Search

Recently, numerous two-dimensional (2D) magnetic materials are predicted with various promising properties, whereas noncollinear antiferromagnetic 2D materials are rarely reported. In this paper, we predicted a stable 2D noncollinear antiferromagnetic triangular lattice T-FeO2. The ground state is [Formula: see text] antiferromagnetic with stronger next nearest neighbor exchange coupling than that of nearest neighbor exchange coupling because of the RKKY interaction. Our Monte Carlo simulations reveal that the magnetic phase transition is from a [Formula: see text] antiferromagnetic state to a stripy state and then to a paramagnetic state with increasing temperature. In addition, by tuning the spin direction from an in plane antiferromagnetic state to a canted weak ferromagnetic state, a nontrivial topological phase transition could be induced. Our investigation about magnetic property and nontrivial topological phase transition is very promising for antiferromagnetic spintronics.

As a promising candidate of current solid-state electrolytes with various advantages, such as broad electrochemical stability window, high thermal stability, and chemical stability, garnet-type solid-state electrolyte Li7La3Zr2O12 (LLZO) attracts extensive research attention. Researchers usually use the element doping method to improve the lithium ion conductivity of LLZO and to stabilize the cubic phase. However, the improvements either increase the cost of raw materials or need complex process. In this work, the preparation process of Al-doped LLZO is optimized by a simple post-doping method (LLZO-Al), and the as-prepared LLZO-Al shows a high lithium ion conductivity of 5.331 × 10−4 S cm−1 and an activation energy of 0.25 eV at room temperature. In addition, the LLZO-Al exhibits excellent stability against Li in LiǁLLZO-AlǁLi symmetric cell, and the LiNi0.8Co0.1Mn0.1O2 (NCM811)ǁLLZO-AlǁLi solid-state cell delivers a stable cycle of 120 cycles at 0.1C. This work offers a low-cost preparation method of LLZO-based solid-state electrolytes with high ionic conductivities for high-energy solid-state lithium metal batteries.

As an emerging approach to charge storage phosphors, upconversion charging (UCC) is attracting increased attention owing to its fundamental and practical perspectives. Despite the potential, further development of the UCC technology is restricted by the limited types of excitation light sources. Here, we use a white flashlight as excitation to investigate the UCC performance of storage phosphors. We demonstrate, as an example, that a Y3Al2Ga3O12:Pr3+ phosphor exhibits long-lasting emissions in the ultraviolet and visible regions after intense illumination from the flashlight. Thermoluminescence investigations reveal that both excited-state absorption and energy-transfer upconversion are involved in the UCC process. Based on the luminescence performance of the white-light charged phosphor, a conceptual thermometry approach is introduced, which can remotely sense the local temperature by monitoring the afterglow intensity ratio. Considering the wide use of flashlight, such a white-light excitability and the associated glow emission may potentially revolutionize the way to utilize storage phosphors.

Funding Information: This work was supported by the National Natural Science Foundation of China (NSFC) (Grant No. 22109022), the Fundamental Research Funds for the Central Universities (Grant Nos. 3203002105A2 and 2242022k30063), and the Postgraduate Research & Practice Innovation Program of Jiangsu Province (No. SJCX22_0040). The support of Open Project of Key Laboratory of Artificial Structure and Quantum Control (Ministry of Education), Shanghai Jiao Tong University is also acknowledged. Publisher Copyright: © 2022 Author(s). Samarium oxide (SMO), a rare-earth oxide, has gathered great interest from researchers because of its variable valences and promising ionic conductivity. Herein, SMOs with cubic and monoclinic phases were synthesized. The changes in the crystal structure of SMOs with sintering temperature were analyzed. The cell based on cubic phase SMO achieves an excellent maximum power density of 0.876 W cm-2 along with a high ionic conductivity at 550 °C, indicating an enhanced ionic conductivity compared with monoclinic phase SMO. Further analysis of x-ray diffraction and x-ray photoelectron spectra results confirmed that there were more oxygen vacancies formed in cubic phase SMO than monoclinic phase SMO, thereby offering more active sites for fast ion transport. Furthermore, both cubic phase and monoclinic phase SMOs are dominated by proton conduction, while cubic phase SMO is further coupled with oxygen ion conduction, which leads to higher ionic conductivity of cubic phase SMO. In this study, the ionic conductivitiesof SMOs with different crystal structures are compared and reasons for the differences are disclosed, which provides guidance for further applications of SMO.

