The 2017 Magnetism Roadmap

Sander, D,Valenzuela, S O,Makarov, D,Marrows, C H,Fullerton, E E,Fischer, P,McCord, J,Vavassori, P,Mangin, S,Pirro, P,Hillebrands, B,Kent, A D,Jungwirth, T,Gutfleisch, O,Kim, C G,Berger, A Institute of Physics Publishing Ltd. 2017 Journal of Physics. D, Applied Physics Vol.50 No.36

<P>Building upon the success and relevance of the 2014 Magnetism Roadmap, this 2017 Magnetism Roadmap edition follows a similar general layout, even if its focus is naturally shifted, and a different group of experts and, thus, viewpoints are being collected and presented. More importantly, key developments have changed the research landscape in very relevant ways, so that a novel view onto some of the most crucial developments is warranted, and thus, this 2017 Magnetism Roadmap article is a timely endeavour. The change in landscape is hereby not exclusively scientific, but also reflects the magnetism related industrial application portfolio. Specifically, Hard Disk Drive technology, which still dominates digital storage and will continue to do so for many years, if not decades, has now limited its footprint in the scientific and research community, whereas significantly growing interest in magnetism and magnetic materials in relation to energy applications is noticeable, and other technological fields are emerging as well. Also, more and more work is occurring in which complex topologies of magnetically ordered states are being explored, hereby aiming at a technological utilization of the very theoretical concepts that were recognised by the 2016 Nobel Prize in Physics.</P> <P>Given this somewhat shifted scenario, it seemed appropriate to select topics for this Roadmap article that represent the three core pillars of magnetism, namely magnetic materials, magnetic phenomena and associated characterization techniques, as well as applications of magnetism. While many of the contributions in this Roadmap have clearly overlapping relevance in all three fields, their relative focus is mostly associated to one of the three pillars. In this way, the interconnecting roles of having suitable magnetic materials, understanding (and being able to characterize) the underlying physics of their behaviour and utilizing them for applications and devices is well illustrated, thus giving an accurate snapshot of the world of magnetism in 2017.</P> <P>The article consists of 14 sections, each written by an expert in the field and addressing a specific subject on two pages. Evidently, the depth at which each contribution can describe the subject matter is limited and a full review of their statuses, advances, challenges and perspectives cannot be fully accomplished. Also, magnetism, as a vibrant research field, is too diverse, so that a number of areas will not be adequately represented here, leaving space for further Roadmap editions in the future. However, this 2017 Magnetism Roadmap article can provide a frame that will enable the reader to judge where each subject and magnetism research field stands overall today and which directions it might take in the foreseeable future.</P> <P>The first material focused pillar of the 2017 Magnetism Roadmap contains five articles, which address the questions of atomic scale confinement, 2D, curved and topological magnetic materials, as well as materials exhibiting unconventional magnetic phase transitions. The second pillar also has five contributions, which are devoted to advances in magnetic characterization, magneto-optics and magneto-plasmonics, ultrafast magnetization dynamics and magnonic transport. The final and application focused pillar has four contributions, which present non-volatile memory technology, antiferromagnetic spintronics, as well as magnet technology for energy and bio-related applications. As a whole, the 2017 Magnetism Roadmap article, just as with its 2014 predecessor, is intended to act as a reference point and guideline for emerging research directions in modern magnetism.</P>

Resistive switching effect in the planar structure of all-printed, flexible and rewritable memory device based on advanced 2D nanocomposite of graphene quantum dots and white graphene flakes

Rehman, Muhammad Muqeet,Siddiqui, Ghayas Uddin,Kim, Sowon,Choi, Kyung Hyun Institute of Physics Publishing Ltd. 2017 Journal of Physics. D, Applied Physics Vol.50 No.33

