X-RAY MICROSCOPY BEAMLINE - Northwestern...

Surface Review and Letters, Vol. 9, No. 1 (2002) 203–211c© World Scientific Publishing Company

THE SCANNING X-RAY MICROPROBE AT THE ESRF“X-RAY MICROSCOPY” BEAMLINE

J. SUSINI, M. SALOME, B. FAYARD and R. ORTEGA

European Synchrotron Radiation Facility, BP220,

F-38043 Grenoble Cedex, France

B. KAULICH

ELETTRA–Sincrotrone Trieste, 1-34102 Basovizza, Trieste, Italy

The development of high brilliance X-ray sources coupled with advances in manufacturing technolo-gies of focusing optics has led to significant improvements in submicrometer probes for spectroscopy,diffraction and imaging applications. For instance, X-ray microscopy in the 1–10 keV energy rangeis better-suited for analyzing trace elements in fluorescence yield. This article will be biased towardssubmicron fluorescence microscopy developed on the ID21 beamline at the ESRF. The main technicaldevelopments, involving new focusing lenses or novel phase contrast method, are presented. Strengthsand weaknesses of X-ray microscopy and spectromicroscopy techniques are discussed and illustratedby examples in biology, materials science and geology.

1. Introduction

X-ray microscopy techniques are emerging as power-

ful and complementary tools for submicron investiga-

tions. Soft X-ray microscopy traditionally offers the

possibility of forming direct images of thick hydrated

biological material in a near-native environment,

at a spatial resolution well beyond that achievable

with visible light microscopy. Natural contrast is

available in the soft X-ray region, in the so-called

“water-window,” due to the presence of absorp-

tion edges of the major constituents (C, N, O).1–3

Recent advances in manufacturing techniques have

enlarged the accessible energy range of microfocus-

ing optics and offer now new applications in a broad

range of disciplines. In particular, X-ray fluores-

cence (XRF) radiation stimulated with monochro-

matic beams in the 1–8 keV range is very well

suited for microanalysis.4 In this energy range, zone

plates can still produce submicron probes and the

sensitivity of XRF is about three orders of mag-

nitude better than obtainable with charged parti-

cles microprobes. This allows not only a tremendous

reduction of the dose required per unit of detected

mass but also opens the possibility of detection of

trace elements. These factors combined with the

capability of imaging relatively thick samples in a

wet environment make XRF a very attractive tool

for microanalysis.

2. The X-Ray Microscopy BeamlineID21

ID21 is a beamline dedicated to X-ray imaging and

spectromicroscopy.5 The beamline is installed on a

low beta straight section, which is equipped with

three undulators and provides beam for two inde-

pendent end-stations on two separate branch-lines

(Fig. 1): the scanning X-ray microscope (SXM)

served by the “direct” branch-line is equipped with

a fixed-exit silicon monochromator operational in

the 2–7 keV energy range, and the full-field imag-

ing transmission X-ray microscope (TXM) is served

by the side branch and optimized for imaging tech-

niques in the 3–7 keV range. Both microscopes use

zone plates as focusing lenses.

In particular, the optical design of the SXM has

been driven by the diffraction properties of Fresnel

203

204 J. Susini et al.

Fig. 1. Layout of the X-ray microscopy beamline, ID21.

Fig. 2. Schematic of the scanning X-ray microscope.

zone-plates: the rejection of unwanted diffraction

orders is performed by combination of a central stop

and an order-selecting aperture (OSA) (Fig. 2). The

central stops consist of 4-µm-thick gold disks with

various diameters (40–300 µm) deposited on a thin

silicon nitride window. A series of pinholes acting

as OSA are mounted downstream of the focusing

optics. Their diameter, ranging from 5 µm to

200 µm, can be adapted to the optical features of

the zone plate. Due to the wide energy range of the

beamline and the diversity of zone plate characteris-

tics, the working distances to be accommodated vary

tremendously from 30 mm up to 1 m for the largest

diameter zone plate (1 mm) at 7 keV. To cope

with large working distances, an additional moto-

rized stage for zone plates, which is external to the

microscope chamber, has been designed. For spec-

troscopy applications, maintaining the focus on the

sample is essential while scanning in energy. For

that purpose the guiding quality of the zone plates

translation stage along the beam axis is even more

critical and has required specific in-house develop-

ments. The sample support includes two superposed

translation stages: the lower stage driven by stepper

motors exhibits a coarse resolution (< 500 nm) for

a range of +/− 4 mm and is used for positioning

of the region of interest of the sample in the beam;