We report a very long wave (14 μm) infrared quantum cascade detector based on a twin-well coupled absorption region operating at temperatures up to 130 K. By introducing two coupled absorption quantum wells that have the same width, the absorption strength and responsivity of the detector are increased relative to the single-well design. At 77 K, we observe a responsivity of 4.06 mA/W at zero bias, which is 4.27 times that of the single-well counterpart. The responsivity is further optimized for reverse bias operation, so that the obstruction of space charge field to electron transport is compensated. The photocurrent reaches a maximum value at 77 K for an applied bias of −1.3 V, and responsivity as high as 23.76 mA/W, which is 5.85 times that under zero bias, is obtained.

Recently, Dirac states in two dimensional materials have drawn great attention because of its desirable transport properties. In this paper, we predicted a two-dimensional hexagonal CrB2C2, which exhibits stable mechanical and thermal properties. Young's modulus of CrB2C2 is 485.67 N/m, which is comparable with that of graphene. In addition, CrB2C2 is half-metallic, and the ferromagnetic Curie temperature is about 1500 K, which is far above room temperature. A CrB2C2 nanosheet exhibits multiple Dirac states in the spin minority channel and forms compensated electron-hole pockets. The Fermi velocity of two different Dirac states is about 4.18×105 and 3.42×105 m/s. In the electronic band structure, the Dirac state at the K point is weakly gapped by 0.38 meV under a spin orbital interaction, while the other one could be topological nontrivially gapped by 37.4 meV, and the bottom Dirac band exhibits a nonzero Chern number at about 0.25 eV above the Fermi energy.

A recent work predicted the tunneling effect between topological edge states where the tunneling probability is tuned by a transverse electric field [Xu et al., Phys. Rev. Lett. 123, 206801 (2019)]. Here we study this tunneling effect between quantum anomalous Hall edge states under a perpendicular magnetic field. It is shown that the tunneling probability depends exponentially on the magnetic field. We propose a magnetic transistor based on a quantum anomalous Hall ribbon to observe this effect experimentally. Numerical simulations show that the conductance of the device is very sensitive to the strength and direction of the magnetic field. The positive/negative magnetic field results in the on/off state of the transistor. A giant magnetoresistance is found, and the on/off ratio reaches up to greater than 1010 for a long ribbon. These findings should be useful for potential applications in magnetic read heads and magnetic field sensors.

All-inorganic halide perovskites (AIHPs) have become one of the most promising materials for commercial perovskite photovoltaics owing to their enhanced efficiency and thermodynamic stability. Output instability, such as current hysteresis, is stressed in organic-inorganic hybrid perovskite photovoltaics but is neglected in AIHP solar cells. Here, the origin and suppression of current hysteresis in AIHP solar cells are addressed from a microscopic viewpoint. The incorporation of fullerene into AIHP films efficiently suppresses ion migration, which alleviates the macroscopic current hysteresis in solar cells. This result is confirmed by both Kelvin probe force microscopy and conductive atomic force microscopy measurements. Our results provide an advanced understanding of the microscopic properties of AIHPs but also clearly clarify how to suppress the macroscopic current hysteresis, which further inspires the optimization of solar cells up to the levels of organic–inorganic hybrid counterparts.

To control the pulsed laser deposition synthesis, knowledge on the relationship between the plasma plume and the grown thin film is required. We show that the oxidation of species in the plasma plume still affects the SrVO3 growth even at low oxygen partial pressures. Optical emission spectroscopy measurements for the plasma plume at different growth conditions were correlated with the film properties determined by Atomic force microscopy, X-ray diffraction, and transport. At reducing oxygen pressures, the background argon pressure can affect the oxidation in the plasma plume, which in turn controls the growth kinetics, stoichiometry, and electrical properties of the films.

Spintronics is one of the most promising information technologies now, especially for nontrivial topological Dirac half-metal, which exhibits extraordinary electronic band and transport properties. In this work, we propose that 1T-CrO2 nanosheet is mechanical stable, large spin-gap, and room temperature ferromagnetic Dirac half metal. It also exhibits a desirable giant magneto band structure effect, and when the spin direction is switched from in-plane to out-of-plane with a spin orbital coupling effect, it will exhibit nontrivial topological phase transition. The topological tunable electronic band property makes it a very promising two-dimensional nanosheet for spintronics.

Multifunctional semiconductor cubic silicon carbide (3C-SiC) is employed for fuel cell electrolyte, which has never been used before. n-type 3C-SiC can be individually employed as the electrolyte in fuel cells, but delivers insufficient open circuit voltage and minuscule current density due to its electronic dominant property. By introducing n-type ZnO to form an n–n 3C-SiC/ZnO heterostructure, significant enhancements in the ionic conductivity of 0.12 S/cm and fuel cell performance of 270 mW cm−2 are achieved at 550 °C. It is found that the energy band bending and build-in electric field of the heterostructure play the pivotal role in the ionic transport and suppressing the electronic conduction of 3C-SiC, leading to a markable material ionic property and fuel cell performance. These findings suggest that 3C-SiC can be tuned to ionic conducting electrolyte for fuel cell applications through the heterostructure approach and energy band alignment methodology.

