Proceedings of the 12th Annual Meeting of Particle Accelerator Society of Japan
August 5-7, 2015, Tsuruga, Japan

PASJ2015 WEOM05

STUDY OF A CORROSION RESISTANT COATING LAYER FOR METALMAGNETIC CORES USING NEUTRON REFLECTOMETORY
K. Akutsu#, M. Sahara, N. Miyata,
Comprehensive Research Organization for Science and Society (CROSS), Tokai, Japan
T. Niizeki, S. Nagayama, Y. Hasegawa, ART KAGAKU Co., Ltd., Tokai, Japan
A. Shimomura, Shimomurashikkiten Co., Ltd., Sabae, Japan
M. Yoshii, J-PARC Center, KEK, Tokai, JapanAbstract
The structure of an SiO2 layer (SiO2(PHPS))
synthesized using perhydropolysilazane (PHPS) on an Si
substrates was studied by Fourier transform infrared
spectroscopy (FT-IR), spectroscopic ellipsometry (SE),and neutron reflectivity (NR) analysis. The FT-IR results
confirmed that the molecular structure of the SiO2(PHPS)
layer can be represented as SiO2. The thickness of the thin
SiO2(PHPS) layer were estimated using both SE and NR
analysis methods. The SE and NR analyses revealed thatthe thin SiO2(PHPS) layer could be uniformly coated inall samples. In addition, the NR results suggested that thedensity of the SiO2(PHPS) layer was altered by varying
the thickness of the SiO2(PHPS) layer. These results
indicate that the variation in the density of SiO2(PHPS)
layer depends on the efficiency of cross-linking reaction
between the silazane oligomers in the coated PHPS layer.

INTRODUCTION
Silicon based ceramics such as Perhydropolysilazane(PHPS) derived ceramic have been studied as coating
materials to protect certain metallic components [1].
PHPS is useful material to be applied for the protection ofmetallic materials in corrosive environments because
PHPS can be easily used to synthesize high-quality SiO2layers on metallic materials through the hydrolysis oroxidation of PHPS [1]. We have used the PHPS/p-xylene
system to synthesize an SiO2-waterproof layer, denoted as
SiO2(PHPS), for the magnetic alloy core of theaccelerator ring in the Japan Proton Accelerator ResearchComplex (J-PARC), Tokai, Japan [2]. Although thewaterproofing properties of the SiO2(PHPS) layer
increases with increasing the thickness of the SiO2 layer(Figure 1), the level of stress in the SiO2(PHPS) layer also
increases, and this can lead to cracking. Therefore, it isimportant to investigate the structure and synthesis
mechanism of the synthesized SiO2 layer in detail for
improving the properties of the SiO2 layer.
A variety of techniques have been used to study thestructure of thin SiO2 layer, including Fourier-transform
infrared spectroscopy (FT-IR), X-ray photoelectron
spectroscopy (XPS), atomic force microscopy (AFM),
spectroscopic ellipsometry (SE), and reflectometry [3-4].
In particular, SE and neutron reflectometry (NR) are
ideally suited to study thin layer structures on surfaces [5].
In this study, we prepared three kinds of the thin
SiO2(PHPS) layer samples with different thickness andused them as the model SiO2(PHPS) layer sample. Using
the FT-IR, SE, and NR techniques, we analysed thestructure of the samples to investigate the thickness,density, and roughness of the SiO2(PHPS) layer in detail.
And then, we discussed the synthesis mechanism of thesynthesized SiO2(PHPS) layer in detail.

Figure 1: Relationship between SiO2 layer thickness and corrosion
rates under the salt-spray test.

EXPERIMENTAL
Sample Preparation
The Si wafers (diameter = 5.08 cm, thickness = 0.3 mm)
and the PHPS polymer (AQUAMICA) were supplied by
SEMITEC Co, Ltd. (Tokyo, Japan), and AZ Electronic
Materials Co, Ltd. (Tokyo, Japan), respectively, and thesecompounds were used without further purification. The
SiO2(PHPS) layers were prepared by spin coating 5 % of
PHPS/p-xylene solution onto Si substrates at a speed of4500 – 6000 rpm using a spin-coater (MS-A150, Mikasa
co. Ltd., Tokyo, Japan). Then, the samples were cured at60 °C for 1 h and allowed to stand for 48 h at room
temperature. The SiO2(PHPS) samples with different
thickness (in this paper, these samples are denoted as
sample-A, sample-B, and sample-C) were prepared forthe NR measurements. These samples were stored in abox under low humidity and dust-free conditions at room
temperature.
FT-IR Measurements
The samples for the FT-IR spectroscopy analysis wereprepared by removing a section from each samples
prepared for the NR measurements.
The FT-IR spectra were measured with an FT/IR4100ST (Nihon Bunko Co. Ltd., Tokyo, Japan) equippedwith an ATR unit (PRO670H-S, Nihon Bunko Co. Ltd.,Tokyo, Japan). The wavenumber range of the FT-IR
spectra was 600 – 4000 cm-1 and the resolution was 4 cm1. Each spectrum was determined from the average resultof 64 scans. All the measurements were performed atroom temperature.