<P>Pursuit of the most appropriate materials and fabrication methods is essential for developing a reliable, rewritable and flexible memory device. In this study, we have proposed an advanced 2D nanocomposite of white graphene (hBN) flakes embedded with graphene quantum dots (GQDs) as the functional layer of a flexible memory device owing to their unique electrical, chemical and mechanical properties. Unlike the typical sandwich type structure of a memory device, we developed a cost effective planar structure, to simplify device fabrication and prevent sneak current. The entire device fabrication was carried out using printing technology followed by encapsulation in an atomically thin layer of aluminum oxide (Al<SUB>2</SUB>O<SUB>3</SUB>) for protection against environmental humidity. The proposed memory device exhibited attractive bipolar switching characteristics of high switching ratio, large electrical endurance and enhanced lifetime, without any crosstalk between adjacent memory cells. The as-fabricated device showed excellent durability for several bending cycles at various bending diameters without any degradation in bistable resistive states. The memory mechanism was deduced to be conductive filamentary; this was validated by illustrating the temperature dependence of bistable resistive states. Our obtained results pave the way for the execution of promising 2D material based next generation flexible and non-volatile memory (NVM) applications.</P>

Transparent arrays of silver nanowire rings driven by evaporation of sessile droplets

Wang, Xiaofeng,Kang, Giho,Seong, Baekhoon,Chae, Illkyeong,Yudistira, Hadi Teguh,Lee, Hyungdong,Kim, Hyunggun,Byun, Doyoung Institute of Physics Publishing Ltd. 2017 Journal of Physics. D, Applied Physics Vol.50 No.45

<P>A coffee-ring pattern can be yielded on the three-phase contact line following evaporation of sessile droplets with suspended insoluble solutes, such as particles, DNA molecules, and mammalian cells. The formation of such coffee-ring, together with their suppression has been applied in printing and coating technologies. We present here an experimental study on the assembly of silver nanowires inside an evaporating droplet of a colloidal suspension. The effects of nanowire length and concentration on coffee-ring formation of the colloidal suspension were investigated. Several sizes of NWs with an aspect ratio between 50 and 1000 were systematically investigated to fabricate coffee-ring patterns. Larger droplets containing shorter nanowires formed clearer ring deposits after evaporation. An order-to-disorder transition of the nanowires’ alignment was found inside the rings. A printing technique with the evaporation process enabled fabrication of arrays of silver nanowire rings. We could manipulate the patterns silver nanowire rings, which might be applied to the transparent and flexible electrode.</P>

The forming-free bipolar resistive switching characteristics of Ag₂Se thin film

Lee, T S,Lee, N J,Lee, H K,Abbas, Y,Abbas, H,Hu, Q L,Yoon, T S,Kang, C J Institute of Physics Publishing Ltd. 2017 Journal of Physics. D, Applied Physics Vol.50 No.20

<P>The resistive switching (RS) characteristics of silver selenide (Ag<SUB>2</SUB>Se) thin film prepared by thermal evaporation are studied. The capacitor structures of 10  ×  10 <I>µ</I>m<SUP>2</SUP> are prepared using Au and Ag pads as top electrodes on the Ag<SUB>2</SUB>Se thin film. The current–voltage (<I>I</I>–<I>V</I>) curves of the Au pad/Ag<SUB>2</SUB>Se/Au structure and Ag pad/Ag<SUB>2</SUB>Se/Au structure are observed. The Ag<SUB>2</SUB>Se thin film shows the RS behavior by the formation and rupture of Ag filaments without the forming process in both Au and Ag pads. The high resistance state (HRS) current measured with the Ag pad is lower than that with the Au pad owing to the atomic rearrangement at the Ag pad/Ag<SUB>2</SUB>Se interface region, showing a better low resistance state (LRS) current to HRS current ratio. In order to further understand the conduction mechanism in Ag<SUB>2</SUB>Se, the temperature dependent characteristics are measured in the temperature range of 300–410 K. It can be seen that the HRS current level increases with temperature in both Au and Ag pads, indicating that the conductivity increases with temperature. From capacitance–voltage (<I>C</I>–<I>V</I>) measurements and transmission electron microscopy (TEM) image, the creation and annihilation of Ag filaments is confirmed.</P>

The energy dependence of <i>p_t</i> angular correlations inferred from mean-<i>p_t</i> fluctuation scale dependence in heavy ion collisions at the SPS and RHIC