A double-interface CoFeB/MgO magnetic tunnel junction (MTJ) has a high thermal stability barrier (E) and high-efficiency magnetization switching with the scaling of device dimensions. However, compared to a single-interface CoFeB/MgO MTJ, its more complicated film stacks and interfaces are more vulnerable to irradiation-induced swift heavy ions. We have studied the irradiation effects of Ta/Kr ions on double-interface CoFeB/MgO MTJs. Structural and physical analyses are performed through transmission electron microscopy, energy dispersive x-ray spectroscopy, and vibrating sample magnetometry. 1907 MeV Ta-ion irradiation damages the interfaces of the double-interface MTJ, resulting in the irreversible decrease in coercivity, while 2060 MeV Kr-ion irradiation damages the bulk properties of the MTJ, leading to the decrease in saturation magnetization. However, the electronic properties of the double-interface MTJ are almost immune to Kr-ion irradiation.

We compare detailed spatio-temporal propagation simulations with experiments on generation of terahertz (THz) pulses in single filaments with two-color optical excitation, which elucidates the mechanism whereby positively chirped optical pulses lead to the maximum THz yield. The long-wavelength components in the leading edge of the positively chirped 2ω-pulse preserve the overlap with the ω-pulse. The THz yield is extremely sensitive to the temporal overlap: for a 35-fs ω-pulse, the yield decreases by an order of magnitude upon a ω–2ω pulse shift of only 5 fs.We compare detailed spatio-temporal propagation simulations with experiments on generation of terahertz (THz) pulses in single filaments with two-color optical excitation, which elucidates the mechanism whereby positively chirped optical pulses lead to the maximum THz yield. The long-wavelength components in the leading edge of the positively chirped 2ω-pulse preserve the overlap with the ω-pulse. The THz yield is extremely sensitive to the temporal overlap: for a 35-fs ω-pulse, the yield decreases by an order of magnitude upon a ω–2ω pulse shift of only 5 fs.

In this work, the ferroelectric characteristics of 0.5Ba(Zr0.2Ti0.8)O-3-0.5(Ba0.7Ca0.3)TiO3 (BCZT) thin films grown on 0.7 wt. % Nb-doped (001)-SrTiO3 (Nb:STO) single-crystal have been investigated. High-resolution transmission electron microscopy and electron energy loss spectroscopy revealed a very sharp Nb:STO/BCZT interface, while selected area electron diffraction revealed the epitaxial growth of the BCZT layer on the Nb:STO substrate. The ferroelectric nature of the BCZT films have been investigated by piezoresponse force microscopy and hysteresis loops. The effect of electric field on polarization switching kinetics has been investigated and has been analyzed by the nucleation limited switching model with a Lorentzian distribution function. The local field variation was found to decrease with the increase in the electric field, and thus, the switching process becomes faster. The peak value of the polarization current and the logarithmic characteristic switching time exhibited an exponential dependence on the inverse of electric field. This model gave an excellent agreement with the experimental polarization reversal transients throughout the whole time range., This work was supported by (i) Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding No. UID/FIS/04650/2013 and (ii) Project Norte-070124-FEDER-000070 Nanomateriais Multifuncionais. Part of this work was supported by the COST Action MP1308 "Towards Oxide-Based Electronics (TO-BE)." The authors acknowledge the CERIC-ERIC Consortium for access to experimental facilities and financial support under Proposal No. 20157018. The authors J.P.B.S. and F.F. are grateful for financial support through the FCT Grant Nos. SFRH/BPD/92896/2013 and SFRH/BPD/80663/2011, respectively. R.F.N. and C.G. acknowledge the financial support from the Romanian Ministry of Research and Innovation in the frame of the Core Program No. PN18-110101. The authors would also like to acknowledge P. B. Tavares, Centro de Quimica da Universidade de Tras-os-Montes e Alto Douro, for the supply of the 0.5BZT-0.5BCT PLD target., info:eu-repo/semantics/publishedVersion

In this letter, a coplanar waveguide (CPW) filter based on spoof surface plasmon polaritons (SSPPs) in the microwave frequency band is proposed, which can achieve multi-band transmission by using periodic holes etched on the middle line of a CPW. Compared to the conventional SSPP designs, the proposed SSPP-based waveguide filter removes the gradual structure for the mode conversion. Simultaneously, the transmission efficiency of high-order modes is obviously improved by employing periodic holes etched on both the side grounds of the CPW. The physical mechanism of the proposed SSPP-based waveguide filter is explained with the aid of the dispersion curves and electric field distributions. Experimental results validate the proposed concept, and the measured results are in good agreement with the simulated ones, which indicates that the proposed SSPP-based waveguide filter can find potential applications in plasmonic integrated circuits at microwave frequencies.

