2023
<4> Strain versus Tunable Terahertz Nanogap Width: A Simple Formula and a Trench below
Hwanhee Kim, Mahsa Haddadi Moghaddam, Zhihao Wang, Sunghwan Kim, Dukhyung Lee, Hyosim Yang, Myongsoo Jee, Daehwan Park and Dai-Sik Kim
Nanomaterials 2526 (2023)
Abstract:A flexible zerogap metallic structure is periodically formed, healing metal cracks on a flexible substrate. Zerogap is continuously tunable from nearly zero to one hundred nanometers by applying compressive strains on the flexible substrate. However, there have been few studies on how the gap width is related to the strain and periodicity, nor the mechanism of tunability itself. Here, based on atomic force microscopy (AFM) measurements, we found that 200 nm-deep nano-trenches are periodically generated on the polymer substrate below the zerogap owing to the strain singularities extant between the first and the second metallic deposition layers. Terahertz and visible transmission properties are consistent with this picture whereby the outer-bending polyethylene terephthalate (PET) substrate controls the gap size linearly with the inverse of the radius of the curvature.
Sunghwan Kim, Bamadev Das, Kang Hyeon Ji, Mahsa Haddadi Moghaddam, Cheng Chen, Jongjin Cha, Seon Namgung, Dukhyung Lee and Dai-Sik Kim
Nanophotonics 1481-1489 (2023)
Abstract:Cracks are formed along the photolithographically pre-determined lines with extremely high yield and repeatability, when Cu clusters are introduced between planarized Au thin films sequentially deposited on a PET substrate. These clusters act as nanometer-sized spacers preventing the formation of contiguous metallic bond between the adjacent Au layers which will render prepatterned-cracking impossible. While the effective gap width is initially zero in the optical sense from microwaves all the way to the visible, outer-bending the PET substrate allows the gap width tuning into the 100 nm range, with the stability and controllability in the ranges of 100 s and Angstrom-scale, respectively. It is anticipated that our wafer-scale prepatterned crack technology with an unprecedented mixture of macroscopic length and Angstrom-scale controllability will open-up many applications in optoelectronics, quantum photonics and photocatalysis.
<2> Nanoscale Etching of La0.7Sr0.3MnO3 Without Etch Lag Using Chlorine Based Inductively Coupled Plasma
Nimphy Sarkar, Jaewoo Han, Daryll Joseph Chavez Dalayoan, Satyabrat Behera, Sang-Hyuk Lee, Cheng Chen, Dai-Sik Kim, Changhee Sohn & Seon Namgung
Electronic Materials Letters (2023)
Abstract: La0.7Sr0.3MnO3 (LSMO) has been considered as a promising material for future electronic and spintronic device application due to its unique properties such as pure spin polarization, colossal magnetoresistance, and high temperature coefficient of resistance (TCR). To apply this promising material for practical application, large epitaxial LSMO layers should be etched into micro- and nano-scale device structures. However, a comprehensive study on the etch of LSMO has not been demonstrated yet. Herein, the etch rates of LSMO are studied using inductively coupled plasma reactive ion etching (ICP-RIE) method, while controlling critical etching parameters such as ICP source power, radio frequency (rf) chuck power, etching gas ratio, and chamber pressure. We found that the etching process can be applied to nanoscale structures (down to 100 nm) without etch lag effect, exhibiting smaller etch depth in smaller features. This study will provide a good reference for the etching and the engineering of LSMO toward future electronic and spintronic devices such as highly sensitive bolometers and low-power memory devices.
Zhihao Wang, Yingde Zhang, Cheng Chen, Hong-Guang Piao, Linjie Ding, Liqing Pan, Jiaohong Huang, Hyeong-Ryoel Park, Dai-Sik Kim, Seong-Cho Yu
Journal of Magnetism and Magnetic Materials 565, 170147 (2023)
Abstract: For the widespread application of solid magnetic refrigeration technology, this is one of the key technologies to realize the wide temperature range of magnetic entropy change near room temperature. In this paper, the effect of Ni-doping on the magnetocaloric properties and the temperature range of magnetic entropy change was studied for La(Fe0.94−xNixCo0.06)11.4Si1.6B0.25 alloy subjected to the industrial high-frequency suspension furnace. The results show that the Curie temperature of the alloy system can be adjusted to room temperature by changing the Ni content, and the temperature range of magnetic entropy change can be expanded effectively. In addition, the critical behavior of the industrial grade purity alloy system was evaluated by modified Arrott-plot and critical isotherm analysis methods, and the optimal values of critical parameters were obtained, providing a novel thermodynamic method to determine the critical behavior of magnetic phase transition in La(FeSi)13 alloy system.