Fons, Paul



Faculty of Science and Technology, Department of Electronics and Electrical Engineering (Yagami)




Books 【 Display / hide

  • Springer handbook of electronic and photonic materials

    Kasap, S. O. (Safa O.), Capper, Peter, Springer, 2017,  Page: xxxvi, 1536 p.

    Scope: Chapter 46: Phase-Change Memory Materials

  • Phase change materials : science and applications

    Raoux, Simone, Wutting, Matthias, Springer, 2009,  Page: xxii, 446 p.

Papers 【 Display / hide

  • Dimensional transformation of chemical bonding during crystallization in a layered chalcogenide material

    Yuta Saito, Shogo Hatayama, Yi Shuang, Paul Fons, Alexander V. Kolobov, Yuji Sutou

    Scientific Reports (NATURE RESEARCH)  11 ( 1 ) 4782 - 4782 2021.12

    Research paper (scientific journal), Joint Work,  ISSN  2045-2322

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    Two-dimensional (2D) van der Waals (vdW) materials possess a crystal structure in which a covalently-bonded few atomic-layer motif forms a single unit with individual motifs being weakly bound to each other by vdW forces. Cr Ge Te is known as a 2D vdW ferromagnetic insulator as well as a potential phase change material for non-volatile memory applications. Here, we provide evidence for a dimensional transformation in the chemical bonding from a randomly bonded three-dimensional (3D) disordered amorphous phase to a 2D bonded vdW crystalline phase. A counterintuitive metastable “quasi-layered” state during crystallization that exhibits both “long-range order and short-range disorder” with respect to atomic alignment clearly distinguishes the system from conventional materials. This unusual behavior is thought to originate from the 2D nature of the crystalline phase. These observations provide insight into the crystallization mechanism of layered materials in general, and consequently, will be useful for the realization of 2D vdW material-based functional nanoelectronic device applications. 2 2 6

  • Recent developments concerning the sputter growth of chalcogenide-based layered phase-change materials

    Yuta Saito, Misako Morota, Kotaro Makino, Junji Tominaga, Alexander Kolobov, Paul Fons


    Research paper (scientific journal), Joint Work,  ISSN  1369-8001

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    This paper reviews recent developments in the sputter growth of chalcogenide thin films for phase-change memory applications. We focus primarily on the growth of highly oriented Sb2Te3, which is a layered material. Sb2Te3 is an end point compound of the GeTe-Sb2Te3 pseudobinary tie-line and an important component of heterogeneously structured phase-change materials. Some key growth parameters are introduced for the fabrication of highly oriented films. The optimization of the sputtering conditions enables the growth of highly oriented films on a variety of substrates even on flexible surfaces. Furthermore, the same techniques are found to be applicable for the deposition of similar materials including Ge-Sb-Te, Bi-Te, Bi2Te3-Sb2Te3, and Bi-Sb alloys. In order to meet the increasing demand for nonvolatile memory as well as other novel electronic devices, the fabrication of high-quality thin films by an industry friendly method is crucial.

  • Polymorphism of CdTe in the Few-Monolayer Limit

    Alexander V. Kolobov, Vladimir G. Kuznetsov, Paul Fons, Yuta Saito, Dmitriy I. Elets, Berangere Hyot


    Research paper (scientific journal), Joint Work,  ISSN  1862-6254

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    Decreasing the thickness of semiconductors to the few monolayer limit often results in structural relaxation and the appearance of new properties. Herein, the bistability of 2ML thick CdTe, where the zinc blende structure of the bulk phase is metastable and the stable (ground) state is represented by an inverted structure with Cd atoms sandwiched by Te planes, is demonstrated. The thermodynamic stability of both phases is demonstrated by the absence of imaginary modes in the phonon dispersion spectra of both phases fully relaxed at 0 K. Both phases are direct-gap semiconductors and the transformation from the zinc blende phase to the inverted phase is accompanied by a marked increase of the bandgap from 0.13 to 1.03 eV. In combination with the stable alpha-CdTe phase, results demonstrate the polymorphism of ultrathin CdTe. A pronounced property contrast between the phases suggests the possible use of few-monolayer CdTe for memory applications.

  • Amorphous-to-Crystal Transition in Quasi-Two-Dimensional MoS2: Implications for 2D Electronic Devices

    Milos Krbal, Vit Prokop, Alexey A. Kononov, Jhonatan Rodriguez Pereira, Jan Mistrik, Alexander Kolobov, Paul J. Fons, Yuta Saito, Shogo Hatayama, Yi Shuang, Yuji Sutou, Stepan A. Rozhkov, Jens R. Stellhorn, Shinjiro Hayakawa, Igor Pis, Federica Bondino

    ACS APPLIED NANO MATERIALS (AMER CHEMICAL SOC)  4 ( 9 ) 8834 - 8844 2021.09

    Research paper (scientific journal), Joint Work,  ISSN  2574-0970

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    Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have demonstrated a very strong application potential. In order to realize it, the synthesis of stoichiometric 2D TMDCs on a large scale is crucial. Here, we consider a typical TMDC representative, MoS2, and present an approach for the fabrication of well-ordered crystalline films via the crystallization of a thin amorphous layer by annealing at 800 degrees C, which was investigated in terms of long-range and short-range orders. Strong preferential crystal growth of layered MoS2 along the < 002 > crystallographic plane from the as-deposited 3D amorphous phase is discussed together with the mechanism of the crystallization process disclosed by molecular dynamic simulations using the Vienna Ab initio Simulation Package. We believe that the obtained results may be generalized for materials. The proposed approach demonstrates a simple and efficient way to fabricate thin 2D TMDCs for applications in nano-and optoelectronic devices.

