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An electrochemical cell with vertical geometry for neutron reflectivity measurements
Physica B: Condensed Matter xxx (2017) 1–4
Contents lists available at ScienceDirect
Physica B: Condensed Matter journal homepage: www.elsevier.com/locate/physb
An electrochemical cell with vertical geometry for neutron reflectivity measurements Mari Mizusawa a, b, *, Kenji Sakurai b, Dai Yamazaki c, Masayasu Takeda d a
Utilization Promotion Division, Comprehensive Research Organization for Science and Society, Tokai, Ibaraki, Japan Research Center for Advanced Measurement and Characterization, National Institute for Materials Science, Tsukuba, Ibaraki, Japan J-PARC Center, Japan Atomic Energy Agency, Tokai, Ibaraki, Japan d Materials Sciences Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki, Japan b c
A R T I C L E I N F O
A B S T R A C T
Keywords: Solid/liquid interface Neutron reflectivity Electrochemical cell
Neutron reflectivity is useful for analyzing solid/liquid interfaces because of its sensitivity to light elements and high transmittance to substances. In most cases, neutron reflectivity measurements on solid/liquid interfaces are carried out using a horizontal geometry. This geometry enables reliable measurements even on relatively unstable systems. However, vertical geometry experiments may be advantageous in certain aspects because a vertical geometry offers higher degrees of freedom in controlling and measuring the sample environments. Therefore, an electrochemical cell that can be used in the vertical geometry is desired. In this report, the fabrication of an electrochemical cell with vertical geometry for neutron reflectivity measurements is described and the preliminary results are analyzed.
1. Introduction
aluminum or borosilicate glass in order to reduce background noise. The electrochemical cell, which contains active materials, needs to be inert. Furthermore, it is desirable to use materials that can be precisely machined because the cell has a complicated architecture consisting of two or more electrodes and sensors and seals a liquid electrolyte inside. The electrochemical cells for vertical geometry have been used in IR spectroscopy [7]. We develop the cell for neutron experiments so as to adjust small glancing angle with goniometer. In this report, the fabrication of an electrochemical cell with vertical geometry for neutron reflectivity measurements is described and the preliminary results are analyzed.
Neutron reflectivity is a useful tool for analyzing solid/liquid interfaces, especially in electrochemical systems. Its sensitivity to light elements and neutron transmittance are advantageous in observing such buried interfaces. Cells for grazing incidence neutron or X-ray studies on electrochemical interfaces have been developed [1]. In most of these studies, measurements were conducted using cells with horizontal geometry [2]. This geometry enables reliable measurements even on relatively unstable systems [3]. Recently, Yonemura et al. [4] reported the development of an electrochemical cell for Li ion batteries. They were successful in evaluating a new Li ion battery material. Nevertheless, an electrochemical cell with vertical geometry may be useful in certain circumstances. A vertical geometry allows higher degrees of freedom in controlling and measuring the sample environments. In experiments using synchrotron X-rays with linear polarization, a vertical geometry can yield a high S/N ratio [5]. Neutron reflectivity experiments in the vertical geometry can be easily compared to such synchrotron experiments. Most neutron reflectometers with a vertical geometry are capable of polarized neutron analysis [6]. Furthermore, they can be used for the analysis of magnetic materials in contact with liquids. The cells used for neutron reflectivity experiments on solid/liquid interfaces, including electrochemical systems, are generally made of
2. Materials and methods 2.1. Electrochemical cell The electrochemical cell is made from commercially available polytetrafluoroethylene (PTFE) tubes and plates (MISUMI) by conventional machining. The reference and counter electrodes were supported with PTFE fittings for a 6 mm tube. A 4 mm screw hole is included for a counter electrode with smaller diameter. The cell is supported on the sample side and set on a goniometer.
* Corresponding author. Utilization Promotion Division, Comprehensive Research Organization for Science and Society, Tokai, Ibaraki, Japan. E-mail address: [email protected] (M. Mizusawa). https://doi.org/10.1016/j.physb.2018.01.050 Received 30 August 2017; Received in revised form 10 January 2018; Accepted 22 January 2018 Available online xxxx 0921-4526/© 2018 Elsevier B.V. All rights reserved.