A graphene-Si junction is an attractive system as it is both CMOS-compatible and representative of very interesting van der Waals (vdW) heterostructures. In this paper, the full spectral photoresponse of the graphene-Si heterojunction is investigated in the photovoltaic mode by using Fourier transform infrared photocurrent spectroscopy. Two photoresponse bands at 980 nm and 1550 nm are measured, which are attributed to the photocarrier generations in Si and in the graphene-Si vdW junction, respectively. Peak detectivities of the Si and the vdW junction photoresponses are measured to be 1.3 × 109 cm Hz1/2/W and 1.3 × 108 cm Hz1/2/W, respectively. The band diagram of the heterojunction suggests an indirect spatial transfer process from graphene to silicon. The results are indicative of great potential of the graphene-Si vdW junction for photodetection in the infrared region.

We investigate photo-induced ferroelectric domain switching in a series of Pb(Zr0.2Ti0.8)O3/La0.7Sr0.3MnO3 (PZT/LSMO) bilayer thin films with varying surface morphologies by piezoresponse force microscopy under light illumination. We demonstrate that reverse poled ferroelectric regions can be almost fully recovered under laser irradiation of the PZT layer and that the recovery process is dependent on the surface morphology on the nanometer scale. The recovery process is well described by the Kolmogorov-Avrami-Ishibashi model, and the evolution speed is controlled by light intensity, sample thickness, and initial write voltage. Our findings shed light on optical control of the domain structure in ferroelectric thin films with different surface morphologies.

A direct writing technique for fabricating micro/nano-structural arrays without using a multi-scanning process, multi-beam interference, or any assisted microlens arrays is reported. Various sub-wavelength micro/nano-structural arrays have been directly written on single crystalline germanium substrate surfaces using femtosecond laser pulses. The evolution of the multiscale surface morphology from periodic micro/nano-structures to V-shaped microgrooves has been achieved, and the relationship between array characteristics and laser polarization directions has been discussed. The self-organization model agrees well with the experimental results in this study.

We report on a waveform control of enhanced THz radiation along a femtosecond laser filament in air with a high voltage technique. By applying a DC high-voltage electric field from two sharp electrodes in a direction parallel to the laser filament and scanning it along the filament, the longitudinal evolution of amplified THz emission was demonstrated. By changing the position of the pair of electrodes along the laser filament, different waveforms of THz radiation were obtained. Due to the change of the plasma density distribution at the leading and trailing ends of a laser filament, the enhanced THz waveforms could have a phase shift of ∼π. The technique is very simple. It could help to understand the THz generation process through external electric field assisted laser filamentation.

Vanadium dioxide is a promising material for THz modulations due to its remarkable insulator-to-metal transition (IMT) properties. Silicon-doped VO2 films, exhibiting excellent IMT properties with giant modulation amplitude and tunable phase transition temperature, greatly adapt in this area. In this paper, we report on a rebound effect of the IMT in Si-doped VO2 films. As the silicon dopants are increasingly introduced into VO2 films, the IMT is first tuned to lower temperature and then is anomalously shifted to higher temperature. This rebound effect is confirmed by crystal structure, valence concentration, and surface morphology. We attribute this rebound behavior to the interstitial and substitutive doping of Si atoms. Due to their distinct impactions on the crystallite, IMT properties of the VO2 films are depressed initially and recovered later.

Hydrogen-doped zinc oxide (ZnO:H) films were deposited by rf magnetron sputtering as transparent conductive films. The resistivity of ZnO:H film was significantly reduced by the addition of H2 in Ar during rf sputtering. The electrical resistivity of ZnO:H films reached 2×10−4Ωcm. The carrier concentration increased with increasing H2 concentration during deposition. X-ray diffraction results showed that the d0002 interplanar spacing increased with increasing H2 concentrations. The carrier concentration was significantly reduced in two orders of magnitude by increasing the substrate temperature from 150 to 250 °C during deposition. Both results suggested that the increase of carrier concentration by adding H2 during sputtering was due to the hydrogen donor rather than the oxygen vacancies in ZnO films, consistent with the theoretical predictions by Van de Walle. UV–visible spectroscopy further showed that the transmittance is high up to 100% in the visible range. The band gap determined by optical absorpt...

