Scientific Program

Please note that the program is tentative and subject to change anytime (even during the conference).

Scientific program: https://drive.google.com/file/d/1cHsjMrDbK_Yt0iKxzH3RIaRlDIwqkuDL/view?usp=sharing

Essential physical properties of graphene nanoribbons:

Roles of sigma bands and lattice defect

Godfrey Gumbs^1*

¹Department of Physics and Astronomy, Hunter College of the City University of New York, 695 Park Avenue, New York, New York 10065, USA

*Author to whom correspondence should be addressed: ggumbs@hunter.cuny.edu

We explore the electronic, optical, and excitation properties of graphene nanoribbons (GNRs) under the influence of sigma bands, edge-defect, and external electric and magnetic fields. We employ the tight-binding model in conjunction with the absorption spectral function and dielectric function. The sigma edge-bands and modification of the edge states give rise to the diverse band structures with striking changes in the band gap and special flat bands at low energy. The optical-absorption spectra exhibit unique excitation peaks in the presence of either the sigma band or the edge-defect. Unconventional plasmon modes and their association with the flat bands of the specially designed GNRs are thoroughly studied. Our obtained plasmon modes are found to be analogous to magnetoplasmons associated with collective excitations of Landau-quantized electrons. We demonstrate the strong dependence of the absorption spectra and novel collective excitations on both the type and period of the edge modification. We discover the special rule governing how the edge-defect influences the electronic, optical, and excitation properties in GNRs. Our theoretical prediction demonstrates an efficient way to manipulate the essential physical properties of GNRs. This might be of importance in the search for suitable materials designed to have possible technology applications in electronics, nano-optical, plasmonic and optoelectronic devices.

Keywords: graphene nanoribbon, edge-defect, electronic, optical, collective excitation, flat bands

Acknowlegdement: G.G. would like to acknowledge the support from the Air Force Research Laboratory AFRL) through Grant No. FA9453-21-1-0046.

Exciton binding energy in 2D symmetric semiconductors

Hieu T. Nguyen-Truong^1,*

¹Laboratory of Applied Physics, Science and Technology Advanced Institute,

Van Lang University, Ho Chi Minh City, Vietnam

*Author to whom correspondence should be addressed: nguyentruongthanhhieu@vlu.edu.vn

In 2D materials, the spatial confinement and reduced Coulomb screening results in a strongly bound exciton, and hence a large exciton binding energy. This quantity can be calculated within the quasiparticle plus Bethe-Salpeter equation theory. However, these calculations require a high computational cost. Here, we introduce an analytical expression to determine the exciton binding energy in 2D symmetric semiconductors. Our predicted values agree well with results obtained from the Monte Carlo and the variational calculations.

Keywords: 2D materials, exciton binding energy

Modeling glassy SiC nanoribbon by rapidly cooling from the liquid: An affirmation of appropriate potentials

Duong Thi Nhu Tranh, Vo Van Hoang, Tran Thi Thu Hanh

Faculty of Applied Science, Ho Chi Minh City University of Technology (HCMUT), 268 Ly Thuong Kiet Street, District 10, Ho Chi Minh City, Viet Nam b Vietnam National University, Ho Chi Minh City, Vietnam, Linh Trung Ward, Thu Duc District, Ho Chi Minh City, Viet Nam

*Author to whom correspondence should be addressed: thuhanhsp@hcmut.edu.vn

Modeling glassy SiC nanoribbon by cooling rapidly the SiC liquid from 8000K to 300K is carried out by molecular dynamics (MD) simulations. Two separated MD simulations are performed, one of which uses the Tersoff potential and the other one uses the Vashishta potential. The temperature dependence of various structural and thermodynamic properties of the systems is analyzed and discussed via the radial distribution functions (RDFs), the coordination number distributions, and the ring statistics. We nd that the Tersoff potential is clearly more appropriate in order to obtain the glassy SiC when rapidly cooling is employed.

Keywords: 2D glassy systems Rapidly cooling Potentials
MD simulation

Essential geometric and electronic properties of nanotubes (Group-IV: C, Si and Ge) induced by spin-orbit coupling

Hsin-Yi Liu¹ and Ming-Fa Lin^2,*

¹ Department of Physics/Hi-GEM, National Cheng Kung University, Tainan 701, Taiwan.

² Department of Physics/QTC/Hi-GEM, National Cheng Kung University, Tainan701, Taiwan.