Adams, J,Aggarwal, M M,Ahammed, Z,Amonett, J,Anderson, B D,Anderson, M,Arkhipkin, D,Averichev, G S,Bai, Y,Balewski, J,Barannikova, O,Barnby, L S,Baudot, J,Bekele, S,Belaga, V V,Bellingeri-Laurikainen, Institute of Physics Publishing 2007 Journal of Physics. G, Nuclear and Particle Physic Vol.34 No.3

<P>We present the first study of the energy dependence of <I>p<SUB>t</SUB></I> angular correlations inferred from event-wise mean transverse momentum ⟨<I>p<SUB>t</SUB></I>⟩ fluctuations in heavy ion collisions. We compare our large-acceptance measurements at CM energies <img SRC='http://ej.iop.org/images/0954-3899/34/3/004/jpg233147ieqn1.gif' ALIGN='MIDDLE' ALT='\sqrt{s_{\rm NN}} = 19.6'/>, 62.4, 130 and 200 GeV to SPS measurements at 12.3 and 17.3 GeV. <I>p<SUB>t</SUB></I> angular correlation structure suggests that the principal source of <I>p<SUB>t</SUB></I> correlations and fluctuations is minijets (minimum-bias parton fragments). We observe a dramatic increase in correlations and fluctuations from SPS to RHIC energies, increasing linearly with <img SRC='http://ej.iop.org/images/0954-3899/34/3/004/jpg233147ieqn2.gif' ALIGN='MIDDLE' ALT='\ln \sqrt{s_{\rm NN}} '/> from the onset of observable jet-related ⟨<I>p<SUB>t</SUB></I>⟩ fluctuations near 10 GeV.</P>

Self-collimation-based photonic crystal notch filters

Lee, Sun-Goo,Kim, Kap-Joong,Kim, Seong-Han,Kee, Chul-Sik Institute of Physics Publishing Ltd. 2017 Journal of Physics. D, Applied Physics Vol.50 No.20

<P>We introduce a design concept of an optical notch filter (NF) utilizing two perfectly reflecting mirrors and a beam splitter. Based on the new design concept, a photonic crystal (PC)-NF based on the self-collimation phenomenon in a two-dimensional PC is proposed and studied through finite-difference time-domain simulations and experimental measurements in a microwave region. The transmission properties of the self-collimation-based PC-NF were demonstrated to be controlled by adjusting the values of parameters such as the radius of rods in the line-defect beam splitter, distance between the two perfectly reflecting mirrors, and radius of rods on the outermost surface of the perfectly reflecting mirrors. Our results indicate that the proposed design concept could provide a new approach to manipulate light propagation, and the PC-NF could increase the applicability of the self-collimation phenomenon in a PC.</P>

Optimized low-temperature fabrication of WO₃ films for electrochromic devices

Bae, Jaehyun,Seo, Dong Gyu,Park, Su Mi,Park, Kyu Tae,Kim, Haekyoung,Moon, Hong Chul,Kim, Se Hyun Institute of Physics Publishing Ltd. 2017 Journal of Physics. D, Applied Physics Vol.50 No.46

<P>We investigated the effect of process conditions on the electrochromic (EC) properties of tungsten trioxide (WO<SUB>3</SUB>) films. When WO<SUB>3</SUB> films deposited using a sol-gel method were thermally treated in air at 150 °C, the majority of tungsten species in the films became W<SUP>6+</SUP>, which is important for the realization of an optically transparent bleached state. On the other hand, annealing in a vacuum required only 60 °C to induce a similar level of W<SUP>6+</SUP> in the WO<SUB>3</SUB> films. However, a cracked film morphology was observed at higher temperatures, regardless of whether the films were annealed in air or vacuum. Using the WO<SUB>3</SUB> films prepared under various conditions, EC devices (ECDs) were fabricated to evaluate EC properties. We concluded that the optimal annealing conditions for WO<SUB>3</SUB> films for ECDs are 60 °C in vacuum, at which the highest coloration efficiency, largest transmittance difference, and fastest bleaching/coloration dynamics were obtained. These mild fabrication conditions at a low temperature (60 °C) provide the opportunity to utilize flexible electrodes on plastic. Therefore, we successfully demonstrated a flexible WO<SUB>3</SUB>-based ECD.</P>