Please cite this article in press as: M. Mizusawa, et al., An electrochemical cell with vertical geometry for neutron reflectivity measurements, Physica B: Condensed Matter (2017), https://doi.org/10.1016/j.physb.2018.01.050
M. Mizusawa et al.
Physica B: Condensed Matter xxx (2017) 1–4
Fig. 1. (a) Schematic of the electrochemical cell. WE: working electrode (sample), RE: reference electrode, and CE: counter electrode. (b) The cell on a reflectometer.
2.2. Cyclic voltammetry
J-PARC (Tokai, Japan). The beam power was 400 kW and the wavelength was varied in the range of 2.2 Å to 8.8 Å, which corresponds to a TOF area in the range of 10,000–40,000 μs. The irradiated area was 13 13 mm2, which is a square region inscribed in the inner diameter of the cell and the thin film is in contact with the electrolyte solution at the whole of this area. The beam divergence was 5%. The beam size is 0.6 mm for the measurement in highest q range. The beam is incident from silicon substrate to avoid the scattering from the solution. These measurements were carried out without and with the H2SO4 solution. The background was measured for each condition.
Cyclic voltammetry measurements are conducted in the off-beam condition using a potentiostat (Gamry Interface1000). A Pt plate (30 mm 30 mm 0.1 mm, 99.98%, NILACO) is used as the working electrode, while Ag/AgCl and a Pt wire (BAS) are used as the reference and counter electrodes, respectively. A 50 mM H2SO4 aqueous solution (Kanto Chemical) is used as the electrolyte. 2.3. Sample An Au thin film sputtered on a Cr-coated Si wafer (30 mm 30 mm 2 mm) is used as the sample for neutron reflectivity experiments. The center area of 20 mm diameter contacts with the solution inside the cell.
3. Results and discussion 3.1. The cell and electrochemical measurements The fabricated electrochemical cell is shown in Fig. 1. The tube part, which has an outer diameter of 30 mm and inner diameter of 20 mm, is used as an electrolyte bath. The sample (working electrode) is set between the PTFE tube and the plate at one end. The sample area in contact
2.4. Neutron reflectivity measurements The neutron reflectivity measurements were conducted at BL17, MLF, 2
M. Mizusawa et al.
Physica B: Condensed Matter xxx (2017) 1–4
current at the peak in the second cycle was 0.38 μA, smaller than the first cycle, 0.45 μA. It is assumed that the initial adsorption/desorption state changed during the voltammetry. It is shown that electrochemical measurements are possible using this cell. The current due to adsorptiondesorption is relatively unstable. Therefore, it is considered that the conductivity and distances between the electrodes should be optimized because of the rather large size of the sample. 3.2. Neutron reflectometry The measured reflection spectra are compared with the background spectra as shown in Fig. 3. The measurements were carried out at four θ/2θ conditions: 0.2/0.4, 0.3/0.6, 0.9/1.8, and 2.7/5.4. The corresponding qz areas were 5.0 103–2.0 102, 7.5 103–3.0 102, 2.2 102–9.0 102, and 6.7 102–2.7 101 [Å1], respectively. The measuring times were 1, 1, 2, and 4 h in live time at angle conditions of 0.2/0.4, 0.3/0.6, 0.9/1.8, and 2.7/5.4. As shown in Fig. 3(a) and (d), the total reflection is measured over a TOF range of 20,000–40,000 μs and some oscillations occur in the film thickness in the range of 10,000–20,000 μs. In Fig. 3(b) and (e), the intensity oscillations arise from the film thickness are observed 1.0 102
Fig. 2. Cyclic voltammograms measured using the electrochemical cell. A Pt plate, Pt wire, and Ag/AgCl were used as the working electrode, counter electrode, and reference electrode, respectively.