the upper stage is a commercial piezoelectric driven

X–Y flexure stage allowing scanning of the sample in

a 100 µm range with 1 nm resolution and scan speed

of 1 ms/pixel. The microscope can operate either in

air of in vacuum. The main fields of applications are

driven by the unique attributes of X-ray microscopy

in the “multi-keV” energy range:

(i) The access to K-absorption edges and fluore-

scence emission lines of medium-light elements

and L, M-edges of heavy materials allows micro-

spectroscopy (e.g. XANES), chemical mapping,

trace element mapping and specimen labeling

with high spatial and spectral resolutions.

(ii) The higher penetration depth compared to soft

X-rays allows imaging of thick samples, in par-

ticular within their natural, wet environment.

(iii) Large focal lengths and depths of focus give

suitable conditions for specific sample environ-

ments and also X-ray tomography.

(iv) The control of the linear or circular polariza-

tion at K-edges of transition metals, L-edges of

rare earths and M-edges of actinides opens new

windows of applications in X-ray magnetic

circular dichroism and magnetic diffraction

within the micron scale.

3. Zone Plates for Multi-keV Energies

The development of high resolution X-ray micros-

copy in this rather unexplored multi-keV energy

range required a considerable effort in technical and

instrumental developments. Various types of zone

plates are currently needed for each type of appli-

cation. (i) Fluorescence or diffraction applications

require large diameter and medium resolution (thus

long focal length) zone plates, offering high flux and

a better access to the sample. (ii) Full-field X-ray

microscopy necessitates high resolution zone plates,

to be used as objective lenses and large diameter

zone plates for condensers. In all cases the effi-

ciency of the lens must be as high as possible, and

for practical reasons the use of apodized zone plates

The Scanning X-Ray Microprobe at the ESRF “X-Ray Microscopy” Beamline 205

(with a central stop) is desirable. Therefore several

European collaborations devoted to the development

of optimized Fresnel zone plates were initiated with

particular emphasis upon high efficiency zone plates

for the 2–7 keV range on one hand and high resolu-

tion zone plates for the Ca K-edge region (∼ 4 keV)

on the other hand. A first project was carried out

by the Institut fur Rontgenphysik (Georg-August-

Universitat Gottingen, Germany). Based on the

development of zone plates generated by electroplat-

ing of gold and nickel, it provided zone plates with

the highest spatial resolution ever obtained at 4 keV.

Ni and Au zone plates were used in the TXM, yield-

ing to a diffraction efficiency of 10% and spatial

resolution of 85 nm.6 A second collaboration with

the Paul Scherrer Institute (Villigen, Switzerland),

aimed to develop on one hand germanium lenses

optimized for operation near the sulphur absorption

K-edge at 2472 eV and on the other hand zinc sul-

phide nanostructures used as test objects (Siemens

star) for the same energy. Features with lateral

dimensions down to below 100 nm were imaged in

fluorescence mode.7 However, the efficiencies of such

zone plates are still far from 100% because a sig-

nificant fraction of incident beam is delivered into

the (undiffracted) zero order. At multi-keV energies,

the efficiencies are usually of the order of 10–20%

and cause a significant loss in the potential photon

flux in the spot. This drawback can be overcome

by optimizing the structure profile of the zones, and

a 100% focussing efficiency can be obtained with a

nonabsorbing lens with parabolic zone profile. In

addition to their high efficiency, these lenses offer the

advantages of low background signal and effective

reduction of unwanted diffraction orders by intro-

ducing selection rules.8 In practice, such profiles are

extremely difficult to produce with existing lithog-

raphy techniques. Quaternary electroplated nickel

zone plate — developed in collaboration with CNR-

IESS (Roma, Italy) and TASC-INFM (Trieste, Italy)

— were tested and used at ID21. The lens tests

were performed at 5.5, 6.0, 7.0 and 8 keV and

demonstrated efficiencies of 43%, 45%, 57% and 45%,

respectively.9

4. Examples of Applications

The experiments on ID21 can be broadly divided

into two categories: (i) morphological studies or

Fig. 3. Elemental distribution of calcium (left) and sul-fur (right) of a hair slice. The images were acquired influorescence yield with a microprobe of 0.3× 0.3 µm2.

elemental detection and (ii) spectromicroscopy or

chemical mapping. A few selected examples are

briefly described in the following paragraph.