___________________________________________#k_akutsu@cross.or.jp- 71 -

Proceedings of the 12th Annual Meeting of Particle Accelerator Society of Japan
August 5-7, 2015, Tsuruga, JapanPASJ2015 WEOM05

Spectroscopic Ellipsometry Measurements
We measured the SE data by using a variable angle
spectroscopic ellipsometer (M-2000U, J. A. Woollam Co.,Inc.) system installed at the Industrial Technology Centerof Tochigi prefecture. The SE spectra were obtained atthree different positions for each sample. The incident
angles were 70, 75, and 80°, and the spectral wavelength
range was from 245 to 1000 nm. The ellipsometric data
were fitted and modelled using the WVASE software
package (J.A. Woollam Co., Inc.) to analyse the thicknessof the thin SiO2 layer on the Si substrate. All
measurements were performed at room temperature.
Neutron Reflectivity Measurements
The NR measurements were performed on a BL17
SHARAKU reflectometer installed at the Materials andLife Science Experimental Facility (MLF) in J-PARC [6].
The incident beam power of the proton accelerator was
400 kW for all the measurements. Pulsed neutron beams
were generated in mercury target at 25 Hz, and the NR
data were measured using the time-of-flight (TOF)
technique [6]. The wavelength (λ) range of the incident
neutron beam was tuned to approximately λ = 2.2 – 8.4 Åby a disk chopper. The incident angle was varied from0.3° to 0.9°, and the exposure times for measurements atincident angles of 0.3° and 0.9° were 0.5 and 1 h,respectively. The covered Qz range was Qz = 0.008 – 0.09
Å–1, where Qz = (4π/λ)sinθ (θ represents the incidentangle). A 20 mm beam footprint was maintained on thesample surface by using six kinds of incident slits [6]. All
the measurements were performed at room temperature.
The data reduction, normalization, and subtraction wereperformed using a program installed in BL17SHARAKU. The Motofit program [7] was used to fit theNR profiles with a least-squares approach to minimize thedeviation of the fit, and the thickness, scattering lengthdensity (SLD, ρ), and Gaussian roughness were evaluatedby using the program.

RESULTS AND DISCUSSION
FT-IR Analysis of the Thin SiO2(PHPS) Layer
Figure 2 shows the FT-IR spectra of the thin
SiO2(PHPS) layer samples in the wavenumber range of
600−4000 cm-1. The absorption of N-H (3400 cm-1) and
Si-H (2200 cm-1), which are attributed to the unreacted
PHPS [8], were not observed in the spectra. This result
indicated that the starting PHPS material completelyreacted in the curing process. The absorption around 3300
cm-1 can be attributed to the O-H stretching of the Si-OH
group, and the absorption peak between 1000 − 1100 cm-1
and the shoulder between 1100 − 1200 cm-1 are mainly
due to the absorption of the Si-O asymmetric stretchingtransverse optical (TO) and longitudinal optical (LO)modes, respectively [9]. In addition, the absorption
between 1100 − 1200 cm-1 can be assigned to thestretching vibration of the Si-O bond in the SiO4
tetrahedral terminal group [10]. These results suggest thatthe synthesized SiO2(PHPS) material primarily consists ofSiO2 and similar compounds as observed from the surface
measurement by the FT-IR method.

Figure 2: FT-IR spectra (mean) of the thin SiO2 layer samples.

Spectroscopic Ellipsometry Analysis
To estimate the thickness of the thin SiO2(PHPS) layer,
we measured and analysed the SE spectra.
Table 1 shows the estimated thickness of each sample.
The SE spectra were measured at three different positions
for each thin SiO2(PHPS) layer sample. The thickness ofthe thin SiO2(PHPS) layer was estimated to be 682.2,681.3, 681.2 Å for sample-A, 784.8, 784.5, 783.2 Å forsample-B, and 1493, 1507, 1485 Å for sample-C,respectively. Although the measurement position waschanged, the estimated thickness values at three different
positions were same. This result revealed that the thin
SiO2(PHPS) layer could be uniformly coated in all
samples. Therefore, it was concluded that the equal SiO2thickness layer could be synthesized using the PHPS/pxylene coating system.
For the reasons mentioned above, the NR data wereanalysed by assuming that the equal SiO2-thickness layer
was formed on the Si substrate, and the average thickness
values were used as the initial parameter for the fitting
analysis of the NR profiles.
Table 1: The Thickness of the Thin SiO2(PHPS) Layer
Estimated by the SE Analysis- 72 -

Thicknss (Å)

Sample-A

Sample-B

Sample-C

Position-1

682.2

Position-2

681.3

Position-3

681.2

Position-1

784.8

Position-2

784.5

Position-3

783.2

Position-1

1493

Position-2

1507

Position-3

1485

AverageThickness (Å)
681.6

784.2

1495

Proceedings of the 12th Annual Meeting of Particle Accelerator Society of Japan
August 5-7, 2015, Tsuruga, JapanPASJ2015 WEOM05

be attributed to the efficiency of the cross-linking reaction
between the silazane oligomers. Therefore, the NR
measurements revealed that a uniform SiO2 layer can besynthesized on a Si substrate by using the PHPS/p-xylene
system, and the density of the SiO2(PHPS) layer could
increase by increasing the thickness of the layer. It could
suggest that if the cross-linking reaction rate is too high(that is, the thickness of the SiO2(PHPS) layer is toothick), a densified SiO2(PHPS) layer is formed and itleads to cracking.
Table 2: Best-fit Parameters for the Reflectivity Model
Data Shown in Figure 3Sample-AFigure 3: Neutron reflectivity profiles of SiO2(PHPS) samples.
The circles represent the experimental data, and the solid lines
represent the best-fit calculated NR profiles.