with the electrolyte is approximately 20 mm in diameter. The distance between the sample and the reference electrode is about 40 mm while that between the sample and the counter electrode is 20 mm. The cell is supported on the sample side and set on the goniometer. The incident beam comes from the side of the substrate and is scattered at the interface with the solution. The cyclic voltammogram shown in Fig. 2 is measured using the electrochemical cell with a Pt working electrode. The voltammetry tests were conducted after measuring the open circuit voltage for 5 s. The scanning potential was in the range of 0.5 V to þ1.5 V and the sweep rate was 10 mV/s. The number of cycles was set to 2. The open circuit voltage was around þ0.51 V. Hydrogen generation and oxygen generation were observed around 0.3 V and þ1.2 V, respectively. Furthermore, a diffuse adsorption/desorption peak appeared at around þ0.19 V. In the second cycle, the peak appeared at þ0.21 V. The absolute value of
Fig. 3. TOF spectra before binning of the reflection (black) compared with the background (white) at different angle conditions. (a)–(c) Without solution and (d)–(f) with solution. 3
M. Mizusawa et al.
Physica B: Condensed Matter xxx (2017) 1–4
4. Conclusions An electrochemical cell with vertical geometry was fabricated for neutron reflectivity experiments with commercially available materials using conventional machining. The cell is available for cyclic voltammetry with the conventionally used reference electrodes. In the neutron reflectivity measurements, background scattering from the cell is low. Direct beam profiles can be measured through the substrate at the required angle conditions. Using the vertical cell, neutron reflectivity can be measured to an intensity of 107. However, in order to maintain the stability of the electrode surface during long-time measurements, it would be necessary to improve the sample holding method. Acknowledgements The authors would like to thank Dr. N. Yamada at J-PARC/KEK and Dr. T. Kuroda at CROSS for their support in designing and fabricating the electrochemical cells used in this work. The neutron reflectivity experiments were performed according to J-PARC MLF proposals No. 2014A0137 and 2014B0179. A part of this work was financially supported by MEXT/JSPS KAKENHI Grant Number JP 16K04968. Appendix A. Supplementary data Fig. 4. Reflectivity profile of the Au/Cr thin film on a Si substrate without (closed square) and with (open circle) electrolyte solution. The background is considered. The simulation result of the solid line calculated using the layered model is shown in the inset.
Supplementary data related to this article can be found at https://doi. org/10.1016/j.physb.2018.01.050. References
subtracted. As shown, the neutron reflectivity can be measured to an intensity of 107 using the electrochemical cell with vertical geometry. The result calculated using the stacked layer model without the solution is indicated by the solid line. It is estimated that the total thickness of the film is 873 Å, and that an intermediate layer exists between Au and Cr layer. The total reflection in the measured profiles is not clear because of the contrast between the Si substrate and the thin films. The profiles are similar for qz < 0.06 Å1 in both cases. When 0.06 < qz < 0.15 Å1, the intensity measured in the presence of the solution is slightly higher than that measured without the solution. This observation is considered to be due to the reflection of the adsorbed layer of the electrolyte solution. The intensity oscillation period is not too influenced by the electrolyte solution. This suggests that the thickness and density of the adsorbed layer are low.
[1] G. Scherb, A. Kazimirov, J. Zegenhagen, Rev. Sci. Instrum. 69 (1998) 512. [2] N.L. Yamada, N. Torikai, K. Mitamura, H. Sagehashi, S. Sato, H. Seto, T. Sugita, S. Goko, M. Furusaka, T. Oda, M. Hino, T. Fujiwara, H. Takahashi, A. Takahara, Eur. Phys. J. Plus 126 (2011) 108. [3] K. Sakurai, M. Mizusawa, M. Ishii, Trans. MRS Jpn. 32 (2007) 181. [4] M. Yonemura, M. Hirayama, K. Suzuki, R. Kanno, N. Torikai, N.L. Yamada, J. Phys. Conf. Ser. 502 (2014), 012054. [5] J. Als Nielsen, D. McMorrow, Elements of Modern X-ray Physics, Wiley & Sons, West Sussex, 2011. [6] M. Takeda, D. Yamazaki, K. Soyama, R. Maruyama, H. Hayashida, H. Asaoka, T. Yamazaki, M. Kubota, K. Aizawa, M. Arai, Y. Inamura, T. Itoh, K. Kaneko, T. Nakamura, T. Nakatani, K. Oikawa, T. Ohhara, Y. Sakaguchi, K. Sakasai, T. Shinohara, J. Suzuki, K. Suzuya, I. Tamura, K. Toh, H. Yamagishi, N. Yoshida, T. Hirano, Chin. J. Phys. 50 (2) (2012) 161–170. [7] K. Ataka, T. Yotsuyanagi, M. Osawa, J. Phys. Chem. 100 (1996) 10664–10672.