Bottom-contact organic thin-film transistors (BC OTFTs) based on inorganic/organic double gate insulators were demonstrated. The double gate insulators consisted of tantalum pentoxide (Ta2O5) with high dielectric constant (κ) as the first gate insulator and octadecyltrichlorosilane (OTS) with low κ as the second gate insulator. The devices have carrier mobilities larger than 10−2cm2∕Vs, on/off current ratio greater than 105, and the threshold voltage of −14V, which is threefold larger field-effect mobility and an order of magnitude larger on/off current ratio than the OTFTs with a Ta2O5 gate insulator. The leakage current was decreased from 2.4×10−6 to 7.4×10−8 A due to the introduction of the OTS second dielectric layer. The results demonstrated that using inorganic/organic double insulator as the gate dielectric layer is an effective method to fabricate OTFTs with improved electric characteristics.

A Raman scattering study of the vibrational modes in K2Al2B2O7 crystals has been performed at room temperature. The vibrational modes are classified by the nuclear site group analysis method and the internal vibrational modes are assigned to vibrations of the BO3 triangle and AlO4 tetrahedron.

Direct evidence of a field-induced magnetic phase transition in LaFe13−xSix intermetallics with a large magneticaloric effect was provided by Fe57 Mossbauer spectra in externally applied magnetic fields. Moreover, Mossbauer spectra demonstrate that a magnetic structure collinear to the applied field is abruptly achieved in LaFe11.7Si1.3 compound once the ferromagnetic state appears, showing a metamagnetic first-order phase transition. In the case of LaFe11.0Si2.0, the Fe magnetic moments rotate continuously from a random state to the collinear state with increasing applied field, showing that a second-order phase transition is predominant. The different types of phase transformation determine the magnetocaloric effects in response to temperature and field in these two samples.

Organic thin-film transistors (OTFTs) having source/drain electrodes sandwiched between copper phthalocyanine (CuPc) and cobalt phthalocyanine (CoPc) layers, CuPc/CoPc SC OTFTs, are investigated. Comparing their properties with that of CuPc-based top-contact OTFT, field-effect mobility increases from 0.04 to 0.11 cm2/Vs, threshold voltage shifts from −13.8 to −8.9 V, and the current on/off ratio maintains at a level of 105. A top-contact OTFT with a layer of CuPc and a layer of CoPc (10%)–CuPc mixture reveals that the combination of CuPc and CoPc enhances charge injection from the source electrode into the active layer and increases the off-state current. The sandwich configuration increases the field-effect mobility, reduce the threshold voltage, and improve the on/off ratio at the same time. Our results indicate that using a double-layer of active organic materials in sandwich configuration is an effective way to improve OTFT performance.

In this letter, we presented a magnetically tunable ferrite-loaded unidirectional waveguide based on magnetic photonic crystals. Two rows of ferrite rods are symmetrically arranged near the two lateral sides of the rectangular waveguide, where they are biased with static magnetic fields with the same amplitude and opposite directions along the rod axis. Since the magnetic one-way transmission is induced by the magnetic surface plasmon resonance, the operating band of the unidirectional waveguide can be tuned by changing the biased magnetic field intensity. To validate the design, a prototype was fabricated and measured. Both the simulation and experiment results verify the unidirectional transmission property.

A series of single-layer nano-carbon (SNC) films, diamond films, and diamond/nano-carbon (D/NC) composite films have been prepared on the highly doped silicon substrate by using microwave plasma chemical vapor deposition techniques. The films were characterised by scanning electron microscopy, Raman spectroscopy, and field emission I-V measurements. The experimental results indicated that the field emission maximum current density of D/NC composite films is 11.8–17.8 times that of diamond films. And the field emission current density of D/NC composite films is 2.9–5 times that of SNC films at an electric field of 3.0 V/μm. At the same time, the D/NC composite film exhibits the advantage of improved reproducibility and long term stability (both of the nano-carbon film within the D/NC composite cathode and the SNC cathode were prepared under the same experimental conditions). And for the D/NC composite sample, a high current density of 10 mA/cm2 at an electric field of 3.0 V/μm was obtained. Diamond layer c...

In this paper, we propose the design of all-dielectric metamaterial band-pass frequency selective surfaces (FSSs) using high-permittivity ceramics based on effective medium theory and dielectric resonator theory. The band-pass response can be determined by the permittivity of the dielectric material, the periodicity, and geometrical shape of the dielectric unit cell. As an example, a band-pass FSS composed of H shaped ceramic resonators is demonstrated. Both the simulation and experiment results show that the FSS can achieve a pass band in X-band. Since such FSSs are made of low-loss high-permittivity ceramics, they are of important application values, especially in high-temperature, high-power environments. The design method can be readily extended to the design of FSSs in other frequencies.

