Current Issue
October 2024
Vol. 66
pISSN 1567-1739eISSN 1567-1739
Abstract : Materials that produce electric charges in response to a mechanical load are known as piezoelectric materials. Materials with a lattice structure devoid of centosymmetry exhibit piezoelectric activity. These days, non-centrosymmetric 2D nanomaterials have been used in many possible applications and have attracted a lot of attention as piezoelectric materials. The crystal structure, crystal nonsymmetry, and nonzero electronic bandgap energy values of two-dimensional nanomaterials have a significant influence on their piezoelectric capabilities. For example, it was discovered that the symmetry of certain mono- or few-layered 2D nanomaterials differed from that of their bulk counterparts. Piezoelectricity is found at the atomic thickness level in many 2D monolayer materials with structurally broken symmetry, but it gradually vanishes with increasing thickness. Secondly, there is a strong correlation between this piezoelectric action and the polarization direction. In this sense, improving the piezoelectric capabilities in 2D mono, few, and multilayer nanomaterials requires a deeper comprehension of the crystal structure and direction of polarization. Based on theoretical and experimental findings, the crystal structure and direction of polarization of various 2D nanomaterials will be the main topics of this review. We will also discuss recent developments and applications of various 2D nanomaterials. © 2024 Korean Physical Society
Abstract : Flexible electronics, such as wearable devices and biosensors, require materials that maintain their properties under mechanical stress. A recent study addresses this by focusing on SrRuO3 (SRO) thin films, which typically suffer reduced coercivity under strain. Herein, we introduce a novel approach by using CoFe2O4 (CFO) as a buffer layer in SRO/CFO/F-mica heterostructures to address this issue. When subjected to a strain of up to ±0.553 %, these heterostructures displayed a mere 11 % variation in saturation magnetic moment and coercive field, significantly outperforming SRO/BaTiO3 configurations, which showed a 95 % reduction in coercivity at only −0.3 % strain. This result demonstrates the effectiveness of the CFO layer in stabilizing the magnetic properties of SRO films against external mechanical deformations. These findings mark a significant advancement in the development of mechanically robust thin films for complex oxide heterostructures in flexible device applications. © 2024 Korean Physical Society
Abstract : Magnesium diboride (MgB2) is a two-band superconductor with a high superconducting critical temperature (Tc) of approximately 39 K. Owing to the lack of vortex pinning centers, MgB2 exhibits an abrupt decline in the critical current density (Jc) in an applied magnetic field. Here, we prepared 1 MeV Nb ion-irradiated MgB2 thin-film samples with doses of 3×1013, 7×1013, and 9×1013 ions/cm2. Temperature-dependent magnetization and x-ray diffraction (XRD) measurements were performed to determine the Tc and c-axis lattice constant of each sample. Furthermore, a Fourier transform infrared (FTIR) spectroscopy was performed to obtain the infrared properties of the Nb-ion-irradiated MgB2 thin-film samples. The optical conductivity of each sample in the low-energy region was fitted with two (narrow and broad) Drude modes. We found that the spectral weight redistribution from the low-to high-frequency regions and the broadening of the narrow Drude mode caused by irradiation are closely related to the reduction in Tc. © 2024 Korean Physical Society
Abstract : Infrared spectroscopy is a powerful and versatile experimental technique for studying the electronic response of condensed matter. Infrared spectroscopy measurements in a broad energy region provide invaluable insights on the electronic excitations and collective modes in condensed matter and thus play pivotal roles in establishing current understandings of various classes of condensed matter. Here we discuss the usefulness and importance of infrared spectroscopy to study the physics of quantum materials, which were formerly known as strongly correlated materials. We will describe the basic principles and experimental methods of infrared spectroscopy and discuss how infrared spectroscopy can be utilized to extract quantitative information on the charge dynamics and electronic band structures of quantum materials. © 2024 Korean Physical Society
Abstract : We developed a geometry of metal-insulated-semiconductor field-effect-transistor for the formation of two-dimensional electron gas (2DEG) in dopant-free GaAs/AlGaAs heterostructures in which the conduction band can be modulated by external electric field. We showed two different kinds of device processes: for simple device fabrication and for the uniform 2DEG. We optimized the process of ohmic contacts and the gate geometry for the high quality 2DEG in a triangular quantum well formed at the GaAs/AlGaAs heterointerface. We use these two types of devices to perform a direct comparison of the magneto-transport properties at a low temperature (1.2 K) to get a relationship between the induced carrier density and external electric field. By using our developed fabrication process, the tunability of a high-quality 2DEG was obtained with a carrier density ranging from 0.8 to 2.3 × 1011 cm−2, for which the corresponding mobility ranged 1.5 to 3.3 × 106 cm2 V−1 s−1. Also, we demonstrated that the 2DEG is well established with a suitable depth, 120 nm below the surface (near the GaAs/AlGaAs heterointerface) which is calculated by the capacitance model. © 2024 Korean Physical Society
Abstract : Herein, the rotary triboelectric nanogenerator (R-TENG) with a modified structure is simulated and fabricated to investigate the effect of changes on the geometric structure experimentally. The R-TENGs were fabricated using cost-effective and easily accessible dry-film lithography based on the PCB approach. This process which is explained step-by-step in detail in this paper, provides uniform electrode layers without using high-tech instruments, resulting in enhanced fabrication speed and electrical performance. R-TENGs with varying electrode and PTFE sector counts (32/16, 16/8, and 8/4) were fabricated and analyzed. At 1000 rpm, the output power of R-TENGs with 8, 16, and 32 electrodes demonstrated escalating output power with increasing electrode numbers: 6.82, 19.52, and 30.64 Wm-2, respectively. Simulation results corroborated the experimental findings, confirming that more electrodes and freestanding sectors yield superior power density and electrical generation. The 32-electrode, 16-sector R-TENG outperformed its counterparts, suggesting that strategic design alterations can significantly optimize energy harvesting in R-TENGs. © 2024 Korean Physical Society
