
Visible diagnostics
BL-24
RRCAT
Soft X-ray
BL-26
RRCAT
Under Construction
being installed/
under construction
Installed
X-ray Multilayer Deposition Laboratory
Reflectivity Beamline Indus-1
Normal incidence soft x-ray reflector:
Mo/Si multilayer
0.8
Reflectivity
10
0.6
Reflectivity
10
0
-1
0.4
0.2
0.0
100
110
120
130
140
150
160
Wavelength A
10
-2
10
-3
0
20
40
60
Incidence angle deg
80
100
X-ray calibration: Soft X-ray Telescope
ASTROSAT :One of the
most ambitious space
astronomy programme
initiated by Space Science
Community in India.
Payload of soft x-ray
imaging telescope (SXT)
sensitive to 0.3 to 8 keV is
planned.
Performance of SXT
grazing incidence foil
mirrors evaluated using
Indus-1 soft x-ray
reflectivity beamline
Archana et al Experimental Astronomy
(2010) 28:11-23
Soft & Deep X-ray Lithography (SDXRL)
beamline -BL7
SDXRL beamline - Applications
MEMS (Micro-Gears, …)
Zone Plate
 Fabrication of Hard x-rays optics
 Small periodicity gratings
Micro Electro Mechanical Systems (MEMS)
 Photonic band gap crystals (for visible radiation)
 Quantum wires and quantum dots devices (high
density pattering over large areas)
 Fabrication of high density hetrostructures for nano
devices
High aspect ratio micro-structures
SDXRL beamline – Present Status
Installed beamline inside hutch
X-ray mirrors with manipulators
Primary slits
X-ray
BL16
Beamline Front End
Beamline optics
DCM
Beam transport
pipes and vacuum
components
KB mirror
Front end
exit
Pre-DCM section
X-ray Microprobe beamline
Beamline optics
Post-DCM section
DC
M
Beam
transport
pipes and
vacuum
components
Road Ahead….
• A modest start has been done at RRCAT with the
availability of synchrotron radiation sources Indus1 and Indus-2. These sources are being operated on
a round the clock basis, week after week.
• Few x-ray beamlines have become operational, with
many more in implementation stage.
• These are national science facilities. Users from
various fields are welcome to plan research using
these facilities, which will significantly help us to
improve the performance further. It will be our
endeavor to support all users of this national
facility.
All are welcome to Indus SR Facility
67
Acknowledgements:
X-ray Diffraction and Scattering
Research Methods
Typical Examples of Research Subjects
Macromolecular
crystallography ( I-2)
Atomic structure and function of proteins.
X-ray diffraction under
extreme conditions (I-2)
Structural phase transition at high pressure / high
or low temperature
X-ray powder diffraction
(I-2)
Precise electron distribution in inorganic crystals
Surface diffraction (I-2)
Atomic structure of surfaces and interfaces. Phase
transition, melting, roughening, morphology and
catalytic reactions on surfaces
Small angle scattering (I-2)
Shape of protein molecules and biopolymers.
Dynamics of muscle fibers
X-ray magnetic scattering
Magnetic structure. Bulk and surface magnetic
properties
X-ray Optics
X-ray interferometry. Coherent X-ray optics. Xray quantum optics
Spectroscopy and Spectrochemical
Analysis
Research Methods
Typical Examples of Research Subjects
Photoelectron spectroscopy
(I-1)
Electronic structure of advanced materials such as
superconductors, magnetic substances, and highly correlated
electron systems.
Atomic and molecular
spectroscopy (I-1)
Photoionization spectra, photoabsorption spectra and
photoelectron spectra of neutral , atoms and simple molecules.
Spectra of multicharged ions.
X-ray fluorescence
spectroscopy (I-2)
Ultra-trace element analysis. Chemical states of trace elements.
Archeological and geological studies.
X-ray absorption fine
structure (I-2)
Atomic structure and electronic state around a specific atom in
amorphous materials, thin films, catalysts, metal proteins and
liquids.
X-ray magnetic circular
dichroism (I-2)
Magnetic properties of solids, thin films and surfaces. Orbital
and spin magnetic moments.
Infrared spectroscopy (I-2)
Infrared microspectroscopy. Infrared reflection and absorption
spectroscopy.
X-ray inelastic scattering
Electronic excitation. Electron correlations in the ground state.
Phonon excitation.
X-ray Imaging
Research Methods
Typical Examples of Research Subjects
Refraction-contrast
imaging (I-2)
lmaging of low absorbing specimens.
X-ray fluorescence
microscopy (I-2)
Imaging of trace elemental distribution with a
scanning X-ray microprobe.
X-ray microscopy (I-2)
Imaging of materials by magnifying with
microfocusing elements.
X-ray topography (I-2)
Static and dynamic processes of crystal growth,
phase transition and plastic deformation in crystals.
Crystal lattice imperfections.
Photoelectron emission
microscopy (I-2)
Element-specific surface morphology. Chemical
reaction at surface. Magnetic domains.
Radiation Effects
Research Methods
Typical Examples of Research Subjects
Material processing (I-2)
Soft X-ray CVD. Microfabrication.
Radiation biology (I-2)
Radiation damage of biological substances.
Mo/Si soft x-ray Polarizer multilayer
1
N=120 layers
Top SiO2 20.7A: 6.7A: 2.78e-2
Si
72.0A; 7.1; 4.22e-3; 1.94e-3
Mo
31.0A; 7.0 ; 7.99e-2; 8.66e-3;
SubS
5.0A
Beam polarization 80%
Reflectivity
0.1
wavelength 138A
0.01
1E-3
Measured
Fit
1E-4
-10
0
10
20
30
40
50
Incidence angle deg
60
70
80