4.1. Calcium in human hair shaft

Among the trace elements in hair, calcium and

chlorine are the most abundant (several hundreds of

ppm concentration). The calcium content in hair was

recently reported to be medical-status-dependent.

In particular, it could be used as an indicator of

prevalence of heart disease. In order to better

understand this relationship, a series of experiments

was undertaken using the SXM in fluorescence yield,

aiming at specifying the concentration of calcium in

human hair shaft (Fig. 3).

Up to now, only low resolution radial concen-

tration profiles have been obtained by the proton

microprobe technique. The use of micro-XANES

techniques in fluorescence yield has permitted one

(i) to map the calcium content in the hair section

at 0.3 × 0.3 µm2 spatial resolution, (ii) to establish

the existence of several binding-states with sulfur,

and (iii) to relate them to various structural and

biochemical components of hair.10 This new infor-

mation will now be exploited for screening natural

variability and diseases.

4.2. Chromium speciation

The combination of submicron X-ray imaging with

XANES spectroscopy is fully exploited in the study

of chromium toxicity. In particular, it allows

direct determination of the spatial distribution of

the Cr(III) and Cr(VI) valence states within various

samples. Several complementary experiments were


carried out on this topic at different levels of

investigation:

(i) Environmental sciences. In an environmental

pollution study, the SXM was used in the anal-

ysis of soils contaminated with chromium ore

processing residue. In particular, determina-

tion of the spatial distribution of the Cr(III)

and Cr(VI) valence states within soil samples

was performed. This has permitted a fuller

understanding of the reduction process of

the highly toxic hexavalent chromium to the

trivalent state and should help in indicat-

ing and evaluating promising soil remediation

methods.11

(ii) Chromium in tissue. Preconception exposure

of male rodents to certain carcinogens may

increase the risk of tumors in offspring, and

a similar phenomenon is suspected in humans,

especially with regard to occupational metals.

In a recent study, a significant increase of

tumors in offspring was observed after exposure

of male Swiss mice to Cr(III), a constituent of

welding fumes. The mechanism of chromium

trans-generation carcinogenicity remains un-

known. There is a need for the determination of

tissue and cellular distributions of chromium in

mice reproductive glands to better understand

the chemicobiological interactions involved in

this process. Using scanning proton probe

X-ray microanalysis detection of chromium was

performed in testes sections from mice 24 h after

intraperitoneal administration of 1 mmol/kg

CrCl3. Chromium concentration was about

5 µg/g dry mass in average close to the detection

limit of the PIXE technique. X-ray fluorescence

measurements on the SXM confirmed for the

first time the presence of chromium in the tu-

nica albuginea and within isolated cells from

the interstitial connective tissue at even lower

concentration.12

(iii) Intracellular chromium speciation. Hexavalent

chromium compounds are established carcino-

gens but their mechanism of cell transforma-

tion is not known. Up to now, there has been

no microanalytical technique sensitive enough

to allow the observation of chromium distribu-

tion and oxidation state in cells at carcinogenic

concentrations. In this experiment, the SXM

was used to map Cr(VI) and Cr(III) distribu-

tions in cells exposed in vitro to carcinogenic

concentrations of soluble and insoluble Cr(VI)

compounds. Exposure to soluble compounds,

weak carcinogens, resulted in a homogeneous

intracellular distribution of Cr(III), confirming

by in situ measurement its suspected presence

in the nuclei. Cr(VI) was never detected in

cells, suggesting a rapid intracellular reduc-

tion. Exposure to insoluble compounds, strong

carcinogens, also resulted in a homogeneous

distribution of Cr(III) in cells. However, in

this case Cr(VI) aggregates were observed on

the cell environment, suggesting that the mech-

anism of Cr(VI) genotoxicity is very probably

dependent on distant, and chronic, oxidation

effects and free radical production. The in-

tracellular and/or extracellular membrane-bond

nature of Cr(VI) aggregates should now be

investigated.