Abstract : Spin-coating stands out as one of the fastest and simplest processes for material solidification. While it is commonly employed for producing polycrystalline thin films, recent endeavors have explored its potential for epitaxial growth, albeit primarily limited to inorganic materials. In this study, we demonstrate the spin-coating method enabling the rapid growth of large-sized organic single crystals (OSCs). Within 2 h, we successfully obtained OSCs with controlled lateral sizes of up to 2 mm, which conventionally takes several weeks using slow solvent evaporation. Raman mapping and UV–Vis absorption measurements confirmed the growths of the OSCs. We propose the growth mechanism by using the supersaturated dynamic fluid model. Furthermore, we demonstrate the device integration of these OSCs for charge-transfer complex channel, revealing ambipolar behavior during gate sweep. This innovative OSCs production method has the potential to advance the various field of science and electronics, traditionally hindered by the scarcity of adequately sized OSCs. © 2024
Abstract : Ge2Sb2Te5 (GST225) thin films are used as a functional element in multilayer cells of phase change random access memory (PCRAM, PCM) and have good prospects in electrically driven tunable reflective metasurfaces and on-chip waveguide devices, including those implemented on a flexible substrate. Knowledge of the mechanical properties of GST225 thin films, their adhesion to conductive layers, and the correct choice of conductive material is critical to the reliable operation of these devices. The present work focuses on the effect of phase change on mechanical parameters such as hardness, Young's modulus and stiffness, as well as on the adhesion of GST225 thin films to various metal sublayers (Al, Ti, TiN, W, Ni). The formation of GST225 films was carried out by vacuum thermal evaporation and DC magnetron sputtering, which made it possible to study layers with different distributions of elements over the thickness. © 2024
Abstract : First-principles calculations on phonon dynamics using density functional theory (DFT) have proven powerful in estimating the phonon dispersion of crystalline structures. However, it remains a challenging task for defective structures due to the computational cost. The main computational bottleneck of the phonon calculation is obtaining the interatomic force constants in many supercells with different configurations of displacements. Here, we employed a machine learning-based force fields (MLFFs) to accelerate DFT calculations of interatomic force constants of Si-doped HfO2. We find that the specific phonon band originated from ferroelectric phase disappears, and imaginary modes are enhanced upon the introduction of a 10 % concentration of Si dopants, which is in good agreement with experimental results. This work demonstrates that MLFFs can be a promising application for predicting the phonon dispersion of both crystalline and defective structures. © 2024 Korean Physical Society
Abstract : In this study, we developed a simple and facile synthesis method for producing CuS films at low temperatures. The method uses self-reducible complex inks comprising copper formate (Cuf) as the copper source and thioacetamide (TA) as both the sulfur source and complexing agent. The thermal properties of complex inks with different TA/Cuf ratios (0.5–2.0) were analyzed. The ink with a TA/Cuf ratio of 1 exhibited a significant decrease in the reduction temperature. The synthesis of a CuS film involved calcination of the ink at 140 °C; however, some residual Cuf was observed. Introducing hexanol to the ink, aimed at prolonging the liquid-phase reaction, yielded a pure CuS film that contained agglomerated particles. The thermal reduction pathway of Cuf to CuS was analyzed through thermogravimetric–mass spectrometric analysis, and the results revealed that the low-temperature synthesis was attributed to the formation of acetonitrile and formic acid during thermal decomposition of the ink. © 2024 Korean Physical Society
Abstract : Solution-processable perovskite solar cells (PSCs) have the potential to revolutionize solar cell technology by enabling low power generation costs via low-cost device fabrication. However, most existing research regarding PSCs relies on the spin-coating method, which is not conducive to large-area film deposition. Therefore, the development of an alternative deposition method for perovskite films has become increasingly important for commercialization, for which electrospray deposition is a promising technique. This study investigates the two-step preparation of methylammonium lead triiodide (MAPbI3) perovskite films via the electrospray deposition of a methylammonium iodide (MAI) solution on a spin-coated PbI2 film. The gradual conversion of PbI2 to MAPbI3 with increasing MAI deposition time was revealed, accompanied by an increase in the size of the perovskite crystals. In addition, PSCs were successfully fabricated by electrospraying MAI, achieving a considerable power conversion efficiency of 7.86 % at the optimal MAI deposition time. © 2024 Korean Physical Society
Abstract : The accuracy of modern scientific research and technological advancement is highly reliant on the ability to accurately measure weak signals. The lock-in amplifier (LIA) represents an indispensable instrument, skillfully extracting these faint signals from a backdrop of noise. As the pursuit of accuracy intensifies, LIA technology has been continuously adapted and optimized. This review offers a comprehensive analysis of the evolution and applications of LIAs in weak signal measurements. It presents a structured introduction to the historical development of LIAs and evaluates their diverse applications across various domains, including impedance, optical, electrochemical, thermal, and biosensing methods. By examining specific examples in each field, it showcases the significant impact of LIAs on enhancing measurement precision. The review concludes by highlighting persistent challenges encountered by LIAs in practical settings and explores potential avenues for their future advancement. Future research aims to address practical challenges, including further noise reduction, improved system stability, and ease of use, ensuring LIAs continue to play a pivotal role in scientific and technological progress. © 2024 Korean Physical Society
• Journal Impact factor 2.4
• Elsevier Site Score 4.8