Neutron Reflectivity Analysis
To investigate the synthesis mechanism of the thin
SiO2(PHPS) layer, the structure of the thin SiO2(PHPS)
layer samples was analysed by the NR analysis method indetail.
The air-solid reflectivity measurements for theSiO2(PHPS)/Si samples are shown in Figure 3. The NR
profiles of the samples were analyzed using the Motofit
reflectometry package, and the calculated theoreticalreflectivity profiles are shown in Figure 3. The symbols
represent the observed NR profiles, while the solid lines
represent the calculated NR profiles determined from thestructural models. Because actually a naturally oxidized
thin SiO2 layer formed between the SiO2(PHPS) layer andtheSisubstrate,a
two-layermodel,
SiO2(PHPS)/SiO2(oxidized)/Si, was applied to fit theobtained NR profiles. The theoretical reflectivity profilesreproduced the experimental NR profiles in the all Qzrange. Table 2 shows the structural parameters obtained
from this analysis. The thickness and SLD values of theSiO2(PHPS) layer were estimated to be 663 Å and 2.01
( × 106 Å-2) for sample-A, 765 Å and 2.01 ( × 106 Å-2) forsample-B, and 1349 Å and 2.28 ( × 106 Å-2) for sample-C,respectively. The estimated thickness values were agreed
with the results of the SE analysis. The estimated ρ values
indicate that the density of the synthesized SiO2(PHPS) islower than that of natural SiO2, since the ρ value ofnatural SiO2 is 3.47 ( × 106 Å-2). The ρ value is defined asρ = ρSiO2･NA･Σibi/M [11], where ρSiO2, NA, bi, and M are
the density of SiO2, Avogadro’s number, the coherent
scattering length of the element, and molecular weight,respectively. Thus, assuming that the dominantcomponent of the SiO2(PHPS) layer is SiO2, the ρSiO2
value of each SiO2(PHPS) layer was estimated to be 1.17(sample-A), and 1.28 (sample-B), and 1.45 (sample-C),
respectively, as shown in Table 2. The density of theSiO2(PHPS) layer was altered by varying the thickness ofthe layer, whereas the condition of the SiO2 coating did
not change. Since the existence of a non-cross-linked
precursor will result in a lower ceramic yield [12], thechange in the density depending on the thickness would

SiO2(PHPS)

Si substrate

Sample-Ct (Å)6637651349

ρ (×106 Å-2)

2.01

2.02

2.28

σ (Å)

8.28

6.38

6.56

ρSiO2 (g/cm )

1.27

1.28

1.45

t (Å)

39.2

36.8

22.4

ρ (×10 Å )

2.39

2.45

2.41

σ (Å)

14.1

21.6

2.86

ρ (×106 Å-2)

2.07

2.07

2.07

σ (Å)

1.43

1.09

25.0

3SiO2(oxidized)

Sample-B

6-2

t: thickness, ρ: SLD, σ: roughness of the surface or interface,ρSiO2: density of SiO2(PHPS) layer calculated from the ρ value.

SUMMARY
In this study, we investigated the structure of the SiO2waterproof layer (SiO2(PHPS)) in detail by using the FTIR, SE, and NR methods. These analyses revealed that theunreacted PHPS material did not remain in theSiO2(PHPS) layer, and a uniform SiO2(PHPS) layer could
be formed in all SiO2(PHPS) layer samples. In addition,
the density of the SiO2(PHPS) layer increases byincreasing the thickness of the layer. This suggests thatthe efficiency of the curing reaction in the PHPS/p-xylene
system would increase with the thickness of theSiO2(PHPS) layer.

ACKNOWLEDGMENT
We thank Mr. N. Takezawa for his support with regard
to the SE experiments. The SE experiments wereconducted at the Industrial Technology Center of Tochigi
prefecture. We also thank Dr. D. Yamazaki (JAEA) andMr. S. Kasai (CROSS TOKAI) for his support withregard to the NR experiments. The NR experiments wereconducted at the BL17 SHARAKU of the Materials andLife Science Experimental Facility (MLF) in J-PARC(Proposal No.2014B0050). The FT-IR measurements
were conducted at the User Experiment Preparation Lab
III provided by CROSS TOKAI.

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Proceedings of the 12th Annual Meeting of Particle Accelerator Society of Japan
August 5-7, 2015, Tsuruga, Japan

PASJ2015 WEOM05

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