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Contents lists available at ScienceDirect
Physica B: Condensed Matter journal homepage: www.elsevier.com/locate/physb
An electrochemical cell with vertical geometry for neutron reflectivity measurements Mari Mizusawa a, b, *, Kenji Sakurai b, Dai Yamazaki c, Masayasu Takeda d a
Utilization Promotion Division, Comprehensive Research Organization for Science and Society, Tokai, Ibaraki, Japan Research Center for Advanced Measurement and Characterization, National Institute for Materials Science, Tsukuba, Ibaraki, Japan J-PARC Center, Japan Atomic Energy Agency, Tokai, Ibaraki, Japan d Materials Sciences Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki, Japan b c
A R T I C L E I N F O
A B S T R A C T
Keywords: Solid/liquid interface Neutron reflectivity Electrochemical cell
Neutron reflectivity is useful for analyzing solid/liquid interfaces because of its sensitivity to light elements and high transmittance to substances. In most cases, neutron reflectivity measurements on solid/liquid interfaces are carried out using a horizontal geometry. This geometry enables reliable measurements even on relatively unstable systems. However, vertical geometry experiments may be advantageous in certain aspects because a vertical geometry offers higher degrees of freedom in controlling and measuring the sample environments. Therefore, an electrochemical cell that can be used in the vertical geometry is desired. In this report, the fabrication of an electrochemical cell with vertical geometry for neutron reflectivity measurements is described and the preliminary results are analyzed.
1. Introduction
aluminum or borosilicate glass in order to reduce background noise. The electrochemical cell, which contains active materials, needs to be inert. Furthermore, it is desirable to use materials that can be precisely machined because the cell has a complicated architecture consisting of two or more electrodes and sensors and seals a liquid electrolyte inside. The electrochemical cells for vertical geometry have been used in IR spectroscopy [7]. We develop the cell for neutron experiments so as to adjust small glancing angle with goniometer. In this report, the fabrication of an electrochemical cell with vertical geometry for neutron reflectivity measurements is described and the preliminary results are analyzed.
Neutron reflectivity is a useful tool for analyzing solid/liquid interfaces, especially in electrochemical systems. Its sensitivity to light elements and neutron transmittance are advantageous in observing such buried interfaces. Cells for grazing incidence neutron or X-ray studies on electrochemical interfaces have been developed [1]. In most of these studies, measurements were conducted using cells with horizontal geometry [2]. This geometry enables reliable measurements even on relatively unstable systems [3]. Recently, Yonemura et al. [4] reported the development of an electrochemical cell for Li ion batteries. They were successful in evaluating a new Li ion battery material. Nevertheless, an electrochemical cell with vertical geometry may be useful in certain circumstances. A vertical geometry allows higher degrees of freedom in controlling and measuring the sample environments. In experiments using synchrotron X-rays with linear polarization, a vertical geometry can yield a high S/N ratio [5]. Neutron reflectivity experiments in the vertical geometry can be easily compared to such synchrotron experiments. Most neutron reflectometers with a vertical geometry are capable of polarized neutron analysis [6]. Furthermore, they can be used for the analysis of magnetic materials in contact with liquids. The cells used for neutron reflectivity experiments on solid/liquid interfaces, including electrochemical systems, are generally made of
2. Materials and methods 2.1. Electrochemical cell The electrochemical cell is made from commercially available polytetrafluoroethylene (PTFE) tubes and plates (MISUMI) by conventional machining. The reference and counter electrodes were supported with PTFE fittings for a 6 mm tube. A 4 mm screw hole is included for a counter electrode with smaller diameter. The cell is supported on the sample side and set on a goniometer.
* Corresponding author. Utilization Promotion Division, Comprehensive Research Organization for Science and Society, Tokai, Ibaraki, Japan. E-mail address: [email protected] (M. Mizusawa). https://doi.org/10.1016/j.physb.2018.01.050 Received 30 August 2017; Received in revised form 10 January 2018; Accepted 22 January 2018 Available online xxxx 0921-4526/© 2018 Elsevier B.V. All rights reserved.