*mflin@mail.ncku.edu.tw

In this talk, we introduced the essential geometric and electronic properties of nanotubes including of carbon, silicon and germanium. The geometric types of nanotubes are divided into achiral and chiral nanotubes. Here we focus on achiral nanotubes, which exhibit a spiral symmetry of mirror image. Snice carbon nanotubes (CNTs) have been discovered in 1991 [1], they arouse every one’s interests due to the tubular structure and distinctive electronic properties. Carbon nanotubes have great potential in various fields, such as field emission sources, lithium ion batteries super capacitors and actuators due to its special mechanical, electronic and optical features. The electronic properties of nanotubes can be either metallic and semiconducting characteristics. The armchair carbon nanotubes present zero-gap semi-metallic characters, however the silicon and germanium of armchair nanotubes are semiconducting. The both generate the energy gap and exhibit the transition state of indirect to direct when the tube size is increased. A single wall zigzag carbon nanotube can be metallic and semiconducting behaviors dependent on its chiral vectors. Silicon and germanium nanotubes are metallic at small tube size and are semiconducting when both of the diameters are increased. It is very significant to realize the spin-orbit coupling in nanotubes due to their curved surfaces. The curved tubular carbon structure compared with graphene is unsymmetrical enhances the intrinsic spin-orbit coupling in carbon nanotubes and silicon and germanium nanotubes as well. The results of spatial charge provide the multi-/single-orbital hybridizations because of various chemical bonds. The orbital-projected density of states (PDOSs) present the orbital-decomposed contributions, especially for the p_z-orbital at low energy.

Keywords: nanotubes, spin-orbit coupling, group IV elements

Acknowlegdement:

References:

[1] Iijima S 1991 Helical microtubules of graphitic carbon Nature 354 56

DFT calculations for two-dimensional materials and topological matter

Chi-Hsuan Lee¹, Joy Lin¹, Yan-Hong Chen², Shun‑Jen Cheng², and Chih-Kai Yang^1*

¹Graduate Institute of Applied Physics, National Chengchi University, Taipei, Taiwan

²Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan

*Author to whom correspondence should be addressed: ckyang@nccu.edu.tw

Ab-initio calculations based on density functional theory are widely used to explore the physical properties of emergent materials. For example, it has been found that lithium atoms can be bonded to a single graphene layer alternately on both sides by distorting the relative positions of the carbon atoms in the honeycomb lattice, and the structure turns out to be a conductor [1]. DFT calculations also reveal that a variety of transition-metal atomic chains deposited on some of the semiconducting MoS₂ nanoribbons is able to transform the semiconductors into half metals, allowing transport of 100% spin-polarized currents [2]. We also found that a Si atomic chain is equally capable of achieving half metallicity when adsorbed on the same nanoribbon. Furthermore, W atoms in semiconducting armchair WS₂ nanoribbons can be replaced by Ti, V, Cr, Mn, Fe, and Co at various positions [3]. Fe-doped ribbons can have two-channel conduction in the middle segment of the ribbon and at the edges, carrying opposite spins separately. Many Co-doped ribbons, however, are transformed into spin filters that exhibit 100% spin-polarized conduction. DFT calculations also reveal topological surface states of Sb thin films adsorbed with impurity atoms [4]. DFT combined with the Bardeen–Cooper–Schrieffer (BCS) theory for traditional superconductors can be used to calculate the critical temperature T_c of the surface layers of FeTe_0.5Se_0.5 with the exchange interaction as the source of attractive force to form the Cooper pairs [5]. The same method also indicates that T_c and superconducting gap for FeTe_0.5Se_0.5 soars under increasing compression, consistent with the results of experiment.

Keywords: Two-dimensional materials, topological matter, transport, density functional calculation, BCS model

Acknowlegdement: This work was supported by the Ministry of Science and Technology

References:

[1] Yang, C.K. (2009). Appl. Phys. Lett. 94, 163115

[2] Lee, C.H., Lin, J. & Yang, C.K. (2018). Sci. Rep. 8, 13307

[3] Chen, Y.H., Lee, C.H., Cheng, S.J. & Yang, C.K. (2020). Sci. Rep. 10, 16452

[4] Lee, C.H. & Yang, C.K. (2013). Phys. Rev. B 87, 115306

[5] Yang, C.K. & Lee, C.H. (2020). New J. Phys. 22, 083065

Electrical characteristics of modern and next-generation Lithium-ion batteries

Hsien-Ching Chung^1,*

¹R&D Manager, Super Double Power Technology Co., Ltd., Changhua City, Changhua County, Taiwan

*Author to whom correspondence should be addressed: hsienching.chung@gmail.com

The widely use of lithium-ion (Li-ion) batteries in various fields, from 3C to grid-scale ESS, has revolutionized our way of life [1-3]. The 2019 Nobel Prize in Chemistry has been awarded to John B. Goodenough, M. Stanley Whittingham, and Akira Yoshino for their contributions in developing Li-ion batteries. In this chapter, we look back at the milestone discoveries that have shaped the modern Li-ion batteries for inspirational insights. Furthermore, the electrical characteristics of some current and next-generation batteries are discussed [4, 5].

