Bayesian estimation analysis of X-ray photoelectron spectra; Application to Si 2p spectrum analysis of oxidized silicon surfaces

Shinotsuka, Hiroshi*; Nagata, Kenji*; Yoshikawa, Hideki*; Ogawa, Shuichi*; Yoshigoe, Akitaka

Applied Surface Science, 685, p.162001_1 - 162001_11, 2025/03

https://doi.org/10.1016/j.apsusc.2024.162001

Silicon (Si) 2p photoelectron spectra of thermally oxidized Si(001) surfaces were analyzed using Bayesian estimation, a type of mathematical statistical processing, considering spin-orbit interactions. The accuracy of the estimation of fitting parameters and the model selection of the number of peaks were discussed. The spectral analysis was performed without any prior information on the positions of other Si peaks, except for the prominent bulk Si peak, and without using chemical-state assumptions. Our method completely verified previous findings on the surface species and the changes in peaks due to oxidation-induced strain as oxidation progressed.

Synchrotron radiation photoemission electron microscopy study on radioactive cesium-bearing microparticle collected in Fukushima

Yoshigoe, Akitaka; Tsuda, Yasutaka; Kobata, Masaaki; Okane, Tetsuo; Satou, Yukihiko; Okochi, Takuo*

e-Journal of Surface Science and Nanotechnology (Internet), 23(1), p.16 - 21, 2025/02

https://doi.org/10.1380/ejssnt.2025-004

Dissociative adsorption of supersonic CHCl on Cu oxide Surfaces; CuO(111) and bulk CuO precursor "29"; Structure on Cu(111)

Hayashida, Koki*; Tsuda, Yasutaka; Murase, Natsumi*; Yamada, Takashi*; Yoshigoe, Akitaka; Dio, W. A.*; Okada, Michio*

Applied Surface Science, 669, p.160475_1 - 160475_6, 2024/10

https://doi.org/10.1016/j.apsusc.2024.160475

Coverage dependence upon early oxidation stages of hafnium-adsorbed Si(111)-77

Kakiuchi, Takuhiro*; Anai, Ryota*; Saiki, Taiju*; Tsuda, Yasutaka; Yoshigoe, Akitaka

Journal of Physical Chemistry C, 128(31), p.13052 - 13063, 2024/08

https://doi.org/10.1021/acs.jpcc.4c02368

0xidation at the interface and the surface of Si(111) substrate with thin Hf films were studied using synchrotron radiation photoelectron spectroscopy in conjunction with supersonic oxygen molecular beams (SOMB). An Hf/Si(111) with a coverage of 0.5 monolayer (ML) included HfSi and HfSi. Following exposures to thermal oxygen molecules with a translational energy (Et) of 0.03 eV, HfSi was oxidized into Hf valence. Following SOMB irradiation with Et of 0.39 eV, the other HfSi could be oxidized into the Hf. Following the thermal O exposures, the metallic Hf was nonlocally oxidized to HfO via trapping-mediated dissociative adsorption. Meanwhile, the segregated Si atoms were oxidized by SOMB irradiation with 2.2 eV and SiO was generated on the surface.

Characterization of nitrided SiC(100) MOS structures by means of electrical measurements and X-ray photoelectron spectroscopy

Kobayashi, Takuma*; Suzuki, Asato*; Nakanuma, Takato*; Sometani, Mitsuru*; Okamoto, Mitsuo*; Yoshigoe, Akitaka; Shimura, Takayoshi*; Watanabe, Heiji*

Materials Science in Semiconductor Processing, 175, p.108251_1 - 108251_7, 2024/06

https://doi.org/10.1016/j.mssp.2024.108251

Atomic bonding state of silicon oxide anodized in extremely diluted hydrofluoric solution

Arai, Taiki*; Yoshigoe, Akitaka; Motohashi, Mitsuya*

Zairyo No Kagaku To Kogaku, 60(5), p.153 - 158, 2023/10

Si oxide films are currently widely used as insulating materials in electronic devices and biomaterials. The atomic bonding state of these films significantly influences the properties of each device, thus it is particularly necessary to understand and control the chemical bonding state between Si and O in the films. In this study, the Si oxide films formed by anodic oxidation on Si substrate surfaces in extremely low concentrations of HF solutions were analyzed by X-ray photoelectron spectroscopy mainly focusing on Si2p and F1s spectra. Although the HF concentration is in the order of ppm, the films contain percent order of F atoms, suggesting the formation of Si-F and Si-O-F bonds in the films. It was also found that the different depth profiles for F and O atoms was observed, indicating that the surface reaction processes seem to be different depending on each element.