Improved efficiency of perovskite-silicon tandem solar cell near the matched optical absorption between the subcells

Iftiquar, S M,Jung, Junhee,Yi, Junsin Institute of Physics Publishing Ltd. 2017 Journal of Physics. D, Applied Physics Vol.50 No.40

<P>Current matching in a tandem solar cell is significant, because in a mismatched device the lowest current generating subcell becomes the current limiting component, and overall device efficiency remains lower than that could be obtained in the current matched device. Recent reports on methyl ammonium lead iodide (MAPbI<SUB>3</SUB>) based thin film solar cell has drawn interest to a perovskite-silicon tandem solar cell. Therefore, we investigated such a tandem solar cell theoretically. We used a MAPbI<SUB>3</SUB> based top and heterojunction with intrinsic thin layer silicon (HIT) bottom subcell. Optimization of the device structure was carried out by varying thickness of perovskite layer of top-cell from 50 to 1000 nm, while thickness of active layer of the HIT cell was kept constant, to 500 <I>µ</I>m. Single-junction solar cell, formed with the bottom subcell had open circuit voltage (<I>V</I> <SUB>oc</SUB>) of 705.1 mV, short circuit current density (<I>J</I> <SUB>sc</SUB>) of 28.22 mA cm<SUP>−2</SUP>, fill factor (FF) of 0.82 and efficiency of 16.4% under AM1.5G insolation. A relatively low thickness (150 nm) of the perovskite absorber layer was found optimum for the top-subcell to achieve best efficiency of the tandem cell, partly because of intermediate reflection at the interface between the two cells. We obtained a maximum of 20.92% efficiency of the tandem solar cell, which is higher by a factor of 1.27 from the starting HIT cell and a factor 1.47 higher from the perovskite cell efficiency. <I>J</I> <SUB>sc</SUB> of the optimized tandem cell was 13.06 mA cm<SUP>−2</SUP>. This was achieved near the matching optical absorption or current-density of the component subcells. For a practical application, the device used in our investigation was without textured front surface. An ordinary HIT bottom-cell was used with lower <I>J</I> <SUB>sc</SUB>. Therefore, with an improved HIT subcell, efficiency of the tandem cell, higher than 21% will be achievable.</P>

Calculation of Appropriate Minimum Size of Isolation Rooms based on Questionnaire Survey of Experts and Analysis on Conditions of Isolation Room Use

Won, An-Na,Song, Hae-Eun,Yang, Young-Kwon,Park, Jin-Chul,Hwang, Jung-Ha Institute of Physics Publishing Ltd 2017 Journal of Physics: Conference Series Vol.870 No.-

Random Si nanopillars for broadband antireflection in crystalline silicon solar cells

Choi, Junhee,Lee, Taek Sung,Jeong, Doo Seok,Lee, Wook Seong,Kim, Won Mok,Lee, Kyeong-Seok,Kim, Donghwan,Kim, Inho Institute of Physics Publishing Ltd. 2016 Journal of Physics. D, Applied Physics Vol.49 No.37

<P>We demonstrate the fabrication of shallow Si nanopillar structures at a submicron scale which provides broadband antireflection for crystalline Si (c-Si) solar cells in the wavelength range of 350 nm–1100 nm. The Si random nanopillars were made by reactive ion etch (RIE) processing with thermally dewetted Sn metals as an etch mask. The diameters and coverages of the Si nanopillars were adjusted in a wide range of the nanoscale to microscale by varying the nominal thickness of the Sn metals and subsequent annealing temperatures. The height of the nanopillars was controlled by the RIE process time. The optimal size of the nanopillars, which are 340 nm in diameter and 150 nm in height, leads to the lowest average reflectance of 3.6%. We showed that the power conversion efficiency of the c-Si solar cells could be enhanced with the incorporation of optimally designed Si random nanopillars from 13.3% to 14.0%. The fabrication scheme of the Si nanostructures we propose in this study would be a cost-effective and promising light trapping technique for efficient c-Si solar cells.</P>