4.3. In situ visualization ofmontmorillonite gels

Phase transitions in colloidal suspensions have at-

tracted considerable attention in recent years due

to the fundamental and applied implications of such

Fig. 4. Silicon fluorescence yield mapping of a montmo-rillonite clay gel at 50 g/l. The arrows show the varioustypes of orientational defects.


systems. A direct in situ visualization of montmo-

rillonite gels at 50 g/l has been obtained for the first

time, using silicon fluorescence yield imaging with

a probe size of 1 µm2 and a dwell time of 100 ms.

An unexpected superstructure formed by alternat-

ing clay-rich and clay-poor domains was evidenced

with mesoscopic orientational order (Fig. 4). The

order and size of the oriented entities extend over

distances at least two orders of magnitude higher

than the dimensions of individual clay platelets.

Such long-range organization must certainly be

considered for assessing the formation mechanisms

and properties of gels in systems of charged colloidal

platelets.13 This particular experiment nicely illus-

trates the possibilities of imaging aqueous samples

in fluorescence mode. A special wet cell was deve-

loped to allow this experiment to be performed in

vacuum.

4.4. The role of sulfur in the organicmatrices biocrystals

Calcium carbonate prismatic units of mollusk shells

illustrate very well the complexity of the crystal-

lization as a biologically driven process. Modeling

of biomineral growth requires the understanding of

the roles of organic matrices and their biochemical

interaction with the mineral phase. However, little

information on the organic matrix is available; in

particular, possible links between its high sulfur

content and the mineralizing process are not yet well

established. Sulfur can be found in both proteins and

glucids, the two major organic compounds that com-

pose organic matrices responsible for calcification in

carbonate-producing organisms. In this prospect,

studying the chemical state of sulfur may be used

as an indicator of the relationship between the

mineralizing matrices and the mineral ions.

The study was carried out on calcitic units that

build the external layer of a mollusk shell, the pele-

cypod species Pinna nobilis. These units appear as

linear prisms, closely and very regularly side-by-side

packed, of 50–75 micrometers in transverse sections

and up to 3–4 millimeters in length. The prisms

of Pinna offer remarkable advantages to investi-

gate the organization of biocrystals. They are the

largest units that globally exhibit a single crystal-like

organization, although they are typical polycyclic

structures. They are chemically characterized by

(a)

(b)

(c)

Fig. 5. Fluorescence yield images of a Pinna shell takenat two energies, 2.473 keV (a) and 2.482 keV (b), specificof the sulfur in sulfate or amino acid forms respectively.The pixel size is 0.5 × 0.5 µm2. An electron microscopeimage is given for comparison (c).

the highest sulfur content ever observed, about

0.3–0.4%. Mapping of sulfur species in both intra-

and interprismatic matrices reveals for the first

time the existence of at least two different sulfur

species, respectively sulfate and amino-acid-type

sulfur (Fig. 5). The spectra measured in the ma-

trices were compared with XANES spectra of pure

standard products (cystine, cysteine and chondroi-

tine sulfate A). The results clearly indicated the

absence — or the very low concentration — of

sulfidic cross-links and a difference in sulfate con-

centrations between the intra- and interprismatic

matrices. This result may be related to the putative


opposite roles (respectively catalyst and inhibitor) of

the two matrices in the biomineralization process.14

4.5. Sulfur and iron micro-XANESin geochemistry

Sulfur (as SO2, H2S) is one of the main elements of

volcanic gas while iron is a major element in mag-

mas under two oxidation states, 2+ and 3+. The

oxidation of SO2 produces sulfate aerosols, which

affect Earth’s temperature and climate by sunlight

backscattering. Prior to the eruption, at high tem-

perature and pressure, sulfur may be dissolved in

silicate melts and sulfur chemical states are then

driven by the native redox conditions. Higher is

the proportion of sulfate in silicate melt; higher

may be the amount of sulfur released into the mag-

matic H2O, CO2-rich vapor phase ex-solved from

silicate melts during decompression. Conversely,

sulfur is mobilized by iron-sulfide immiscible liquid

under reducing conditions. Therefore, a better

knowledge of both the concentration and speciation

of sulfur is one of the prerequisites for modeling the

outgassing processes, which affect the uprising mag-

mas prior to the volcanic eruptions.