Keywords:

Lithium-ion battery, electrical characteristic

Acknowledgement:

The author (H. C. Chung) thanks Prof. Ming-Fa Lin for the invitation to the conference as a keynote speaker and for inspiring him to study this topic. H. C. Chung would like to thank the contributors to this article for their valuable discussions and recommendations, Jung-Feng Jack Lin, Hsiao-Wen Yang, Yen-Kai Lo, and An-De Andrew Chung. The author (H. C. Chung) thanks Pei-Ju Chien for English discussions and corrections as well as Ming-Hui Chung, Su-Ming Chen, Lien-Kuei Chien, and Mi-Lee Kao for financial support. This work was supported in part by Super Double Power Technology Co., Ltd., Taiwan, under the project “Development of Cloud-native Energy Management Systems for Medium-scale Energy Storage Systems (https://osf.io/7fr9z/)” (Grant number: SDP-RD-PROJ-001-2020).

References:

[1] Chung H.C. (2020) Engineering integrations, potential applications, and outlooks of Li-ion batteries engrXiv DOI: 10.31224/osf.io/swcyg

[2] Chung H.C. and Cheng Y.C. (2019) Action Planning and Situation Analysis of Repurposing Battery Recovery and Application in China J. Taiwan Energy 6 425 DOI: 10.31224/osf.io/nxv7f

[3] Chung H.C. and Cheng Y.C. (2020) Summary of Safety Standards for Repurposing Batteries Monthly J. Taipower's Eng. 860 35 DOI: 10.31224/osf.io/d4n3s

[4] Chung H.C. (2021) Charge and discharge profiles of repurposed LiFePO4 batteries based on the UL 1974 standard Scientific Data 8 165 DOI: 10.1038/s41597-021-00954-3

[5] Chung H.C. (2018) Failure mode and effects analysis of LFP battery module engrXiv DOI: 10.31224/osf.io/acxsp

Optical management of low-dimensional heterostructures for key optoelectronic applications

Chia-Yun Chen^*

Department of Materials Science and Engineering, National Cheng Kung University, Tainan, Taiwan

*E-mail: timcychen@mail.ncku.edu.tw

Heterostructures stand for the artificial structures composed of two or more different solid-state materials. When the dimensionality of materials scales down to nanoscale, the interfaces associated with constitute materials play the dominant role on their materials chemistry, materials physics and even being decisive for the correlated device performances. In this talk, three examples, including transparent photodetectors, inorganic/organic hybrid solar cells and all-day active photocatalytic applications based on heterostructure design will be presented to address their intriguing properties and underlying physics.

Photoluminescence Enhancement with All-dielectric Coherent Metasurfaces

Yu-Tsung Lin¹, Amir Hassanfiroozi¹, Wei-Rou Jiang¹, Chih-Chia Huang¹, Mei-Yi Liao², Wen-Jen Lee², Pin Chieh Wu¹*

¹ Department of Photonics, National Cheng Kung University, Tainan 70101, Taiwan

² Department of Applied Physics, National Pingtung University, Pingtung 90003, Taiwan

*E-mail: pcwu@gs.ncku.edu.tw

Mie resonances have recently attracted much attention in research on dielectric metasurfaces, owning to their enriched multipole resonances, negligible optical loss, and efficient light emitter integration. Although there is a rapid advancement in this field, some fundamental developments are still required to provide a simpler and more versatile paradigm for photoluminescence (PL) control. In this work, we proposed that an all-dielectric coherent metasurface can engineer the PL response by tuning the array size. Such PL manipulation is attributed to the collective Mie resonances that mediate the inter-unit interactions between unit elements and alter the PL intensity. Metasurfaces with different chip sizes are utilized to explore the array size effect on the collective Mie resonances, field enhancement, and Q-factor in TiO2 metasurfaces. Incorporating the all-dielectric coherent metasurface with fluorescent photon emitters, we performed the dependence of PL enhancement on array size, which achieves an enhancement factor of ~10 at the central area of a 90 × 90 μm2 TiO2 metasurface array. These findings provide an additional degree of freedom to engineer the near-field confinement and enhancement, allowing one to manipulate incoherent photon emission and tune light-matter interaction at the nanoscale.

Keywords: TiO₂ metasurface; collective resonance; Mie resonance; photoluminescence enhancement; array size effect.