Please cite this article in press as: M. Mizusawa, et al., An electrochemical cell with vertical geometry for neutron reflectivity measurements, Physica B: Condensed Matter (2017), https://doi.org/10.1016/j.physb.2018.01.050
M. Mizusawa et al.
Physica B: Condensed Matter xxx (2017) 1–4
Fig. 1. (a) Schematic of the electrochemical cell. WE: working electrode (sample), RE: reference electrode, and CE: counter electrode. (b) The cell on a reflectometer.
2.2. Cyclic voltammetry
J-PARC (Tokai, Japan). The beam power was 400 kW and the wavelength was varied in the range of 2.2 Å to 8.8 Å, which corresponds to a TOF area in the range of 10,000–40,000 μs. The irradiated area was 13 13 mm2, which is a square region inscribed in the inner diameter of the cell and the thin film is in contact with the electrolyte solution at the whole of this area. The beam divergence was 5%. The beam size is 0.6 mm for the measurement in highest q range. The beam is incident from silicon substrate to avoid the scattering from the solution. These measurements were carried out without and with the H2SO4 solution. The background was measured for each condition.
Cyclic voltammetry measurements are conducted in the off-beam condition using a potentiostat (Gamry Interface1000). A Pt plate (30 mm 30 mm 0.1 mm, 99.98%, NILACO) is used as the working electrode, while Ag/AgCl and a Pt wire (BAS) are used as the reference and counter electrodes, respectively. A 50 mM H2SO4 aqueous solution (Kanto Chemical) is used as the electrolyte. 2.3. Sample An Au thin film sputtered on a Cr-coated Si wafer (30 mm 30 mm 2 mm) is used as the sample for neutron reflectivity experiments. The center area of 20 mm diameter contacts with the solution inside the cell.
3. Results and discussion 3.1. The cell and electrochemical measurements The fabricated electrochemical cell is shown in Fig. 1. The tube part, which has an outer diameter of 30 mm and inner diameter of 20 mm, is used as an electrolyte bath. The sample (working electrode) is set between the PTFE tube and the plate at one end. The sample area in contact
2.4. Neutron reflectivity measurements The neutron reflectivity measurements were conducted at BL17, MLF, 2
M. Mizusawa et al.
Physica B: Condensed Matter xxx (2017) 1–4
current at the peak in the second cycle was 0.38 μA, smaller than the first cycle, 0.45 μA. It is assumed that the initial adsorption/desorption state changed during the voltammetry. It is shown that electrochemical measurements are possible using this cell. The current due to adsorptiondesorption is relatively unstable. Therefore, it is considered that the conductivity and distances between the electrodes should be optimized because of the rather large size of the sample. 3.2. Neutron reflectometry The measured reflection spectra are compared with the background spectra as shown in Fig. 3. The measurements were carried out at four θ/2θ conditions: 0.2/0.4, 0.3/0.6, 0.9/1.8, and 2.7/5.4. The corresponding qz areas were 5.0 103–2.0 102, 7.5 103–3.0 102, 2.2 102–9.0 102, and 6.7 102–2.7 101 [Å1], respectively. The measuring times were 1, 1, 2, and 4 h in live time at angle conditions of 0.2/0.4, 0.3/0.6, 0.9/1.8, and 2.7/5.4. As shown in Fig. 3(a) and (d), the total reflection is measured over a TOF range of 20,000–40,000 μs and some oscillations occur in the film thickness in the range of 10,000–20,000 μs. In Fig. 3(b) and (e), the intensity oscillations arise from the film thickness are observed 1.0 102
Fig. 2. Cyclic voltammograms measured using the electrochemical cell. A Pt plate, Pt wire, and Ag/AgCl were used as the working electrode, counter electrode, and reference electrode, respectively.
