[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Dye-sensitized solar cells (DSCs) offer the possibilities to design solar cells with a large flexibility in shape, color, and transparency. DSC research groups have been established around the worl ...

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Dye-Sensitized Solar Cells

BiFeO3 is perhaps the only material that is both magnetic and a strong ferroelectric at room temperature. As a result, it has had an impact on the field of multiferroics that is comparable to that of yttrium barium copper oxide (YBCO) on superconductors, with hundreds of publications devoted to it in the past few years. In this Review, we try to summarize both the basic physics and unresolved aspects of BiFeO3 (which are still being discovered with several new phase transitions reported in the past few months) and device applications, which center on spintronics and memory devices that can be addressed both electrically and magnetically.

Physics and Applications of Bismuth Ferrite

Multiferroic magnetoelectric materials, which simultaneously exhibit ferroelectricity and ferromagnetism, have recently stimulated a sharply increasing number of research activities for their scientific interest and significant technological promise in the novel multifunctional devices. Natural multiferroic single-phase compounds are rare, and their magnetoelectric responses are either relatively weak or occurs at temperatures too low for practical applications. In contrast, multiferroic composites, which incorporate both ferroelectric and ferri-/ferromagnetic phases, typically yield giant magnetoelectric coupling response above room temperature, which makes them ready for technological applications. This review of mostly recent activities begins with a brief summary of the historical perspective of the multiferroic magnetoelectric composites since its appearance in 1972. In such composites the magnetoelectric effect is generated as a product property of a magnetostrictive and a piezoelectric substance. A...

Multiferroic magnetoelectric composites: Historical perspective, status, and future directions

R J Baxter 1982 London: Academic xii + 486 pp price £43.60 Over the past few years there has been a growing belief that all the twodimensional lattice statistical models will eventually be solved and that it will be Professor Baxter who solves them. Baxter has inherited the mantle of Onsager who started the process by solving exactly the two-dimensional Ising model in 1944.

Exactly Solved Models in Statistical Mechanics

Flexible organic field effect transistors (OFETs) are a promising class of flexible nonvolatile memories. However, fabrication of flexible OFET devices that offer low-voltage and high-speed operation remains a challenge. Here, we report a flexible OFET memory unit based on a novel gate stack consisting of pentacene as a semiconducting channel, poly(α-methylstyrene) as a charge-trapping layer, and amorphous Al2O3 as a charge-blocking layer, deposited sequentially on an Au-coated flexible muscovite substrate. The optimized flexible OFET structure has excellent electrical performance and mechanical flexibility, with an operating voltage as low as −4 V, an operating speed as fast as 100 μs, the largest memory window (1.73 V) provided +6 V, 100 μs program and −4 V, 100 μs erase pulses, a retention time far longer than 104 s, and program–erase endurance greatly exceeding 3000 cycles. The device can endure at least 5000 bending–unbending cycles. Of all flexible OFET nonvolatile memories reported to date, this OFET device offers the best overall electrical and mechanical properties and is extremely promising for future applications in flexible, lightweight, low-power, and high-speed nonvolatile memories.

A flexible memory with low-voltage and high-operation speed using an Al2O3/poly(α-methylstyrene) gate stack on a muscovite substrate

Using the first principles calculations, the electronic and optical properties of C, Mo and Mo-C-doped anatase TiO2 are studied. For the Mo mono-doped TiO2, the band gap reduces little, and the largest perturbation occurs at the CBM of TiO2. C mono-doping suppresses the effective band gap, but the partially occupied subbands in the gap probably also serve as the recombination centers for electrons and holes. Therefore, the Mo-C co-doping is investigated for the charge compensation consideration. We discuss six doped configurations and find that the total energy of the system is increased with increasing distance of C and Mo. It is found that co-doped configurations with C nearest to Mo possess the lowest total energy. Then, we focus on discussing three possible Mo-C adjacent co-doped configurations. The subbands mainly induced by C-2p states in the band gap become fully occupied because the Mo atom contributes sufficient electrons to C anion for compensation. At the same time, the effective band gap is narrowed about 0.9 eV and the perturbation at the CBM occurred in Mo mono-doped TiO2 disappears, which means the band edges of doped system still straddle the redox potentials of water. Furthermore, the optical properties of the compensated Mo-C adjacent co-doped TiO2 and pure TiO2 are calculated. The optical absorption edges of the Mo-C co-doped TiO2 shift towards the visible light region.

First principles calculations of electronic and optical properties of Mo and C co-doped anatase TiO 2

In this proceeding, recent theoretical investigations by the authors on the multiferroic $R$MnO$_3$ perovskites are briefly reviewed at first. Using the double-exchange model, the realistic spiral spin order in undoped manganites such as TbMnO$_3$ and DyMnO$_3$ is well reproduced by incorporating a weak next-nearest neighbor superexchange ($\sim10%$ of nearest neighbor superexchange) and moderate Jahn-Teller distortion. The phase transitions from the A-type antiferromagnet (as in LaMnO$_3$), to the spiral phase (as in TbMnO$_3$), and finally to the E-type antiferromagnet (as in HoMnO$_3$), with decreasing size of the $R$ ions, were also explained. Moreover, new results of phase diagram of the three-dimensional lattice are also included. The ferromagnetic tendency recently discovered in the LaMnO$_3$ and TbMnO$_3$ thin films is explained by considering the substrate stress. Finally, the relationship between our double-exchange model and a previously used $J_1$-$J_2$-$J_3$ model is further discussed from the perspective of spin wave excitations.

Double-exchange model study of multiferroic $R$MnO$_3$ perovskites

A flexible and high temperature tolerant strain sensor of La0.7Sr0.3MnO3/Mica

The waveguiding Ba2NaNb5O15 films have been prepared on KTiOPO4 substrates by pulsed laser deposition technique. Characterizations of the as-grown films by the x-ray θ–2θ scan and β scan and the scanning electron microscopy revealed that epitaxial (110)-oriented Ba2NaNb5O15 films with small surface roughness were achieved on (100)-oriented KTiOPO4 plates. The x-ray photoelectron spectrometer was employed to probe the chemical constitution of the as-grown films. Favorable optical waveguiding properties were demonstrated by m-line measurement and evaluation of propagation loss on the order of 1.0 dB/cm of TM and TE multimodes.

J.-M. Liu

Papers

A flexible memory with low-voltage and high-operation speed using an Al2O3/poly(α-methylstyrene) gate stack on a muscovite substrate

First principles calculations of electronic and optical properties of Mo and C co-doped anatase TiO 2

Double-exchange model study of multiferroic $R$MnO$_3$ perovskites

A flexible and high temperature tolerant strain sensor of La0.7Sr0.3MnO3/Mica

Epitaxial growth of optical Ba2NaNb5O15 waveguide film by pulsed laser deposition