We reveal the underlying physics of the anomalous Josephson effect in a magnetic Josephson junction between two noncentrosymmetric superconductors. The key point is that the two effective superconducting gaps provide two sets of Andreev bound states which carry two supercurrents with different amplitudes. When the magnetization direction of the ferromagnet is suitably chosen, the two supercurrents experience opposite phase shifts from the conventional sinusoidal current-phase relation. Then the total Josephson current results in a continuously tunable ground-state phase difference by adjusting the ferromagnet parameters and the triplet-singlet ratio of noncentrosymmetric superconductors. The emergence of anomalous Josephson current can definitely confirm the existence of triplet pairing and the ground-state phase difference serves as a tool to determine the triplet-singlet ratio of noncentrosymmetric superconductors.

The coarsening of Ni in Ni–yttria-stabilized zirconia (YSZ) anodes is a potential cause of long term solid oxide fuel cells (SOFC) performance degradation. The specifics of the Ni-YSZ structure—including Ni/YSZ ratio, porosity, and particle size distributions—are normally selected to minimize anode polarization resistance, but they also impact long-term stability. A better understanding of how these factors influence long-term stability is important for designing more durable anodes. The effect of structural details, e.g., Ni-YSZ ratio, on Ni coarsening has not been quantified. Furthermore, prior measurements have been done by comparing evolved structures with control samples, such that sample-to-sample variations introduce errors. Here, we report a four dimensional (three spatial dimensions and time) study of Ni coarsening in Ni-YSZ anode functional layers with different Ni/YSZ ratios, using synchrotron x-ray nano-tomography. The continuous structural evolution was observed and analyzed at sub-100 nm res...

Organic-inorganic halide perovskite semiconductors with the attractive physics properties, including strong photoluminescence (PL), huge oscillator strengths, and low nonradiative recombination losses, are ideal candidates for studying the light-matter interaction in nanostructures. Here, we demonstrate the coupling of the exciton state and the cavity mode in the lead halide perovskite microcavity system at room temperature. The Purcell effect in the coupling system is clearly observed by using angle-resolved photoluminescence spectra. Kinetic analysis based on time-resolved PL reveals that the spontaneous emission rate of the halide perovskite semiconductor is significantly enhanced at resonance of the exciton energy and the cavity mode. Our results provide the way for developing electrically driven organic polariton lasers, optical devices, and on-chip coherent quantum light sources.

We present a scheme for tuning the photonic band gap (PBG) by an external electric field in a ferroelectric inverse opal structure. The inverse opals, consisting of ferroelectric (Pb,La)(Zr,Ti)O3 (PLZT) ceramics, were synthesized by a sol–gel process. Optical reflection spectra show that the PBG of the PLZT inverse opals shifts continuously with the change in the applied electric field. As the photonic crystals (PCs) consist of the high-refractive-index constituent and possess an “all-solid” structure, it should supply a more reliable mode to tune the PBG by the electric field for the superprism effect in PCs. It should be of high interest in device applications.

High-quality c-axis epitaxial ferroelectric thin films of Bi4Ti3O12 (BTO) and Nd-substituted BTO, Bi3.15Nd0.85Ti3O12 (BNT), were prepared on (001)-LaNiO3-coated (001) LaAlO3 substrates by pulsed-laser deposition. The epitaxial alignments were established by the x-ray diffraction, including θ–2θ and φ scans. Compared to the BTO films, the BNT films have significantly improved electrical properties with about 2 times larger remanent polarization, 0.6 times lower coercive field, better fatigue-resisting characteristics, and 1.7 times larger dielectric constant. These results showed experimentally that Nd substitution could enhance the c-axis electrical properties of BTO. The reason for the improved properties of BNT films was discussed.

Output polarization and output wavelength of titania zirconia organically modified silicate distributed feedback waveguide lasers were found to be dependent on the polarization of the crossing pump beams. Output waves with transverse electric polarization were obtained when the pump beams were s-polarized. Transverse electric and transverse magnetic optical waves belonging to the same propagation mode were generated by crossing two circularly polarized or p-polarized pump beams. Tuning of the polarized laser output was also achieved by varying the crossing angle. Up to sixteen output wavelengths corresponding to eight pairs of polarized output from eight propagation modes were observed simultaneously for a planar waveguide with a thickness of 6.7 μm.

