Development of in-situ sample cells for scanning transmission x-ray microscopy
Takuji Ohigashi, Masanari Nagasaka, Toshio Horigome, Nobuhiro Kosugi, Scott M. Rosendahl, and Adam P.
HitchcockCitation: AIP Conference Proceedings 1741, 050002 (2016); doi: 10.1063/1.4952922
View online: http://dx.doi.org/10.1063/1.4952922
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Development of In-situ Sample Cells for Scanning
Transmission X-ray Microscopy
Takuji Ohigashi1, a), Masanari Nagasaka1, Toshio Horigome1, Nobuhiro Kosugi1,
Scott M. Rosendahl2 and Adam P. Hitchcock3
1

UVSOR Synchrotron, Institute for Molecular Science, 38 Nishigo-naka, Myodaiji, Okazaki, Aichi, 444-8585, Japan
2Canadian Light Source, 44 Innovation Boulevard,Saskatoon, SK S7N 2V3,Canada
3
McMaster University, 1280 Main Street West, Hamilton, Ontario, L8S4L8,Canadaa)

Corresponding author: ohigashi@ims.ac.jp

Abstract. An azimuthal rotatable sample cell, an electrochemical cell and a controlled humidity cell for in-situ scanningtransmission X-ray microscopy (STXM) were developed at UVSOR-III Synchrotron (Okazaki, Japan). By using thesesample cells, the polarization dependence of sodium titanate nanoribbons, in-situ electrochemistry of 0.1M FeSO4solution, and in-situ morphological change of a functional polymer with changing humidity were successfully measured.

INTRODUCTION
In-situ spectromicroscopic measurements can reveal dynamics of morphological, physical and chemical
processes. In-situ techniques have been developed for spectromicroscopic studies of heavy elements using hard Xrays with high transmittance in samples and long focal length of optical elements (i.e. long working distance) at
photon energies >4 keV. On the other hand, in-situ measurements in the soft X-ray region for spectromicroscopic
studies of light elements face significant technical challenges due to several difficulties, such as low transmittanceand short focal lengths of optical elements. Scanning transmission X-ray microscopy (STXM) in the soft X-ray
region is a promising technique for in-situ observation, considering its characteristics, such as high energy resolving
power, high spatial resolution, low radiation damage and 2-dimensional (and 3-dimensional) chemical state analysis
by using near edge X-ray absorption fine structure (NEXAFS). In UVSOR-III Synchrotron, Institute for Molecular
Science (Okazaki, Japan), a STXM system was installed on the in-vacuum soft X-ray undulator beamline BL4U in2012 and started user operation in 2013 [1]. Since then, we have been developing several types of sample cells andin-situ measurement methods to study soft matter such as polymer and biological systems. The sample cells
described in this article are compatible with Bruker ASC (now, Research Instruments) STXM systems installed atSLS, BESSY-II, PLS, DLS, Soleil and so on.

NEW DESIGN OF A FRESNEL ZONE PLATE
One of the technical challenges for in-situ measurements by STXM is the very short working distance. A
schematic of the optical system of STXM is shown in Fig. 1. TheFZP
Central StopSample
OSA
incoming X-rays are focused by a Fresnel zone plate (FZP) onto aDetector
sample through an order sorting aperture (OSA). The working
X-ray
distance is defined as the distance between OSA and the sample. In
some in-situ sample cells described below (e.g. the electrochemicalcell and the humidity control cell), a silicon nitride membrane
Working Distance(frame thickness of 200 µm) and a top cover plate (thickness ofFig. 1: Schematic of the opticalsystem of STXM
Proceedings of the 12th International Conference on Synchrotron Radiation Instrumentation – SRI2015
AIP Conf. Proc. 1741, 050002-1–050002-4; doi: 10.1063/1.4952922
Published by AIP Publishing. 978-0-7354-1398-6/$30.00

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~100 µm) are used and additional clearance of 100 µm is needed for safety. To apply STXM of UVSOR-III
Synchrotron to soft matter study, the C K-edge has to be covered as the lowest energy (i.e. condition of the shortestworking distance) for the in-situ devices. In order to meet this requirement, a new FZP with the working distancemore than 400 µm is required at 275 eV. Therefore, we have acquired a new FZP with outermost zone width of 35nm, diameter of 240 µm and central stop diameter of 95 µm. By using the new FZP with an OSA of diameter of 65µm, the working distance is >500 µm at the C K-edge.

AZIMUTHAL ROTATABLE SAMPLE CELL [2]The absorption spectra of samples with anisotropic chemical bonding can show spectral changes as thepolarization of the incoming linearly polarized X-rays is changed [3]. Samples with random orientations do notshow polarization dependent X-ray absorption spectra. STXM can be used to measure polarized 2-dimensional mapsof individual molecular orientations [4]. Typically, this kind of measurement is performed with a polarization
tunable insertion device, such as an elliptical polarizing undulator. BL4U at UVSOR-III Synchrotron is equippedwith an in-vacuum undulator which has fixed horizontal linear polarization. Therefore, we developed a sample cellwhich can rotate the sample azimuthally from outside of the STXM chamber. This cell is modeled on that reported
by Hernández-Cruz et al [5]. A photo of the azimuthal rotatable sample cell (ARSC) is shown in Fig. 2. The ARSC
uses a small stepping motor (AM1020, Faulhaber) to adjust the azimuthal angle of the sample.
Polarization dependent spectra of sodium titanate nanoribbons (STN) were measured using the ARSC. O 1s
image sequences were obtained at several azimuthal angles. Figure 3a shows the azimuthal dependence of the O 1s
spectrum of an individual nanoribbon, extracted from the same area of the sample (green rectangle in Fig. 3b). End
member spectra corresponding to parallel and perpendicular orientation of the STN were extracted and used to fit
the polarization dependent data, yielding a dichroic composite map (Fig. 3c).
(a)