The Fe(III)/ΣFe ratio is also an excellent indica-

tor of the oxygen partial pressure along the course

of the magma crystallization prior to the eruption.

Therefore, determining the oxidation states of both

iron and sulfur are two independent methods to

assess the redox conditions,15 which may apply to

magmas in route to the surface. These data have

direct implication for sulfur behavior and ex-solution

into the gas phase and thus contribute to the volcanic

eruption forecasting.

Although standard X-ray absorption methods

are best-suited for analyzing geological inclusions

trapped in glass matrices, the size of natural glass

inclusions, ranging from a few micrometers to several

tenths of micrometers, makes microspectroscopy

necessary. Micro-XANES spectra at the sulfur and

iron K-edges of natural glass inclusions hosted in

olivine grains from 900 to 1700 ppm for sulfur and

around 6 wt% for Fe were recorded with a spatial

resolution of about 0.5 × 0.5 µm2. Various species

of sulfur (S2−, SO42− and SO3

2−) were identified

(Fig. 6). Although the presence of S2−, SO42−

has been previously demonstrated, the presence of

SO32− had never been proven yet. A mapping of a

Fig. 6. Sulfur K-edge XANES spectra of three glassinclusions of three different volcanic origins: (a) FamousZone (1250◦C and 900 ppm of sulfur); (b) Piton de laFournaise (1250◦C and 900 ppm of sulfur); (c) Strom-boli (1250◦C and 1700 ppm of sulfur). Acquisition influorescence yield with a probe size of 0.3 × 0.3 µm2.

Fig. 7. Sulfur fluorescence yield images acquired atthree energies (see S-K-edge XANES spectra) of theimmiscible phase (Piton de la Fournaise). Probe size:0.3× 0.3 µm2.

sulfide globule within an inclusion revealed hetero-

geneities in the local environment of sulfur (Fig. 7).

The first estimates on the sulfur chemical envi-

ronment obtained on melt inclusions established the

existence of a high fraction of sulfur dissolved as

sulfate in H2O-rich K-basaltic melts, through the


melt inclusions trapped in olivine grains. The pro-

portion of SO4 is increasing from about 3.2% in

MORB-type glass to nearly 63% in arc mantle-

derived melts (arc magma). The same glass inclu-

sions were analyzed at the iron K-edge. A silicon

[220] had to be used to resolve the two prepeaks

relative to Fe(II) and Fe(III), respectively. This

micro-XANES pre-edge information was used to

estimate the ferric/ferrous ratio.16 For the same

samples, the Fe(III)/ΣFe ratio increases from 0.10

to 0.22 and confirms the same evolution of the

redox conditions.17 This experiment outlines the in-

terest of performing complementary measurements

in similar experimental conditions of the same

samples at different absorption edges.

4.6. Bone mineralization

Bone is a calcified tissue made of a collagen matrix

forming a template for calcification. Most of the

mineral phase of bone consists of a crystallized

calcium phosphate. Several techniques may be used

for the study of bone mineralization. Ash weight

and chemical analysis techniques allow a global

measurement of bone mineral content, but at the

expense of spatial information. However, the study

of the mineral content of bone at a microscopic

scale is of particular interest, since it can give new

insights into remodeling activities, the mineraliza-

tion process and related mechanical properties. A

traditional technique to measure spatial variations of

mineral content in bone is microradiography. Other

techniques offering higher spatial resolution, such as

backscattered electron imaging (BSE), energy dis-

persive X-ray microanalysis (EDX), electron energy

loss spectroscopy (EELS) or Fourier-transformed

infrared microspectroscopy (FT-IRM), provide valu-

able information. X-ray microscopy, which offers

submicron spatial resolution, is an ideal comple-

mentary tool for the morphological study of calci-

fied tissues at the structural unit and cellular scale

(e.g. bone resorption lacunae, osteocytes lacunae).