Photocatalytic degradation of Enrofloxacin by TiO₂ and Bi₂Se₃/TiO₂ nanomaterials

Phuoc Huu Le^1,*, Le Thi Cam Tuyen², Tho Chau Minh Vinh Do³

¹ Department of Physics and Biophysics, Faculty of Basic Sciences, Can Tho University of Medicine and Pharmacy, Vietnam

² Faculty of Basic Sciences, Nam Can Tho University, Vietnam

³ Faculty of Pharmacy, Can Tho University of Medicine and Pharmacy, Vietnam

*Correspondence: lhuuphuoc@ctump.edu.vn

Abstract

Antibiotic residues in aquaculture wastewater are considered as an emerging environmental problem. To degrade antibiotic residues in aqueous environment, we fabricated TiO₂ nanotube arrays (TNAs), Bi₂Se₃ nanoparticle (NP)-decorated-TNAs, which were applied for assessing the photocatalytic degradation of enrofloxacin. The TNAs was synthesized by anodization using an aqueous NH₄F/ethylene glycol solution. Bi₂Se₃ NPs were synthesized by plasma- assisted exfoliation method, and used to decorate on TNAs. The photocatalytic performance of TNAs and Bi₂Se₃/TNAs was studied by monitoring the degradation of enrofloxacin under ultraviolet (Uv)-visible (Vis) illumination by LC-MS/MS method. All the TiO₂ nanostructures exhibited anatase phase and well-defined structure of nanotube arrays. The TNAs and Bi₂Se₃/TNAs nanomaterials degraded effectively and rapidly enrofloxacin with initial concentration 500 mg/L. In addition, the enrofloxacin removal percentages of TNAs and Bi₂Se₃/TNAs were 94.4% and 100% after 20 min treatment under UV-VIS irradiation (120 mW·cm^–2), respectively. Moreover, the reaction rate constant of Bi₂Se₃/TNAs was higher than that of TNAs (0.263 min^-1 vs. 0.157 min^-1), which could be attributed to the localized surface plasmon resonance effect of Bi₂Se₃ NPs and the enhanced charge separation effect occurring in the hydrid Bi₂Se₃/TNAs system. Briefly, TNAs and Bi₂Se₃/TNAs were synthesized successfully and possessed high-performance in photocatalytic degradation of a representative antibiotic of enrofloxacin.

Keywords: TiO₂ nanotube arrays, Bi₂Se₃, enrofloxacin, photocatalysts, LC-MS/MS.

Orbital- and spin-dependent optical excitations of group IV monolayer systems

Vo Khuong Dien¹ and Ming-Fa Lin^1,*

1Department of Physics, National Cheng Kung University

*Author to whom correspondence should be addressed: mflin@mail.ncku.edu.tw

Group IV materials have attracted enormous interest due to their fascinating optical and electronic properties [1, 2]. Here, we present the first-principles calculations to evaluate the geometric, electronic and optical properties of group IV monolayer systems. The critical factors due to the various atoms, orbitals and spin configurations. Moreover, the significant mechanisms, the π/σ/sp²/sp³ chemical bondings, the on-side spin-up/down interactions and spin-orbit couplings, are completely identified from the relevant physical/chemical quantities. The main features of crystal symmetries, electronic energy spectra, wave functions, and optical excitations are directly linked together only under this unified viewpoint [3, 4]. The current study is of paramount importance, not only for basic sciences but also for high-tech applications, e.g., spintronic, and hydrogen energy storage applications.

Keywords: Excitonic effects, Orbital hybridations, Spin-dependent optical excitations, GW+BSE calculations.

Acknowlegdement: This work was financially supported by the Hierarchical Green-Energy Materials (Hi-GEM) Research Center, the Featured Areas Research Center Program within the framework of the Higher Education Sprout Project by the Ministry of Education (MOE), and the Ministry of Science and Technology (MOST 110-2634-F-006 -017) in Taiwan.

References:

[1] A. K. Geim and K. S. Novoselov, "The rise of graphene," in Nanoscience and technology: a collection of reviews from nature journals, ed: World Scientific, 2010, pp. 11-19.

[2] H. Oughaddou, H. Enriquez, M. R. Tchalala, H. Yildirim, A. J. Mayne, A. Bendounan, et al. Silicene, a promising new 2D material. Progress in Surface Science. 2015, 90,46-83.

[3] V. K. Dien, N. T. Han, W.-P. Su, and M.-F. Lin. Spin-dependent optical excitations in LiFeO2. ACS omega. 2021, 6,25664-25671.

[4] V. K. Dien, H. D. Pham, N. T. T. Tran, N. T. Han, T. M. D. Huynh, T. D. H. Nguyen, et al. Orbital-hybridization-created optical excitations in Li 2 GeO 3. Scientific reports. 2021, 11,1-10.