Formation of high-quality SiO/GaN interfaces with suppressed Ga-oxide interlayer via sputter deposition of SiO

Onishi, Kentaro*; Kobayashi, Takuma*; Mizobata, Hidetoshi*; Nozaki, Mikito*; Yoshigoe, Akitaka; Shimura, Takayoshi*; Watanabe, Heiji*

Japanese Journal of Applied Physics, 62(5), p.050903_1 - 050903_4, 2023/05

https://doi.org/10.35848/1347-4065/acd1ca

While the formation of an GaO interlayer is key to achieving SiO/GaN interfaces with low defect density, it can affect the reliability and stability of metal-oxide-semiconductor (MOS) devices if the annealing conditions are not properly designed. In the present study, we aimed to minimize the growth of the GaO layer on the basis of the sputter deposition of SiO on GaN. Synchrotron radiation X-ray photoelectron spectrometry measurements confirmed the suppressed growth of the GaO layer compared with a SiO/GaN structure formed by plasma-enhanced chemical vapor deposition. Negligible GaO growth was also observed when subsequent oxygen annealing up to 600C was performed. A MOS device with negligible capacitance-voltage hysteresis, nearly ideal flat-band voltage, and low leakage current was demonstrated by performing oxygen and forming gas annealing at temperatures of 600C and 400C, respectively.

Evaluation of doped potassium concentrations in stacked two-Layer graphene using real-time XPS

Ogawa, Shuichi*; Tsuda, Yasutaka; Sakamoto, Tetsuya*; Okigawa, Yuki*; Masuzawa, Tomoaki*; Yoshigoe, Akitaka; Abukawa, Tadashi*; Yamada, Takatoshi*

Applied Surface Science, 605, p.154748_1 - 154748_6, 2022/12

https://doi.org/10.1016/j.apsusc.2022.154748

Immersion of graphene in KOH solution improves its mobility on SiO/Si wafers. This is thought to be due to electron doping by modification with K atoms, but the K atom concentration C in the graphene has not been clarified yet. In this study, the C was determined by XPS analysis using high-brilliance synchrotron radiation. The time evolution of C was determined by real-time observation, and the C before irradiation of synchrotron radiation was estimated to be 0.94%. The C 1s spectrum shifted to the low binding energy side with the desorption of K atoms. This indicates that the electron doping concentration into graphene is decreasing, and it is experimentally confirmed that K atoms inject electrons into graphene.

Restoration of oxygen vacancies on an anatase TiO(001) surface with supersonic seeded oxygen molecular beam

Katsube, Daiki*; Ono, Shinya*; Inami, Eiichi*; Yoshigoe, Akitaka; Abe, Masayuki*

Vacuum and Surface Science, 65(11), p.526 - 530, 2022/11

https://doi.org/10.1380/vss.65.526

The oxidation of oxygen vacancies at the surface of anatase TiO (001) was investigated by synchrotron radiation photoelectron spectroscopy and supersonic O beam (SSMB). The oxygen vacancies at the top surface and subsurface could be eliminated by the supply of hyperthermal oxygen molecules. Oxygen vacancies are present on the surface of anatase TiO(001) when it is untreated before transfer to a vacuum chamber. These vacancies, which are stable in the ambient condition, could also be effectively eliminated by using oxygen SSMB. This result is promising as a surface processing for various functional oxides.

Electrical properties and energy band alignment of SiO/GaN metal-oxide-semiconductor structures fabricated on N-polar GaN(000) substrates

Mizobata, Hidetoshi*; Tomigahara, Kazuki*; Nozaki, Mikito*; Kobayashi, Takuma*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; Watanabe, Heiji*

Applied Physics Letters, 121(6), p.062104_1 - 062104_6, 2022/08

https://doi.org/10.1063/5.0095468

The interface properties and energy band alignment of SiO/GaN metal-oxide-semiconductor (MOS) structures fabricated on N-polar GaN(000) substrates were investigated by electrical measurements and synchrotron-radiation X-ray photoelectron spectroscopy. They were then compared with those of SiO/GaN MOS structures on Ga-polar GaN(0001). Although the SiO/GaN(000) structure was found to be more thermally unstable than that on the GaN(0001) substrate, excellent electrical properties were obtained for the SiO/GaN(000) structure by optimizing conditions for post-deposition annealing. However, the conduction band offset for SiO/GaN(000) was smaller than that for SiO/GaN(0001), leading to increased gate leakage current. Therefore, caution is needed when using N-polar GaN(000) substrates for MOS device fabrication.