In combination with microfluorescence detection and

energy tunability, the technique provides in addi-

tion elemental and chemical state sensitivities, and is

suitable for performing quantitative mapping of the

mineral components of calcified tissues (e.g. the

Ca/P ratio in bone). On the SXM, the microflu-

orescence technique allows simultaneous elemental

Fig. 8. Elemental mapping of calcium, phosphorus andthe Ca/P ratio in a human iliac biopsy.

mapping of calcium, phosphorus and the Ca/P

molar ratio inside a bone trabecula (Fig. 8). The

Ca/P ratio is used as an indicator of the hydroxy-

apatite stoechiometry.18

5. Phase Contrast Techniques

Multi-keV X-ray microscopy often suffers from a

lack of absorption resulting in low contrast images.

Furthermore, absorption contrast can subject the,

specimen to a massive dose of radiation leading to

possible structural changes. The use of phase con-

trast techniques leads to a tremendous reduction of

the X-ray dose applied to the specimen.19 Beside

from element absorption edges, phase shift is domi-

nating with increasing photon energy, especially for

multi-keV and hard X-rays. Different approaches

to using the real, phase-shifting part of the refrac-

tive index were successfully used.20–24 Most of the

samples imaged in fluorescence yield are not absorb-

ing enough to provide good images in transmission

mode. Therefore accurate morphological localiza-

tion of trace elements is difficult or even impossible.

The development of phase contrast methods fully

compatible with detection in fluorescence yield is

therefore mandatory. Two original geometries are

currently under investigation at ID21.

5.1. Differential phase contrast with aconfigured detector

In a conventional SXM, a single detector mounted

downstream of the specimen collects all transmit-

ted photons. In this configuration, the result is

an incoherent bright-field image that contains only

absorption contrast and all the phase contrast is lost.

Such an imaging geometry is equivalent to a full-

field microscope operating with illumination from

an extended incoherent source. If a four-quadrant


detector now replaces the transmitted X-ray detec-

tor, then the sum signal provides the usual incohe-

rent qbright-field signal, while the difference signals

yield information about the intensity distribution in

the detector plane. Variations in this intensity distri-

bution arise from local variation of the phase shift of

the X-rays in the sample. The result is called a dif-

ferential phase contrast (DPC) image. DPC imaging

was first suggested for use in the scanning transmis-

sion electron microscopes and has since been success-

fully exploited by Morrison et al.25 Inspired by these

original developments, the use of a fast read-out

configured detector (80 × 80 pixels) developed by

G. Morrison and W. Eaton26 aimed to extend this

method to higher energies. A DPC image from

essentially pure phase objects at sub-100 nm reso-

lution was recovered at 3.3 keV with < 10 ms/pixel

dwell time.27

5.2. Differential interferential contrastwith a configured zone plate

Intrinsically, differential interferential contrast (DIC)

is based on optical systems which create two images

of the object in the image plane, with the condi-

tion that the lateral separation of the two images

is below the diffraction limited spatial resolution of

the optical system. In this case, the two images can

interfere without restrictions to the coherence pro-

perties of the illumination and give strong image

contrast in the vicinity of object edges. In vi-

sible light (Nomarski) DIC optics, the requested

beam splitting and combining are accomplished by

polarizing optical components such as birefringent

crystals and circular and linear polarizers. Due to

the extreme difficulties in fabricating X-ray polariz-

ers, a different approach was made to achieve beam

splitting for short wavelengths, based on diffractive

optics, which produce several diffraction orders.28

Furthermore, development of new lithography and

nanostructuring techniques made possible the fa-

brication of a doublet of zone plates: the two lenses

are displaced transversely to their optical axis within

their optical resolution, which means that also the

Airy disks of their focal spots are displaced within

the optical resolution. Thus, the wave front shearing

by the zone plate doublet can be used for DIC.29,30

The main assets of the DIC technique are briefly:

