Self-assembled Superparamagnetic Clusters of Vanadium Selenide
Yu-Ting Chow1, Pei-Cheng Jiang1, Cheng-Hsun-Tony Chang1*
1Department of electronic engineering, Minghsin University of Science and Technology, Hsinchu, Taiwan
* Presenter:Cheng-Hsun-Tony Chang,
In recent years, 2D materials have attracted much attention in researches. Especially, any heterogenic interfaces between non-ferromagnetic materials which can show magnetic properties are the most interesting in researches. For example, vanadium selenide has great potential in various applications. In this project, vanadium is deposited on HOPG by RF sputtering and selenium is then deposited on top of vanadium by DC sputtering. Superconducting quantum interference device (SQUID), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) are employed to study the magnetic properties, crystalline structures and chemical compositions of Se/V bilayers on HOPG. From SQUID, a superparamagnetic loop can be observed and well fitted by Langevin function. In order to find the origin of superparamagnetic properties, XPS and XRD is employed. From depth profiling of XPS, vanadium and selenium are found to have some mixes by observing the trend of XPS intensities and the VSe2 compounds can be confirmed by comparing the binding energies for vanadium and selenium with their uncompounded states.[1] After XRD analysis, the lattice parameter can be calculated from the peak position by Bragg’s law which represents VSe2 exactly exist. [2] The peak intensities and relative lattice parameters implies that there are VSe2 with united crystalline axis formed at the interfaces between vanadium and selenium. Furthermore, after calculating the full width at half maximum (FWHM) for each peak representing VSe2, the average size of VSe2 clusters can be determined. [3] The anisotropy energy is first reported for VSe2 clusters by combining the average size and superparamagnetic properties which have great potential in develop 2D magnetic devices such as recording media, MRAM, MFET or qubits.

[1] J. F. Moulder, W. F. Stickle, P. E. Sobol and K. D. Bomben, Handbook of X-ray Photoelectron Spectroscopy: A Reference Book of Standard Spectra for Identification and Interpretation of XPS Data, Physical Electronics Division, 1993.
[2] E. Hoschek, Vanadinselenide, Zeitschrift fuer Anorganische und Allgemeine Chemie, 1939, 242, 49-49.
[3] C. H. T. Chang, S. C. Chang, J. S. Tsay and Y. D. Yao, enhanced exchange bias fields for CoO/Co bilayers: influence of antiferromagnetic grains and mechanisms, Appl. Surf. Sci., 2017, 405, 316–320.

Keywords: self-assembled, vanadium selenide, superparamagnetic