(b)

(c)

Sample

10 mm

Energy [eV]Fig. 2 Photo of the azimuthal
rotatable sample cellFig. 3 (a) Angle dependence of the O 1s spectrum of the green highlighted STN.
(b) Optical density image of several STN. (c) Color composite mapping (carbon
support as red, parallel component as green and perpendicular component as blue)

ELECTROCHEMICAL CELL [6]In-situ spectroscopic measurements of electrochemical reactions have been performed widely
using infrared [7], hard X-rays [8,9] and soft X-rays[10,11]. By using STXM, 2-dimensional
distribution of electrochemical reactions occurringon or near electrodes can be analyzed with highspatial resolution. An important advance in thiswork relative to earlier electrochemical STXM
studies [12,13] is that it is capable of continuous
and interrupted flow of electrolytes, as opposed toprevious systems which only used static (no-flow)
conditions. The basic concept of a liquid flow cell(b) Cover plate(a)
Inlet/outlet
tubes

Base plate

SpacerO-rings
Inlet

Observation
pointElectrodes

X-ray

SiN membranewith electrodes

SiN
membrane
Outlet

10 mm

Fig. 4 (a) Photo and (b) cross sectional schematic of theelectrochemical cell

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was developed by Nagasaka [14] and was modified for electrochemical experiments in the STXM. A photo andcross-sectional image of the electrochemical cell are shown in Fig. 4. The electrochemical cell consists of twosilicon nitride membranes (thickness of 100 nm), teflon™ spacers (thickness of 20 µm) and two viton o-rings. The
liquid electrolyte flows through a few micron gap between these membranes, driven by a peristaltic pump fromoutside of the STXM chamber via a fluidic feed through. The thickness of the gap can be optimized to get better
contrast of target species by changing the pressure of helium gas in the STXM chamber. Three electrodes (50 nm
thick gold with a Cr adhesion layer) - working (WE), counter (CE) and reference electrode (RE) - are deposited on
the top (upstream) membrane. Electrical connections are made using a small home-made multi-pin connector.
By using this flow electrochemical cell, in-situ Fe 2p spectroscopy of the electrochemical reaction of an 0.1 M
FeSO4 aqueous solution was performed [6]. Figure 5a shows Fe 2p spectra of Fe(II) and Fe(III) measured in thissystem. These spectra were used to fit the Fe L3-edge energy stack data to obtain component maps of Fe(II), Fe(III)and the electrodes (constant), from which a color coded composite is presented in Fig. 5b. In the composite map, theFe(II)-rich region of the solution is in red, the Fe(III)-rich region is in green, and the gold electrodes (WE, CE andRE) are in blue. The distribution of Fe(III) and Fe(II) was opposite from our expectation since the WE was positive
relative to the CE. These results are under investigation.
(a)(b)
Fig. 5 (a) Fe(II) and Fe (III) spectra from anenergy stack of 0.1 M FeSO4 (aq) at 0 V (Fe(II)and 0.6 V (Fe(III). (b) Composite of component
maps of Fe(II) in red, Fe (III) in green and theelectrodes in blue.

HUMIDITY CONTROL CELL
A humidity control cell has been developed for in-situ measurements of the effects of water vapor on various
materials [15-17]. The humidity control cell consists of a small chamber with two silicon nitride membranes for Xrays, a relative humidity (RH) sensor, and three ports for gas inlet/outlet (Fig. 6). The sample (polymer film on aTEM grid) is mounted on the top (upstream) silicon nitride membrane by scotch tape. By using the three ports fordry/wet gas inlet, the humidity in the sample cell is controlled by filling the cell with humid helium gas.
Temperature and humidity inside the chamber are monitored by a small RH sensor (SHT7x, Sensirion AG) placednear the sample.
The effect of humidity on a thin section (100 nm) of a functional polymer was studied by changing the humidity
in-situ. Figures 7a and 7b show STXM images of the polymer with 8 % and 84 % RH at room temperature,respectively. The images were taken with an X-ray energy of 285.5 eV and were converted to optical density. In
these images, bright areas (i.e. high optical density) show high density regions of the polymer and dark areas (i.e.
low optical density) show voids in the polymer. By changing the humidity from 8% to 84%, 8% of the dark area, forexample shown in red circles in Figs. 7a and 7b, decreased. This change of the area was caused by swelling of thepolymer as it absorbed water vapor.
SensSensor

(b)

(a)

Base plateSamSample

10 mmFig. 6 Photo of the main chamber (interior) and thebase plate of the humidity control sample cell.

500 nmFig. 7 Optical density images (285.5 eV) of afunctional polymer at RH of (a) 8% , (b) 83%.

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SUMMARY
We have developed in-situ measurement methods by designing and commissioning an azimuthal rotatablesample cell, an electrochemical cell, and a humidity control cell for chemical and biological applications of STXM.
These sample cells and automated control systems are under further improvement. These in-situ measurement
methods will allow users of the STXM to explore new fields in soft materials science. Access to the STXM inUVSOR-III Synchrotron is either by peer reviewed proposals twice a year, or by purchased access.

ACKNOWLEDGEMENTS
This research was conducted at the UVSOR Synchrotron Facility in the Institute for Molecular Science (IMS),
supported by Nanotechnology Platform Program (Molecule and Material Synthesis) of the Ministry of Education,Culture, Sports, Science and Technology (MEXT), Japan. SMR and APH thank UVSOR for its hospitality andfinancial support from the UVSOR-RIKEN collaboration program for participating in this research.

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