(i) the intrinsic resolution is determined by the zone

plate resolution, assuming a diffraction-limited ge-

ometry; (ii) the alignment of a doublet is rather

simple and similar to that of a single lens; (iii) this

technique is usable for both complementary X-ray

microscopy techniques, i.e. the full-field imaging and

the scanning type, (iv) the image acquisition does

not require data processing; (v) due to small shear

of the wave front division and small optical path dif-

ferences, this method makes no use of coherence of

the X-ray beam and can also be used with incohe-

rent sources. The DIC mode was successfully used

on both types of microscopes at ID21. Commission-

ing of the DIC method on the SXM was performed

at 4 keV photon energy with a zone plate doublet

with the following parameters: zone plate radius —

37.75 µm; focal length in first diffraction order —

50 mm; outermost zone width ∆r = 200 nm. The

substrate consisted of a 1-µm-thick Si3N4 foil. At

4 keV photon energy, λ = 0.31 nm, the depth of

focus was ±260 µm. The lateral separation of the

zone plates was 100 nm, which corresponds to about

∆r/2. A configured detector consisting of a silicon

photodiode and a 50 µm aperture was used. Figure 9

Fig. 9. Comparison of bright field (top) with DIC X-ray images (bottom) recorded on the SXM at a photonenergy of 4 keV.


shows an example of images recorded in two geome-

tries, bright field and DIC. The test object was a

2 µm feature size structure written in PMMA resist

with a transmission of 99%. The absorption image

shows contrast of about 1% while the DIC imaging

mode leads to a contrast enhancement in excess of

20%.

Acknowledgments

The authors are very grateful to colleagues for

providing material and results. In particular, we

wish to thank R. Barrett and R. Baker for their

invaluable involvement in the X-ray microscopy

project at the ESRF. We are indebted to external

collaborators for technical and scientific develop-

ments: G. Schneider and M. Panitz (IRP, University

of Gottingen), C. David (PSI, Villigen), E. di

Fabrizio (TASC/INFM–ELETTRA, Trieste), P.

Charalambous and G. Morrison (King’s College,

London), T. Wilhein (RheinAhrCampus Rema-

gen), M. Robert-Nicoud (Albert-Bonniot Institute,

Grenoble), M. Bonnin-Mosbah and N. Metrich

(CEA–Saclay).

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12. R. Ortega., G. Deves, M. Bonnin-Mosbah, M. Sa-lome, J. Susini, L. M. Anderson and K. S. Kasprzak,Nucl. Instrum. Methods B181, 485 (2001).

13. Bihannic, L. J. Michot, B. S. Lartige, D. Vantelon,J. Labille, F. Thomas, J. Susini, M. Salome andB. Fayard, Langmuir 17(14), 4144 (2001).

14. M. Salome, Y. Dauphin, J. Susini, J. Doucet,B. Fayard and J. P. Cuif, in preparation.

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16. M. Wilke, F. Farges, P. E. Petit, G. E. Brown Jr. andF. Martin, American Mineralogist 86, 714 (2001).

17. M. Bonnin-Mosbah, N. Metrich, J. Susini, M. Sa-lome, D. Massare and B. Menez, Spectrochimica ActaPT B, to be published (2001).

18. M. Salome, M. H. Lafage-Prouqst, L. Vico,D. Amblard, B. Kaulich, S. Oestreich, J. Susini andR. Barrett, in 6th Int. Conf. on X-Ray Microscopy(Berkeley, 1999), eds. W. Meyer-Ilse, T. Warwick andD. Attwood, AIP Conf. Proc. 507, 178 (2000).

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27. G. R. Morrison, W. Eaton and R. Barrett, ESRFexperiment report (Sept. 1999).

28. T. Wilhein, B. Kaulich and J. Susini, Opt. Commun.193, 26 (2001).

29. T. Wilhein, B. Kaulich, E. Di Fabrizio, F. Romanato,S. Cabrini and J. Susini, Appl. Phys. Lett. 78(14),2082 (2001).

30. B. Kaulich, T. Wilhein, E. Di Fabrizio, F. Romanato,M. Altissimo, S. Cabrini, B. Fayard and J. Susini,JOSA, in press (2001).

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