Local structure of the Fe-doped La$_{1-x}$Ca$_{x}$MnO$_{3}$ (x=0.00-1.00) compounds has been investigated by means of M\"{o}ssbauer spectroscopy. $^{57}$Fe M\"{o}ssbauer spectra provide a direct evidence of Jahn-Teller distortion in these manganites. On the basis of M\"{o}ssbauer results, the Jahn-Teller coupling was estimated. It is noteworthy that Ca-concentration dependence of Jahn-Teller coupling strength is very consistent with the magnetic phase diagram. Our results reveal that M\"{o}ssbauer spectroscopy can not only detect the local structural distortion, but also provide a technique to investigate Jahn-Teller coupling of Fe-doped La$_{1-x}$Ca$_{x}$MnO$_{3}$ colossal magnetoresistive perovskites., Comment: 3 figures, will appear in Applied Physics Letters

Using tertiarybutylphosphine (TBP) as phosphorus precursor, high-quality AlGaInP epilayers and AlGaInP/GaInP multiple-quantum-well (MQW) structures have been grown by metalorganic chemical vapor deposition. The photoluminescence results indicate that the AlGaInP materials are as good as those grown using PH3 in terms of optical quality. Finally, AlGaInP MQW red laser structures have been grown, and the electrically pumped AlGaInP red lasers grown by TBP have been demonstrated with the emission wavelength of 647 nm, indicating that TBP can be used to grow high-quality AlGaInP epilayers and AlGaInP-based red lasers, which presently is dominated by the highly toxic gas source PH3.

An organic thin-film transistor (OTFT) having a low-dielectric polymer layer between gate insulator and source/drain electrodes is investigated. Copper phthalocyanine (CuPc), a well-known organic semiconductor, is used as an active layer to test performance of the device. Compared with bottom-contact devices, leakage current is reduced by roughly one order of magnitude, and on-state current is enhanced by almost one order of magnitude. The performance of the device is almost the same as that of a top-contact device. The low-dielectric polymer may play two roles to improve OTFT performance. One is that this structure influences electric-field distribution between source/drain electrodes and semiconductor and enhances charge injection. The other is that the polymer influences growth behavior of CuPc thin films and enhances physical connection between source/drain electrodes and semiconductor channel. Advantages of the OTFT having bottom-contact structure make it useful for integrated plastic electronic devices.

In this letter, the design of reflective frequency selective surface (RFSS) using low-permittivity dielectrics is proposed based on effective medium theory. The effective medium approach is based on quasi-static extension of the Maxwell-Garnett model. Unlike conventional RFSSs, such RFSS is composed of low-permittivity dielectrics rather than high-permittivity or metallic materials. By drilling periodic hole arrays in multi-layer continuum dielectric plates, strong electric and magnetic resonances are introduced to produce drastic changes in effective parameters, leading to impedance mismatch and band-stop response. The band-stop response can be tailored by adjusting the size and spacing of the unit cell. As an example, an RFSS with rectangular hole element is demonstrated at K-band. The mechanism is analyzed by presenting the effective electromagnetic parameters and dynamic field distributions. A prototype was fabricated and measured. Excellent agreements between measured and simulated results were obtained. The method can also be used to design RFSS in THz and optical frequencies.

Zirconia and zirconia-organically modified silicate waveguides of refractive index from 1.56 to 1.64 and thickness from 0.6 to 1.4 μm were prepared by the sol-gel method. Narrow linewidth (

A very large magnetic entropy change ΔS has been observed in Fe-based cubic NaZn13-type compound LaFe11.2Co0.7Si1.1 near the Curie temperature TC of 274 K. The value of the entropy change is ∼20.3 J/kg K under a magnetic field of 5 T at TC=274 K. It markedly exceeds that of pure Gd at the corresponding temperature range [V. K. Pecharsky & K. A. Gschneidner, Jr., Phys. Rev. Lett. 78, 4494 (1999)]. The great entropy change produced by the sharp change of magnetization is associated with a large negative lattice expansion at TC. The very large magnetic entropy change and low cost suggest that the compound LaFe11.2Co0.7Si1.1 has great potential for applications as magnetic refrigerants near room temperature.

808 nm lasers grown by molecular beam epitaxy show extremely high internal quantum efficiency and low internal loss, which results in very high slope efficiency at a long cavity length, and consequently, extremely high total power conversion efficiency at high continuous-wave power output.

In this letter, we propose the design of all-dielectric metamaterial frequency selective surface (FSS) using high-permittivity ceramics. The FSS is composed of 2D arrays of rectangular ceramic resonators. By adjusting the geometrical parameters of the ceramic resonator, the first two resonant modes are merged to achieve broadband band-stop property. As an example, a nearly 1.5 GHz wide stop-band is demonstrated both numerically and experimentally in X band. Since such FSSs are made of low-loss high-permittivity ceramics, they are of important values especially in high-temperature or high-power applications. The method can also be used to design all-dielectric FSS in other frequencies by simply scaling the geometry parameters.