  • Understanding the low resistivity of the amorphous phase of Cr2Ge2Te6 phase-change material: Experimental evidence for the key role of Cr clusters

    Shogo Hatayama, Keisuke Kobayashi, Yuta Saito, Paul Fons, Yi Shuang, Shunsuke Mori, Alexander V. Kolobov, Yuji Sutou


    Research paper (scientific journal), Joint Work,  ISSN  2475-9953

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    Different from the prototypical elemental semiconductors such as Si and Ge, chalcogenide-based phasechange materials (PCMs) generally show very high resistivity contrast between the amorphous and crystalline phases. In contrast to conventional PCMs, such as Ge-Sb-Te alloys, where the amorphous phase possesses higher resistivity, Cr2Ge2Te6 (CrGT) exhibits the opposite dependence. Namely, the amorphous phase is characterized by a lower resistivity than the crystalline phase. Although density functional theory calculations suggest that Cr clusters are responsible for the low resistivity of amorphous CrGT, the effects of composition on the electrical properties have yet to be investigated. In this work, the dependence of the electrical properties on Cr content and the role of the Cr clusters were investigated experimentally using Hall effect, hard x-ray photoelectron spectroscopy (HAXPES), and optical propertymeasurements. The electrical properties were found to be dependent on the Cr content. From a HAXPES core-level spectra analysis, it was found that the increased carrier density correlated with the extent of Cr clusters, indicating that the hole carriers present likely originated from Cr clusters. The increased concentration of Cr clusters was also found to lead to a shift of the valence band edge toward the Fermi level as well as to a decrease in the optical band gap. It has been suggested that the Cr clusters may induce the formation of new energy states close to the valence band edge. These results indicate that the Cr clusters play an essential role in determining the electrical properties of amorphous CrGT, and that tuning the film composition is an effective way to optimize device properties for nonvolatile memory applications.

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Reviews, Commentaries, etc. 【 Display / hide

  • Understanding local structure of Cr2Ge2Te6 phase change material for non-volatile memory application

    畑山祥吾, YI Shuang, FONS Paul, FONS Paul, 齊藤雄太, KOLOBOV Alexander V., KOLOBOV Alexander V., 小林啓介, 進藤怜史, 安藤大輔, 須藤祐司

    応用物理学会春季学術講演会講演予稿集(CD-ROM) 67th 2020

    Other, Joint Work

  • スパッタ法による高配向Bi-Te薄膜の成膜と電子状態解析

    齊藤雄太, FONS Paul, 牧野孝太郎, MITROFANOV Kirill V., 上杉文彦, 竹口雅樹, KOLOBOV Alexander V., 富永淳二

    日本金属学会講演概要(CD-ROM) 164th 2019

    Other, Joint Work,  ISSN  2433-3093

  • 不揮発性相変化メモリ用遷移金属カルコゲナイド相変化材料の開発

    齊藤雄太, 畑山祥吾, YI Shuang, 進藤怜史, FONS Paul, KOLOBOV Alexander V., 小林啓介, 小林啓介, 小林啓介, 須藤祐司

    応用物理学会春季学術講演会講演予稿集(CD-ROM) 66th 2019

    Other, Joint Work

  • 1T’-MoTe2バルク結晶におけるコヒーレントフォノンの観測

    福田拓未, 牧野孝太郎, 齊藤雄太, FONS Paul, KOLOBOV Alexander V., KOLOBOV Alexander V., 上野啓司, MONDAL Richarj, 長谷宗明

    応用物理学会秋季学術講演会講演予稿集(CD-ROM) 80th 2019

    Other, Joint Work

  • Erratum: Effects of RbF postdeposition treatment and heat-light soaking on the metastable acceptor activation of CuInSe<inf>2</inf> thin film photovoltaic devices (Applied Physics Letters (2018) 113 (063901) DOI: 10.1063/1.5031898)

    Ishizuka S., Shibata H., Nishinaga J., Kamikawa Y., Fons P.

    Applied Physics Letters (Applied Physics Letters)  113 ( 11 )  2018.09

    ISSN  00036951

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    © 2018 Author(s). We have found an error in Fig. 3(d) in the original published version of our paper.1 The annotations -6V and +3.0V are incorrect and should be +0.6V and -30 V, respectively. Figure 1 is a corrected version for the original Fig. 3(d). (Figure Presented).

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Research Projects of Competitive Funds, etc. 【 Display / hide

  • Understanding the crystallization mechanism of amorphous van der Waals layered materials


    MEXT,JSPS, Grant-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B), Principal investigator


Courses Taught 【 Display / hide











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