“In silico” studies of some emergent monolayers for high-performance electronic, optoelectronic, and thermoelectric applications

Duy Khanh Nguyen^1,2,*

High-Performance Computing Lab (HPC Lab), Thu Dau Mot University, Binh Duong Province, Vietnam

^*Corresponding at khanhnd@tdmu.edu.vn

Increasing demand for “in silico” sciences drives the need for greater computing power that parallel/high-performance computing technology becomes a critical tool. In this talk, I will present recent advances in high-performance computing technology and parallel computing clusters to serve for “in silico” studies. Besides, some results of “in silico” studies performed in HPCC are presented. Specifically, the essential properties of the β-antimonene monolayer under external biaxial strain effects studied through the DFT calculations are reported. At equilibrium, the β-antimonene exhibits an indirect bandgap of 1.31 eV and 1.78 eV predicted by the PBE and HSE06 functionals, respectively. The indirect-direct gap transition and significant variation of energy gap are induced under external strains. The calculated optical spectra indicate the enhancement of the optical absorption in a wide energy range from infrared to ultraviolet as induced by the applied strains. In the visible and ultraviolet regime, the absorption coefficient can reach values as large as 82.700 (10⁴/cm) and 91.458 (10⁴/cm). This suggests that the thermoelectric performance is considerably improved by applying proper external strains with the figure of merit reaching a value of 0.665. Using the DFT calculations, the structural and electronic properties of germanene- and silicene-based nanoribbons under hydrogen and carbon doping are also reported. For the H-functionalized germanene nanoribbons, the bandgap of 2.01 eV is opened as compared with the pristine system that is suitable for optoelectronic applications. As for C-substituted silicene nanoribbons, the opened bandgaps are diversified under different carbon concentrations and distributions that are compatible with various electronic applications.

Structural properties, electronic properties and electron transport

of the pentagonal nanoribbons

Nguyen Thanh Tien¹, Pham Thi Bich Thao¹, Le Vo Phuong Thuan¹, Tran Thi Ngoc Thao¹ and Nguyen Duy Khanh²

¹College of Natural Sciences, Can Tho University, 3-2 Road, Can Tho City, Vietnam

²Institute of Applied Technology, Thu Dau Mot University, No 06, Tran Van On, Thu Dau Mot City, Binh Duong Province, Vietnam

*Author to whom correspondence should be addressed: nttien@ctu.edu.vn

Numerous works so far have shown that graphene, particularly for chemical modified graphene, possesses abundant excellent electronic properties [1], thus promising a fascinating application prospect [2]. Following graphene, penta-graphene (PG), a new two-dimensional (2D) carbon allotrope composed of carbon pentagons, was theoretically proposed recently [3] and predicted that it is a quasi-direct band gap semiconductor with an intrinsic band gap of 3.25 eV. Similarly to the works made to study the characteristics of graphene nanoribbons (GNRs) [4], many investigations have been done to explore the geometry as well as electronic and magnetic properties of penta-graphene nanoribbons (PGNRs) [5, 6] and PG-like nanoribbons [7].

In this work, we employ a first-principles calculation based on density functional theory (DFT) combined with non-equilibrium Green’s function (NEGF) formalism to investigate the structural properties, electronic properties and electron transport of the pentagonal nanoribbons.

Keywords: Structural property, electronic property and electron transport, pentagonal nanoribbon, first principle

Acknowlegdement: Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 103.01- 2020.16.

References:

[1] Castro Neto A. H., Guinea F., Peres N. M. R., Novoselov K. S., & Geim A. K. (2009), Rev. Mod. Phys. 81, 109.

[2] Wang Y., Huang B. C., Zhang M., & Woo J. C. S. (2012), Microelectron. Reliab. 52, 1602–1605.

[3] Zhang S.H., Zhou J., Wang Q., Chen X.H., Kawazoe Y., Jena P. (2015), Proc. Natl. Acad. Sci. USA 112, 2372.

[4] Yu Z. L., Wang D., Zhu Z., Zhang Z. H. (2015), Phys. Chem. Chem. Phys. 17, 24020.

[5] Tien N. T., Thao P. T. B., Phuc V. T., Ahuja R. (2020), J. Phys. Chem. Solids 146, 109528.

[6] Tien N. T., Thao P. T. B., Thuan L. V. P., Chuong D. H. (2021), Comput. Mater. Sci. 203, 111065.

[7] Mi T. Y., Khanh N. D., Ahuja R., & Tien N. T. (2020) Mater. Today Commun. 26, 102047.