with the electrolyte is approximately 20 mm in diameter. The distance between the sample and the reference electrode is about 40 mm while that between the sample and the counter electrode is 20 mm. The cell is supported on the sample side and set on the goniometer. The incident beam comes from the side of the substrate and is scattered at the interface with the solution. The cyclic voltammogram shown in Fig. 2 is measured using the electrochemical cell with a Pt working electrode. The voltammetry tests were conducted after measuring the open circuit voltage for 5 s. The scanning potential was in the range of 0.5 V to þ1.5 V and the sweep rate was 10 mV/s. The number of cycles was set to 2. The open circuit voltage was around þ0.51 V. Hydrogen generation and oxygen generation were observed around 0.3 V and þ1.2 V, respectively. Furthermore, a diffuse adsorption/desorption peak appeared at around þ0.19 V. In the second cycle, the peak appeared at þ0.21 V. The absolute value of
Fig. 3. TOF spectra before binning of the reflection (black) compared with the background (white) at different angle conditions. (a)–(c) Without solution and (d)–(f) with solution. 3
M. Mizusawa et al.
Physica B: Condensed Matter xxx (2017) 1–4
4. Conclusions An electrochemical cell with vertical geometry was fabricated for neutron reflectivity experiments with commercially available materials using conventional machining. The cell is available for cyclic voltammetry with the conventionally used reference electrodes. In the neutron reflectivity measurements, background scattering from the cell is low. Direct beam profiles can be measured through the substrate at the required angle conditions. Using the vertical cell, neutron reflectivity can be measured to an intensity of 107. However, in order to maintain the stability of the electrode surface during long-time measurements, it would be necessary to improve the sample holding method. Acknowledgements The authors would like to thank Dr. N. Yamada at J-PARC/KEK and Dr. T. Kuroda at CROSS for their support in designing and fabricating the electrochemical cells used in this work. The neutron reflectivity experiments were performed according to J-PARC MLF proposals No. 2014A0137 and 2014B0179. A part of this work was financially supported by MEXT/JSPS KAKENHI Grant Number JP 16K04968. Appendix A. Supplementary data Fig. 4. Reflectivity profile of the Au/Cr thin film on a Si substrate without (closed square) and with (open circle) electrolyte solution. The background is considered. The simulation result of the solid line calculated using the layered model is shown in the inset.
Supplementary data related to this article can be found at https://doi. org/10.1016/j.physb.2018.01.050. References
subtracted. As shown, the neutron reflectivity can be measured to an intensity of 107 using the electrochemical cell with vertical geometry. The result calculated using the stacked layer model without the solution is indicated by the solid line. It is estimated that the total thickness of the film is 873 Å, and that an intermediate layer exists between Au and Cr layer. The total reflection in the measured profiles is not clear because of the contrast between the Si substrate and the thin films. The profiles are similar for qz < 0.06 Å1 in both cases. When 0.06 < qz < 0.15 Å1, the intensity measured in the presence of the solution is slightly higher than that measured without the solution. This observation is considered to be due to the reflection of the adsorbed layer of the electrolyte solution. The intensity oscillation period is not too influenced by the electrolyte solution. This suggests that the thickness and density of the adsorbed layer are low.
[1] G. Scherb, A. Kazimirov, J. Zegenhagen, Rev. Sci. Instrum. 69 (1998) 512. [2] N.L. Yamada, N. Torikai, K. Mitamura, H. Sagehashi, S. Sato, H. Seto, T. Sugita, S. Goko, M. Furusaka, T. Oda, M. Hino, T. Fujiwara, H. Takahashi, A. Takahara, Eur. Phys. J. Plus 126 (2011) 108. [3] K. Sakurai, M. Mizusawa, M. Ishii, Trans. MRS Jpn. 32 (2007) 181. [4] M. Yonemura, M. Hirayama, K. Suzuki, R. Kanno, N. Torikai, N.L. Yamada, J. Phys. Conf. Ser. 502 (2014), 012054. [5] J. Als Nielsen, D. McMorrow, Elements of Modern X-ray Physics, Wiley & Sons, West Sussex, 2011. [6] M. Takeda, D. Yamazaki, K. Soyama, R. Maruyama, H. Hayashida, H. Asaoka, T. Yamazaki, M. Kubota, K. Aizawa, M. Arai, Y. Inamura, T. Itoh, K. Kaneko, T. Nakamura, T. Nakatani, K. Oikawa, T. Ohhara, Y. Sakaguchi, K. Sakasai, T. Shinohara, J. Suzuki, K. Suzuya, I. Tamura, K. Toh, H. Yamagishi, N. Yoshida, T. Hirano, Chin. J. Phys. 50 (2) (2012) 161–170. [7] K. Ataka, T. Yotsuyanagi, M. Osawa, J. Phys. Chem. 100 (1996) 10664–10672.
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