The coalescence of selective area grown GaAs regions has been performed on patterned 1.8 μm GaAs buffer layer on Si via metal-organic chemical vapor deposition. We propose a promising method of three-stage epitaxial lateral overgrowth (ELO) to achieve uniform coalescence and flat surface. Rough surface caused by the coalescence of different growth fronts is smoothened by this method. Low root-mean-square surface roughness of 6.29 nm has been obtained on a 410-nm-thick coalesced ELO GaAs layer. Cross-sectional transmission electron microscope study shows that the coalescence of different growth fronts will induce some new dislocations. However, the coalescence-induced dislocations tend to mutually annihilate and only a small part of them reach the GaAs surface. High optical quality of the ELO GaAs layer has been confirmed by low temperature (77 K) photoluminescence measurements. This research promises a very large scale integration platform for the monolithic integration of GaAs-based device on Si.

In this letter, we report on the resistive switching originating from the rupture/rejuvenation of single-crystalline Cu filaments in a nitrogen-doped porous carbon-based memristive device Cu/CN0.15/Pt. Cu filaments are confined in conical nanopores in CN0.15 thin films. Dislocations exist in the Cu filaments, resulting in obvious crystal lattice distortions. The Cu/CN0.15/Pt device shows outstanding high temperature retention performance for both ON and OFF states, indicating that it is promising for resistance memory applications. Furthermore, continuous RESET (ON-to-OFF switching) and SET (OFF-to-ON switching) processes could be realized indicating the adaptive learning ability of Cu/CN0.15/Pt, which has potential applications in synaptic devices.

We demonstrate the realization of quantum key distribution (QKD) when combined with classical optical communication, and synchronous signals within a single optical fiber. In the experiment, the classical communication sources use Fabry-Perot (FP) lasers, which are implemented extensively in optical access networks. To perform QKD, multistage band-stop filtering techniques are developed, and a wavelength-division multiplexing scheme is designed for the multi-longitudinal-mode FP lasers. We have managed to maintain sufficient isolation among the quantum channel, the synchronous channel and the classical channels to guarantee good QKD performance. Finally, the quantum bit error rate remains below a level of 2% across the entire practical application range. The proposed multiplexing scheme can ensure low classical light loss, and enables QKD over fiber lengths of up to 45 km simultaneously when the fibers are populated with bidirectional FP laser communications. Our demonstration paves the way for application of QKD to current optical access networks, where FP lasers are widely used by the end users.

Magnetostriction at room temperature under various conditions of compressive prestress and applied fields of TbyDy1−y(Fe1−xTx)2 (T=Al, Mn) twin-free single crystals was investigated. The substitution of Al or Mn for Fe lowers the magnetostriction under ordinary temperature and pressure, and decreases the saturation field, which enables these materials with potential benefits for applications. Moreover, Tb0.5Dy0.5(Fe0.9Mn0.1)2 shows negative magnetostriction at room temperature under zero prestress, due to the rotation of domains 109.5° away from 〈111〉. Under appropriate compressive stress, a quite large magnetostriction of 2160 ppm with a saturation field of 900 Oe and high d33 of 4.8 ppm/Oe can be obtained.

Wurtzite GaN films have been grown on (001) Si substrates using gamma-Al2O3 as an intermediate layer by low pressure (similar to 76 Torr) metalorganic chemical vapor deposition. Reflection high energy electron diffraction and double crystal x-ray diffraction measurements revealed that the thin gamma-Al2O3 layer of "compliant" character was an effective intermediate layer for the GaN film grown epitaxially on Si. The narrowest linewidth of the x-ray rocking curve for (0002) diffraction of the 1.3 mu m GaN sample was 54 arcmin. The orientation relationship of GaN/gamma-Al2O3/Si was (0001) GaN parallel to(001) gamma-Al2O3 parallel to(001) Si, [11-20] GaN parallel to[110] gamma-Al2O3 parallel to[110] Si. The photoluminescence measurement for GaN at room temperature exhibited a near band-edge peak of 365 nm (3.4 eV). (C) 1998 American Institute of Physics.

The optical absorption of graphene strips covered on a multilayer subwavelength grating (MSG) surface is theoretically investigated. The absorption of graphene strips with MSG is enhanced in the wavelength range of 1500 nm to 1600 nm by critical coupling, which is associated with the combined effects of a guided resonance of MSG and its photonic band gap effect. The critical coupling of the graphene strips can be controlled by adjusting the incident angle without changing the structural parameters of MSG. The absorption of graphene strips can also be tuned by varying key parameters, such as grating period, strip width, and incident angle.